AN ABSTRACT OF THE THESIS OF
Jeffrey P. McMorran for the degree of Doctor of Philosophy in Crop
Science presented on June 22, 1994.
Title: Effects of Potato Cropping Practices on Nitrate Leaching in the
Columbia Basin.
Abstract approved:
Redacted for Privacy
(Alvin R. Vosley)
This study examined the contribution of irrigation and nitrogen (N)
fertilization to leaching of nitrates below the potato rooting zone.
Virgin desert and an intensively cultivated site were cropped to
Russet Burbank potato under a range of irrigation frequencies (IF = 1,
2, or 3 days), irrigation rates (IR = 0.7, 1.0, or 1.3 x recommended),
and N fertilization rates (NR = 220, 390, or 560 kgha-1).
Soil and soil solution to 1.2 m, and petiole samples taken throughout
the season were analyzed for NO3-N, NH4-N, pH, electrical conductivity
(EC), organic matter, and/or moisture content as appropriate.
Porous
cup lysimeters (PCL) at 0.6 and 1.2 m were used to extract soil
Aerial biomass and tuber yield and quality were determined.
solution.
EC, NO3-N, and NH4-N levels increased linearly with increasing NR at
both sites.
Soil pH did not change at the desert site but decreased
linearly with increasing NR at the cultivated site.
Organic matter
The response of soil to
Soil water content
NR was generally limited to the 0-0.3 m depth.
decreased linearly with increasing NR at the uncultivated site, but
not at the cultivated site.
(OM) was not affected by NR at either site.
IR and IF did not affect soil pH, EC, or NO3-N levels. However, NH4-N
decreased linearly with increasing IR in the top 0.3 m, and OM
increased with IR at 0.6-0.9 m but decreased below 0.9 m.
Soil NO3-N levels increased to 1.2 m on the uncultivated site in
response to 390 kgha-1 NR and to 0.9 m for 560 kgha-1, but did not
respond to 220 kgha-1 NR. At the cultated site, soil NO3-N
but only to 0.3 m for
increased to 0.9 m in response to 560 ky
lower NR.
PCL's reliably extracted sufficient soil solution, but were not
consistently reliable for monitoring soil NO3-N.
Petiole NO3-N concentrations increased with increasing NR, and
decreased with increasing IR, but were not affected by IF.
Tuber
yields increased with increasing IR, but were not affected by either
NR or IF.
Tuber numbers decreased with increasing NR and IR. Tuber
solids and hollow heart were not affected by the treatments.
Fry
color darkened linearly with increasing irrigation rate.
Results of this study tend to refute claims that responsible potato
producers in the Lower Umatilla Basin are contributing insignificantly
to increased groundwater NO3-N levels.
Effects of Potato Cropping Practices
on Nitrate Leaching in the Columbia Basin.
by
Jeffrey P. McMorran
A THESIS
submitted to
Oregon State University
in partial fulfillment of
the requirements for the
degree of
Doctor of Philosophy in Crop Science
Completed June 22, 1994
Commencement June 1995
APPROVED:
Redacted for Privacy
Professor of Crop and Soil Sc' nce in charge of major
Redacted for Privacy
Head of Department of Crop and Soil Science
Redacted for Privacy
Dean of Graduate
hool
Date thesis is presented
Typed by researcher for:
June 22, 1994
Jeffrey P. McMorran
Acknowledgements
This research was funded primarily through the Center for Applied
Agricultural Research (CAAR) and the Oregon Potato Commission.
Supplemental support was also provided by the Oregon State University
Agricultural Research Foundation and by the staff at the Hermiston
Agricultural Research and Extension Center. It would not have been
possible without funding and labor furnished by these sources.
Each member of my committee, which included Drs. Alvin Mosley, George
Clough, Benno Warkentin, Max Hammond, Russell Ingham, and Delbert
Hemphill contributed in unique ways to the completion of this research
effort, for which I express my deepest appreciation. I particularly
wish to thank Dr. George Clough for invaluable assistance with
statistical analyses and review of the original draft of each chapter,
and Dr. Alvin Mosley for the financial and moral support offered
during the course of this project.
I am indebted to cooperators at the Hermiston Agricultural Research
and Extension Center, Dan Hane and Gary Reed, as well as the entire
staff, for making this project a truly worthwhile learning experience
which became pleasurable with time.
And above all I thank my wife, Kristi, for showing me there are more
important things in life than obtaining a doctoral degree, and in
doing so, gave me the strength to carry this dissertation to its
completion.
Jubilate Deo.
Table of Contents
INTRODUCTION
1
CHAPTER 1
LITERATURE REVIEW
Description of Area Soils, Climate, and Practices
Current Groundwater Situation (EPA, DEQ, Other)
Implications of Nitrate in Groundwater
Natural Sources of Nitrates in Arid Soils
Sources of Nitrate in Agricultural Soils
Nitrate Leaching in Agricultural Soils
Nitrogen Budgets and Models to Estimate NO3-N Leaching
Techniques for Estimating Soil Nitrate Levels
Potato as a "High Risk" Crop
Porous Cup Lysimeters for Determining Nitrate Movement
in Soils
References
2
2
3
5
7
8
8
14
16
18
21
23
CHAPTER 2
METHODS AND MATERIALS
Treatments
Plot Design and Preparation
Irrigation Scheduling
Monitoring, Sampling, and Analysis
Chemical Analysis of Soil Samples
Soil Water Sampling and Analysis
Plant and Tuber Sampling and Analysis
Site Nutrient Profile
Comparison of Hermiston and OSU Soils Lab Results
Data Analyses
Weather Data for 1992 and 1993 Growing Seasons
References
32
32
34
36
38
40
41
42
44
44
49
53
57
CHAPTER 3
EFFECTS OF POTATO CROPPING PRACTICES ON SOIL NITRATE, AMMONIA,
ACIDITY, ELECTRICAL CONDUCTIVITY AND ORGANIC MATTER
Pre-plant Soil Characteristics
Post-harvest Soil Characteristics
Overall Comparison of Pre-plant and Post-harvest Levels of
Soil Variables
Monthly Soil NO3-N
Effect of N-rate, Irrigation Rate, and Irrigation Frequency
on the Soil Gravimetric Water Fraction (GWF)
Overall Summary of Results
Discussion & Conclusions
References
58
58
61
69
72
86
87
89
91
CHAPTER 4
EFFECTS OF POTATO CROPPING PRACTICES ON SOIL SOLUTION
NITRATE LEVELS
92
Efficiency of Lysimeters for Collection of Soil Solution
Soil Solution NO3-N Concentrations (direct analysis)
Soil Solution NO3-N after Conversion to ppm NO3-N in Oven-
dried Soil
Comparison of the Two Methods Used to Analyze Lysimeter Data
Discussion & Conclusions
References
.
.
92
92
102
105
108
109
CHAPTER 5
EFFECTS OF POTATO CROPPING PRACTICES ON PLANT NITROGEN STATUS,
AERIAL BIOMASS AND TUBER PRODUCTION
Petiole NO3-N Status
Mid-season Aerial Biomass and Tuber Yield
Tuber Yield, Size Distribution, and Internal Quality
Summary of Results
Discussion and Conclusions
References
110
110
112
118
130
131
133
CHAPTER 6
RELATIONSHIP AMONG SOIL NITRATE CONTENT, SOIL SOLUTION, AND
PETIOLE TISSUES, AND OVERALL CONCLUSIONS OF STUDY
.
Comparison of Values and Significant Effects
Estimates of NO3-N Changes in the Soil
Estimates of NO3-N Leaching
Discussion and Conclusions
References
BIBLIOGRAPHY
.
134
134
145
145
151
153
154
List of Figures
Figure 1.1. Results of Oregon DEQ well water sampling, 1992
.
.
6
Figure 2.1. Regression of CAL lab values for soil solution NO3-N
on electrode values.
49
Figure 2.2. Regression of CAL lab values for soil NO3-N on
electrode values.
50
Figure 2.3. Regression of CAL lab values for soil NH4 -N on
electrode values
51
Figure 2.4. Regression of electrode NH4 -N values for soil
sub-sample 1 on sub-sample 2.
52
Figure 2.5. Weather Data for October 1991
Hermiston, Oregon.
55
Figure 2.6. Weather Data October 1992
Oregon
September 1992,
September 1993, Hermiston,
56
Figure 4.1. Relationship between % of PCL extracting more than 30
ml of fluid from the soil and soil gravimetric water fraction
in 1992 and 1993.
93
Figure 4.2. Volume of fluid extracted by PCL vs. soil
gravimetric water fraction.
94
Figure 6.1. Petiole vs. soil NO3-N values, 1993 desert site.
Figure 6.2. Petiole vs. soil NO3-N values, 1993 pivot site.
137
.
138
Figure 6.3. Regression of petiole NO3-N on soil NO3-N, 1992.
139
Figure 6.4. Regression of petiole NO3-N on soil NO3-N, 1993.
140
List of Tables
Table 1.1. EPA National Pesticide Survey (1990)
5
Table 2.1. Experimental treatments
33
Table 2.2. Watering regime used at the desert site
37
Table 2.3. Initial nutrient analyses, desert and pivot sites, fall
1991.
39
Table 2.4. Conversion of neutron probe numbers to the soil's
gravimetric water fraction
42
Table 2.5. Treatment plots showing significant soil differences
prior to commencement of trials.
45
Table 2.6. Comparison of initial nutrient analyses results from
CAL and HL lab for desert and pivot sites.
46
Table 2.7. Weather Data, Oct. 1991
54
Sept. 1993, Hermiston, Oregon.
Table 3.1. Soil pH, electrical conductivity (EC), organic matter
(OM), NO3-N, NH4-N, and gravimetric water fraction (GWF)
before planting.
59
Table 3.2. Pre-plant gravimetric water fraction.
60
Table 3.3. Effect of year, site location and depth on post-harvest
soil pH, electrical conductivity (EC), organic matter (OM),
NO3-N, NH4-N, and gravimetric water fraction (GWF).
62
Table 3.4. Effect of year, N-rate, irrigation rate and frequency,
and depth on post harvest soil pH, electrical conductivity
(EC), organic matter (OM), NO3-N, NH4-N, and moisture,
desert plot.
63
Table 3.5. Effect of year, N rate, and depth on post-harvest soil
pH, electrical conductivity (EC), organic matter (OM), NO3-N,
NH4-N, and gravimetric water fraction (GWF), pivot plot.
64
Table 3.6. Post-harvest soil pH as affected by interaction of
N-rate and depth, pivot plot.
65
Table 3.7. Post-harvest soil electrical conductivity (EC) as
affected by interaction of year, N-rate, and depth (desert
site) or N-rate and depth (pivot site)
66
Table 3.8. Effect of N rate x depth interaction on post-harvest
soil NH4-N, pivot site.
67
Table 3.9. Effect of site, year, and N rate on post-harvest soil
gravimetric water fraction
67
Table 3.10. Post-harvest soil OM as affected by interaction of
irrigation rate and depth.
68
Table 3.11. Post-harvest soil NH4-N as affected by interaction of
year, irrigation rate, and depth
68
Table 3.12. Comparison of pre-plant (PP) and post-harvest (PH)
soil pH, electrical conductivity (EC), and organic matter (OM).
70
.
.
.
Table 3.13. Comparison of pre-plant (PP) and post-harvest (PH)
soil NO3-N, NH4-N, and gravimetric water fraction (GWF).
71
Table 3.14. Effect of year, site location and depth on soil
NO3-N throughout the season.
73
Table 3.15. Year x site effects on soil NO3-N concentrations
throughout the season.
74
Table 3.16. Year x depth effects on soil NO3-N concentrations
during weeks 10 and 14, and post-harvest
75
.
Table 3.17. Effect of year, N rate, irrigation rate, and irrigation
frequency, on soil NO3-N throughout the season, desert plot.
76
Table 3.18. Effect of year, N rate and sampling depth on soil NO3-N
throughout the season, pivot plot.
77
Table 3.19. Soil NO3-N concentrations in weeks 10 and 14, and
post-harvest as affected by interaction of year, depth, and
site (where appropriate)
78
Table 3.20. Year x N-rate x site effects on soil NO3-N
concentrations in weeks 10 and 14.
79
Table 3.21. N-rate x depth effects on soil NO3-N concentrations,
desert site, in weeks 10 and 14, and post-harvest.
80
Table 3.22. Effect of N rate and depth on seasonal changes in soil
NO3-N between sampling dates, desert plot.
81
Table 3.23. N-rate x depth effects on soil NO3-N concentrations,
pivot site, weeks 14, 18, and post harvest.
82
Table 3.24. Year x N-rate x depth effects on soil NO3-N
concentrations, pivot site, week 14.
83
Table 3.25. Affect of N rate and depth on changes in soil NO3-N
concentration between sampling date, pivot plot.
84
Table 3.26. Year x depth x irrigation frequency effects on soil
NO3-N concentration, desert site, week 14.
85
Table 3.27. Effect of year, N rate, irrigation rate, and irrigation
frequency on soil gravimetric water fraction (GWF).
88
Table 3.28. Year x N-rate effects on soil gravimetric water
fraction at 10 weeks from planting and post-harvest, desert
site.
89
Table 4.1. Comparison of within plot and among plot coefficients
of variation for PCL soil solution NO3-N concentration.
95
Table 4.2. Effect of year, location, and depth on NO3-N
concentration in PCL solution.
96
Table 4.3. Year x site effects on NO3-N concentrations in PCL-
extracted soil solution, week 10.
97
Table 4.4. Year x depth effects on NO3-N concentrations in PCL-
extracted soil solution, week 16
97
.
.
.
Table 4.5. Year x site x depth effects on NO3-N concentrations in
PCL-extracted soil solution.
98
Table 4.6. Effect of year, N rate, irrigation rate, and irrigation
frequency, on NO3-N concentrations in lysimeter-extracted soil
solution, desert site.
99
Table 4.7. Year x N-rate effects on NO3-N concentration in
PCL-extracted soil solution, desert site.
100
Table 4.8. Depth x irrigation frequency effects on NO3-N
concentration in PCL-extracted soil solution, desert site,
week 10.
100
Table 4.9. Year x N-rate effects on NO3-N concentration in
PCL-extracted soil solution, pivot site.
101
Table 4.10. Year x depth effects on NO3-N concentration in
PCL-extracted soil solution, pivot site week 12.
101
Table 4.11. Effect of year, site location, and depth on NO3-N
concentration in PCL-extracted soil solution transformed to ppm
NO3-N on a dry-soil weight basis.
103
Table 4.12. Year x site effects on NO3-N concentration in
PCL-extracted soil solution transformed to ppm NO3-N on a dry-
soil weight basis.
104
Table 4.13. Site x depth effects on NO3-N concentration in
PCL-extracted soil solution transformed to ppm NO3-N on a
dry-soil weight basis, week 8.
104
Table 4.14. Year x depth effects on NO3-N concentration in
PCL-extracted soil solution transformed to ppm NO3-N on a
dry-soil weight basis, week 12.
105
Table 4.15. Effect of year, N rate, irrigation rate, and irrigation
frequency on NO3-N concentration in PCL-extracted soil solution
transformed to a dry-soil weight basis, desert site.
106
.
.
.
.
Table 4.16. Effects of year and N rate on NO3-N concentration in
PCL-extracted soil solution transformed to a dry-soil weight
basis, pivot site.
107
Table 4.17. Effect of year and N-rate on NO3-N concentration
transformed to dry-soil weight basis, desert site week 6.
107
Table 4.18. Effect of depth and irrigation frequency on NOB-N
concentration transformed to dry-soil weight basis,
desert site week 10.
108
Table 5.1. Year and site effects on potato petiole NO3-N
concentrations
111
Table 5.2. Effect of year, N rate, and irrigation rate and
frequency on potato petiole NO3-N concentrations, desert site
112
Table 5.3. Effect of year and N-rate on potato petiole NO3-N
concentrations, pivot site
113
Table 5.4. Year x N-rate interaction effects on petiole NO3-N
concentrations at week 15, desert site.
113
Table 5.5. Effect of N-rate, irrigation rate and irrigation
frequency on petiole NO3-N concentrations in comparison to
recommended sufficiency ranges.
114
Table 5.6. Effect of site location on mid-season aerial biomass,
tuber yields and numbers.
115
Table 5.7. Effect of year, N rate, and irrigation rate and
frequency on mid-season production of aerial biomass, and
tuber yield and number, desert site.
116
Table 5.8. Effect of year and N rate on mid-season aerial biomass
and tuber yield and number, pivot site
117
Table 5.9. Effect of year and irrigation frequency on mid-season
tuber numbers
117
Table 5.10. Effect of site location on number and size of tubers.
119
Table 5.11. Effect of year and site interaction on the total
number of tubers
120
Table 5.12. Effect of year and site interaction on weight of
tubers >340 g.
120
Table 5.13. Effect of year, N-rate, and irrigation rate and
frequency on tuber number and yield, desert site.
121
Table 5.14. Effect of year and N-rate interactions on the total
number of tubers, desert site.
122
Table 5.15. Interaction of year and irrigation rate on tuber
yields.
123
Table 5.16. Interaction of year and irrigation frequency on tuber
yields of tubers >340 g.
124
Table 5.17. Effect of year and N rate on number and yield of
tubers, pivot site.
125
Table 5.18. Effect of year and N-rate interactions on the weight
of tubers <116 and >340 g, pivot site.
126
Table 5.19. Effect of site location on specific gravity, hollow
heart (HH), internal discoloration (ID), and fry color after
storage.
127
Table 5.20. Effect of year, N rate, and irrigation rate and
frequency on tuber specific gravity, hollow heart (HH),
internal discolorations (ID), and fry color after storage,
desert site.
128
Table 5.21. Effect of year and N-rate on specific gravity, hollow
heart (HH), internal discoloration (ID), and fry color after
storage, pivot site.
129
Table 5.22. Effect of year and N-rate on internal discoloration
(ID) of tubers at harvest and after 3 months in storage.
129
.
.
Table 6.1. Comparison of soil, lysimeter, and petiole estimates
of plot variation in NO3-N concentrations.
135
Table 6.2. Effects of N-rate on petiole and soil (0.0-0.6 m)
NO3-N content.
136
Table 6.3
.
Comparison of soil and lysimeter estimates of year,
site, and depth effects on soil NO3-N.
Table 6.4
.
Comparison of soil and lysimeter estimates of year,
depth, N-rate, and irrigation rate, on soil NO3-N, desert site.
Table 6.5
depth,
.
142
Comparison of soil and lysimeter estimates of year,
and N-rate, on soil NO3-N, pivot site.
143
144
Table 6.6. Change in soil NO3-N between sampling dates in response
to N rate and depth, desert site.
146
Table 6.7. Change in soil NO3-N between sampling dates in response
to N rate and depth, pivot site.
147
Table 6.8. Effects of N-rate on potential NO3-N leaching budget
between successive soil layers, desert site.
149
Table 6.9. Effect of N-rate on potential NO3-N leaching budget
between successive soil layers, pivot site
150
Effects of Potato Cropping Practices
on Nitrate Leaching in the Columbia Basin
INTRODUCTION
Wells in eastern Oregon's Treasure Valley region, and the Lower
Columbia Basin area of north central Oregon have unacceptably high
levels of nitrate-nitrogen contamination. As of July, 1991, 26 of 150
wells tested in western Umatilla and northern Morrow counties by the
Oregon Department of Environmental Quality (ODEQ) exceeded the federal
standard of 10 ppm.
Consequently 144,000 ha of this area, which
accounts for most of Oregon's potato production, has been declared a
"groundwater management area" as defined by the "Groundwater
Protection Act" adopted by the Oregon legislature in 1989 (Oregon
House Bill 3515, sections 17 through 66).
The actual sources of the nitrates found in the groundwater of this
area have not been determined, but potential sources of nitrate in
contaminated wells include agricultural fertilizers, vegetable
processing wastes (primarily effluent from potato processing plants),
industrial waste, domestic septic systems, and animal waste from feed
lots.
The lack information on the impact of potato production on the
groundwater NO3 -N situation was the stimulus for this thesis project.
This study was designed to determine to what extent, if any, selected
potato production practices including irrigation and nitrogen
fertilization contribute to leaching of nitrates below the rooting
zone.
The "working hypothesis" of this study was that under best
management practices, there should be minimal NO3 -N leaching under a
commercial potato field in the Lower Columbia Basin. For this study,
"best management practices" called for the crop to be irrigated at
recommended replacement rates, every 2 days, and to receive
390 kg. ha-1 N.
2
CHAPTER 1
LITERATURE REVIEW
Description of Area Soils, Climate, and Practices
Soils used for potato production in the Hermiston-Boardman area of
Oregon, are generally deep, well-drained fine sandy loams of eolian
origin located on terraces and terrace scarps of the Columbia River.
They contain little organic matter (0.7-1%), are low in clay content
(4-8%), have a medium to high pH (6.7-7.8 near the surface and up to
9.0 at 0.9-1.5 meters), and are inherently low in nutrients.
The
permeability of these soils is moderate to high with an available
water holding capacity averaging about 9 to 18 cm of water per meter
of soil.
Though water erosion is slight, soil losses to wind erosion
can be substantial (Johnson and Makinson, 1988). These soils have a
high leaching potential for nitrates and other readily soluble
materials if sufficient water is present (Vogue et al., 1990).
The
National Pesticide/Soils Database and User Decision Support System for
Risk Assessment of Ground Water and Surface Water Contamination model
(NPRIG) (Jenkins et al., 1991), which incorporates soil
characteristics and average monthly rainfall and irrigation values,
characterizes these soils as having a low nitrate leaching index (NLI)
for rain-fed, dryland farming conditions but a high NLI for irrigated
crop production.
Without added water and fertilizers, most of the land in the
Hermiston-Boardman area is suitable only for low volume grazing use
due to low natural fertility and inadequate rainfall (20-30 cm
annually).
Under non-cultivated conditions little leaching of
nitrates would be expected.
Prior to 1900, only small areas
immediately adjacent to the Umatilla River were irrigated.
The
development of irrigation districts in the early 1900's, construction
of the McNary dam and locks on the Columbia, and the advent of center
pivot irrigation have led to a rapid expansion of irrigated acreage.
Crops such as potatoes, small grains, corn, and alfalfa are now grown
on more than 65,000 irrigated ha (Johnson and Makinson, 1988).
3
Production of beans, peppers, watermelons, peas, carrots, onions and
other high-value irrigated crops is increasing.
The Hermiston-Boardman area is moderately cold and humid in the winter
(average daily temperature 1.7 C) and hot and dry in the summer
(average daily maximum 29 C). Winds and blowing dust are common
during the growing season. Crop evapotranspiration demands are high;
an average late-harvested potato crop may require up to 0.68 meters of
water (Umatilla Electric Weekly Reports, IRZ Consulting, Hermiston,
Oregon). Moisture-sensitive crops, such as potatoes, which require
soil water levels at or above 509,: of field capacity for maximum yield
and quality, require irrigation almost daily in mid-season (Harris,
1978; Middleton et al., 1975). Water use of this magnitude has been
shown to contribute to the leaching of nitrates in sandy soils under
conditions less arid than in the Columbia Basin (Hergert, 1986;
Middleton et al., 1975; Penman, 1948).
Whether similar leaching
losses occur in the Hermiston-Boardman area is not known. Agronomic
principles suggest that, with equal water application, high
evapotranspiration would contribute to substantially lower nitrate
leaching in the Columbia Basin than in more humid regions.
Nitrogen fertilization has increased even more markedly than
irrigation in the Hermiston-Boardman area over the last 40 years
(Mosley, PC 1992). Nitrogen application of up to 900 kgha-1 have
been reported for potatoes but N rate now averages between 225 and 450
kgha-1 depending on the variety and intended crop use (Fitch, PC
1991).
Later-maturing potato varieties for processing out of storage,
which account for most of the Columbia Basin production, require high
levels of nitrogen for maximum yields.
Much of the nitrogen is
applied as urea, ammonium nitrate, or ammonium sulfate either pre-
plant or at planting; supplemental nitrogen is applied in irrigation
water during the season based on results of petiole and soil analyses
(Fitch, PC 1991; Pumphrey et al., 1991).
Current Groundwater Situation (EPA, DEQ, Other)
The groundwater of the Umatilla River Basin is predominately confined
to scoriaceous fractured zones at the top of ancient lava flows buried
deep beneath a surface of dry eolian sands (Hogenson, 1956; Robison,
1971).
The lava flows form relatively impenetrable layers which
4
restrict vertical movement of groundwater, however the fractured
scoriaceous zones are very porous and permeable which allows water to
move laterally parallel to each flow with relative ease.
Such flows
results in high artesian pressure where the buried lava bed has become
tilted from uplifting. The tabular groundwater bodies are not
perfectly continuous, because each lava flow tends to "lens out"
thus cuts off or merges with the underlying flow (Hodge, 1942).
and
Faults and fractures, in addition to wells open to several zones, are
important sources of vertical mixing between each tabular aquifer, and
permit recharge from surface sources. Major recharge of these
aquifers is slow, and predominantly originates in the uplands of the
Blue Mountains where the basalt flows surface. Groundwater is also
found in the sediments overlying the basalt, which in most cases
contain only a small amount of available water (Vaccaro, 1986).
Historically, concern over nitrate levels in area wells has been very
low.
In an area-wide sampling reported by the United States
Geological Survey in 1971, water from over 100 well samples was
analyzed for 5 cationic species, and 4 anionic species, but not for
nitrate (Robison, 1971).
However, sampling of "Hansell Aquifer
water" in ca. 1973 yielded nitrate nitrogen levels ranging from 25 to
31 ppm throughout the year (Fitch, PC 1993a).
In 1990, the Environmental Protection Agency (EPA) compiled results of
a nationwide testing of urban community and rural domestic wells for a
variety of agrichemicals including nitrate (U.S. EPA, 1990).
Over 52%
of community and rural wells were found to have detectable levels of
nitrate, with around 2% of these sources exceeding the 10 ppm minimum
contaminate level (MCL) set as acceptable by the EPA (Table 1.1).
Wells in the Treasure Valley region of eastern Oregon, and the lower
Columbia Basin area of north central Oregon have unacceptably high
levels of nitrate-nitrogen contamination (Pettit, 1990). As of July,
1991, 26 of 150 wells in western Umatilla and northern Morrow counties
tested by the Oregon Department of Environmental Quality (ODEQ)
exceeded the federal standard of 10 ppm.
Consequently 144,000 ha of
this area, which accounts for most of Oregon's potato production, has
been declared a "groundwater management area" as defined by the
"Groundwater Protection Act" adopted by the Oregon legislature in 1989
(Oregon House Bill 3515, sections 17 through 66). Under this act, a
citizens' advisory committee has been appointed to develop a plan for
5
Table 1.1. EPA National Pesticide Survey (1990)
FOUND IN WELL WATER
detected
(exceeding MCL)
Urban
Nitrate
Pesticide
NO3 + Pesticide
52.1%
10.4%
7.1%
(1.2 %)
(0.80)
Rural
57.0%
4.2%
3.2%
(2.4 %)
(0.6 %)
protecting groundwater quality in the Hermiston-Boardman area.
Subsequently, during the summer of 1992, the ODEQ conducted a synoptic
sampling of 876 wells in the Umatilla-Boardman area (Figure 1.1).
The actual sources of the nitrates found during this survey have not
been determined, but wells with the highest nitrate levels are often
clustered around food processing plants (primarily potato) and feed
lots (Oregon DEQ, 1994). The nitrate levels are not uniformly
distributed in the alluvial groundwater, nor do they conform to any
regional pattern; however, isolated peak concentrations along flow
paths and the irregular distribution of nitrate levels are consistent
with point source nitrate loading (IRZ Consulting, 1993).
Potential
sources of nitrate in contaminated wells in this area include
agricultural fertilizers, vegetable processing wastes (primarily
effluent from potato processing plants), industrial waste, domestic
septic systems, and animal waste from feed lots (Doerge et al., Fitch,
1991 & 1993b; U.S. EPA, 1991). Wright (1964) observed that the major
source of nitrate contamination of water in most agricultural appeared
to be animal and human waste.
Implications of Nitrate in Groundwater
Contamination of groundwater by nitrate and other agrichemicals has
become a serious concern in many areas of the United States (CAST,
1992; Doerge et al. 1991). Wright and Davidson (1964) reviewed the
health problems associated with high nitrate levels in drinking water
and foods for human and animal consumption. They pointed out that the
nitrate ion is relatively nontoxic to non-ruminant animals, and that
6
Figure 1.1. Results of Oregon DEQ well water sampling, 1992
OREGON DEQ WELL WATER SAMPLING
SUMMARY OF RESULTS FOR NITROGEN
300
100
272
90
250
80
70
MEAN
3
MED
150
sari ples
8.57 PP m
AN= 4. 70 ppm
N= 576
200
60
139
50
100
40
66
60
30
49
50
16
:5+;>;
0
1
5
10
15
20
4
5
7559
6
VI,
6
PZ79
1
15 20 25 30 35 40 45 50 100200
10
PPM NO3+NO2 IN SAMPLE
"nitrate toxicity", as commonly used, actually refers to nitrite
toxicity. Nitrite is produced following the reduction of nitrate to
nitrite within the gastrointestinal tract. Once absorbed by the
blood, it oxidizes the ferrous iron of the red blood pigment to ferric
iron, which impairs the blood's ability to carry oxygen. Ruminant
animals are particularly susceptible to nitrate toxicity which can
reduce growth, lactation, and reproduction rates (Wright and Davidson,
1964).
In humans, nitrate contamination of water poses the greatest
risk to infants who can develop methemoglobinemia (blue baby
syndrome).
Adults drinking water which may cause methemoglobinemia in
infants are usually unaffected.
Nitrate in soil solution may also be
linked to stomach cancer in adults, by reacting with amines in
solution to form carcinogenic nitroso compounds (Doerge et al., 1991;
Ginocchio, 1984).
In addition to direct heath effects, the appearance of increased
nitrate levels in groundwater is an indication that other, potentially
7
more hazardous, agrichemicals may be leaching below the rooting zone
(CAST, 1992; Connell and Binning, 1991).
The presence of elevated
nitrate levels in groundwater may also indicate economic loss by over
application of nitrogen fertilizers and/or irrigation water.
Natural Sources of Nitrates in Arid Soils
The existence of virgin soils with nitrate levels exceeding 100 ppm is
well documented (Marrett et al., 1990; Sullivan et al., 1979; Viets
and Hageman, 1971).
In some caliches of arid regions of the western
United States, elevated nitrate levels have been attributed, in part,
to the rapid evaporation of surface waters of ancient lakes or seas,
leaving concentrated layers of sodium nitrate (Marrett, et al., 1990).
Low rainfall in these areas precludes the leaching of such layers
deeper into the soil profile and restricts denitrification by soil
microbes (Viets and Hageman, 1971).
Mansfield and Boardman (1932)
found that caliche and playa deposits, protected by arid climates, or
subsequently formed impervious layers, could contain deposits of up to
605:5 NaNO3.
Goldschmidt (1954) postulated that some of the nitrate
soils in arid regions of North America may be connected to the
oxidative weathering of marine hydrolysate sediments from the Eocene
age.
Sullivan et al.
(1979) perusing earlier work by Dyer (1965b) studied
soils with high naturally occurring nitrate levels (300
700
mgliter-1) in the western San Joaquin Valley of California. Deep
cores into marine sediment contained nitrate concentrations of up to
2,000 mgliter-1. The soil nitrogen concentrations of each area did
not necessarily show any strong correlation with the adjacent geologic
nitrogen sources, perhaps providing evidence for long distance
leaching of nitrates from other sources.
Recently, Marrett et al.
(1990) reported that deep cores taken from
uncultivated desert alluvial fans contained sections of coarse soil
with high NO,-N levels (20-208 mg. liter-1 in water saturation extracts)
that were unpredictable both laterally and vertically and unrelated to
alluvial strata. They appeared to be a natural phenomenon, having
been derived by the weathering of the native rocks in the area,
followed by leaching of concentrated solutions to certain depths.
8
Sources of Nitrate in Agricultural Soils
Nitrogen differs from most other nutrients applied to soils in its
ability to be transformed by soil micro-organisms into vastly
differing forms, including cationic, anionic, and gaseous.
Major
contributors to inorganic nitrogen in agricultural soils include
fertilizers, biological fixation, and the mineralization of organic
matter.
Nitrogen is removed from agricultural soils primarily by
denitrification into gaseous form, volatilization (of NH3 after
ammonification), crop uptake, leaching beyond the root zone, and
organic incorporation (Mengel and Kirkby, 1987).
Investigations of nitrate accumulation comparing "virgin" and cropped
land for nitrate levels and distribution have received broad attention
(Hubbard et al., 1984; Sullivan et al., 1979; Viets and Hageman,
1971).
Viets and Hageman (1971) examined several studies involving
paired sites.
In general, virgin soil contained higher levels of
nitrate in the surface profiles than cropped land, but the cropped
land contained higher levels of nitrate deeper in the soil profiles
(15.2 meters).
Nitrate Leaching in Agricultural Soils
In well-aerated sandy soils, the major loss of nitrogen from the
rooting zone (other than crop removal) is by nitrate leaching during
winter (Hergert, 1986; Rauschkolb, 1984; Schepers, 1988). The
leaching potential of nitrate in soils is a function of many factors
including:
1. depth of the rooting zone (potential and active) and the
activity of the crop in uptake of moisture and nitrogen;
2. the amount of precipitation in excess of evapotranspiration as
well as the hydraulic conductivity and texture of the soil
(Bergstrom and Johansson, 1991);
3. the rates of transformations taking place (i.e.,
mineralization,
nitrification, denitrification) which are
influenced by soil temperature, moisture content and organic
matter content;
4. quantity and types of residual nitrogen present from the
previous crop (Viets and Hagman, 1971).
9
Thomas (1970) discussed effects of soil physical and chemical
properties on nitrate leaching, and the influence of climate on
nitrate mobility.
He notes that the four properties which most affect
the mobility of NO3-N in soil are capillary conductivity, water
content, pore size, and distance to the water table.
Sandy loams,
such as found in the Hermiston area, are especially prone to leaching
under irrigation regimes, because the low capillary conductivity and
high surface evaporation rates prevent the soil from drying out to any
considerable depth with the cessation of irrigation or rain. When
winter rains or irrigation water is then applied, the large pore size
of these soils, results in rapid infiltration of water and soluble
salts deep into the moist soil layers.
Thomas surveyed the nitrate
mobility characteristics of different geological areas of the United
States, and concluded that the high leaching efficiency of western
soils was due to anion exclusion, high permeability, and lack of water
restricting zones.
Dyer (1965a) noted that the nitrate leaching
potential of western soils is much higher than those of more humid
regions
.
Quoting from Allison (1965), Viets and Hageman, 1971 noted that
"leaching of available nitrogen beyond the plant root zone usually
does not occur to any marked extent in cultivated, medium textured
soil in the United States, unless the rainfall [or total applied
water] is above about 50 inches (1.27 meters)".
In most of the
studies they reviewed, Veits and Hageman (1971) found that
distribution of rainfall was found to be a critical factor, because
most leaching occurred in the late fall when evapotranspiration
demands were low.
The potential for pollution of groundwater with high rates of nitrogen
fertilizer is greater than for low rates, but high rates do not
necessarily cause nitrate leakage into the aquifer (Veits and Hageman,
1971).
Nitrate leakage is affected by the crop species, soil type,
the amount and distribution of precipitation, and many other factors.
Nitrate leaching below the root zone will eventually reach the water
table, but this "fact" could not be accepted as proven in 1971 (Veits
and Hageman). Nitrate in groundwater appears to be much more stable
biologically than that in surface waters, but its concentration is
subject to wide fluctuations caused by dilution, mixing, and
stratification.
In nearly all studies examined in their 1971 review,
Veits and Hagmean found that fertile soils produced drainage water
much richer in nitrate than rainfall or irrigation water, but the
10
effect of this downward movement of nitrate on groundwater quality
depended on characteristics of the aquifer. They stressed the need
for more intensive investigations of factors leading to nitrate
contamination of groundwater, and in particular the necessity for
agronomists and hydrologists to work together to reduce this hazard.
Application of irrigation water or rainfall to sandy soils can result
in nearly complete movement of all applied N from the surface zone of
placement. In the Columbia Basin of Washington, nearly all nitrogen
fertilizer applied to the surface 0.6 m of a potato field was leached
through the 0.6 to 1.2 meter layer within one growing season under
furrow irrigation (Middleton et al., 1975).
Middleton et al. (1975)
found large differences between the amount of nitrogen leached under
furrow and sprinkler irrigated fields, and attributed this to deeper
leaching from the bottom of flooded furrows than from furrow bottoms
in sprinkler irrigated fields. In the loamy sand found in the potato
growing areas of the Sandhills of Nebraska, Schepers and Martin (1987)
estimated that the average area precipitation could leach 20-80% of
the residual soil N below the roots by mid-June.
Hergert (1986) studied nitrate leaching rates through sandy soil under
sprinkler irrigation, and found that the rates of NO3-N leaching to
groundwater could be substantially reduced by more closely matching N
fertilizer rates with crop yield requirements.
The highest NO3-N
leaching losses resulted from precipitation in winter and early spring
which caused leaching of the previous years' residual nitrate.
This
observation was confirmed by Prunty and Montgomery (1991) who found
that nitrate levels collected in drainage lysimeters at 2.3 m deep in
a loamy fine sand under corn, increased within 30 days in response to
higher irrigation rates, while higher rates of N fertilizer were not
reflected by increased concentrations of NO3-N in drainage water until
325 days after application and persisted for 500 days.
The effect of irrigation and fertilizer regimes on the movement of
nitrate below the root zone Rhodes grass grown on sandy soils in
Israel was studied by Rawitz (1980).
Under high frequency applica­
tions, crop yields increased, but at the expense of nitrogen
utilization efficiency.
High frequency irrigation left a large
percentage of the residual nitrate in the lower portion of the soil
profile at the end of the season, subject to leaching by winter rains.
Under optimum conditions, less than 5% of the applied nitrogen
remained in the soil at the end of the season, 90% was accounted for
11
by crop uptake, and crop yields were satisfactory.
Rawitz concluded
careful management of this, and other solid-stand summer crops, grown
on sandy soil under a Mediterranean rainfall pattern, can result in
both high yields and low groundwater nitrate pollution.
Pratt (1984) described the ideal agricultural system as one in which
the crop root is efficient at absorbing nitrates, there is no increase
in leachable nitrates at maximum yield, the crop has a predictable N
requirement, and little water movement occurs through the soil during
periods when large amounts of nitrate are available.
Pratt compared
this ideal system with "real" systems in which nitrate leaching does
occur, in an attempt to bring the two approaches closer together.
Processes effecting NO3-N transformations remain active between
October and May, including periods during which soils are frozen
throughout a 0.6 m profile (Heaney and Nyborg, 1988). In a typic
Agrisol of north-central Alberta, commonly used for potato production,
Heaney and Nyborg (1988) found evidence that NO3-N moved upward during
the winter months as a result of ice lens formation. The levels of
NO3-N increased an average of 6.4 mgkg" N in the upper 0.30 m of the
soil profile during the winter months.
Webster and Goulding (1989) studied the effects of organic matter (OM)
content of soils following spring barley on winter nitrate leaching
rates.
The primary effect of organic matter was an increase in the
denitrification rate in the early fall while the soil was still
relatively warm, thereby removing some of the residual NO3-N prior to
winter rains. Gaseous losses from low OM soils (fertilized with
inorganic fertilizers) were 4.5 kgha" N, while losses from high OM
soils were 29 kgha" N.
Soil macropores strongly affect the depth and dispersion of nutrients
in soils.
Priebe and Blackmer (1989) found that dispersion of
018-labeled water and N18-labeled urea through the soil profile was
much greater than would be expected based on standard saturated flow
models not accounting for flow through soil macropores, and concluded
that a complete understanding of the role of macropores in leaching
rates of N and other nutrients is lacking.
They stressed that
increased efforts are needed to identify management practices that
will reduce such losses of nitrogen to sub-root zones.
12
Brouwer (1989) reviewed factors affecting leaching rates in
agricultural soils, and found that movement into the vadose zone
ranged from 1 mm/year in semiarid climates, to 500 mm/year in humid
areas.
Brouwer concluded that prevention of high NO3-N concentrations
in the vadose zone requires that best management plans for both
irrigation and nitrogen application be used.
The predicted rates of
NO3 movement into the vadose zone were generally greater than those
predicted by the Darcy flow equation which failed to account for
preferred flow of nitrates through cracks, worm holes, root channels,
etc., and for spatial variability in infiltration rates.
Recently,
modifications of Darcy's law to reflect solute mobility under field
conditions and develop simple field methods for measuring the soil's
effectively mobile water fraction during near-saturated flow have been
advanced (Clothier et al., 1992; Smith et al., 1984).
The amount of nitrate leaching from tiled potato fields in New
Brunswick, Canada was found to vary from 1 to 65 mg liter' N with
substantial changes in NO3-N concentrations within flow events
(Milburn et al., 1990).
Flow-weighted averages of the five fields
studied were 10 mgliter' regardless of whether the sites were
established potato production fields or from low input production
systems (all fields treated the same during the study).
Substantial
variation in the concentration of NO3 in the drainage effluent among
fields was attributed to the different mineralization potentials of
the sites.
The greater than 10 mg liter' leachate levels of the
established potato rotation fields remained through the following non-
potato year.
Stenitzer (1988) substantially reduced the amount of nitrate leaching
in shallow sandy soils of eastern Australia by the use of gypsum
blocks to improve irrigation scheduling. He found 90% of the nitrate
leached to the groundwater was due to spring rains, and not directly
from irrigation water during the cropping season. To reduce nitrate
loading of the groundwater, Stenitzer recommended modifying the
cropping pattern and fertilizer application timing to reduce high
levels of residual N and water in the upper soil profile at the end of
the growing season.
Etreiby and Laudelout (1988) studied the movement of nitrate through a
loess soil to determine potential transfer of nitrate to the aquifer.
Titration of chloride and nitrate ions through columns of undisturbed
soil showed that the
spatial variation of the main transfer
13
properties were within limits of commonly measured soil properties.
They concluded that the variability of parameters controlling the rate
of solute transfer from the plow layer to the water table are not so
great as to make the parameters useless.
Reviewing nitrogen management in the Pacific states, Rauschkolb (1984)
pointed out that it is nearly impossible to avoid loss of nitrogen
below the root zone in sandy soils under furrow and flood irrigation,
and suggested that maximum efficiency of nitrogen application could be
achieved by adding small amounts of N (usually less than 25 kgha')
with each irrigation. This is now common practice for potatoes grown
under pivots in the north-central Oregon area.
He also recommended
the use of anhydrous or aqua ammonia to minimize leaching losses due
to the low mobility of NH4' and delayed nitrification.
Effects of cropping systems on quality of groundwater were discussed
by Stewart (1970) and more recently by Schepers (1988).
Rainfall
pattern is a key factor in nitrate leaching. Heavy rains during cold
periods of late fall, winter and early spring which coincide with: (1)
high soil nitrate levels due to residual nitrogen, (2) reduced
denitrification rates, and (3) lack of crop uptake, often result in a
substantial increase in nitrate leaching.
In drier areas, years of
abnormally high rainfall leach lower profile nitrate deep into the
soil profile, beyond the reach of most crops.
Stewart (1970) stated
that many fertilized soils contribute less nitrate to the groundwater
supplies than when first cultivated due to reduced total organic
matter caused by cropping.
Because of the high solubility of nitrates and very permeable nature
of soils in the Hermiston-Boardman area, irrigation rates are thought
to be even more important than fertilization rates in determining
nitrate leaching during the cropping season (IRZ Consulting, 1993).
Since water-holding capacity of Hermiston-Boardman area soils is low,
winter rains after harvest cause additional leaching independent of
irrigation.
The use of winter cover crops following potato to trap
residual nitrogen during the winter may be of more importance than
previously thought in preventing nitrate leaching (Pumphrey and
Rasmussen, 1983a,b).
The additional rooting depth of some rotation
and cover crops relative to potato may provide a useful technique for
a "reverse flow" of nitrogen from below the potato rooting zone to the
surface as nitrogenous compounds in plant tissues (Miller et al.,
1989) .
14
Nitrogen Budgets and Models to Estimate NO3-N Leaching
The use of a nitrogen budget (Garman, 1970) to estimate levels of
nitrate leaching into the groundwater has been the subject of several
studies.
Many examples of how such a concept has been used to
estimate the relative rates of nitrogen loss by denitrification,
leaching, and crop removal were noted by Viets and Hageman (1971).
Estimated rates of nitrate leaching in the studies reviewed varied
widely depending on factors such as soil type, water applied (rainfall
+ irrigation), experimental techniques and nitrogen sources (manure
vs. inorganic).
In extreme cases, nitrate percolate was equal to
about 45 percent of the nitrogen applied; in other cases rates as low
as 2.5t were estimated. They noted that, in many cases, losses of
fertilizer of little direct economic significance to the grower could
significantly contribute to eutrophication of surface waters.
Adriano et al.
(1972) examined soil nitrogen balance in selected row
crops in southern California and concluded that fertilization
practices used on row crops at the time should be modified to reduce
the NO3 leaching to the groundwater.
Reduced leaching could be
accomplished without sacrificing economic returns by increased use of
fertility tests, closer monitoring of water usage, and more crop
specific fertilization.
The Burns model for movement of nitrate in wet sandy soils was
evaluated by Khanif et al. (1984). Agreement between calculated and
observed values was generally good when the groundwater table was low
and layers impeding flow were absent.
Several nitrogen cycling models have been developed in recent years
from these earlier works (Aslyng, 1986; Jenkins et al., 1991; Shaffer,
et al., 1991; Vogue et al., 1990). Most are designed primarily to
(1) increase fertilization efficiency; and/or (2) to decrease
environmental pollution caused by nitrate leaching or runoff. Among
the more traditional nitrogen cycle topics, Steenvoorden (1987)
discusses the use of computer modelling to predict the behavior of N
in soil and groundwater, and the application of modelling to soil
surveys.
Some specific models include:
15
(1) NITCROS
NITrogen balance in CROp production Simulation model,
developed by Aslying (1986), incorporates average rates of
mineralization, denitrification, crop uptake, and leaching.
tested in several field experiments on sandy soil, results
When
confirmed the expected value of winter and late growing crops in
reducing leaching of NO3- to groundwater.
Reductions in nitrate-N
leaching with cover crops averaged 20 kgha-1.
(2) NLEAP - Nitrate Leaching and Economic Analysis Package (Shaffer
et al., 1991) is a comprehensive model developed to implement the
theories, methods, and equations that have been generated on
nitrogen transformations and movement, into a user-friendly
package designed to answer fundamental questions about how various
inputs (soil factors, cropping histories, nutrient levels, etc.)
may affect NO3-N leaching and overall N budgets.
This package is
somewhat unique in its emphasis on production economics. Its
stated audience includes farmers and extension personnel along
with soil scientists and SCS personnel though the comprehensive
level of inputs required to run this program may limit its appeal
for "rough and dirty" estimates.
(3) NPURG and The Vogue Models
two models which give quick, though
admittedly less accurate, estimates of nitrate leaching useful for
north-central Oregon soils, are (a) NPURG
National
Pesticide/Soils Database and User Decision Support System for Risk
Assessment of Ground Water and Surface Water Contamination
(Jenkins et al., 1991) and (b) "Guidelines for minimum movement of
Pesticides to Groundwater" (Vogue et al., 1990).
The NPURG is a
computerized information delivery system used, among other things,
to analyze the potential for pesticides and nitrates to move below
the rooting zone.
It uses a SCS Soils-5 database and monthly
precipitation values to rank the nitrate leaching index of a
specific soil in a specific climate.
The Vogue model, used
primarily to assess the risk of pesticides leaching through the
Oregon soils, ranks all the major Oregon soil series into their
respective leaching potential, which are in turn related to their
nitrate leaching potentials.
16
Recent work in the area of deep soil nitrogen transport and
transformations indicates that the assumption of minimal
denitrification in deeper soil profiles may be erroneous (Balkwill and
Ghiorse, 1985; Francis and Dodge, 1986; Klein and Bradford, 1980;
Yeomans et al., 1992).
Both insoluble organic substrate and
substantial denitrifying microbial populations have been found at
depths to several hundred meters in some soils, along with coinciding
conditions of low oxygen levels, high redox potentials, and nitrate
concentrations adequate for denitrification to occur.
Measurable
denitrification was found to occur at these depths by Francis and
Dodge (1986). Obenhuber and Lowrance (1991) found significant
increases in the denitrification activity of an aquifer microcosm by
the addition of glucose. The slow rate of denitrification in subsoils
of Iowa corn and soybean fields (2-3 m) was correlated with the lack
of organic carbon, not lack of denitrifying organisms or nitrate
(Yoemans et al., 1992).
Matthes (1982) and Ronen et al.
(1984) point
out that significant amounts of transformation may occur in this zone,
despite the slow denitrification rates, due in part to the very long
transit times of water moving in these deep soils.
Techniques for Estimating Soil Nitrate Levels
Ammonium and nitrate are the forms of soil nitrogen most readily taken
up by plant roots, and thus comprise an important component of soil
fertility analysis.
These ionic forms of nitrogen are also those most
likely to be transported in soil fluids and consequently are important
factors in environmental purity studies (Keeney and Nelson, 1982;
Marschner, 1986).
The most efficient sampling strategy for estimating mean field NO3
concentrations in New Zealand silt loam used small localized clusters
of samples separated by at least 12 m (Bramley and White, 1991).
Spatial variability of the NO3 and exchangeable NH4 concentration in
these soils was high, and conformed to lognormal distributions.
Estimation of the mean field nitrate levels with 95% probability
( +/­
5%) required 12 clusters of samples consisting of 3 cores each bulked
as a single sample, representing a very large sampling effort. An
auger sampler which was found to be as reliable as a core sampler in
determining soil nitrate levels under field conditions with four
differing soil types (Shapiro and Kranz, 1992)
17
Considerable temporal and spatial variation in soil nitrate and
ammonium are found in field soils (Lockman and Storer, 1990).
Van
Noordwijk and Wadman (1992) discussed the impact that spatial
variability in a field plot soil can have on environmental concerns
over nitrate leaching to groundwater.
While the so-called
Environmentally Acceptable Production (EAP) rates of nitrogen
application are based on an average application rate per field, the
presence of spatial variability in the soil may result in excessive
nitrate leaching under areas of high nitrate levels. They conclude
that the choice of relatively homogeneous sites for field experiments
has introduced a bias in existing quantitative data dealing with
environmental effects on crop response to fertilizer applications.
Spacial variability in the N supply of a soil should be explicitly
taken into account when conflict arises between environmental and
production targets.
Levels of inorganic forms of nitrogen in soils can be analyzed by a
variety of techniques (Bremner, 1965; Munter, 1990; Page et al.,
1989).
Most methods require some type of fluid extraction, though
direct soil analysis (Haby, 1989), or analysis of NO3-N content of
packets of resin beads placed in the soil (Somasiri and Edwards, 1992;
Torbert and Elkins, 1992) has been successful. Soil analysis
techniques for inorganic nitrogen include steam distillation (Preez et
al., 1987; Rice et al., 1984), microdiffusion (Kelley et al., 1991),
colorimetric reactions in a liquid or solid phase (Burton et al.,
1989), conductimetric systems involving chromatographic and membrane
separations (Nieto and Frakenberger, 1985a, 1985b), and ammonia and
nitrate ion sensing electrodes (Banwart et al., 1972; Bremner and
Tabatabai, 1972; Byrne and Power, 1974; Milham et al., 1970). More
specialized methods of soil nitrogen analysis include the use of mass
spectroscopy (Barrie and Lemley, 1989; Liu and Mulvaney, 1992), near
infra-red spectral analysis (Niemeyer et al., 1992), nuclear magnetic
resonance, and gas chromatography (Munter, 1990).
Ion specific electrodes have been reliably used since the early 1970's
for the detection of ammonia and nitrate in various media.
et al.,
Banwart,
(1972) found the ammonia electrode to be a rapid, simple and
precise method to analyze soil and water samples which agreed
favorably with results obtained by steam distillation.
Bremmer and
Tabatabai (1972) used an ammonia electrode to replace the distillation
step in a total Kjeldahl N analysis, noting that the electrode option
was simple, rapid, and precise, and yielded results that closely
18
agreed with those obtained by the customary distillation-titration
method.
Byrne and Power (1974) determined that the ammonia electrode
was a simple, rapid and precise method to determine the ammonium
nitrogen content of animal slurries yielding results that closely
agreed with steam distillation.
More recently, the ammonia electrode
was used to measure both the ammonia and nitrate content of soil
samples by converting the nitrate to ammonia by cadmium reduction
using Orion test kit No. 700005 (Lockman and Storer (1990).
The
nitrate electrode has been successfully used to measure nitrate
content of plants, soils and water yielding results favorable to
steam distillation (Milham, et. al., 1970). More recently, activities
within cells of excised barely roots have been measured by a nitrate
electrode (Zhen, et. al., 1992).
Tissue analysis to assess plant and soil nitrogen status has become a
widely effective practice (Doerge et al., 1991; Prasad and Spires,
1984).
Tissue testing for NO3- has been found to be more reliable
than soil testing to evaluate N supply to the crop, and are routinely
used for evaluating nutritional status of potatoes (Rauschkolb et al.,
1984).
Reliable hand-held nitrate and chlorophyll meters are
increasingly available as fertilizer management tools.
Petiole
nitrate tests have been used to estimate the degree of nitrate
leaching from potato plots under both conventional "full rate" and
"reduced rate" fertilizer regimes (Connell and Binning, 1991) and
accurately reflect the differences in soil nitrate profiles under
potato crops (Sanderson and MacLeod, 1992).
Rizzio et al. (1984),
found that petiole nitrate levels in the Hermiston-Boardman area were
positively correlated with the number of years in which fields had
been in potato production.
In all cases the petiole nitrate levels
fell into the "excessive" range (2.12% to 2.88%, with 1.6% =
excessive), indicating that, historically, the potato fields had been
over-fertilized with nitrogen.
Potato as a "High Risk" Crop
Hypothetical nitrate leaching from potato fields has received a great
deal of attention and is of concern to responsible growers, but
objective data quantifying the relative contribution of potato
fertilization to Columbia Basin groundwater nitrates is limited.
Residual nitrate in potato production fields can result in loss by
19
leaching during the winter months resulting in both economic loss and
potential groundwater pollution problems (Connell and Binning, 1991;
Doerge et al., 1991; Hergert, 1986).
Field survey results indicate
that under best management practices there is not a large amount of
nitrate leaching from the rooting zone of potato fields into the
vadose zone below these fields (IRZ consulting, 1993) In general,
significant nitrate leaching was only observed from fields receiving
higher than recommended levels of irrigation water and/or fertilizer.
High nitrogen application rates have been reported to reduce yields of
some varieties of potatoes (Harris, 1978; Lauer, 1986; Westermann,
1993).
Yield of the variety Nooksack, was reduced by N levels
greater than 200 kgha-1 on silt loams and greater than 300 kgha-1 on
Quincy sands, with the difference being attributed to variations in
the rates of nitrate leaching and soil nitrogen mineralization (Lauer,
1986)
.
North-central Oregon fields previously used for potato production are
particularly prone to nitrate leaching during the winter months
because:
A. Potatoes are generally fertilized at a higher rate than many
other crops (200
500 kgha-1 N) and leave a significant
amount of nitrogen and organic matter in the soil profile at
harvest (Connell and Binning, 1991; Kirkby, 1983; Pumphrey and
Rasmussen, 1983)
B. Potatoes are very sensitive to water stress, requiring frequent
irrigations throughout the summer months, thus leaving the soil
profile moist at harvest (Harris, 1978; Middleton et al. 1975).
The very low soil water holding capacity in this area
(approximately 4.6 cm-m-1, or less) coupled with the very high
evapotranspiration demands (hot, dry, windy conditions of mid­
summer) mean delays in watering beyond 3 days quickly cause
plant stress. Frequent heavy irrigations contribute to NO3-N
leaching in sandy soils under conditions less arid than found
in the Columbia Basin (Hergert, 1986; Middleton et al., 1975;
Penman, 1948).
C. Potatoes are relatively shallow-rooted (0.46 meters) and not
able to effectively utilize deep profile NO3-N (Harris, 1988).
D. Potatoes grown in north-central Oregon are harvested in late
summer or early fall, at a time when the soil is relatively
warm and microbiological mineralization activity is high.
This
results in the mineralization and nitrification of significant
20
amounts of organic matter nitrogen that is incorporated into
the soil at harvest, and which can leach into the "vadose zone"
with the winter rains (Thomas, 1970);
Residual nitrate levels as high as 337 kgha' (upper 1.5 meters) were
found in fields previously cropped to potato in Umatilla and Morrow
counties (Pumphrey and Rasmussen, 1983).
Such high levels were
attributed to both excessive use of nitrogen fertilizer and high
nitrification rates following potato harvest. However, in this study,
soil texture had no effect on the rates of nitrate leaching from the
rooting zone under winter wheat.
The winter wheat crop was found to
use up almost all of the residual nitrogen in the soil, but high
nitrate levels resulted in excessive lodging and yield reductions.
Connell and Binning (1991) reported similar rates of nitrate leaching
from potato plots under both conventional "full rate" and "reduced
rate" nitrogen according to petiole nitrate tests.
Nitrate leaching
rates for the Wisconsin soils were found to be high throughout the
season for both systems.
Potato plants recovered larger amounts of N15-labeled NO3 than NH4*
early in the season with no apparent difference later in the season,
probably due to delayed nitrification in cool spring soils (Roberts et
al., 1992).
In this same study, banding, when compared to broadcast,
greatly increased total N recovery for NH4*-N but not for NO3-N, due to
the greater ability of nitrate to leach out of the rooting zone.
Rainfall and sprinkler infiltration patterns under a potato canopy are
non-uniform when traced with Rhodamine WT dye (Saffigna et al., 1975).
From 20 to 400 of the irrigation water applied to the canopy flowed
down the stems and increased the soil water content around the base of
the plants. Deep movement of the dye beneath the furrows was caused
by runoff from the hills and by leaf drip from the outer foliage,
resulting in a very uneven zig-zag infiltration beneath the field.
Winter wheat after a September potato harvest reduced drainage water
nitrate levels in the fall and early winter to less than 10 ppm.
Incorporation of a legume cover crop in September resulted in more
winter leaching of nitrates than did an incorporation of the cover
crop in October or the next spring (MacLeod et al., 1992; Sanderson
and MacLeod, 1992).
21
Under continuous potato cropping, Hill (1985) found significant
temporal variations in NO3--N and Cl- concentrations which were
associated with percolation.
Little leaching occurred during the
summer months, with major loses of NO3--N occurring during heavy
episodes of soil drainage in autumn.
Chloride data indicated that
denitrification was not an important N-loss mechanism. Mass balance
data indicated that as much as 78-220 kgha-1 N were leached from a
field fertilized with only 160-210 kgha-1 N during heavy rainfall
years.
Porous Cup Lysimeters for Determining Nitrate Movement in
Soils
Hansen and Harris (1975) found substantial bias and variability (±
30%) in the representativeness of nitrate and phosphate samples
collected by porous cup lysimeters (PCL)
They attributed this
variation to factors affecting collection as the sample is drawn
through the ceramic wall including intake rate, leaching, diffusion,
.
sorption, and screening, with screening being the most important.
Peters and Healy (1988) concluded, however, that these devices
reliably reflected the concentrations of major cations and anions in
the soil water solution with little effect on pH.
Trace metal
concentrations were found to be significantly altered by the
collection procedures at low concentrations.
Hergert (1986) used a "ceramic candle" to study the rate of nitrate
leaching through corn plots on sandy soils as affected by sprinkler
irrigation management. While not significantly affecting grain yield,
variation of the applied water by 85% and 130% of the evapotranspira­
tion (ET) demands had a large effect on the amount of NO3-N collected
(12 and 75 kgha-1, respectively). He concluded that to effectively
reduce NO3-N leaching on these sandy soils, N fertilizer rates must
match crop yield requirements to reduce NO3-N carry over, and
irrigation scheduling must be tailored to reduce soil water content in
late fall.
Barbee and Brown (1986) compared abilities of suction and free-
drainage soil solution samplers (pan lysimeters) to monitor chloride
movement through three diverse soil textures (sand, silt loam, clay).
While both types of samplers collected sufficient volumes in the sand
22
and silt loam, the pan lysimeters generally gave larger and more
consistent samples than did the porous cup lysimeters (PCL). The PCL
were found to be ineffective in sampling well-structured clay soils
due to the rapid movement of fluid through large pores where it
bypassed the PCL but was intercepted and collected by the larger
surface area of the pan lysimeters.
Hammond and Neilan (1993) used porous cup lysimeters to study rates of
nitrate leaching in various soil types planted to corn.
The water
samples collected from PCL proved to be a reliable source of
information on the status of nitrate leaching through the soil
profile, and were well-correlated with soil samples when converted to
ppm NO3 -N on an oven-dry-soil basis by using the conversion formula:
soil moisture content (neutron probe data) x soil solution NO,-N
concentration (PCL data)
X 0.0568 (conversion constant) = soil NO3 -N
in ppm.
The performance and validity of six of the foremost vadose zone water
sampling devices including PCL, tank lysimeters, agricultural tile
lines, soil coring, pan lysimeters, and shallow wells, were evaluated
under a preferred flow regime by Steenhuis et al. (1991). They
concluded that the most accurate representation of vadose zone
transport can be obtained by employing a combination of methods: a
wick pan lysimeter in the top meter of the soil, a porous cup
lysimeter in the capillary fringe, and tile line sampling of the upper
groundwater.
In several of the case studies, the PCL failed to give
a representative picture of the solute transport, attributable, at
least in part, to excessive "fingering" of the flow paths in these
soils.
In one case (Kung, 1990), water that was evenly distributed in
the rooting zone was channeled through about 50% of the soil matrix
between 1.5 and 2 meters, 10% at 3 meters, and only 1% at 6 meters.
Several recent reports advocate the use of capillary-wick samplers to
more accurately assess nitrate content and flow volumes for the
unsaturated zone in course soils (Gee and Campbell, 1990; Holder et
al., 1991).
23
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48:252-258.
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1991.
In situ vadose zone water quality
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of the ASTM "Symposium on groundwater and vadose zone
investigations: through the 1980's and into the 1990's. San Diego,
CA.
30
Steenvoorden, J.H.A.M. 1987.
Optimizing the use of soils: new
agricultural and water management aspects. (pg 389-408) IN: H.
Barth, and P. L'Hermite (eds). Scientific Basis for Soil
Protection in the European Community; Elsevier Applied Science
Publishers, Barking, Essex, UK.
Stenitzer, E. 1988.
Irrigation scheduling with gypsum blocks to save
water and prevent leaching of nitrate. Proceedings 15th ICID
European Regional Conference. No. 4, 379-392.
Stewart, B.A.
1970.
A look at agricultural practices in relation to
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Mobility in Soils: Accumulation and Losses.
Special Publication
#4.
Soil Sci. Soc. America, Madison, WI.
Sullivan, P.J., G. Sposito, S.M. Strathhouse, and C.L. Hansen.
1979.
Geologic nitrogen and the occurrence of high nitrate soils in the
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Hilgardia 47:15-49.
Thomas, G.W., and M. McMahon.
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Determining differential water
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1992.
An exchange resin method
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Recent investiga­
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EPA570/9-9-015 U.S
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EPA21Z-1020 Office of the
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Denitrification
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32
CHAPTER 2
METHODS AND MATERIALS
Treatments
Production variables included nitrogen fertilization rate and
irrigation rate and frequency (Table 2.1).
"High", "control", and
"low" rates were used for each treatment variable with "control"
corresponding to the average rate used commercially in the area and
the "low" and "high" approximating the lower and upper limits of
common practice (Fitch, PC 1991).
Nitrogen Rate
Fertilizer N totalling 84 kgha-1 N was uniformly applied to all plots
by pre-plant broadcast of 22 kgha-1 N on the pivot site, and banding
of 84 or 62 kgha-1 N (desert or pivot, respectively) at planting.
Differential application of nitrogen began after emergence in early
June and continued at weekly intervals for 10 weeks. Weekly N
treatment applications were delivered as dry NH4NO3 by a hand-held
applicator with minimal disturbance to the area.
Weekly N
application varied from 1 to 2 times a "base rate" of 10.7, 21.4, or
32.1 kgha-1 N (for low, control, and high N-rates, respectively)
depending on seasonal requirements.
Irrigation Rate (IR)
Water was applied at 0.7, 1.0, or 1.3 times the recommended
replacement rate, based on regional evapotranspiration (ET) values
provided by the Boardman/Echo AgriMet remote-sensing weather stations.
The actual "replacement rate" values are based on a Penman equation
(Penman, 1948) modified by IRZ Consulting, Hermiston, Oregon to
reflect crop growth stage and local weather forecast. Replacement
33
Table 2.1. Experimental treatments.
Treatment variables and rates
1. NITROGEN RATES: 220, 390, 560 kgha-1 N;
2. IRRIGATION RATES: 0.7, 1.0, and 1.3 times recommended replacement
levels based on ET predictions;
3. IRRIGATION FREQUENCIES: daily, every 2 days, and every 3 days;
TREATMENTS
No.
Symbol
C
Description'
Rate
CONTROL
2
NR-L
1.0 x rec replacement, watered every other
day, fertilized at 392 kgha-1 N
low nitrogen rate,
224 kgha-1 N
3
NR-H
high nitrogen rate
4
IR-L
low irrigation rate
5
IR-H
high irrigation rate
6
IF-L
low irrigation frequency
7
IF-H
high irrigation frequency
1
560 kgha-1 N
0.7 x rec.
1.3
x rec.
3 day intervals
daily
'All rates at control level except as noted.
values were then divided by an efficiency factor of 0.9 to calculate
the amount of water to apply.
Water application was varied by changing the duration of watering
(1992) or sprinkler nozzle size (1993). Daily catchcan readings made
immediately after watering and weekly readings of oil-covered rain
gages were used to verify amounts.
34
Irrigation Frequency (IF)
Irrigation water was applied daily, every second day, or every third
Except for the irrigation rate treatments, total water applied
day.
was identical for each plot and equal to the recommended daily
replacement for that week.
In 1992, a constant volume of water was
applied, despite different irrigation frequencies, by altering the
duration of each application, and in 1993 by modifying delivery rates
per minute by changing the sprinkler nozzle insert or increasing/
decreasing the spray "fan width" of each sprinkler.
These soils have
a very high infiltration capacity, and no run-off was observed with
increased application rates.
Plot Design and Preparation
Plot Layout
Soil type at the two HAREC sites was an Adkins fine sandy loam
(coarse-loamy, mixed mesic Xerollic Camborthi&). One site was
previously uncropped semidesert while the second had been cropped for
more than 50 years.
Two different sites were used in order to compare
treatment effects on nitrogen leaching rates on "long term" and virgin
soils, and to determine prolonged cultivation effects on spatial
variability and levels of NO3-N, NH4 -N, acidity, soluble salts, and
organic matter.
The uncultivated "desert site" was previously used only for light
grazing.
This site contained all treatment variables in 21 9.1 x 9.1
m plots. Plots were separated by 6.1 m of planted borders. The
cultivated site was located under a center pivot irrigation system and
contained only the nitrogen treatments in nine 9.1 x 9.1 m plots
surrounded by 1.8 m of planted borders. An additional site was
established in 1992 on the corner of the pivot field. This "side
plot" contained three plots at the "control" N-rate, irrigation rate
and irrigation frequency levels watered by the use of reversible solid
set sprinklers.
The "side plot" permitted comparison of effects of
1 See Table 2.3 for information on pH, and nutrient profile.
35
center pivot and solid set irrigation on NO,-N leaching in the same
field.
Plots in the two major trials were arranged in randomized incomplete
block experimental designs. Plots on the "desert site" were irrigated
with solid-set reversible impact sprinklers placed on each corner and
adjusted to cover approximately 110°. Each plot was controlled by an
individual valve to permit differential watering times. The
uniformity of this sprinkler arrangement was investigated prior to
planting and found to be acceptable for wind speeds less than 2.2
msec-1. The previously cultivated site ("pivot site") was irrigated
by center pivot with drop lines and low pressure nozzles.
Planting and Initial Fertilizer Application
In early April, certified 'Russet Burbank' seed pieces weighing 50­
100 g each were planted 0.23 m apart, 15 cm deep, in rows 0.86 m
apart.
Commercially recommended cultural practices were followed.
Ethoprop at 4.4 kgha-1 a.i., and aldicarb at 3.4 kgha-1 a.i.
were
added at planting to control soil and foliar feeding insects. Metri­
buzin at 0.84 kgha-1 a.i. was applied through the irrigation water 4
weeks later to control weeds, along with Asana at 0.035 kgha-1 a.i.
to control insects, with one additional application of Asana in mid
July in 1992, and two additional applications of permethrin at 0.2
kgha-1 in early and late July 1993 to control Colorado Potato Beetle.
Fertilizer (19:90:168:2 kgha" N:P:K:B) was broadcast and
incorporated 2 weeks prior to planting, followed by 62:66:0:38 kgha'
N:P:K:S banded at planting. Fertilizer treatments were initiated by
an application of NI14:NO3 broadcast by hand-held spreader immediately
after planting and followed by weekly applications beginning at
emergence in early June.
Installation of Monitoring Devices
Porous cup lysimeters (PCL) and neutron probe access tubes (NPAT) were
installed with the aid of a tractor-mounted hydraulic soil sampling
probe (Giddings Machine Co, Ft. Collins, Co.) adapted with a rear-
mounted standing platform and wheels that spanned three rows to
prevent compaction around the PCL's and NPAT's. Both NPAT's and PCL's
36
were installed in the 5th row of each plot.
A 7.6 cm diameter tube
was driven to 0.8 and 1.4 m to prepare PCL access holes.
Supplemental
hand auguring was occasionally used to deepen holes.
The soil from
the bottom of each PCL hole was saved and used in installing the PCL.
The NPAT were made of 5.1 cm outside diameter aluminum irrigation
pipe, cleaned, buffed, and inserted to 1.4 m, with 0.15 m remaining
above the surface. A small cone of soil was packed around the base.
Each NPAT was capped when not in use to prevent entry of irrigation
water, rain, or animals.
The PCL's were installed according to Hammond and Neilan (1993), with
minor modifications. After the hole was dug approximately 0.15 m
deeper than the sampling depth, a thick slurry made of water combined
with the soil removed from the lowest depth, was poured into the hole
and the PCL was inserted to the proper depth.
Approximately 0.24
liters of a thick slurry of silicon flour (equal parts of silicon
flour mixed with water) was poured into the hole around the PCL.
Remaining soil from the lower depth was packed around the silicon
flour slurry with a long thin wooden stick until approximately 0.15 m
below the soil surface. A thick slurry of surface soil was then poured
around the base of the PCL, and each PCL was capped with a Bentonite
clay seal at surface level which was covered with a small cone of
surface soil. Any PCL not performing well on the initial sampling was
removed and resealed.
A wooden frame (0.6 x 1.2 m) overlain by thick hogwire grating (0.1 x
0.1 m) was placed alongside the row of PCL and NPAT as an anti-
compaction platform upon which to stand during weekly samplings.
In addition to the PCL and NPAT, a rain gauge and elevated mount for a
3.8 liter irrigation catch can was installed in the center of each
plot.
Irrigation Scheduling
Except as noted for the frequency treatment, all plots were watered
every second day during the calmest part of the day, generally at
sunrise, though occasionally at sunset.
37
Table 2.2. Watering regime used at the desert site.
DAY
1
2
3
4
5
6
PLOTS WATERED
All plots
Only high frequency plots
All plots except low frequency plots
Only high and low frequency plots
All plots except low frequency plots
Only high frequency plots
Day, Treatments Watered
Irrigation
treatment
1
2
3
4
5
6
High frequency
Controlz
Low frequency
x
x
x
x
x
x
x
x
x
x
x
zControl includes all plots except high and low frequency plots.
Irrigation scheduling was based on a 6-day cycle (Table 2.2).
The
schedule was updated every three days with the most recent recommended
replacement rates.
A 6-day watering schedule was prepared by entering
the current recommended replacement rate into a Quattro Pro
spreadsheet programmed to automatically calculate the amount of water
and duration of watering required on each plot to replace calculated
losses.
At the end of each 6-day cycle, actual crop water-use values for the
previous 6 days, along with rainfall and rain gauge data, were used to
calculate moisture adjustments needed.
When possible, weekly
adjustment irrigations were made on the whole-plot watering day to
avoid disrupting frequency treatments. If a major adjustment was
required (i.e. when a rain storm, or unpredicted cool, moist period
occurred) the adjustment was spread out over several regularly
scheduled irrigations for each plot.
Minor adjustments were also made
immediately after watering, based on catch can data for each plot.
Catch can data were also used to adjust nozzle insert size and spray
angle so that the planned amounts more closely matched the actual
amounts applied to each plot.
38
Scheduled irrigations would be delayed for up to 24 hours during
periods of prolonged windy weather (i.e. continuous winds greater than
3 m-sec-1).
Monitoring, Sampling, and Analysis
Soil Sampling
General
Pre-plant and post-harvest soil samples were taken with a truck-
mounted hydraulic probe (Gidding Machine Co, Ft. Collins, Co.). Mid-
season soil samples were taken with a hand probe to minimize crop
damage.
The samples were taken at 0.3 m intervals to the 1.2 m depth,
or to the calichefied rocky layer ("caliche layer"). No attempt was
made to auger through rock layers. All core samples of the same
interval for a plot were combined, mixed by hand, and dumped into
plastic bags which were then sealed, except as noted for the initial
sampling date. Samples were kept as cool as possible in the field,
and held at approximately 4 C until processing.
Initial sampling
Ten cores were taken from each site in the fall preceding crop
establishment. Portions of each core were sent to the Central
Analytical Laboratory, Oregon State University for complete nutrient
analyses (Table 2.3).
Pre-planting sample
Two cores were taken from each desert plot and 3 cores from each of
the pivot plots in late March prior to any field preparation.
Pre-
plant samples were maintained individually by core and depth in 1992.
Cores of the same depth were bulked at all other sampling dates.
Pre-plant soil samples were analyzed for water content, NO3-N, NH4-N,
pH, and EC.
In 1992, samples were analyzed for % organic matter (OM).
39
Table 2.3. Initial nutrient analyses, desert and pivot sites,
fall 1991.
Sample-depth
pH
EC
ds-cm-I
OM
NH4-N
%
ppm
0.78
0.47
2.55
1.16
0.82
0.86
3.42
0.31
0.10
0.31
0.04
0.02
0.02
0.02
0.06
0.03
0.02
0.02
NO3-N
ppm
total N
%
Desert site
0.0-0.3 m
0.3-0.6 m
0.6-0.9 m
0.9-1.2 m
8.3
8.6
8.7
400
250
250
400
0.31
0.31
Pivot site
0.0-0.3 m
0.3-0.6 m
0.6-0.9 m
0.9-1.2 m
6.9
7.5
7.9
8.0
450
300
210
320
0.78
0.36
0.31
0.21
2.40
0.90
4.45
1.95
0.26
0.28
Sample-depth
P
K
Ca
Mg
Na
SO4
meq
ppm
%
7.8
ppm
meq
1.71
1.78
00g
meq
meq
-100g
00g
00g
Desert site
CaCO3
0.0-0.3 m
0.3-0.6 m
0.6-0.9 m
0.9-1.2 m
10
5
2
2
371
281
176
156
7.5
8.2
13.4
23.9
1.3
1.9
1.7
2.1
0.04
0.04
0.05
0.03
2.25
0.00
0.00
0.00
1.64
1.93
2.68
Pivot site
0.0-0.3 m
0.3-0.6 m
0.6-0.9 m
0.9-1.2 m
13
5
3
3
261
117
105
94
5.3
5.9
6.9
1.9
2.0
2.0
17.2
1.8
0.20
0.36
0.30
0.26
2.52
0.00
0.00
2.18
1.83
1.83
3.53
2.93
4.00
Monthly sampling
Cores were taken to 1.2 m from each plot by hand probe at monthly
intervals during the growing season.
Samples were collected in
clusters of five cores to avoid damaging foliage. Only the "control"
plots were sampled on the first and third sample dates in 1992.
Samples were analyzed for gravimetric water and NO3-N content.
40
Post-harvest sample
Six post-harvest soil core samples were taken from each plot shortly
after harvest.
Samples taken from rows 2-3 and 8-9 of each plot were
maintained separately for analysis of NO3-N, NH,-N, pH, and EC.
Chemical Analysis of Soil Samples
Soil samples were held at 40 C until air-dry (no further change in
weight with further drying), sieved through a screen with 2.0-mm
openings and stored in re-sealable plastic bags at ambient
temperatures until analysis. Approximately 20 g of soil was removed
from each bag and transferred into a 60 ml whirl-pac bag and weighed.
A 1:1 addition of either distilled water (for NO3-N, pH and EC) or 0.1
M KC1 solution (for ammonia) was then made.
The bags were inverted a
few times and placed on a shaker for 15 minutes, inverted again a few
times and allowed to settle for at least 15 minutes. Bags were then
opened and placed on a vibrating surface (i.e., mis-aligned stir plate
on high). The pH and EC electrodes were then gently lowered until the
tip of the pH electrode was slightly submerged into the soft upper
layer of the settled soil material and pH and EC were measured.
A 10 ml aliquot of the solution described above was removed and added
to 10 ml of "nitrate ion extract buffer" (Orion Research Inc., 1983)
in a 4 ml vial, allowed to stand for at least 10 minutes and then
analyzed for NO3-N content (Orion Research Inc. 1983).
A standard
soil extract was measured after every 8th sample and the electrode was
recalibrated when drift exceeded 2%.
The ammonia analysis protocol was altered from that presented in the
operation manual for the ammonia electrode (Orion, 1979b) which proved
to be unsatisfactory for these soils. An 0.2M KC1 1:1 extract was used
rather than the suggested 2M, and the solution was brought to pH 11.1
by placing a 20 ml aliquot of the unfiltered extract into capped vials
to which approximately 0.07 g baked MgO2 and a stir bar had been
added (Stevenson, 1982).
The capped vial was shaken intermittently
for at least 1 minute and the contents analyzed for ammonia gas
2
Heavy MgO heated in an electric muffle furnace at 600
for 2 hours, then stored in a desiccator.
700 C
41
concentration which is directly proportional to NH4-N content (Orion,
1979b).
The response slope of the electrode was determined with
standard NH4-N solutions and the electrode was calibrated with a soil
standard, a uniform soil sample used for all soil analysis. A fresh
standard soil extract was measured after every 8th sample and the
electrode was recalibrated when drift exceeded 2%.
Soil Water Sampling and Analysis
Moisture Content of Soil Profile
Neutron probe (NP) readings and gravimetric analysis of soil samples
were used to monitor soil moisture content. NP readings for all plots
were made at intervals of 0.3 m depth every two weeks (more frequent
readings were made for some plots in 1992).
Plots were sampled
approximately 24 hours after the last watering, but this was not
always possible for the high frequency plots. Neutron probe values
were converted into gravimetric water percentage by using the formula
derived by Pumphrey and Hane (1981) for these soils (Table 2.4).
Gravimetric analyses of the soil samples were calculated by comparing
the sampled weight (wet weight) with weight after drying for 12 hours
at 105 C (Black, 1965).
Nitrate Content of Soil Solution
Soil water samples from Porous Cup Lysimeters installed at 0.6 and 1.2
m depths (4/plot) were collected either every week (1992) or every two
weeks (1993) from mid-May through late August to monitor soil water
NO3-N content. When sampled weekly, a continuous vacuum was
maintained on each PCL, otherwise a vacuum of around 40 cm Hg was
applied 24 hours before sample removal.
Samples were kept at
approximately 4 C until analysis, at which time a 20 ml portion was
combined with 20 ml of nitrate extract buffer (Orion, 1984). This
combined solution was allowed to equilibrate at room temperature for
at least 30 minutes before analysis with the nitrate electrode (Orion,
1979a, and Orion 1983). A control standard was measured after every
42
Table 2.4. Conversion of neutron probe numbers to the soil's
gravimetric water fraction.
Formulae for converting neutron probe readings (NP#) to gravimetric
water fration (GWF).
(from Pumphrey & Hane calibration, Valley field, 1981)z
Depth
0.0-0.3
0.3-0.6
0.6-0.9
0.9-1.2
Formula
m
m
m
m
GWF=(NP#x0.001637)-1.000964
GWF=(NP#x0.001857)-2.193659
GWF=(NP#x0.001832)-2.536077
GWF=(NP#x0.001638)-2.776579
NP#
GWF
0.0-0.3 m
Field Capacity
Perm. Wilting Point
8900
3400
13.57
4.56
0.6-0.9 m
Field Capacity
Perm. Wilting Point
8400
3300
12.85
3.51
NP#
GWF
0.3-0.6 m
7700
3300
12.11
3.93
0.9-1.2 m
10500
5300
14.42
5.90
5th sample and the electrode was recalibrated as needed. Samples of
irrigation water were collected daily and analyzed for NO3-N content
(ppm) in the same manner.
Plant and Tuber Sampling and Analysis
Plant Nitrogen Status
Plant N status was monitored monthly by analysis of petiole samples.
Twenty petioles/plot were selected from the 4th leaf of plants 0.6 m
from the end of each row. Petioles were dried for 24 hours at 60 C,
and stored in plastic bags in darkness at room temperature until
ground in a Wiley mill to pass through a screen with 0.425 mm pores
(Lockman, 1980) and stored in capped glass vials until analyzed for
43
nitrate content by nitrate electrode.
Nitrate analysis involved
placing an 0.3 g sample into a vial with 30 ml of the nitrate extract
buffer, shaking for 30 minutes, and analyzing directly without
filtering for NO3-N content (Orion Research Inc. 1983).
Mid-season Foliage and Tuber Sampling
Above ground biomass (AGE) and tubers beneath 6 plants (3 per side)
were taken from plants in row 1 and 10 at mid-season (early July).
AGB samples were held in a warm ventilated room ranging from 20-30 C
until air dry (i.e., no further change in sample weight occurred with
longer drying) and weighed after removing soil and debris. All tubers
beneath a 0.68 m section of row (0.11 m from the base of the outer
plants) were removed, sorted by size, counted and weighed.
Yield Data
Tubers from 6.1 m sections of rows 2-3, and 8-9 of each plot were
lifted by level bed digger and hand-harvested.
Samples from each side
of the plots were analyzed for total tuber count and distribution
within weight ranges of (1) <113 g, (2) US#1 tubers between 113 g and
340 g,
(3) US#1 tubers >340 g, (4) US#2, and (5) culls (Ag. Marketing
Service, 1983).
At harvest, 20 tubers from weight group 2 were
weighed in air and water to determine the specific gravity, sliced
length-wise and visually evaluated for internal defects (hollow heart,
brown center, and internal discoloration). After 3 months of storage
at 4.4 C and 10 C 20 tubers were again assessed visually for internal
defects.
Internal discoloration included all discoloration of a
physiological nature, including brown center and internal brown spot,
etc, but not fungal or bacterial diseases, etc.
Bruise was not
encountered.
Fry color was assessed on 10 tubers stored at 4 and 10 C for three
months. Four 2 mm "chip" slices from 10 tubers were cooked in 357 C
oil for 5 minutes, hand crushed, and placed into a glass petri dish.
An Agtron light reflectance measuring device set on "green" adjusted
to white = 90.0 and black = 0.0 was used to measure "Fry color".
Fry
color was also evaluated using a standard photographic Fry Color Chart
(Potato Chip/Snack Food Association, 1992) which was used to prepared
a regression formula for the Agtron values.
44
Site Nutrient Profile
The soil properties from these two sites (Table 2.3) are typical of
soils found in North Central Oregon: alkaline, pH increasing with
depth; high in dissolved soluble salts and CaCO3; and low in organic
matter and total N (Gilkerson, 1958).
Organic matter, total N, Mg, PO4, NH4-N, SO4, and soluble salts were
similar between the two sites. CaCO3, pH and K were higher at the
desert site than the pivot site, but NO3-N was slightly lower, and Na
was much lower.
In addition to analyzing each site for pre-plant pH, EC, OM, NH4-N,
and NO3-N, each set of treatment plots was analyzed for statistically
significant differences among the plots used for the nitrogen rate,
irrigation rate, and irrigation frequency treatments. Essentially no
differences were found, with minor exceptions presented in Table 2.5.
Comparison of Hermiston and OSU Soils Lab Results
Pre-planting Soil Samples
Agreement between the values obtained by electrode at the Hermiston
lab (HL) and from the Central Analytical Laboratory (CAL) of Oregon
State University in Corvallis varied with property measured
(Table 2.6).
Table 2.5. Treatment plots showing significant soil differences prior to commencement of trials.
Significantly different plot groups
Values and significance levels
Treatment block sett
Year
Site
Treatment block
Depth (m)
Variable
High
Medium
Low
1992
Desert
Nitrogen rate
0.0-0.3
NO3-N, ppm
2.5 b
3.5 a
3.4 a
1992
Desert
Irrigation rate
0.9-1.2
pH
8.4 a
8.2 b
8.2 ab
1992
Desert
Irrigation freq.
0.9-1.2
pH
8.4 a
8.2 ab
8.1 b
*
1993
Desert
Irrigation rate
0.0-0.3
NO3-N
2.9 a
1.9 ab
1.0 b
*
1993
Desert
Nitrogen rate
0.3-0.6
NO3-N
1.0 ab
1.3 a
0.5 b
**
1993
Pivot
Irrigation rate
0.3-0.6
EC
136 b
183 a
126 b
*
1993
Pivot
Nitrogen rate
0.9-1.2
EC
340 a
213 b
188 b
*
zSet of plots to be used for the high, normal, and low treatments (three plots per treatment set).
Plot numbers vary with each treatment, and site.
*
**
Table 2.6. Comparison of initial nutrient analyses results from CAL and HL lab for desert and pivot
sites.
Sample-depth
pH
CALL
EC
HL
CAL
OMY
HL
ds.cm-1
fall spring
%,­
%.
Desert site
0.0-0.3 m
0.3-0.6 m
0.6-0.9 m
0.9-1.2 m
7.8
8.3
8.6
8.7
7.2 a
7.8 b
8.0 c
8.2 d
***
40
25
25
40
128 ab
116 b
114 a
146 a
***
0.78
0.47
0.31
0.31
0.65
0.43
0.38
0.19
***
Pivot site
0.0-0.3 m
0.3-0.6 m
0.6-0.9 m
0.9-1.2 m
6.9
7.5
7.9
8.0
6.6 a
7.0 b
6.9 b
7.5 c
***
45
30
21
32
237
177
226
258
NS
0.78
0.36
0.31
0.21
0.70
0.36
0.31
0.21
***
a
b
b
c
a
b
be
c
NH4-N
CAL
HL
NO3-N
CAL
HL
ppm
ppm
ppm
pp
2.6
1.2
0.8
0.9
1.6 a
1.3 b
1.3 b
1.1 c
***
3.42
0.31
0.10
0.31
2.6
2.1
2.6
2.5
NS
2.4
1.7
1.8
0.9
4.5 a
2.5 b
2.7 b
1.4 b
***
4.5
2.0
0.3
0.3
3.7
5.5
6.4
6.7
NS
NS, "*Not significant or significant at P=0.001, respectively.
LCAL, HL = Central Analytical Laboratory, Oregon State University,
Corvallis, OR, or work done by author
at lab in Hermiston, OR. Only the HL could be analyzed statistically, CAL samples bulked.
Both
samples taken prior to major disturbance of the site, CAL samples
taken in September, HL samples taken
in March the following spring.
YFall and spring samples both analyzed by CAL.
47
The CAL samples were collected in fall, while the HL samples were
collected early in the following spring, though both were collected
prior to any major disturbance to the sites. Soil NO3-N varies
between fall and spring as a function of plant uptake, leaching rates
and rates of mineralization of incorporated organic matter, and has
been found to move up or down the soil profile in response to drying
or wetting conditions (Dahnke and Johnson, 1990).
Soil pH can
fluctuate as much as 2 pH units during the growing season due to
prevailing moisture regime, and gradually increases during periods of
high rainfall (Van Lierop, 1990).
Differences between the two labs may also be a factor of analytical
technique. The CAL determines pH on a 1:2 soil:water extract and EC
of a saturated paste (Horneck et al., 1989), but the HL used a 1:1
water extract for both. This increase in dilution for pH measurements
would tend to give higher pH values (Van Lierop, 1990), and the
saturate paste would have a higher (and more reliable) EC value than a
1:1 water extract (Rhoades and Miyamoto, 1990).
The pH values obtained by the HL were similar to those reported by the
CAL with regard to differences between sites and depth (Desert >
Pivot, by about one pH unit at all depths) but the HL results were
about 0.5 pH unit lower. The shift in pH may be caused by either the
extract dilution, or possibly the seasonal change in the soil.
The CAL showed little difference in the EC between sites (both sites
averaged 0.32 mmhoscm-1), whereas the HL showed a large difference
between sites (Desert < Pivot, avg. 133 vs 224 dscm-1, x100).
However, as with the pH measurements, no direct comparison between
results obtained by the CAL and the HL can be made because the former
measured EC of a saturated paste, and the HL measured EC on a 1:1
water extract, but comparison of the site and depth patterns can be
made.
The CAL results demonstrate an EC pattern on the pivot site
of 0.0-0.3 m > 0.9-1.2 m = 0.3-0.6 m > 0.6-0.9 m, whereas the HL
showed 0.9-1.2 m > 0.0-0.3 m = 0.6-0.9 m > 0.3-0.6 m.
For the desert
site, CAL gave 0.0-0.3 m = 0.9-1.2 m > 0.3-0.6 m = 0.6-0.9 m,
gave 0.9-1.2 m = 0.6-0.9 m > 0.0-0.3 m > 0.3-0.6 m.
and HL
48
The CAL results showed little difference in NH4-N between sites (1.7
ppm for pivot and 1.4 ppm for desert), while those from the HL showed
a large difference (Desert < Pivot, avg. 1.34 vs 2.78 ppm).
Both labs
showed similar changes with depth (0.0-0.3 m > 0.3-0.6 m = 0.6-0.9 m >
0.9-1.2 m), though the values were not identical. The CAL values were
less than the HL values for the pivot site, and greater than the HL
values for the desert site. This discrepancy may be due to seasonal
differences.
Both labs reported fairly low soil NO3-N levels for both sites.
The
CAL showed the highest NO3-N concentrations in the surface sample and
rapid decreases with depth, especially for the desert site. The HL
results showed fairly uniform distribution of NO3-N with depth for
both sites.
The CAL analyzed both samples for OM content, with similar results,
less than 1% OM at both sites, 0.78% at the surface, and dropping to
0.31% OM at the 0.9-1.2 m level.
Quality Assurance Samples 0103-N and NH4 -N)
The results of CAL lab and electrode analysis of NO3-N concentrations
in extracted soil solution (Figure 2.1) and for soil (Figure 2.2)
correlated well, having r2 values of 0.93 for water samples, and 0.95
for soil samples.
Regression of soil NH4-N analysis from the two labs
was less favorable with r2 value of only 0.627 (Figure 2.3) probably
because the low NH4 -N in these soils was approaching the sensitivity
limit of the ammonia electrode.
Despite the poor correlation between
the two labs,
the ammonia electrode was found to give consistent and
repeatable values (r2= 0.964) for sets of sub-samples of the same soil
bags analyzed sequentially (set after set) on the same day
(Figure 2.4).
49
Figure 2.1. Regression of CAL lab values for soil solution NO3-N on
electrode values.
200
180
.1
,...,160
MI
E
'1140
a
z
I
120
ro
0
100
80
60
IN
40
r squared = 0.927
y= 0.936x + 0.640
20
0
0
20
40
80
100 120
60
140
Electrode value (NO3-N ppm)
160
180
200
Data Analyses
Lysimeter Data
Lysimeter data were analyzed as:
(1) ppm NO3-N in collected solution
("raw"); or (2) ppm on an oven-dry soil basis ("dry soil based").
The
conversion of ppm NO3-N in solution to ppm on an oven-dry soil basis
was accomplished by multiplying the gravimetric water fraction
obtained from the neutron probe readings by the NO3-N concentration in
soil solution
.
50
Figure 2.2. Regression of CAL lab values for soil NO3-N on electrode
values.
50
Regression formula
45
0-50 ppm
y=(1.034x ) + ( 0.651)
si
40
0-10 ppm
10-50 ppm y=(1.063x) + (-0.327)
z 30
0 25
0
0
/All
y=(0.817x) + ( 0.576)
0.35
.
.41111111
ACM.
20
15
11111.11.111P.
10
5
1111111.1P
IN
r s uared values
0-50 ppm = 0.95
0-10 ppm = 0.86
11.
10-50 ppm = 0.86
0
5
10
15
20
25
30
35
Electrode value (NO3-N ppm)
40
45
50
Statistical Analyses
Data were analyzed statistically using the SAS general linear model
(GLM) procedures (SAS Institute, 1988) with a Duncan test to separate
the means at P=0.05.
In addition, the N-rate and irrigation-rate
treatments were evaluated for linearity by orthogonal contrast.
Letters denoting separate means by the Duncan test were only listed on
the tables when linearity was not present, and when there were no
interactions involving those means. The means for "site effect" are
weighted by 21 for the desert site and 9 for the pivot site because
this trial comprised an incomplete factorial with 21 plots at the
desert site, and 9 plots at the pivot site. For the average of the
site means to equal the average of the "year" or "depth" means on the
main effects tables, the site means must be multiplied by 21 and 9 for
the desert and pivot, respectively.
51
Figure 2.3. Regression of CAL lab values for soil NH4-N on electrode
values.
A
A
A
r squared = 0.627
y = (2.292x) + (-0.562)
.
A
.
A
AA
All statistical analysis was conducted in a methodical manner to help
answer the following questions:
(1) YEAR EFFECTS: When comparable, were there statistically
significant differences between means; i.e. were there significant
year effects? If not, data were analyzed independent of year.
(2) SITE EFFECTS: Were there statistically significant differences
between site means; i.e. was there a significant site effect?
If not, data for similar treatments were analyzed independent of
site.
(3) YEAR BY SITE INTERACTIONS: If significant year by site
interactions were found, additional analyses were conducted after
sorting by year and analyzing each main site effect separately.
52
Figure 2.4. Regression of electrode NH4 -N values for soil sub-sample
1 on sub-sample 2.
5
w
4
a
a
-1.3
z
N
2
r squared = 0.964
0
AK
y
=-- (1.172K) +
(-0.269
1
0
0
2
3
5
Soil set #1 (NH4N ppm)
(4) TREATMENT & DEPTH EFFECTS: Were there statistically significant
differences among treatment means; i.e. were there significant
treatment effects?
If not, data were not analyzed further. If so,
were there differences by depth? Which treatments significantly
effected the means? Did these treatment have a positive or
negative influence on variables tested (NO3-N, NH4 -N, yield, etc.).
In addition, where there significant Treatment by Depth
interactions? If so data were sorted by depth, and reanalyzed for
significant treatment effects for each depth.
(5) ADDITIONAL INTERACTIONS: Were there significant interactions
between other independent variables, like year and treatment,
and depth (by site), or any three way interactions?
If so,
year
additional analysis was conducted after sorting by these classes
to answer the questions of how these interactions affected the
53
values of each variable, what limitations did it put upon
interpretation, and what were the possible explanations for the
interactions?
Weather Data for 1992 and 1993 Growing Seasons
The 1992 growing season was preceded by an unusually dry fall and
winter (13.3 cm rainfall), followed by a hot dry growing season
(Table 2.7, Figure 2.5).
The 1993 growing season was preceded by a
winter of relatively heavy precipitation (17.2 cm) and cooler
temperatures, followed by a cool and moist growing season (Table 2.7,
Figure 2.6). Though the average maximum and minimum temperatures were
similar for the two season, during the April-September period of 1992
the total ETp was 130.4 cm, whereas during this same period in 1993,
the ETp was only 117.1 cm.
54
Table 2.7. Weather Data, Oct. 1991
Oregon.
Month
Oct-91
Nov "
Dec "
Jan-92
Feb "
Mar "
Apr "
May "
Jun "
Jul "
Aug "
Sep "
Avg/Total
Oct-Mar 92/93
Apr-Sept 1992
1992
Daily Temp (C)
Rainfall
Max
Min
18.9
9.9
3.4
2.2
0.8
-0.1
1.6
1.9
4.9
8.1
13.6
14.6
13.5
8.8
cm
1.68
5.49
1.78
1.09
2.29
0.94
3.00
0.18
3.10
1.83
1.22
1.32
(total)
1.6
10.6
6.1
13.3
10.6
23.9
7.2
7.9
10.3
16.6
17.1
25.8
30.3
31.2
32.7
24.8
(Avg)
11.8
27.0
9.4
Daily Temp (C)
Max
Oct-92
Nov "
Dec "
Jan-93
Feb "
Mar "
Apr "
May "
Jun "
Jul "
Aug "
Sep "
Avg/Total
Oct-Mar 92-93
Apr-Sept 1993
1993
Sept. 1993, Hermiston,
18.8
8.8
3.8
-0.5
3.9
10.8
20.0
25.3
25.8
27.3
29.0
26.9
7.6
25.7
16.7
Min
Rainfall
ETp
cm
11.43
3.33
3.30
2.72
3.40
8.23
12.09
19.91
24.84
26.95
28.50
18.06
32.4
130.4
162.8
ETp
5.0
2.0
-3.8
-9.1
-4.9
0.9
7.2
9.3
10.7
12.4
13.0
9.0
cm
1.80
3.18
1.73
3.76
0.36
6.40
0.81
3.96
2.54
0.97
1.30
0.08
cm
10.41
3.28
2.21
0.86
2.21
5.51
12.73
20.32
21.62
23.65
21.77
17.04
-1.6
10.3
4.3
17.2
9.7
26.9
24.5
117.1
141.6
Figure 2.5. Weather Data for October 1991 - September 1992, Hermiston, Oregon.
10/91
11/91
12/91
1/92
2/92
3/92
4/92
5/92
9/92
6/92
Month and year
Daily high
0 Daily low
Rainfall
Pan ET
57
References
Agricultural Marketing Service. 1983. United states standards for
grades of potatoes. USDA, U.S. Government Printing Office,
Washington, DC.
Dahnke, W.C., and G.V. Johnson.
1990.
Testing soils for available
nitrogen. pp 127-140. IN: R.L. Westerman (ed) Soil Testing and
Plant Analysis.
Soil Sci. Soc. Amer. Book Series No. 3.
Madison, WI.
Gilkerson, R.A.
1958.
Washington soils and related physiography
Columbia Basin Irrigation Project.
Station Circular 527. Wash.
Ag. Exp. Station, Washington State University, Pullman, WA.
Horneck, D.A., J.M. Hart, K. Topper, and B. Koepsell. 1989. Methods
of soil analysis used in the soil testing laboratory at Oregon
State University. Agr. Exp. Sta. SM 89:4. Oregon State Univ.,
Corvallis, OR.
Lockman, R.B. 1980. Review of soil and plant tissue preparation
procedures.
J. Assn. Offic. Anal. Chem. 63:766-769.
Orion Research Inc. 1979a. Methods Manual
Orion Research Inc.
Cambridge, MA.
93 series electrodes.
Orion Research Inc. 1979b.
Instruction Manual
ammonia gas sensing
electrode. Orion Research Inc.
Cambridge, MA.
Orion Research Inc. 1983. Instruction Manual
Nitrate ion
electrode
model 93-07.
Orion Research Inc.
Cambridge, MA.
Orion Research Inc. 1984.
Instruction Manual
model 901
microprocessor Ionalyzer. Orion Research Inc.
Cambridge, MA.
Potato Chip/Snack Food Association, 1992 "Fry color standards for
potatoes for chipping" Dallas, TX.
Pumphrey, V. and D. Hane, 1981 Personal Communication. "Soil Moisture
Calibration
Inches Water per foot of Soil" and "Hydroprobe
Calibration" HAREC, Hermiston, OR.
Rhoades, J.D., and S. Miyamoto.
1990.
Testing soils for Salinity and
Sodicity. pp 299-336. IN: R.L. Westerman (ed) Soil Testing and
Plant Analysis.
Soil Sci. Soc. Amer. Book Series No. 3. Madison,
WI.
SAS Institute.
1988.
SAS users's guide: Statistics.
SAS Institute, Cary, NC.
Version 6.03
Stevenson, F.L.,
1982.
Nitrogen - Organic forms. Pg 625-641
IN: A.L. Page (ed). Methods of Soil Analysis, Part 2. Soil Sci.
Soc. Amer.,
Madion, WI.
Van Lierop, W. 1990.
Soil pH and lime requirement determination.
pp
73-126.
IN: R.L. Westerman (ed) Soil Testing and Plant Analysis.
Soil Sci. Soc. Amer. Ameri Book Series No. 3. Madison, WI.
58
CHAPTER 3
EFFECTS OF POTATO CROPPING PRACTICES ON SOIL NITRATE,
AMMONIA, ACIDITY, ELECTRICAL CONDUCTIVITY AND
ORGANIC MATTER
Pre-plant Soil Characteristics
Two cores were taken from each desert plot and 3 cores from each pivot
plot in late March prior to any field preparation.
Samples were taken
at 0.3 m intervals to 1.2 m depth, or to the rock layer. Cores of the
same depth were bulked, and analyzed for water content, NO3-N, NH4-N,
pH, and EC. In 1992, samples were also analyzed for organic matter
(OM) content.
The pre-plant soil pH did not differ between 1992 and 1993
(Table 3.1).
The soil pH of the desert site was about one pH unit
higher than that of the pivot site at all depths in both years.
Soil EC was higher in 1992 than 1993, and the EC of the desert site
was about half that of the pivot site (Table 3.1). EC was lowest at
0.3-0.6 m depth and highest at 0.9-1.2 m depth for both sites.
The soil OM content did not vary between sites, and is very low
relative to other soils in the Pacific Northwest (Gilkerson, 1958) but
fairly typical for soils of this area (Johnson and Makinson, 1988)
(Table 3.1).
Soil OM decreased from 0.68% to 0.20% as depth
increased.
Soil NO3-N before planting was higher in 1992 than in 1993, possibly
due to the heavy rainfall that had occurred in the winter of 1992-93
(see chapter 2, Table 7) (Table 3.1).
Soil NO3-N of the desert site
was less than half that of the pivot site.
soil NO3-N with depth for either site.
There was no difference in
59
Table 3.1. Soil pH, electrical conductivity (EC), organic matter (OM),
NO3-N, NH4 -N, and gravimetric water fraction (GWF) before planting.
Soil characteristic
pH
EC
OM
ds.cm-1
Year
1992
1993
Site
Desert
Pivot
s-plot
Year*site
%-
7.5
7.6
NS
171
151
***
0.40
7.8
7.0
***
6.8
133
244
0.41
0.39
NS
0.36
NS
***
* * *
241
NO3-N
NH4 -N
ppm
ppm
4.3
2.5
1.8
6.4
12.0
***
1.3
2.8
8.9
9.9
* * *
-
2.5
5.6
***
3.7
* * *
GWF
5.1;
*
3.2
9.4
NS
*
SitexDepth
Desert
0.0-0.3
0.3-0.6
0.6-0.9
0.9-1.2
Pivot
0.0-0.3
0.3-0.6
0.6-0.9
0.9-1.2
s-plots
0.0-0.3
0.3-0.6
0.6-0.9
0.9-1.2
m
m
m
m
m
m
m
m
m
m
m
m
7.3
7.8
8.0
8.2
***
d
c
b
a
*
b
b
b
a
ab
b
0.65 a
0.43 b
0.38 b
0.19 c
***
2.6
2.1
2.6
2.5
NS
1.6
1.3
1.3
1.1
***
a
b
b
237
177
226
258
NS
0.70 a
0.35 b
0.30 bc
0.22 c
***
3.7
5.5
6.4
6.7
NS
4.5
2.5
2.7
1.4
a
b
b
b
273
117
288
288
NS
0.70 a
0.32 b
0.27 bc
0.16
c
***
4.0
3.6
3.6
3.5
NS
4.6
2.5
3.5
2.1
NS
* *
6.6 c
7.0 b
6.9 b
7.5 a
***
6.4
6.7
6.6
7.6
128
116
144
146
a
a
**
c
8.3 b
9.0 ab
9.6 a
8.6 b
***
11.3 a
9.3 bc
9.0 c
9.7 b
***
9.3
9.2
8.9
10.0
NS
NS,
**' ***Not significant, or significant at P=0.05, 0.01, or 0.001.
Means followed by different letters are significantly different at
P=0.05 (DMRT).
'''
The NH4 -N of the desert site was about half that of the pivot site
(Table 3.1).
Ammonia concentration decreased as depth increased at
both sites.
60
Soil GWF was less in 1992 than in 1993 (Table 3.1). However, GWF was
affected by a year and site interaction.
In 1992, the desert site was
wettest at 0.3-0.6 m and 0.6-0.9 m, and driest at 0.9-1.2 m, but in
1993 there was no difference in water content with depth (Table 3.2).
Table 3.2. Pre-plant gravimetric water fraction.
Desert site
Depth
1992
1993
5.6
6.7
6.7
4.5
10.9
11.3
12.3
12.9
NS
Pivot site
1992
1993
8.9
7.6
6.7
6.1
13.9
11.1
11.2
13.2
-%-
0.0-0.3
0.3-0.6
0.6-0.9
0.9-1.0
m
m
m
m
***
b
a
a
c
***
a
b
c
c
a
b
b
a
***
NS, ***Not
significant, or significant at P= 0.001.
Means followed by different letters are significantly different at
P=0.05 (DMRT).
At the pivot site in 1992, the surface depth (0.0-0.3 m) was wettest
with the soil becoming drier with increasing depth; in 1993 the
surface and lowest depth (0.9-1.2 m) were equally wet, and the middle
two depths (0.3-0.6 m and 0.6-0.9 m) were drier
These differences
can be attributed to the difference in winter rainfall and lower ETp
levels between the two years (Chapter 2, Table 6).
.
The s-plot soils were analyzed for comparison purposes (Table 3.1).
In general, the s-plot values were similar to the pivot site, with
fewer significant differences in the means, probably as a result of
smaller sampling numbers (only 3 plots and one year).
61
Post-harvest Soil Characteristics
Overall Effects
Post-harvest soil EC and NO3-N were higher in 1992 than in 1993
(Table 3.3). The GWF content was lower in 1992 than in 1993. Soil pH
and NH4 -N did not differ between years.
These values reflect the same
overall patterns as the pre-plant samples.
Soil pH and NO3-N were higher, OM content similar, and EC and GWF
lower at the desert site than the pivot site, as found for the pre-
plant soil. Soil NH4 -N was higher at the desert site than the pivot
site which was the opposite of pre-plant soil. Effects of site and
depth interacted for all traits, except NH4-N and GWF.
The pH increased with depth at both the desert (Table 3.4) and pivot
(Table 3.5) sites. In the desert plot, EC decreased as depth
increased from 0.0-0.3 to 0.3-0.6 m, but did not change below 0.6 m
(Table 3.4). In the pivot site, EC also decreased as depth increased
from 0.0-0.3 to 0.3-0.6 m, but then increased below 0.6 m (Table 3.5).
OM decreased with depth at both sites, following a pattern similar to
pre-plant samples.
NO3-N decreased linearly with depth at both sites;
the site x depth interaction is due to different NO3-N levels at these
two sites.
NH4 -N decreased from 0.0-0.3 to 0.3-0.6 m, but did not
change with increasing depth, following the same depth distribution
patterns shown by the pre-plant soils for both sites. At the desert
site soil, GWF increased with depth, but at the pivot site, GWF did
not change with depth.
Nitrogen Fertilizer Effects Observed in Post-Harvest Soil
Soil pH was not affected by N-rate at the desert site (Table 3.4), but
decreased linearly with increasing N-rate at the pivot site
(Table 3.5).
Soil pH increased with depth at both sites, but at the
pivot site, N-rate and depth interacted such that decreases of pH with
increasing N-rate was limited to the 0.0-0.3 m depth (Table 3.6).
62
Table 3.3. Effect of year, site location and depth on post-harvest
soil pH, electrical conductivity (EC), organic matter (OM), NO3-N,
NH4 -N, and gravimetric water fraction (GWF).
Soil characteristic'
pH
EC
ds.cm-1
OM
%
NO3-N
NH4 -N
ppm
ppm
%
10.5
9.43
1.2
1.1
NS
6.9
8.8
7.3
9.1
***
6.1
***
GWF
Year
1992
1993
7.4
7.3
230
211
*
*
7.7
6.6
***
6.6
207
253
***
288
0.32
0.41
**
***
0.49
20.0
1.3
0.9
***
1.4
NS
***
***
***
***
0.35
***
***
Site'
Desert
Pivot
s-plot
YearxSite
Depths (m)
0.0-0.3
0.3-0.6
0.6-0.9
0.9-1.2
6.7
7.2
7.5
7.9
***
NS,
m
m
m
m
c
b
a
332
175
186
189
***
a
b
b
b
0.56
0.34
0.31
0.21
***
a
b
be
c
19.8
8.3
6.7
5.1
a
b
c
d
***
2.0
0.9
0.9
0.7
***
a
b
b
b
7.4
7.4
8.2
8.4
***
**
***
**
***
NS
NS
***
***
-
***
***
*
6.2
6.6
6.5
7.2
582
160
192
218
49.5 a
NS
*
2.7
0.9
0.9
1.0
NS
a
b
b
b
0.76
0.43
0.40
0.27
***
a
b
b
c
9.8 b
12.2 b
7.3 b
**
b
b
a
a
*
***
***
YearxDepth
NS
***
SitexDepth
YearxSitexDepth
s-plots
0.0-0.3
0.3-0.6
0.6-0.9
0.9-1.2
d
8.0
14.7
7.0
6.3
5.1
6.1
NS
**'
** *Not significant, or significant at P=0.05, 0.01, or 0.001.
Means followed by different letters are significantly different at
P=0.05 (DMRT).
'Desert site means included AN, AW, and FI treatment plots.
Pivot site means include AN treatment plots.
S-plot included for comparison purposes only.
YData from desert and pivot sites only.
'''
63
Table 3.4. Effect of year, N-rate, irrigation rate and frequency, and
depth on post harvest soil pH, electrical conductivity (EC), organic
matter (OM), NO3-N, NH4 -N, and moisture, desert plot.
Soil characteristic
pH
EC
OM
NO3-N
NH4-N
GWFZ
ds.cm-1
%
ppm
ppm
%
Year
1992
1993
7.7
7.6
*
199
215
NS
0.33
187
207
228
L*
0.31
0.34
0.28
NS
6.9
9.0
1.3
1.2
NS
NS
6.4
8.3
***
N-rate (kg' ha -1)
220
390
560
YearxN-rate
7.7
7.7
7.6
NS
NS
3.6
7.8
12.9
L***
NS
*
Irrigation rate (IR) ( %)
70
7.6
100
7.7
130
7.8
NS
207
206
212
NS
0.8
1.3
1.7
L***
NS
8.1
7.3
6.6
L***
**
0.30
0.32
0.41
L*
8.5
7.8
8.1
NS
1.2
0.9
5.6
7.4
8.7
L***
L***
7.1
8.1
8.2
1.2
1.3
1.2
7.3
7.2
7.9
NS
NS
2.0
Irrigation frequency (days)
1
2
3
Depth (m)
0.0-0.3
0.3-0.6
0.6-0.9
0.9-1.2
YearxDepth
7.6
7.7
7.7
205
207
209
0.32
0.33
0.32
NS
NS
NS
7.1
7.6
7.9
8.2
***
299
174
184
172
***
NS
*
DepthxN-rate
NS
YearxDepthxN-rate
DepthxlR
as,
d
c
b
a
NS
NS
**
a
b
b
b
0.49
0.33
0.31
0.19
***
a
b
b
c
14.7
6.9
5.9
4.2
***
a
b
b
c
2.0
1.0
1.1
0.9
***
a
b
b
b
***
***
***
NS
***
NS
NS
NS
NS
NS
*
NS
NS
**
**' ***' LNot significant, or significant at P=0.05,
0.01,
or linear, respectively.
ZGWF = gravimetric water fraction.
'''
6.5
6.9
7.8
8.0
NS
***
NS
NS
c
be
b
a
0.001,
64
Table 3.5. Effect of year, N rate, and depth on post-harvest soil pH,
electrical conductivity (EC), organic matter (OM), NO3-N, NH4-N, and
gravimetric water fraction (GWF), pivot plot.
Soil characteristic
pH
EC
OM
ds.cm-1
NO3-N
NH4 -N
ppm
ppm
GWF
Year
1992
1993
N-rate (kg. ha-1)
220
390
560
YearxN-rate
Depth (m)
0.0-0.3
0.3-0.6
0.6-0.9
0.9-1.2
6.7
6.5
NS
303
202
***
0.41
18.9
10.4
***
0.9
0.8
NS
6.6
6.7
6.4
L***
NS
222
241
295
L***
0.41
0.41
0.42
NS
7.1
14.6
22.4
L***
NS
0.6
0.7
1.3
5.9
6.4
7.0
7.4
***
YearxDepth
N-ratexDepth
YearxN-ratexDepth
NS,
*
d
c
b
a
410
179
192
299
***
NS
*
**
**
***
NS
-
a
c
bc
b
0.73
0.37
0.31
0.25
***
a
b
b
c
31.5
11.6
8.4
7.2
L***
NS
a
b
bc
c
***
*
NS
***
NS
***' LNot significant, or significant at P.0.05,
or linear.
2.0 a
0.6 b
0.5 b
0.4 b
***
NS
***
NS
0.01,
8.2
10.0
***
9.0
9.1
9.0
NS
**
9.3
8.4
9.0
9.5
NS
NS
NS
NS
0.001,
EC increased linearly with N-rate at both sites, but at the desert
site year, N-rate and depth interacted (Table 3.4), and at the pivot
site N-rate and depth interacted (Table 3.5). At the desert site EC
increased linearly with increased N-rate in the 0.0-0.3 in 1992, and
at all depths except 0.6-0.9 m in 1993 (Table 3.7). However, at the
pivot site, EC increased with increasing N-rate to 0.6 m.
Soil OM was not affected by the N-rate at the desert (Table 3.4) nor
pivot (Table 3.5) sites.
65
Table 3.6. Post-harvest soil pH as affected by interaction of N-rate
and depth, pivot plot.
N rate (kg.ha-1)
Depth (m)
220
390
560
pH
0.0-0.3
0.3-0.6
0.6-0.9
0.9-1.2
6.1
6.4
6.6
7.5
c
be
b
a
***
ms,
* *,
6.0
6.5
6.9
7.5
***
d
c
b
a
5.5
6.4
6.5
7.3
***
c
b
b
a
L**z
NS
NS
NS
***. LNot significant, or significant at P=0.05, 0.01,
linear.
0.001, or
Column means followed by different letters are significantly different
at P=0.05 (DMRT).
zSignificance across rows.
Soil NO3-N increased linearly with N-rate at the desert (Table 3.4)
and pivot (Table 3.5) sites. Desert site soil NO3-N was about half
that of the pivot site.
Soil NH4-N levels increased linearly with increasing N-rate at both
desert (Table 3.4) and pivot (Table 3.5) sites, however at the pivot
site N-rate and depth interacted such that increases in NH4-N with
increasing N-rate were limited to the 0.0-0.3 m depth (Table 3.8).
Soil GWF was not affected by N-rate at the pivot site in either year
or at desert site in 1992 (Table 3.9).
However, GWF at the desert
site in 1993 decreased linearly as N-rate increased. The lack
differences in GWF with changing N-rates at the pivot site appears to
be due to higher overall soil NO3-N levels at this site.
Irrigation Effects on Soil
Soil pH, electrical conductivity, and NO3-N were not affected by
irrigation rate (Table 3.4).
Soil OM increased linearly with
increasing irrigation rate at 0.6-0.9 m, but at 0.9-1.2 m OM decreased
linearly with increased irrigation (Table 3.11).
NH4-N decreased
linearly with increased irrigation rate to 0.9 m (Table 3.11).
66
Table 3.7. Post-harvest soil electrical conductivity (EC) as affected
by interaction of year, N-rate, and depth (desert site) or N-rate and
depth (pivot site).
N rate (kg' ha-1)
Depth (m)
220
390
560
EC (ds.cm-1)
Desert Site
1992
0.0-0.3
0.3-0.6
0.6-0.9
0.9-1.2
194
133
147
125
a
*
343
162
173
145
***
400
206
133
158
NS
278
193
190
172
***
b
b
b
a
b
b
b
372
154
181
155
a
L*'
b
b
b
NS
NS
NS
a
L***
L***
NS
L**
**
1993
0.0-0.3
0.3-0.6
0.6-0.9
0.9-1.2
Pivot Site (1992 and 1993)
0.0-0.3
411 a
0.3-0.6
142 c
0.6-0.9
270 b
0.9-1.2
288 b
**
416
209
234
298
*
a
b
b
b
a
b
b
ab
353
238
221
150
***
600
222
240
308
b
b
c
a
b
b
b
NS
NS
NS
NS
**
NS,
**' ***' LNot significant, or significant at P=0.05, 0.01,
0.001,
or linear.
Column means followed by different letters are significantly different
at P=0.05 (DMRT).
'Significance across rows.
Irrigation frequency did not affect any of the soil characteristics
measured (Table 3.4).
The s-plot soils were analyzed for comparison purposes (Table 3.3).
In general, the s-plot values closely followed the trends for the
pivot site, with fewer significant differences in the means, probably
due to smaller sampling size (only 3 plots and only in 1992).
Assuming plot variance of the s-plot is the same pivot site, the
s-plot was drier at all depths, and had higher NO3-N content in the
0.0-0.3 m sample than the pivot site.
67
Table 3.8. Effect of N rate x depth interaction on post-harvest soil
NH4-N, pivot site.
N rate (kg-ha-1)
Depth (m)
220
390
560
NH, -N (ppm)
0.0-0.3
0.3-0.6
0.6-0.9
0.9-1.2
1.0
0.5
0.5
0.4
a
b
b
b
1.5
0.5
0.5
0.4
***
a
b
b
b
**
3.4
0.7
0.6
0.4
a
b
b
b
L***
NS
NS
NS
***
NS, **, **, L
--Not significant, or significant at P= 0.01, 0.001,
or
linear.
Column means followed by different letters are significantly different
at P=0.05 (DMRT)­
2Significance across rows.
Table 3.9. Effect of site, year, and N rate on post-harvest soil
gravimetric water fraction.
Desert
N rate (kg.ha-1)
220
390
560
Pivot
1992
1993
6.2
6.5
5.8
10.1
8.1
NS
L***
NS' ***' /-Not significant,
7.4
1992
***
***
***
8.3
8.2
8.0
NS
1993
9.7
**
10.1 **
10.1
*
NS
or significant at P=0.001, or linear.
68
Table 3.10. Post-harvest soil NH4-N as affected by interaction of
year, irrigation rate, and depth.
Irrigation rate (%)
Depth (m)
70
100
130
NH4 -N (ppm)
0.0-0.3
0.3-0.6
0.6-0.9
0.9-1.2
3.6
1.7
1.3
1.1
*
NS,
'''
or
a
b
b
b
1.9
1.1
1.0
0.9
a
b
b
b
***
1.3
0.9
0.8
0.7
a
b
b
b
L**'
L*
L*
NS
*
**' ***' LNot significant, or significant at P=0.05, 0.01,
linear.
0.001,
Column means followed by different letters are significantly different
at P=0.05 (DMRT).
'Significance across rows.
Table 3.11.
Post-harvest soil OM as affected by interaction of
irrigation rate and depth.
Irrigation rate (%)
Depth (m)
70
100
130
Organic Matter (%)
0.0-0.3
0.3-0.6
0.6-0.9
0.9-1.2
0.43
0.25
0.21
0.32
NS
0.48
0.32
0.30
0.17
***
a
b
b
c
0.57
0.41
0.48
0.16
a
b
ab
c
NSZ
NS
L**
L*
*
NS,
**' ***' LNot significant, or significant at P=0.05, 0.01, 0.001, or
linear.
'''
Column means followed by different letters are significantly different
at P=0.05 (DMRT).
'significance across rows.
69
Summary of Results
Soil pH, EC, OM, NO3-N, NH4 -N, and GWF differed between sites.
Pre-
planting soil GWF was higher at the pivot site than the desert site
both years as a result of increased water storage from previous year's
irrigations at the pivot site, despite an attempt to match the water
content of each by a pre-season soak of the desert site by water
tanker.
The soil EC, NO3-N, and NH4 -N levels increased linearly with
increased N-rate at both sites. The soil pH at the desert site did
not change with N-rate, however soil pH decreased linearly as N-rate
increased at the pivot site. Water content decreased linearly as N-
rates increased at the desert site, but not at the pivot site. OM was
not affected by N-rate at either site.
In most cases the response to
N-rate was limited to the surface sample (0.0-0.3 m), though
exceptions include electrical conductivity, which increased with N-
rates to the 0.6-0.9 sampling depth in 1993.
Soil NH4 -N decreased linearly as irrigation rate increased in the
0.0-0.3 m sample, and OM varied with irrigation rates (increasing at
0.6-0.9 m, decreasing at 0.9-1.2 m).
Soil pH, electrical
conductivity, and NO3-N were not affected by irrigation rate.
Overall Comparison of Pre-plant and Post-harvest Levels of
Soil Variables
All soil variables measured changed significantly between the pre-
plant and post-harvest sample dates (Table 3.12 and Table 3.13) in
response to the various cropping practices applied and/or seasonal
changes occurring between March and September.
The average soil pH
decreased 0.2 pH units, EC increased 55 dscm-1, NO3-N increased 6 ppm.
Soil OM decreased by 0.099.- at the desert site, and did not
significantly change at the pivot site. NH-N did not change at the
desert site but decreased by 1.9 ppm at the pivot site. However, site
and depth interacted, so these responses will be discussed separately
by site.
70
Table 3.12. Comparison of pre-plant (PP) and post-harvest (PH) soil
pH, electrical conductivity (EC), and organic matter (OM).
pH
PP
OM
EC
PH
PP
PH
PH
PP
ds.cm-1
%
Year
1992
1993
7.5
7.6
7.4 ***
7.3 ***
171
151
230 ***
7.8
7.0
6.8
7.7 ***
6.6 ***
6.6 NS
133
Desert
0.0-0.3
0.3-0.6
0.6-0.9
0.9-1.2
7.3
7.8
8.0
8.2
7.1
7.6 *
7.9
NS
8.2 NS
Pivot
0.0-0.3
0.3-0.6
0.6-0.9
0.9-1.2
6.6
7.0
6.9
7.5
6.4
6.7
6.6
7.6
0.40
0.35
207 ***
253 NS
288
NS
0.41
0.39
0.36
0.32 ***
0.41 NS
0.47 ***
128
116
144
146
299 ***
0.65
0.43
0.38
0.19
0.49
0.33
0.31
0.19
5.9 ***
6.4 **
7.0 NS
7.4 NS
237
410
177
179
192
**
NS
NS
NS
0.70
0.35
0.30
0.22
0.73
0.37
0.31
0.25
6.2 NS
6.6
NS
273
6.5
7.2
288
288
582
NS
160 NS
192 NS
218 NS
0.70
0.32
0.27
0.16
0.76
*
0.43 ***
0.40 ***
0.27 **
211 ***
Site
Desert
Pivot
s-plot
244
242
SitexDepth (m)
s-plot
0.0-0.3
0.3-0.6
0.6-0.9
0.9-1.2
**
NS
NS
226
258
177
174 ***
184 ***
172 NS
229
**
**
*
NS
*
NS
NS
NS
Not significant, or significant at P=0.05, 0.01, or 0.001.
Soil pH decreased from pre-plant to post-harvest in the upper two
sampling depths (0.0-0.3 m and 0.3-0.6 m) at both sites. The
magnitude of the change was larger at the pivot site than the desert
site.
EC increased from pre-plant to post harvest for depths 0.0-0.3, 0.3­
0.6, and 0.6-0.9 m at the desert site, but at the pivot site
71
Table 3.13.
Comparison of pre-plant (PP) and post-harvest
NO3-N, NH4-N, and gravimetric water fraction (GWF).
NO3-N
GWF
NH4 -N
PH
PP
PH
PP
ppm
(PH) soil
PP
PH
ppm
Year
1992
1993
4.3
2.5
10.5
9.4
***
***
2.5
5.6
3.7
8.0
14.7
19.7
***
***
2.6
14.7
2.1
6.9
5.9
4.2
***
***
***
***
1.8
1.2
***
1.1
6.4
6.9
**
12.0
8.8
***
8.9
9.9
7.3
***
9.1
**
9.4
6.1
**
Site
Desert
Pivot
s-plot
SitexDepth (m)
Desert
0.0-0.3
0.3-0.6
0.6-0.9
0.9-1.2
Pivot
0.0-0.3
0.3-0.6
0.6-0.9
0.9-1.2
s-plots
0.0-0.3
0.3-0.6
0.6-0.9
0.9-1.2
NS'
2.6
2.5
*
***
3.7
5.5
6.4
6.7
31.5
11.6
8.4
4.0
3.6
3.6
49.5
9.8
*
12.2
7.3
NS
NS
3.5
7.2
NS
NS
*
1.3
1.3
2.8
0.9
3.2
1.4
*
1.6
2.0
**
1.3
1.0
*
1.3
1.1
1.1
0.9
4.5
2.5
2.7
1.4
2.0
4.6
2.5
3.5
2.7
0.9
0.9
2.1
1.0
0.6
0.5
0.4
NS
***
*
***
**
***
***
***
NS
NS
NS
NS
***
8.2
9.0
9.6
8.6
6.5
6.9
7.8
8.0
11.3
9.3
***
9.3
8.4
***
9.0
9.0
9.7
9.5
NS
NS
9.3
9.2
8.9
10.0
7.0
NS
6.3
5.1
6.1
**
***
***
NS
**
*
-Not significant, or significant at P=0.05, 0.01, or 0.001.
significant increases in EC between pre-plant and post-harvest were
limited to the 0.0-0.3 m sampling depth.
Soil OM decreased from pre-plant to post-harvest for sampling depths
to 0.9 m at the desert site, but significant decreases between pre-
plant and post-harvest were limited to the 0.0-0.3 m sampling depth at
the pivot site.
72
Soil NO,-N increased from pre-plant to post harvest at all depths at
the desert site, but only in the upper two sampling depths at the
pivot site.
Ammonium decreased from pre-plant to post harvest at all depths at
both sites, except at the 0.0-0.3 m sampling depth at the desert site
where it increased.
Soil moisture content decreased from pre-plant to post-harvest at both
sites, though changes were not observed at the lowest depth (0.9-1.2
m) at the desert site or the lower two depths (0.6-0.9 m,0.9-1.2 m) at
the pivot site.
Monthly Soil NO3-N
Soil NO3 -N was higher in 1992 than in 1993, and was higher in the
pivot than the desert site, but year and site interacted to influence
soil NO3 -N (Table 3.14).
In 1992, at all sampling times, soil NO,-N
was higher at the pivot than the desert site (Table 3.15). In 1993,
soil NO3 -N was higher at the pivot than the desert site at pre-plant
and week 14, but at post-harvest and week 10, the values were similar
at both sites.
Sampling depth interacted with year and with site to affect soil NO3-N
(Table 3.14). At week 10, 14 and post-harvest, year and depth
interacted, due to the different levels of soil NO3-N found between
1992 and 1993, and at post-harvest, due to the differing distribution
patterns between the two years (Table 3.16). At the desert site,
NO3 -N did not vary with depth at pre-plant and week 18 (Table 3.17);
at the pivot site, soil NO,-N did not vary with depth pre-plant
(Table 3.18). At all other sampling times at both sites, soil NO,-N
decreased from the 0.0-0.3 m to the 0.3-0.6 m sampling depth; at
week 6 in the desert site and after harvest at both sites, soil NO3 -N
decreased more with deeper depth of sampling.
Year and depth
interacted on week 14 at the desert site, and weeks 10, 14, and post
harvest at the pivot site because of higher levels of soil NO3 -N in
1993 than 1992, however distribution patterns were similar for both
years (Table 3.19).
73
Table 3.14. Effect of year, site location and depth on soil NO3-N
throughout the season.
Weeks from plantingz
Pre-plant
harvest
10
6
14
18
Post­
4.7
10.5
9.4
***
(ppm NO3-N)
Year
1992
1993
4.3
2.5
7.9
***
_
2.5
5.6
***
3.4
7.3
9.3
-
7.6
3.5
***
8.5
2.5
***
3.8
9.1
***
8.8
4.9
6.9
***
9.7
***
***
10.7
4.0
3.2
11.6
4.1
3.1
3.2
SiteY
Desert
Pivot
s-plot
YearxSite
Depth" (m)
0.0-0.3
0.3-0.6
0.6-0.9
0.9-1.2
YearxDepth
SitexDepth
s-plots
0.0-0.3
0.3-0.6
0.6-0.9
0.9-1.2
m
m
m
m
NS
12.5
*
3.0
3.1
3.8
3.7
NS
19.7
4.9
3.6
3.4
3.7
***
***
NS
*
*
4.0
3.6
3.6
3.5
NS
34.7
9.0
2.9
3.3
*
a
b
c
bc
4.7
4.6
NS
8.0
14.7
***
19.7
***
7.5
3.4
3.4
4.5
***
a
b
b
b
***
19.8
8.3
6.7
5.1
***
***
***
_
***
*
**
***
***
25.7
4.2
2.1
3.4
*
a
b
c
bc
25.0
8.2
2.8
2.9
***
a
b
c
c
-
NS,
49.5 a
9.8 b
12.2 b
7.3 b
**
*' **' ** *Not significant, or significant at P=0.05, 0.01,
or 0.001.
Means followed by different letters are significantly different at
P=0.05 (DMRT) .
zWeek 6 and week 18 include 1993 data only.
YDesert site means included AN, AW, and FI treatment plots;
Pivot site means include AN treatment plots;
S-plot included for comparison purposes only.
"Means of S-plot not included.
74
Table 3.15. Year x site effects on soil NO3-N concentrations
throughout the season.
Weeks from planting
Sitez
Pre-plant
10
14
Post-harvest
NO3-N (ppm)
1992
Desert site
Pivot site
3.2
6.9
***
4.6
14.6
***
7.6
10.8
***
6.9
19.0
***
1.7
4.3
***
3.0
3.6
NS
2.3
3.0
4.7
4.6
NS
1993
Desert site
Pivot site
NS,
*
** *Not significant, or significant at P=0.05, 0.01, or 0.001.
zDesert site means included AN, AW, and FI treatment plots.
Pivot site means include AN treatment plots.
'''
Table 3.16. Year x depth effects on soil NO3-N concentrations during weeks 10 and 14, and post-harvest.
Weeks from planting
10
Depth (m)
0.0-0.3
0.3-0.6
0.6-0.9
0.9-1.2
1992
16.0 a
5.8 b
4.1 b
4.9 b
***
14
1993
1992
NO3-N (ppm)
***z
6.4 a
**
1.9 b
**
2.0 b
**
2.3 b
19.9 a
6.4 b
***
Post-harvest
1993
4.3 c
4.3 c
***
3.9
2.0
2.0
2.2
***
a
b
b
b
***
***
***
***
1992
1993
24.7 a
8.1 b
7.0 b
17.4
8.7
6.8
4.8
5.6 c
***
NS, ** *Not significant,
or significant at P=0.001, respectively.
Column means followed by different letters are significantly different at P=0.05 (DMRT).
zSignificance accross rows.
***
a
b
c
d
NS
NS
NS
NS
76
Table 3.17. Effect of year, N rate, irrigation rate, and irrigation
frequency, on soil NO3-N throughout the season, desert plot.
Weeks from plantingz
Pre-plant
10
6
14
18
harvest
Post­
NO3-N (ppm)
Year
1992
1993
3.2
1.7
7.3
* *
N-rate (kg-ha-1)
220
2.9
390
2.5
560
1.8
L***
Year*N-rate
NS
Irrigation rate
70
100
130
Year*IR
(IR)
2.1
2.4
3.0
L**
5.5
7.1
10.5
4.6
3.0
7.6
2.3
**
***
2.5
3.6
5.9
L***
L***
4.7
6.9
9.0
***
2.6
5.1
6.6
L***
2.8
4.5
7.2
L***
**
3.6
7.8
12.9
L***
NS
(96)
7.0
7.7
6.8
NS
**
3.7
3.9
3.4
NS
NS
4.5
4.9
5.6
NS
NS
3.9
4.8
5.1
NS
8.5
7.8
8.1
3.6
2.9
3.2
NS
4.9 b
4.7 b
6.3 a
4.1
4.8
5.0
NS
7.1
8.1
8.2
NS
NS
NS
Irrigation frequency (IF)(days)
1
2
3
Depth (m)
0.0-0.3
0.3-0.6
0.6-0.9
0.9-1.2
YearxDepth
N-ratexDepth
IFxDepth
YearxlFxDepth
2.4
2.4
2.7
NS
6.0
7.6
9.1
NS
2.6
2.1
2.6
2.5
NS
17.5
5.0
3.6
3.2
NS
NS
NS
NS
NS
NS
**
*
a
b
c
c
7.9
2.7
2.4
2.1
a
b
b
b
***
*
10.4
3.3
2.9
2.8
***
6.3
3.5
3.8
5.2
NS
NS
***
***
**
NS
NS
*
*
Ns,
a
b
b
b
14.7
6.9
5.9
4.2
***
a
b
b
C
NS
NS
NS
***
NS
NS
**' ***' T-Not significant , or significant at P=0.05, 0.01, 0.001, or
linear, respectively.
Means followed by different letters are significantly different at
P=0.05 (DMRT) .
zWeek 6 and week 18 include 1993 data only.
77
Table 3.18. Effect of year, N rate and sampling depth on soil NO3-N
throughout the season, pivot plot.
Weeks from planting'
harvest
Pre-plant
10
6
14
18
Post­
11.0
10.4
***
NO3-N (ppm)
Year
1992
1993
6.9
4.3
9.3
*
_
N-rate (kcrha-1)
220
4.9
390
6.4
560
5.2
NS
5.6
9.9
12.3
L**
YearxN-rate
Depth (m)
0.0-0.3 m
0.3-0.6 m
0.6-0.9 m
0.9-1.2 m
YearxDepth
NS
N-ratexDepth
NS
YearxN-ratexDepth
NS
10.8
3.0
***
4.6
4.8 b
13.0 a
9.6 a
3.9
6.7
10.0
L***
2.3
3.7
7.9
**
**
NS
3.7
5.5
6.4
6.7
NS
14.6
3.6
***
24.8
4.7
3.4
4.1
a
b
b
b
17.3
7.0
5.5
6.7
**
a
b
b
b
14.6
5.2
3.6
4.1
***
***
***
NS
NS
***
***
NS
*
**
ms,
L***
7.0
14.6
22.4
L***
NS
10.9
3.0
2.5
2.8
***
31.5
11.6
8.4
7.2
***
***
***
*
**, ***' LNot significant, or significant at P.0.05, 0.01,
linear, respectively.
'Week 6 and week 18 include 1993 data only.
NS
0.001, or
Effect of N-rate on Soil NO3-N Levels
Desert site
Prior to application of fertilizer treatments (pre-plant), soil NO3-N
levels decreased linearly with increasing N-rate plots due to random
spatial variability of the soil.
Thereafter, soil NO3-N levels
increased with increasing N-rates (Table 3.17), however year and N-
rate interacted on weeks 10 and 14.
On week 10 soil NO3-N increased
linearly with increasing N-rate both years, but only in 1993 at the
pivot site. On week 14, soil NO3-N increased linearly with increasing
78
Table 3.19. Soil NO3-N concentrations in weeks 10 and 14, and post­
harvest as affected by interaction of year, depth, and site (where
appropriate).
Desert site
Depth (m)
1992
Pivot site
1993
1992
1993
NO3-N (ppm)
Week 10
0.0-0.3
0.3-0.6
0.6-0.9
0.9-1.2
28.9 a
11.8 b
8.2 b
9.7 b
5.7
2.2
2.9
3.8
**
Week 14
0.0-0.3
0.3-0.6
0.6-0.9
0.9-1.2
17.3
5.3
3.9
3.7
***
Post-harvest
0.0-0.3
0.3-0.6
0.6-0.9
0.9-1.2
a
b
b
b
3.4
2.0
1.9
1.9
***
a
b
b
b
***
***
***
***
24.1
8.3
5.2
5.6
**
**
*
a
b
b
b
***
39.5
14.4
11.1
10.9
***
a
b
b
ab
5.0
2.1
2.0
2.7
a
b
***
***
b
b
**
*
*
a
b
b
b
23.6 a
8.8 b
5.8 b
3.4 b
***
NS
NS
**
NS,
** ***Not significant, or significant at P=0.05, 0.01, or 0.001,
respectively.
Column means followed by different letters are significantly different
at P=0.05 (DMRT).
zSignificance accross rows.
N-rate both years at both sites, but soil NO3-N levels were lower in
1993 than 1992 at all N-rates (Table 3.20).
N-rate interacted with
depth on weeks 10, 14, and post harvest.
Soil NO3-N varied with depth
for the 390 and 560 kgha-1 N, but not for 220 kgha-1 N, except for
week 10 (Table 3.21). When differences occurred, soil NO3-N was
greater at 0.0-0.3 m depth than at all of the lower depths, except for
post-harvest at 390 kgha-1 N, when soil NO3-N at 0.0-0.3 was greater
than at 0.0-0.9, which was greater than at 0.9-1.2 m. Depth and N-
rate interacted during weeks 10 and 14 and post harvest (Table 3.17).
Soil NO3-N concentrations increased linearly with increasing N-rate to
0.6 m on week 10, at 0.3-0.9 m on week 14, and to 0.9 m at post­
harvest (Table 3.21).
At 560 kgha-1 N, soil NO3-N increased during
79
Table 3.20. Year x N-rate x site effects on soil NO3-N concentrations
in weeks 10 and 14.
Desert site
Pivot site
N-rate
(kg. ha-1 N)
1992
1993
1992
NO3 -N
1993
(ppm)
Week 10
220
390
560
Week 14
220
390
560
3.4
4.6
5.7
L**
1.7
2.6
6.2
L***
3.9
7.8
10.2
L***
1.7
2.6
3.0
L***
*z
***
NS
*
***
**
* *
* *
**
2.5
3.4
5.0
L**
6.0
10.8
14.6
L***
1.8
2.7
4.5
L**
**
7.1 b
22.7 a
14.2 ab
*
*
**
NS,
**' ***' LNot significant, or significant at P=0.05, 0.01,
0.001, or
linear, respectively.
Column means followed by different letters are significantly different
at P=0.05 (DMRT).
zSignificance accross rows.
the season to 0.9 m, whereas at 390 kgha-1 N soil NO3-N increased to
1.2 m.
Soil NO3-N was not increased during the season at any depth by
the 220 kgha-1 N treatment (Table 3.22).
Pivot site
At the pivot site, soil N increased linearly with increasing N-rates
on week 6, 14, 18, and post-harvest, but not at pre-plant or on week
10 (Table 3.18). On week 10, soil NO3-N in plots receiving 390 and
560 kgha-1 N were higher than the soil NO3-N in plots receiving only
220 kgha-1 N. Year and N-rate interacted in weeks 10 and 14 to
affect soil NO3-N. In 1992 in week 10, soil NO3-N was highest for the
390 kgha-1 rate, and lowest for the 220 kgha-1 N-rate, whereas in
1993 soil NO3-N increased linearly with N-rate (Table 3.20).
N-rates
interacted with depth on weeks 14, 18, and post-harvest. Soil NO3-N
varied with depth for the 390 and 560 kgha-1 N, but not for 220 kgha­
1 N, except for post-harvest (Table 3.23). Where differences occurred,
soil NO3-N at 0.0-0.3 m was greater than lower depths, except for
post-harvest at 560 kgha-1 N, where soil NO3-N at 0.0-0.3 was greater
80
..
Table 3.21. N-rate x depth effects on soil NO3-N concentrations,
desert site, in weeks 10 and 14, and post-harvest.
N rate (kg-ha-1)
Depth (m)
220
390
560
NO3-N (ppm)
Week 10
0.0-0.3
0.3-0.6
0.6-0.9
0.9-1.2
Week 14
0.0-0.3
0.3-0.6
0.6-0.9
0.9-1.2
Post-Harvest
0.0-0.3
0.3-0.6
0.6-0.9
0.9-1.2
4.4
1.9
2.2
1.7
a
b
b
b
7.4
2.5
2.1
2.4
*
***
5.0
1.8
1.8
2.1
NS
10.5
3.7
3.0
2.8
4.8
2.4
3.0
4.1
NS
14.3
7.1
5.8
4.2
a
b
b
b
a
b
b
b
L***z
L*
NS
NS
a
b
b
b
NS
L*
L*
NS
a
b
b
b
L***
L***
L**
NS
***
a
b
b
b
***
**
14.2
4.1
2.5
3.0
13.8
5.3
3.8
3.6
*
a
b
b
c
27.0
10.9
9.3
4.6
*
**' ***' LNot significant, or significant at P=0.05, 0.01, 0.001, or
linear, respectively.
Column means followed by different letters are significantly different
at P=0.05 (DMRT).
zWeek 6 and week 18 include 1993 data only.
Ns'
'''
than 0.0-0.6 which was greater than 0.9-1.2 m.
N-rate interacted
with year and depth on week 14, to affect soil NO3-N, with soil NO3-N
increasing linearly with increasing N-rates to 0.9 m in 1992, but only
at depth 0.3-0.9 in 1993 (Table 3.24).
At 560 kgha-1 N, soil NO3-N
increased during the season to 0.9 m depth, whereas at 390 and 220
kgha-1 N soil NO3-N increases were limited to 0.0-0.3 m (Table 3.25).
81
Table 3.22. Effect of N rate and depth on seasonal changes in soil
NO3-N between sampling dates,
desert plot.
Sample depth (m)
and
N-rate (kg. ha-1)
Weeks from planting
Pre-plant
10
NO3-N
14
Post-harvest
5.0
10.8 c
13.8 b
4.8
NS
14.3 b ***
27.0 a ***
(ppm)
0.0-0.3
220
390
560
0.3-0.6
220
390
560
2.9
2.8 e
1.8 c
4.4
7.4 d
14.2 b
3.1
2.0 c
1.7 b
2.2
2.5 c
4.1 b
1.8
3.7 b
5.3 b
3.0
NS
7.1 a ***
10.9 a **
3.1
2.7 b
2.0 b
2.2
2.1 b
2.5 b
1.8
3.8 b
3.8 b
3.0
NS
5.8 a ***
9.3 a ***
2.6
2.6 b
1.9
1.7
2.4 b
3.0
2.1
2.8 b
3.6
4.1
NS
4.2 a
***
4.6
NS
0.6-0.9
220
390
560
0.9-1.2
220
390
560
NS, , **' *"' 1Not significant, or significant at P=0.01,
0.001,
respectively.
Row means followed by different letters are significantly different at
P=0.05 (DMRT).
Irrigation Treatments
Soil NO3-N levels were not affected by either irrigation rate or
irrigation frequency except at week 14, when year, irrigation
frequency and depth interacted (Table 3.17)1.
In 1992, soil NO3-N
levels decreased with irrigation frequency at 0.0-0.3 m, but not below
this depth, or in 1993 (Table 3.26). Differences in soil NO3-N were
found for all irrigation frequencies in 1992, but only for the 2-day
irrigation frequency in 1993.
soil NO3-N levels of treatment plots prior to commencement of
treatments (pre-plant) are discussed in materials and methods,
chapter 2.
82
Table 3.23. N-rate x depth effects on soil NO3-N concentrations, pivot
site, weeks 14, 18, and post-harvest.
N rate (kg' ha-1)
Depth (m)
220
390
560
NO3-N (ppm)
Week 14
0.0-0.3
0.3-0.6
0.6-0.9
0.9-1.2
Week 18Y
0.0-0.3
0.3-0.6
0.6-0.9
0.9-1.2
Post-Harvest
0.0-0.3
0.3-0.6
0.6-0.9
0.9-1.2
6.2
3.1
2.7
3.6
16.0
5.0
2.7
3.3
NS
**
3.3
1.8
1.7
2.6
NS
7.4
2.4
2.1
2.7
14.3
4.0
4.4
5.6
**
ms,
a
b
b
b
30.8
12.0
7.7
7.9
***
a
b
b
b
L*z
NS
L*
NS
*
a
b
b
b
19.5
5.0
3.8
3.2
a
b
b
b
L**
NS
NS
NS
**
*
a
b
b
b
21.6
7.6
5.5
5.5
a
b
b
b
49.6
18.9
13.2
8.0
***
a
b
be
c
L***
L***
L**
NS
**' "*. I-Not significant, or significant at P=0.05, 0.01, 0.001, or
linear, respectively.
Column means followed by different letters are significantly different
at P=0.05 (DMRT)
zsignificance across rows.
YWeek 18 includes 1993 data only.
.
83
Table 3.24. Year x N-rate x depth effects on soil NO3-N
concentrations, pivot site, week 14.
N rate (kg. ha-1)
Depth (m)
220
390
560
NO3-N (ppm)
1992
0.0-0.3
0.3-0.6
0.6-0.9
0.9-1.2
1993
0.0-0.3
0.3-0.6
0.6-0.9
0.9-1.2
10.7
5.0
3.8
4.5
NS
1.6
1.2
1.6
2.6
**
NS,
.,
26.5
8.3
3.9
4.6
b
b
b
a
a
b
b
ab
35.2
11.6
8.0
7.6
***
***
5.4
1.6
1.5
2.1
NS
8.0
3.6
3.3
3.0
NS
a
b
b
b
L**z
L*
L*
NS
NS
L***
L**
NS
* *,
*,
LNot significant, or significant at P=0.05, 0.01, 0.001, or
linear, respectively.
Column means followed by different letters are significantly different
at P=0.05 (DMRT).
zSignificance across rows.
* *
84
Table 3.25. Affect of N rate and depth on changes in soil NO,-N
concentration between sampling date, pivot plot.
Sample depth (m)
and
N-rate (kg. ha-1)
Weeks from planting
Pre-plant
10
NO3-N
0.0-0.3 m
220
390
560
3.6 b
4.3 b
3.3 c
8.4 ab
24.3 ab
19.2 b
3.8
8.0
4.8 b
3.0
10.8
14
Post-harvest
(ppm)
6.2 b
16.0 ab
21.6 b
14.3 a
30.8 a
49.6 a
***
7.1 b
3.1
5.0
5.5 b
4.0
12.0
18.9 a
NS
NS
***
3.4
7.4
5.8 b
2.7
2.3
5.5 b
4.4
7.7
13.2 a
*
*
0.3-0.6 m
220
390
560
0.6-0.9 m
220
390
560
0.9-1.2
220
390
560
NS,
5.7
8.3
5.4 b
6.3
6.5
7.3
4.4
9.6
6.2
3.6
3.3
5.5
5.6
7.9
8.0
NS
NS
***
NS
NS
NS
***Not significant, or significant at P=0.05, or 0.001,
respectively.
Row means followed by different letters are significantly different at
P=0.05 (DMRT) .
85
Table 3.26. Year x depth x irrigation frequency effects on soil NO,-N
concentration, desert site, week 14.
Irrigation frequency (days)
Depth (m)
1
2
3
NO3-N (ppm)
1992
0.0-0.3
0.3-0.6
0.6-0.9
0.9-1.2
1993
0.0-0.3
0.3-0.6
0.6-0.9
0.9-1.2
16.0
3.9
3.7
4.0
a
b
b
b
16.0
5.3
3.9
3.8
***
***
4.5
2.3
2.1
2.5
NS
3.1
1.6
1.8
1.8
**
a
b
b
b
a
b
b
b
25.5 a
6.6 b
4.1 be
2.9 c
***
3.7
3.2
2.5
1.9
NS
*z
NS
NS
NS
NS
NS
NS
NS
NS,
** *Not significant,
or significant at P=0.05, or 0.001,
respectively.
Column means followed by different letters are significantly different
at P=0.05 (DMRT).
zSignificance across rows.
Summary of Results for Monthly Soil Samplings for NO3,N
At the desert site, significant increases in soil NO3-N levels were
found to 1.2 m for the 390 kgha-1 N-rate, to 0.9 m for the 560 kgha-1
N-rate, but not at any depth for the 220 kgha-1 N-rate. At the pivot
site, significant soil NO3-N occurred to 0.9 m at 560 kgha-1 N-rate,
whereas significant increases in soil NO3-N in response to 220 and 390
kgha-1 N-rates were limited to the 0.3 m depth.
Irrigation rates and
frequencies had little effect on soil NO3-N levels.
86
Effect of N-rate, Irrigation Rate, and Irrigation
Frequency on the Soil Gravimetric Water Fraction (GWF)
Evaluation of treatment effects on soil GWF measures the effectiveness
of meeting the water application goals. Ideally, equal amounts of
water to all N-rate and irrigation frequency plots would have been
applied, and rates of 70, 100, and 1300 of recommended replacement
applied to the irrigation rate plots.
The GWF of the soil in these
trials is a function of the initial (pre-planting) GWF, water
applications, leaching, and evapotranspiration.
Thus, GWF would
increase linearly with increasing irrigation rate, but should not be
greatly affected by irrigation frequency.
Increasing N-rates
generally result in larger crop canopies, which have elevated
evapotranspiration rates (Harris, 1978) and thus soil GWF should
decrease with N-rate, at least in mid-season.
The GWF was higher in 1993 than 1992 throughout the season at both
sites (Table 3.27), except at pre-plant at the pivot site where GWF
was higher in 1992 than in 1993.
In the desert site, GWF decreased
linearly with increasing N-rate on weeks 6, 182.
On week 10 and
post-harvest soil GWF did not vary with N-rate in 1992 (Table 3.28).
In 1993, however, at week 10 GWF was highest at 220 kgha-1 N, and
lowest at 390 kgha-1 N, whereas at post-harvest GWF decreased
linearly with increasing N-rate. In the pivot site the soil GWF was
not affected by N-rate except at week 14 where the GWF increased
linearly with N-rate (Table 3.27).
Soil GWF increased linearly with irrigation rate at weeks 10, 14, 16,
and post-harvest, but was not affected by irrigation rates at week 6.
Soil GWF in plots watered at 700 of the recommended replacement rates
had GWF at 0.80, 0.72, 0.79, and 0.76 times the 100% rate plots for
weeks 10, 14, 18, and post-harvest, respectively.
Plots receiving
130% of the recommended replacement rates had soil GWF at 1.20, 1.07,
1.11, and 1.18 times the 100% plots for weeks 10, 14, 18, and post­
harvest, respectively.
The soil GWF was not affected by irrigation
frequency except for week 18 where the GWF for daily and alternate day
watering was less than the GWF found with watering at 3 day intervals.
2
GWF not measured in 1992 for week 6 and 18, pre-plant
differences discussed in chapter 2.
87
Thus, the watering strategy had the desired effects on the GWF of the
soil in these plots.
Irrigation rate resulted in the 70% plots having
an average GWF at 0.77 times the 100% level (after week 6), and the
130% plots had an average GWF at 1.14 times the 100% rate.
Soil GWF
decreased with increasing N-rate, and was largely unaffected by
irrigation frequencies.
Overall Summary of Results
Evidence of 1\103-N Leaching Below the Rooting Zone
Nitrate leaching was evident below the rooting zone, but occurrence
was not consistent over sites or depths.
Significant increases in
NO3-N concentrations in response to increasing N-rates were not found
at the lowest sampling depth (0.9-1.2 m).
Significant increases
during the season were found to 1.2 m at the desert site in response
to the 390 kgha-1 N-rate, and to 0.9 m for 560 kgha-1 N-rate.
At the
pivot site, however, significant increases in soil NO3-N
concentrations were limited to 0.3 m, except for 560 kgha-1 rate
which increased soil NO3-N to 0.9 m.
Change in Soil pH, Electrical Conductivity, OM and
to the Various Treatments
NH4
-N in Response
Soil pH, EC, OM and NH4-N levels changed between pre-planting and post
harvest.
Changes that occurred were predictable based on the
treatments.
Significant changes were generally limited to the upper
two sampling depths (0.0-0.3 and 0-3.6 m).
Major exceptions to this
trend were for EC which increased with N-rates to the third sampling
depth, and for NH4-N which decreased between pre-plant and
post-harvest samples for all depths and trials, except the highest N-
rate in one trial.
88
Table 3.27. Effect of year, N rate, irrigation rate, and irrigation
frequency on soil gravimetric water fraction (GWF).
Weeks from planting
Pre -plant
10
6
harvest
14
18
11.6
11.2
13.5 a
11.2 b
11.5 b
13.2 a
11.1 b
10.5 b
Post­
%-.
DESERT SITE
Year
1992
1993
5.9
11.8
***
_
7.6
8.8
***
N-rate (kg-ha-1)
220
10.3
390
8.6
560
8.7
L***
9.7
8.4
7.8
L*
8.5
8.1
8.1
NS
Year*N-rate
***
Irrigation rate (IR)
70
100
130
8.5
8.1
9.0
8.9
NS
*
*
­
L**
-
6.4
8.3
***
8.1
7.3
6.6
L***
**
(%)
7.7
8.7
8.9
NS
Irrigation frequency (IF) (days)
1
8.0 b
9.0
2
8.8 ab
8.5
3
9.8 a
8.5
*
NS
6.5
8.1
9.8
L***
11.9
12.7
L***
7.6
8.1
8.8
NS
10.5
11.6
12.1
NS
10.6 b
11.2 b
12.6 a
6.9
10.1
***
10.4
10.3
8.4
8.4
8.7
NS
9.2
10.5
11.5
L**
8.6
9.2
11.6
12.9
L***
5.6
7.4
8.7
L***
7.3
7.2
7.9
*
NS
-
8.2
10.0
PIVOT SITE
Year
1992
1993
7.4
4.3
***
N-rate (kg.ha-1)
220
9.6
390
9.8
560
10.0
NS
-
10.2
-
9.8
10.6
10.3
NS
***
9.9
10.5
10.6
NS
9.0
9.1
9.0
NS
LNot significant, or significant at P=0.05, 0.01, 0.001, or
linear, respectively.
Means followed by different letters are significantly different at
P=0.05 (DMRT).
89
Table 3.28.
Year x N-rate effects on soil gravimetric water fraction
at 10 weeks from planting and post-harvest, desert site.
Week 10
N rate (kg. ha')
220
390
560
Post-harvest
1992
1993
1992
1993
7.0
7.8
7.1
NS
10.2 a ***z
8.4 b
***
9.0 ab ***
6.2
6.5
5.8
NS
10.1 ***
8.1 ***
***
7.4
L**
*
NS,
**' ***' LNot significant, or significant at P=0.05, 0.010, 0.001,
or linear.
Column means followed by different letters are significantly different
at P=0.05 (DMRT).
zSignificance accross rows.
'''
Effect of Irrigation Rate and Frequency on Soil Characteristics
Below 0.6 m
Irrigation frequency had little effect on measured soil
characteristics at any depth. Increasing irrigation rate decreased
NH4-N above 0.6 m, and decreased OM below 0.6 m.
As anticipated, the
soil GWF increased with irrigation rates.
Discussion & Conclusions
Long term cultivation of fine loamy sand in an arid climate slowly
decreases soil pH as much as one pH unit to 1.2 m depth. Soil pH
changes with cultivation are not obvious in a single season.
Fertilization, irrigation, and cultivation over long periods increase
salt (as determined by EC), NO3-N and NH4-N concentrations in such
soils.
However, much of the added salt leaches below the rooting
zone (0.6 m), in wetter than average winters.
Increases in soil NO3-N
below the rooting zone are sometimes evident within a single season of
fertilizer N applications, but such short-term applications do not
noticeably increase the soil EC.
90
Cultivated virgin desert soil accumulated more NH4-N than a long-term
cultivated field of the same soil type, probably due to higher
mineralization rates or lower nitrification rates in cultivated virgin
soils.
With increased water applications, net accumulation of NH4 -N
was reduced.
Despite the application of NH4-N:NO3-N fertilizers and
large increases in the NO3-N levels between pre-plant and post harvest
sampling dates, NH4 -N levels decreased at the pivot site and at the
desert site below 0.3 m between these two sampling dates.
Possible
explanations include an increase in the rate of nitrification activity
occurring at high N levels, and/or an increase in NH4 -N uptake caused
by more vigorous plant growth at the higher soil NO3-N levels (Mengel
and Kirkby, 1987).
Cultivation of virgin soils generally decreases OM (Stewart, 1970);
however, soils in the Hermiston-Boardman area are so low in OM that no
decline is observed with long-term cultivation.
Low rainfall winters, as observed in 1991-1992, leach less salts and
NO3-N out of the upper soil profile than do heavy rainfall winters
such as 1992-1993. The increased short term leaching seems to have
little effect on soil pH, OM or NH4 -N levels.
The increased EC and
NO3-N levels of the upper 0.3 m of soil found after dry winters
persist throughout the growing season.
Soils planted to potato in the Hermiston area respond similarly to
N-rate and irrigation rates whether they are irrigated by pivot or
solid set lines, even when application rates (cmhour-1) are higher
under set lines.
91
References
Gilkerson, R.A.
1958.
Washington soils and related physiography ­
Columbia Basin Irrigation Project.
Station Circular 527.
Wash.
Ag. Exp. Station, Washington State University, Pullman, WA.
Harris, P.M.
1978.
The Potato Crop: The scientific basis for
improvement.
Chapman and Hall, London, UK.
Johnson, D.R., and A.J. Makinson.
1988.
Soil Survey of Umatilla
County Area, Oregon. USDA-Soil Conservation Service.
Mengel, K. and E.A. Kirkby. 1987.
Principles of Plant Nutrition.
International Potash Inst. Bern, Switzerland.
Stewart, B.A.
1970.
A look at agricultural practices in relation to
nitrate accumulation. p. 47-60 In O.P. Engelstad (ed.) Nutrient
Mobility in Soils: Accumulation and Losses.
Special Publication
#4.
Soil Sci. Soc. America, Madison, WI.
92
CHAPTER 4
EFFECTS OF POTATO CROPPING PRACTICES ON SOIL SOLUTION
NITRATE LEVELS
Efficiency of Lysimeters for Collection of Soil Solution
Seventy-six and 94% of the porous cup lysimeters (PCL) effectively
extracted adequate water samples (>30 ml) in 1992 and 1993,
respectively. Lysimeters extracting adequate samples ranged from 70 to
88% in 1992, and 90 to 98% in 1993 (Figure 4.1).
In general, adequate
water samples were extracted when the gravimetric water fraction
remained above 6.5% GWF (or approximately 40% of the available water)
(Figure 4.2).
Comparison of paired PCL's within plots showed as much NO3-N
variability in the soil solution within the plots as between plots
(Table 4.1) making detection of significant treatment effects
difficult.
Soil Solution NO3-N Concentrations (direct analysis)
The concentration of NO3-N in the extracted soil solution was higher in
1992 than in 1993, except for the final sampling date which showed no
difference (Table 4.2). Soil solution NO3-N was higher at the pivot
site than at the desert site on all sample dates.
However, a year by
site interaction affected solution NO3-N concentrations on all sampling
dates except week 16; further, year, site and depth interacted on all
dates except weeks 10 and 16. During week 10, NO3-N concentrations at
the pivot site were 6 and 3 times greater than at the desert site in
1992 and 1993, respectively. NO3-N concentrations in extracted soil
solution remained constant for both years at the desert site, but were
2 times greater in 1992 than 1993 at the pivot site (Table 4.3).
There
was little difference in the concentration of NO3-N in soil solution
between the 0.6 and 1.2 m depths at either the desert or pivot site,
except: (1) in week 16 when NO3-N concentrations in extracted soil
93
Figure 4.1. Relationship between Is of PCL extracting more than 30 ml
of fluid from the soil and soil gravimetric water fraction in 1992
and 1993.
100
m
m .
im
95
.
90
ill
85
m m
1993
80
mu
m
75
m a
m
1992
im
70
65
7.5
8
8.5
9
9.5
10
10.5 11
11.5
Gravimetric Water Fraction (average)
12
12.5
solution were greater at 0.6 m than 1.2 m both years, though more
obviously so in 1993 than in 1992 (Table 4.4); and (2) in weeks 6 and
of the 1992 pivot trial, when soil solution NO3-N at 1.2 m was about
twice as high as at 0.6 m (Table 4.5).
8
Treatment Effects - Desert Site
The concentration of NO3-N in soil solution at 0.6 and 1.2 m at the
desert site was not affected by N-rate, irrigation rate, or irrigation
frequency (Table 4.6) except: (1) during weeks 14 and 16 when the
concentration of NO3-N in extracted soil solution increased linearly
with N-rates in 1993, but not in 1992 (Table 4.7); and (2) in week 10
when the concentration of NO3-N in soil solution at 1.2 m was higher
94
Figure 4.2. Volume of fluid extracted by PCL vs. soil gravimetric
water fraction.
120
X
100
X X MNIMCNNICIMOSC
80
60
40
Ne+ehalEllE ADE
)+DIAIE
20
volume= (GWF)(1 5.6 9) +( -6 4.0 2)
0
r squared = 0.75
20
40
2
3
4
5
6
7
8
9
10
11
12
Gravimetric Water Fraction (7.)
)K
grouped volumes + regressed values
with daily irrigation than with 2- or 3-day irrigation frequencies.
Lysimeters placed at 0.6 m were not affected by irrigation frequency
(Table 4.8).
During week 6, however, year and N-rate interacted
affecting solution NO3-N concentrations (Table 4.6) such that NO3-N
concentration did not vary with N-rates either year.
However, in plots
receiving 220 and 560 kgha-1 N, NO3-N concentrations were greater in
1992 than in 1993. Plots receiving 390 kgha-1 N produced similar NO3-N
concentrations both years (Table 4.7).
95
Table 4.1. Comparison of within plot and among plot coefficients of
variation for PCL soil solution NO3-N concentration.
Weeks from planting
Source
6
8
10
12
14
16
avg
Coefficient of Variation (.90
Between lysimeters
A and B of same plot
Desert site
Pivot site
S-plots
79
76
108
86
82
56
83
92
63
92
95
64
102
90
84
107
83
82
56
88
99
79
77
97
67
53
76
64
92
85
73
Among lysimeters
of the same treatment plots
Desert site
Pivot site
S-plots
73
69
106
85
73
50
77
60
88
75
67
Treatment Effects - Pivot Site
N-rate did not affect NO3-N concentrations in soil solution extracts at
the pivot site, except during week 16 when NO3-N concentrations
increased linearly with increasing N-rates (Table 4.9).
In week 12,
NO3-N concentrations at 0.6 and 1.2 m were similar for both years, but
greater in 1992 than 1993 at both depths (Table 4.10).
Soil solution NO3-N concentrations at 0.6 m in the side plots were
consistently about twice those at 1.2 meters. However, differences
were significant only in weeks 10 and 16. At the pivot site soil
solution NO3-N concentrations were higher at 1.2 m than at 0.6 m, and
at the desert site there was no difference between the NO3-N level at
0.6 and 1.2 m.
The reason for this site by depth effect is not clear,
but may be related to the rate of water application (inches/hour)
or
the difference in the GWF of the sites.
Sprinklers in the side and
desert plot delivered water approximately 3 times as fast as the pivot
sprinklers, resulting in more rapid infiltration (run-off was not
observed under either system).
Infiltration rate of water from surface
sources effects flow patterns in the soil (Steenhuis et al., 1988,
Steenvoorden, 1987). Because the GWF of the pivot site was greater
96
Table 4.2. Effect of year, location, and depth on NO3-N concentration
in PCL solution.
Weeks from planting
Treatment
6
8
10
12
14
16
64.0
34.5
***
38.0
43.0
NS
NO3 -N (ppm)
Year'
1992
1993
52.7
31.0
42.6
26.6
***
43.4
28.6
***
***
66.8
28.1
***
23.0
87.9
***
53.8
18.4
78.5
***
23.9
16.6
77.4
***
30.0
21.1
105.0
***
40.8
27.5
93.4
***
45.8
30.2
64.7
***
49.2
***
***
***
***
***
NS
37.9
46.3
29.1
42.5
32.0
36.2
NS
42.8
48.6
**
**
NS
NS
***
NS
NS
NS
**
NS
**
**
NS
Site
Desert
Pivot
s-plot
YearxSite
Depth (m)
0.6
1.2
**
**
YearxDepth
SitexDepth
*
YearxDepthxSite
*
***
*
49.5
46.1
NS
**
s-plots
0.6 m
1.2 m
NS,
73.0
34.6
NS
30.0
18.6
NS
41.0
20.4
*
50.6
31.0
NS
64.4
29.5
NS
53.4
29.0
***
*
66.9
33.8
*
**' ***Not significant, or significant at P=0.05, 0.01, or 0.001.
'Means of S-plot not included in year, site, or depth effects.
YDesert site means included AN, AW, and FI treatment plots;
Pivot site means include AN treatment plots;
S-plot included for comparison purposes only.
97
Table 4.3. Year x site effects on NO3-N concentrations in PCL-extracted
soil solution, week 10.
Year
Sitez
1992
1993
NO3-N (ppm)
Desert
Pivot
***
17.6
109.0
***
15.8
52.0
NS
* * *
NS, ***Not
significant, or significant at P=0.001, respectively.
zDesert site means included 21 plots;
Pivot site means 9 plots.
Table 4.4. Year x depth effects on NO3-N concentrations in PCL-
extracted soil solution, week 16.
Year
Depth (m)
1992
1993
NO3-N (ppm)
0.6
1.2
45.8
31.4
*
NS,
***Not significant, or significant at
respectively.
59.1
26.9
***
NS
NS
P=0.05, or 0.001,
than that of the set line site on the same field, water applied to the
pivot site would tend to penetrate deeper than on set line plot, thus
leaching more NO3-N into the 0.6 m zone from the surface layers. The
relative significance of each factor (watering rate and initial GWF of
soil) can be differentiated from the data available.
If the water
application rate was found to be critical, it could hold great
significance for extrapolating results obtained by experimental trials
under set line irrigation to situations under a pivot, and is worthy of
further experimentation.
98
Table 4.5. Year x site x depth effects on NO3-N concentrations in PCL-
extracted soil solution.
Weeks from planting
Depth (m)
6
12
8
14
NO3-N (ppm)
1992
Desert sitez
0.6
1.2
25.8
30.8
NS
17.1
23.7
NS
23.3
29.3
NS
32.0
29.1
NS
89.6
141.7
73.4
135.9
*
*
133.1
203.2
NS
115.1
159.9
NS
73.0
34.6
NS
30.0
18.6
NS
50.6
31.0
NS
64.4
29.5
NS
Pivot site
0.6
1.2
Side plots
0.6
1.2
1993
Desert site
0.6
1.2
15.9
19.6
NS
13.7
19.3
NS
17.1
16.0
NS
27.8
22.7
NS
65.4
64.1
NS
52.9
60.9
NS
64.5
45.5
NS
70.3
41.7
NS
Pivot site
0.6
1.2
NS, *Not
significant, or significant at P=0.05, respectively.
zDesert site means included AN, AW, and FI treatment plots;
Pivot site means include AN treatment plots;
S-plot included only control plots (3)­
99
Table 4.6. Effect of year, N rate, irrigation rate, and irrigation
frequency, on NO3-N concentrations in lysimeter-extracted soil
solution, desert site.
Weeks from planting
6
8
10
12
14
16
30.4
25.3
NS
26.9
32.7
NS
NO3-N (ppm)
Year
1992
1993
28.3
17.8
***
20.3
16.5
NS
17.6
15.8
NS
26.4
16.5
20.8
25.1
NS
15.3
21.4
NS
14.6
18.6
NS
19.8
22.3
NS
29.5
25.8
NS
41.0
20.8
17.6
19.2
14.8
NS
NS
14.5
17.1
16.4
NS
NS
18.2
21.1
24.2
NS
NS
18.1
28.2
34.7
NS
15.8
31.1
42.9
15.5
18.4
21.7
NS
14.6
17.0
16.5
NS
21.4
21.7
17.4
NS
25.9
27.8
27.5
NS
19.6
33.0
25.3
NS
15.6
15.4
23.4
16.9
20.7
27.0
NS
NS
30.5
26.2
30.6
NS
NS
35.0
29.0
30.9
NS
NS
*
Depth (m)
0.6
1.2
N-rate (kg-ha-1)
220
27.8
390
22.0
560
23.1
NS
Year*N-rate
Irrigation rate
70
100
130
*
(IR)
*
*
L*
*
(%)
17.4
23.8
24.1
NS
Irrigation frequency (IF)(days)
1
2
3
DepthxlF
NS,
'''
21.5
22.9
24.8
NS
NS
17.0
17.6
23.7
NS
NS
*
**
"' * * *, LNot significant, or significant at P=0.05, 0.01, 0.001, or
linear, respectively.
100
Table 4.7. Year x N-rate effects on NO3-N concentration in PCL-
extracted soil solution, desert site.
Weeks from planting
Year and
N-rate (kg. ha-1)
6
1992
14
1993
1992
16
1993
1992
1993
28.0
27.3
21.7
NS
4.7 NS
34.1 NS
53.6 NS
L***
NO3-N (ppm)
220
390
560
NS,
**'
38.1
24.9
35.6
NS
17.5
19.1
11.5
NS
* * *. LNot significant,
*z
29.6
32.1
18.9
NS
NS
7.6
25.1
**
*
43.9 NS
L**
or significant at P=0.05, 0.01, 0.001, or
linear, respectively.
zSignificicance across rows.
Table 4.8. Depth x irrigation frequency effects on NO3-N concentration
in PCL-extracted soil solution, desert site, week 10.
PCL depth (m)
Irrigation
frequency (days)
0.6
1.2
NO3-N (ppm)
1
2
3
NS,
13.8
15.1
13.4
NS
33.1 a
15.7 b
17.8 b
*
NS
NS
**
*' **Not significant, or significant at P=0.05, or 0.01,
respectively.
Column means followed by different letters are significantly different
at P=0.05 (DMRT).
101
Table 4.9. Year x N-rate effects on NO3-N concentration in PCL-
extracted soil solution, pivot site.
Weeks from planting
6
10
8
12
14
16
NO3-N (ppm)
Year
1992
1993
113.3
64.7
***
103.6
56.9
***
109.0
52.0
***
166.9
55.0
***
136.8
56.0
***
62.0
67.0
NS
77.5
99.4
NS
NS
62.6
95.0
74.1
80.9
NS
NS
95.7
114.5
NS
91.4
95.5
NS
NS
78.3
49.8
93.1
62.7
77.9
NS
114.9
86.8
113.7
NS
88.2
83.7
106.8
NS
50.1
58.3
84.4
Depth (m)
0.6
1.2
YearxDepth
N-rate (kcrha-1)
220
110.2
390
74.9
560
80.0
NS
*
NS
95.2
65.0
77.6
NS
*
*
NS
NS,
L*
***' Ligot significant, or significant at P=0.05, 0.001, or linear,
respectively.
'',
Table 4.10. Year x depth effects on NO3-N concentration in PCL-
extracted soil solution, pivot site week 12.
Year
Depth (m)
1992
1993
NO3-N (ppm)
0.6
1.2
NS,
'''
133.1
203.2
NS
64.5
45.5
NS
*
***
** *Not significant,
or significant at P=0.05, or 0.001,
respectively.
102
Soil Solution NO3-N after Conversion to ppm NO3-N in
Oven-dried Soil
Soil solution NO3-N concentrations for each lysimeter were multiplied
by the gravimetric water fraction (obtained by concurrent neutron probe
readings) to obtain ppm NO3-N of each sample on an oven-dry soil basis
to: (1) improve detection of significant treatments by converting the
quantity of NO3-N extracted from an unknown volume of soil into the
amount of NO3-N in a specific quantity of soil (i.e., ug of NO3-N per g
of oven dry soil); (2) relate better to the soil sampling results; and
(3) aid estimation of the degree of NO3-N change in the soil profile
over time.
Based on this conversion, soil NO3-N concentrations were similar in
1992 and 1993 during weeks 6, 8, and 10, but soil NO3-N concentration
at the pivot site was greater than the desert site (Table 4.11). Soil
NO3-N concentrations were greater at the pivot site than the desert
site on weeks 12, 14, and 16 of 1992, but the sites were similar in
1993 (Table 4.12).
Soil NO3-N concentrations did not differ between 0.6 and 1.2 m at
either site, except: (1) on week 8 soil NO3-N concentration was greater
at 1.2 m than 0.6 at the pivot site, but the same at the desert site
(Table 4.13); and (2) soil NO3-N concentration at 0.6 m was greater
than 1.2 m on week 12 of 1993, but depths were similar in 1992; (3)
Soil NO3-N concentrations were similar at 0.6 m each year, but were
greater at 1.2 m in 1992 than 1993 (Table 4.14); and (4) soil NO3-N
concentrations from 0.6 m were higher than at 1.2 m on week 16
(Table 4.11).
Soil NO3 -N at 0.6 m in the side plot was consistently about 2x larger
than at 1.2 m (though only statistically significant in week 8), a
pattern not seen in either the desert or pivot sites for reasons
previously discussed.
103
Table 4.11. Effect of year, site location, and depth on NO,-N
concentration in PCL-extracted soil solution transformed to ppm NO3-N
on a dry-soil weight basis.
Weeks from planting
Treatment
6
8
10
12
14
16
NO3-N (ppm)
Yearz
1992
1993
3.8
3.8
3.5
3.6
3.3
3.2
NS
NS
NS
**
2.2
7.7
***
8.2
1.8
7.7
***
4.7
1.6
7.3
***
3.9
NS
NS
3.8
3.7
NS
2.9
4.1
***
NS
NS
NS
9.2
7.2
5.9
3.7
NS
*
5.0
4.4
5.3
1.9
***
5.1
4.5
4.4
5.2
NS
4.9
2.2
10.8
9.7
3.1
8.5
***
7.6
NS
**
***
**
3.1
3.3
NS
5.0
4.4
NS
*
SiteY
Desert
Pivot
s-plot
YearxSite
Depth (m)
0.6
1.2
YearxDepth
SitexDepth
s-plots
0.6 m
1.2 m
**
NS
NS
4.6
3.4
NS
**
4.2
3.8
NS
NS
NS
NS
6.7
3.2
NS
14.0
5.9
NS
5.8
3.8
*
NS
NS
8.3
6.8
NS
NS,
**' ***Not significant, or significant at P=0.05, 0.01, or 0.001.
Means followed by different letters are significantly different at
P=0.05 (DMRT).
zMeans of S-plot not included in year, site, or depth effects.
YDesert site means included AN, AW, and FI treatment plots;
Pivot site means include AN treatment plots;
S-plot included for comparison purposes only.
Effect of N-rate, Irrigation rate, and Irrigation Frequency on Soil
NO3-N Concentrations as Estimated by Soil Solution NO3-N Converted to
Dry-soil Basis
Soil NO3-N concentrations at 0.6 and 1.2 m were not affected by N-rate
on either the desert (Table 4.15) or pivot (Table 4.16) sites, except:
(1) at the desert site on week 6, soil NO3-N decreased with increasing
104
Table 4.12. Year x site effects on NO3-N concentration in PCL-extracted
soil solution transformed to ppm NO3-N on a dry-soil weight basis.
Weeks from planting, year
12
Location
1992
14
1993
1992
16
1993
1992
1993
NO3-N (ppm)
Desert
Pivot
4.4
6.6
**
4.5
4.0
NS
NS'
2.4
11.7
***
**
1.9
2.2
NS
NS
NS
2.1 2.9
11.0 3.8
***
NS
NS
NS
** *Not significant,
or significant at P= 0.01, or 0.001,
respectively.
'Significicance across rows.
NS, **'
Table 4.13. Site x depth effects on NO3-N concentration in PCL-
extracted soil solution transformed to ppm NO3-N on a dry-soil weight
basis, week 8.
Site
Depth (m)
Desert
Pivot
NO3 -N (ppm)
0.6
1.2
NS,
'''
** *Not significant,
1.6
2.0
NS
6.4
9.1
*
or significant at
P=0.05, or 0.001,
respectively.
N-rate in 1993 but not in 1992 (Table 4.17); and (2) on week 12, soil
NO3-N concentrations at the desert site were greater at 560 kgha-1 N
than 390 kgha-1 N (but not greater at N-rate of 220 kgha-1); and (3)
desert site soil NO3-N increased linearly with increasing N-rates on
week 16.
Soil NO3-N concentrations were also generally not affected by
irrigation rates or irrigation frequencies (Table 4.15)
except:
(1)
105
Table 4.14. Year x depth effects on NO3-N concentration in PCL-
extracted soil solution transformed to ppm NO3-N on a dry-soil weight
basis, week 12.
Year
Depth (m)
1992
1993
NO3 -N (ppm)
0.6
1.2
5.0
5.1
NS
5.0
3.8
NS
*
NS, *Not significant, or significant at P=0.05, respectively.
soil NO3-N increased linearly with increasing irrigation rates on
week 6; and (2) during week 10 soil NO3-N was greater with daily
watering than at 2-day irrigation frequency (but not different than
3-day watering) at 1.2 m but not at 0.6 m (Table 4.18).
Comparison of the Two Methods Used to Analyze
Lysimeter Data
Of the two methods used for analyzing NO3-N data from the PCL presented
here (unaltered vs. converted values), the former had a clear advantage
over the other in regard to resolving significant differences between
years, sites, or universal depths.
Neither had an advantage in
resolving treatment effects shown to be significantly different based
on soil sampling data.
106
Table 4.15. Effect of year, N rate, irrigation rate, and irrigation
frequency on NO3 -N concentration in PCL-extracted soil solution
transformed to a dry-soil weight basis, desert site.
Weeks from planting
6
8
10
NO3 -N
12
14
16
(ppm)
Year
1992
1993
2.5
2.0
**
1.7
1.8
NS
1.4
1.7
NS
4.4
4.5
NS
2.4
1.9
NS
2.1
2.9
NS
1.6
2.0
1.5
1.7
NS
4.8
4.1
NS
2.5
1.9
NS
3.6
1.5
1.7
1.9
1.2
NS
NS
1.3
1.7
1.3
NS
NS
4.6 ab
4.1 b
6.1 a
1.3
2.5
1.7
NS
NS
0.9 b
2.8 a
2.8 a
1.5
1.8
2.2
NS
1.3
1.6
1.8
NS
5.1
4.5
3.4
NS
2.1
2.1
2.4
NS
1.9
2.5
2.6
NS
2.1
1.5
1.6
NS
3.4
5.7
3.6
NS
NS
3.0
1.9
2.6
NS
NS
2.5
2.3
3.2
NS
NS
Depth (m)
0.6
1.2
2.2
2.3
NS
**
N-rate (kg. ha-1)
220
2.6
390
2.2
560
2.2
NS
Year*N-rate
Irrigation rate
70
100
130
*
(IR)
1.3
2.4
2.5
L*
*
NS
**
**
NS
(%)
Irrigation frequency (IF)(days)
1
2
3
DepthxIF
NS,
2.5
2.2
2.3
NS
NS
2.2
1.7
1.8
NS
NS
*
**' LITot significant, or significant at P=0.05, 0.01, or linear,
respectively.
Means followed by different letters are significantly different at
P=0.05 (DMRT).
'''
107
Table 4.16. Effects of year and N rate on NO3-N concentration in PCL-
extracted soil solution transformed to a dry-soil weight basis, pivot
site.
Weeks from planting
6
10
8
12
14
16
11.7
2.2
***
11.0
3.8
***
10.2
11.5
NS
10.2
10.4
NS
10.8
10.6
11.1
NS
7.9
10.2
13.0
NS
NO3-N (ppm)
Year
1992
1993
7.7
7.8
8.0
7.5
NS
7.4
8.1
NS
6.6
4.0
NS
8.1
6.7
NS
6.4
9.1
NS
7.1
7.5
NS
5.3
5.1
8.9
6.3
8.2
NS
8.2
5.9
7.9
NS
6.3
4.1
**
Depth (m)
0.6
1.2
N-rate (ko-ha-1)
220
9.6
390
6.6
560
7.1
NS
NS
5.4
NS
* *Not significant, or significant at P=0.01, respectively.
Table 4.17. Effect of year and N-rate on NO3-N concentration
transformed to dry-soil weight basis, desert site week 6.
Year
N-rate (kg' ha-1)
1992
1993
NO3 -N (ppm)
220
390
560
NS, ** *Not
3.0
2.2
3.4
NS
2.2
2.2
1.0
NS
NSZ
NS
***
significant or significant at P.0.001, respectively.
°Significance across rows.
108
Table 4.18. Effect of depth and irrigation frequency on NO3-N
concentration transformed to dry-soil weight basis, desert site
week 10.
depth
Irrigation
frequency (days)
0.6 m
1.2 m
NO3-N (ppm)
1
2
3
1.3
1.5
1.4
NS
2.8 a
1.4 b
1.9 ab
NS'
NS
NS
**
NS,
* *Not significant, significant at P=0.01, respectively.
Means followed by same letter not significantly different at P=0.05
(DMRS).
'Significance across rows.
Discussion & Conclusions
1\03,N Leaching Below the Rooting Zone
The PCL provided no evidence for NO3-N leaching below the rooting zone.
N-rate did not affect soil solution NO3-N concentrations at either 0.6
or 1.2 m at any sampling date. The NO3-N concentration at 1.2 m did
slightly increase, but apparently unrelated to treatments. A large
amount of variation among individual lysimeters was evident. This
spatial variability was clearly demonstrated in the CV values for the
lysimeter data sets which averaged 82 and 85 for "raw" and "converted"
versions, whereas the soil and petiole data sets averaged only 51 and
16.
Thus any statistical evidence of leaching may have been masked by
a large random variation (MSE) value for the lysimeter data.
Differential Treatment Response Between the Desert and Pivot Sites
The desert and pivot sites generally responded similarly to treatment.
However, the similarity of response was due to insufficient data to
indicate significant effects of treatment, rather than an absence of
potential differences, based on CV values.
109
Efficiency of the PCL in Estimating Soil Solution NO3-N
The PCL did not reliably indicate the level of NO3-N in the soil,
mostly because of high variability between lysimeters in the same
plots.
Lysimeters reliably extracted adequate soil solution when
placed correctly, and when the soil moisture level did not fall below
7.5% GWF, however they required soil disturbing installation, plant
disruption with each sampling, and conversion to a ppm dry-soil basis
(which required accurate knowledge of the GWF via concurrent NP
readings), all of which caused a compounding of errors.
References
Steenhuis, T.S., J.R. Hageerman, N.B. Pickering, N.W.F. Ritter, 1989.
Flow path of pesticides in the Delaware and Marland portion of the
Chesapeake Bay region. pp 397-419.
IN: National Well Water Ass.
"Proceedings of Groundwater Issues in Solution in the Potomac
River Basin, Chesapeake Bay Region" Washington D.C. March 1989.
Dublin, OH.
Steenvoorden, J.H.A.M. 1987.
Optimizing the use of soils: new
agricultural and water management aspects. pp 389-408. IN: H.
Barth and P. L'Hermite (eds). Scientific basis for soil protection
in the European Community; Elsevier Applied Science Publishers,
Barking, Essex, UK.
110
CHAPTER 5
EFFECTS OF POTATO CROPPING PRACTICES ON PLANT NITROGEN
STATUS, AERIAL BIOMASS AND TUBER PRODUCTION
Petiole NO3-N Status
Petiole NO3-N concentrations for the desert site were higher than for
the pivot site on weeks 7 and 15, but not different on weeks 11 and 19
(Table 5.1).
However, a significant Year x Site interaction occurred
at week 15.
Petiole NO3-N concentration averaged 14,000 ppm for the
desert and pivot sites in 1992, but was 16,800 ppm for the desert site
and 12,000 for the pivot site in 1993.
Petiole NO3-N concentrations
at the desert site were similar in 1992 and 1993 except at week 7 when
they were higher in 1993 (Table 5.2). At the pivot site, however,
petiole NO3-N concentrations were higher in 1993 than 1992 at week 7,
not different on week 11, and lower in 1993 than 1992 on weeks 15 and
19 (Table 5.3).
Effect of N -rate, Irrigation Rate, and Irrigation Frequency on Petiole
NO3-W Levels
Petiole NO3-N concentrations increased linearly with increasing N-
rate, except at week 7 when N-rate did not affect petiole NO3-N
concentration at desert (Table 5.2) and pivot (Table 5.3) sites.
However, in the desert site, N-rate and year interacted in week 15
such that petiole NO3-N concentrations were lower in 1992 than 1993
for the low (220 kgha-I) N-rate but similar for the higher rates
(Table 5.4).
Petiole NO3-N concentrations varied considerably from
the recommended levels (Table 5.5); Jones and Painter, 1975). Petiole
NO3-N concentrations fell in the "excess range" for all three N-rates
at the first sampling, were "adequate" for 560 kgha-1 N and were
"inadequate" for 390 kgha-1 and 220 kgha-1 N on week 11, and again
were in the "excess" range by the last sample date (week 19) for all
but the low application rate in the desert site which produced
111
Table 5.1. Year and site effects on potato petiole NO3-N
concentrations.
Weeks from planting
7
11
15
19
NO3-N (ppm x 100)
Year
1992
1993
271 a
334 a
***
143 c
139 b
NS
137 c
153 b
NS
180 b
147 b
***
***y
321 a
261 a
***
206
137 d
149 b
NS
151 c
132 b
170 b
149 b
NS
201
***
***
* * *
Sitez
Desert
Pivot
S-plot
YearxSite
NS
132
***
154
NS
***
NS
NS, ***Not
significant or significant at P=0.001, respectively.
zDesert site means included N-rate, irrigation rate and
irrigation
frequency plots.
Pivot site means included N-rate plots.
S-plot included for comparison purposes only.
Means within a row followed by different letters are significantly
different at P=0.05 (DMRT).
"adequate" levels.
Petiole NO3-N concentrations for the pivot site
were "inadequate" for 220 kgha-1 N, "adequate for 390 kgha-1 N, and
"excess" for 560 kgha-1 N on week 15. These same N-rates (220, 390,
and 560 kgha-1 N) resulted in inadequate, adequate, and adequate,
levels, respectively, on the desert site in 1992, and inadequate,
excess, and excess, respectively, in 1993.
Petiole NO3-N concentrations decreased linearly with increasing
irrigation rates (Table 5.2). Petiole NO3-N concentration was
greatest on week 7 and lowest on week 11 and week 15 in 1992, and week
11 in 1993.
Petiole NO3-N concentrations were not affected by
irrigation frequency (Table 5.2).
112
Table 5.2. Effect of year, N rate, and irrigation rate and frequency
on potato petiole NO3-N concentrations, desert site.
Weeks from planting
7
11
15
19
NO3-N (ppm x 100)
Year
1992
1993
291 a
350 a
***
N-rate (kg-ha-1)
220
320 a
390
317 a
560
338 a
NS
Year*N
NS
Irrigation rate (%)
70
318 a
100
327 a
130
292 a
***
140 c
134 c
NS
135 c
168 b
NS
183 b
157 b
NS
90 b
140 d
170 c
L***
61 c
159 c
204 b
L***
76 bc
179 b
220 b
L***
NS
173 c
137 c
100 c
L**
Irrigation frequency (days)
1
327 a
131
2
318 a
136
3
329 a
148
NS
NS
c
c
c
**
192 bc
148 bc
125 bc
L*
152 bc
148 bc
165 bc
NS
NS
220 b
166 b
138 b
***
***
***
L**
167 b
169 b
175 b
NS
***
***
***
NS,
**' ***' LNot significant or significant at P=0.05,
0.01, 0.001, or
linear, respectively.
zMeans within a row followed by different letters are significantly
different at P=0.05 (DMRT).
Mid-season Aerial Biomass and Tuber Yield
Aerial Biomass (AB) Production
The AB for the desert site was about 25% less than for the pivot site,
however effects of year and site interacted (Table 5.6). At the
desert site, AB was greater in 1993 than 1992 (Table 5.7), but at the
pivot site AB was the same for both years (Table 5.8). The AB
increased linearly with increasing N-rate at both sites. The AB
increased linearly with increases in irrigation rate, but was not
affected by irrigation frequency (Table 5.7).
113
Table 5.3. Effect of year and N-rate on potato petiole NO3 -N
concentrations, pivot site.
Weeks from planting
7
11
15
19
NO3-N (ppm x 100)
Year
1992
1993
244 a
298 a
* * *
N-rate (kg-ha-1)
220
257 a
390
263 a
560
263 a
NS
149 c
150 b
NS
144 c
120 c
119 b
149 b
180 b
69 c
153 b
175 b
L***
L**
173 b
125 be
***z
* * *
**
*
89 c
164 b
194 b
L***
***
***
***
NS,
**' ***' lliot significant or significant at P=0.05,
0.01, 0.001,
or
linear, respectively.
zMeans within a row followed by different letters are significantly
different at P=0.05
(DMRT).
Table 5.4. Year x N-rate interaction effects on petiole NO3-N
concentrations at week 15, desert site.
Year
N-rate (kg. ha-1)
1992
1993
NO3-N (ppm x 100)
220
390
560
NS,
111
150
155
L*
98
*
133
195
NS
NS
L***
***' /Slot significant or significant at P=0.05, 0.001, or linear,
respectively.
114
Table 5.5. Effect of N-rate, irrigation rate and irrigation frequency
on petiole NO3-N concentrations in comparison to recommended
sufficiency ranges.
A. RECOMMENDED RANGES
Growth stage
Critical levels
Early
season
Early
tuber
NO3-N
Excessive
Inadequate
>250
<205
Midseason
Late
season
(ppm x 100)
>215
<170
>161
<120
>80
<52
B. MEASURED VALUES
Weeks from planting
Treatment
7
11
Petiole NO3-N
15
19
(ppm x 100)
N-rate (kg. ha-1) Desert Site
220
320 ez
390
317 e
560
338 e
140 i
170 a
61 i
159 a
204 e
76 a
179 e
220 e
N-rate (kg. ha-1) Pivot Site
220
257 e
390
263 e
560
263 e
119 i
149 i
180 a
69 i
153 a
175 e
89 e
164 e
194 e
173 a
137 i
100 i
192 e
148 a
125 a
220 e
166 e
138 e
131 i
136 i
148 i
152 a
148 a
165 e
167 e
169 e
175 e
90 i
Irrigation rate (%)
70
100
130
318 e
327 e
292 e
Irrigation frequency (days)
1
2
3
327 e
318 e
329 e
Z e=excessive, a=adequate, i=inadequate according to Jones E. Painter,
1975.
115
Table 5.6. Effect of site location on mid-season aerial biomass,
tuber yields and numbers.
Tuber size class (g)
Tuber
weight
ABY
<116
mt. ha-1 x
116-227
228-340
tubers-ha-1
total
(x1000)"
Year
1992
1993
5.2
6.0
NS
35.0
33.6
Desert
Pivot
5.0
6.8
s-plot
6.1
32.9
37.6
NS
23.0
110
597
556
-
NS
531
679
-
222
256
**
Site'
***
YearxSite
**
177
330
280
229
120
***
*
NS
88
**
558
***
NS,
**' ** *Not significant or significant at P=0.05, 0.01, or 0.001,
respectively.
'Desert site means include N-rate, irrigation rate, and irrigation
frequency plots.
Pivot site means included only N-rate plots.
S-plot included for comparison purposes only.
YAB = aerial (above ground) biomass based on 2 samples of three
plants,
air-dried.
'Based on 2 sample areas of 69cm by 86cm (3 plants, 1 row, each).
Tuber Production at Mid-season
Tuber yield and number were higher on the desert site than the pivot
site in 1992, but in 1993, yield was higher on the pivot site than the
desert site, while tuber numbers were similar (Table 5.6). Yield
(weight) of tubers in mid-season was higher in 1992 than 1993, but
numbers of tubers were similar both years at both the desert
(Table 5.7) and pivot (Table 5.8) sites.
The yield and number of tubers at mid-season (13 weeks) were not
affected by N-rate at either desert (Table 5.7) or pivot (Table 5.8)
sites.
Mid-season tuber yields (weight) increased linearly with increasing
irrigation rate (Table 5.7). The number of tubers was not affected by
irrigation rate, except the number of tubers weighing 228-340 g
116
Table 5.7. Effect of year, N rate, and irrigation rate and frequency
on mid-season production of aerial biomass, and tuber yield and
number, desert site.
Tuber size class
Tuber
weight
ABz
<116
mt-ha-1 Y
(g)
116-227 228-340
total
tubers-ha-1 (x1000) Y
Year
1992
1993
4.3
5.7
***
N-rate (kg-ha-1)
220
4.3
390
5.1
560
5.6
L*
30.3
35.4
177
280
120
487
575
***
211
170
174
NS
329
256
337
NS
105
125
105
NS
566
517
570
NS
312
293
182
135
125
73
L*
463
553
494
NS
*
32.5
32.4
35.4
NS
Irrigation rate (9.- of recommended)
70
4.4
21.9
155
100
130
5.1
5.5
L*
34.6
35.0
L***
184
155
NS
NS
Irrigation frequency (IF)(days)
1
2
3
Year*IF
5.1
5.1
4.8
NS
NS
36.9
32.0
33.2
NS
NS
351
265
281
NS
NS
115
116
138
NS
NS
223
164
197
NS
576
531
485
NS
*
NS
NS,
**' *"' ''Not significant or significant at P=0.05, 0.01, 0.001, or
linear,
respectively.
zAB = aerial (above ground) biomass based on 2 samples of three
plants,
air-dried.
YBased on 2 sample areas of 69cm by 86-cm (3 plants, 1 row, each).
decreased linearly with increasing irrigation rate. The major effect
of the irrigation rate was reduced tuber yield with the low-rate
treatment.
Tuber weights at mid-season were not affected by the irrigation
frequency.
Likewise, the number of tubers was not affected by
irrigation frequency, except that the total number was highest for the
2-day frequency and lowest for the 3-day frequency in 1992
(Table 5.9).
117
Table 5.8. Effect of year and N rate on mid-season aerial biomass and
tuber yield and number, pivot site.
Tuber size class (g)
Tuber
weight
ABZ
116-227
<116
mt-ha-1 Y
tubers ha-1
228-340
total
(x1000)Y
Year
1992
1993
7.2
6.5
NS
45.8
29.0
330
229
88
383
340
266
NS
145
211
244
NS
93
98
71
***
713
645
NS
N-rate (kg-ha-1)
220
390
560
5.8
7.2
7.5
L*
40.0
41.1
31.7
NS
NS
716
721
603
NS
***, L
-Not significant or significant at P=0.05, 0.001, or linear,
respectively.
zAB = aerial (above ground) biomass based on 2 samples of three
plants,
air-dried.
YBased on 2 sample areas of 69cm by 86cm (3 plants, 1 row, each).
NS,
Table 5.9. Effect of year and irrigation frequency on
mid-season tuber numbers.
Year
Irrigation
frequency (days)
1992
tubers ha-1
1
2
3
463 ab
587 a
354 b
*
1993
(x1000)z
688
581
615
NS
**
NS
**
NS,
**Not significant or significant at P=0.05, or 0.01,
respectively.
Column means followed by different letters
significantly different at P=0.05 (DMRT).
zBased on 2 sample areas of 69cm by 86cm (3 plants,
1 row, each).
118
Tuber Yield, Size Distribution, and Internal Quality
Tuber Numbers and Weight of Sizes Classes and Grades
More tubers were produced in 1993 than 1992, however year and site
interacted (Table 5.10). In 1993, more tubers were produced at the
desert site than the pivot site, but there was no difference between
sites in 1992 (Table 5.11).
More tubers were produced in 1993 than in
1992 at both sites.
The weight of all size classes and grades were similar for the desert
and pivot sites (Table 5.10), except (1) more culls were produced at
the pivot site, and (2) more tubers >340 g were produced at the pivot
site in 1993 but not in 1992 (Table 5.12).
Table 5.10. Effect of site location on number and size of tubers.
Size class (g)
Number
total
Culls
<116
tubers' ha-1 (x1000) Y
116-340
>340
US#2
US#1
total
mtha-1 Y
Year
1992
1993
617
1028
***
0.23
0.35
NS
11.2
14.7
***
29.2
50.0
***
3.7
3.3
NS
2.3
1.7
NS
36.0
53.2
***
3.4
4.1
2.2
1.7
NS
2.8
5.9
45.9
45.6
NS
35.5
58.3
60.1
NS
41.3
NS
NS
43.3
70.0
***
Sitez
Desert
Pivot
846
770
S-plot
562
NS
YearxSite
**
0.16
0.59
***
0.76
NS
12.9
14.0
NS
11.6
NS
41.0
40.8
NS
26.9
NS
***
NS
NS
NS, ***Not significant or significant at P.0.001, respectively.
zDesert site means included N-rate, irrigation rate, and irrigation frequency plots;
Pivot site means included only N-rate plots.
S-plot included for comparison purposes only,
YBased on 2 sample areas of 6.1 x 1.7 m (2 rows) each.
120
Table 5.11. Effect of year and
site interaction on the total
number of tubers.
Table 5.12. Effect of year and
site interaction on weight of
tubers >340 g.
Year
Site
1992
Year
1993
Site
tubers-ha-1 (x 1000)
Desert
Pivot
603
651
NS
1088
888
***
***
***
1992
1993
mt-ha-1
Desert
Pivot
4.39
2.41
NS
2.33
**
5.86
**
***
Ns, ***Not significant or
Ns'**'***Not significant or
significant at P=0.001,
respectively.
significant at P=0.01, or
0.001,
respectively.
At the desert site, tuber numbers were increased linearly with
increasing N-rate (Table 5.13) but only in 1993 (Table 5.14). Numbers
of tubers increased linearly with increasing irrigation rate both
years but were not affected by irrigation frequency (Table 5.13).
N-
rate did not affect weight of any size class or grade. Both the
weight and grade of tubers produced increased linearly with increasing
irrigation rates in 1992 but not in 1993 (Table 5.15). Neither weight
nor grade were affected by irrigation frequency (Table 5.13), except
for the weight of tubers sized greater than 340 g, which were higher
in 1993 with daily watering than watering at 2-day or 3-day intervals,
with no difference in 1992 (Table 5.16).
Table 5.13. Effect of year, N-rate, and irrigation rate and frequency on tuber number and yield,
desert site.
Size class
(g)
Number
total
culls
<116
116-340
>340
tuhers.ha-1 (x1000)'
US#2
US#1
Total
37.7
53.5
***
46.2
70.3
***
46.3
43.1
42.7
NS
NS
50.0
54.7
54.2
NS
NS
mt. ha-1 '
Year
1992
1993
N-rate (kg* ha-1)
220
390
560
516
935
***
0.12
0.21
NS
10.9
14.8
744
704
574
**
30.8
51.3
***
4.4
2.3
**
2.5
1.8
***
0.09
0.17
0.17
NS
NS
14.2
12.4
12.4
NS
NS
41.9
37.9
38.3
NS
NS
3.2
3.5
2.8
NS
NS
2.1
2.5
2.0
NS
NS
L**
NS
0.08
0.16
0.24
NS
NS
13.0
13.0
12.1
NS
(days)
751
740
722
0.41
0.13
0.06
13.3
13.0
12.0
NS
NS
L***
***
YearxN-rate
Irrigation rate
(IR)
(t)
70
100
130
Year*IR
Irrigation frequency (IF)
1
2
3
Year*IF
646 b
733 a
787 a
NS
NS
NS
NS
**
30.2
42.6
44.1
L***
***
43.0
40.5
41.9
NS
NS
0.9
3.7
4.3
L***
***
3.3
2.1
1.8
L*
NS
31.5
47.3
49.5
L***
***
45.3
60.2
61.2
L***
***
4.7
3.0
3.9
NS
2.2
2.2
2.3
NS
NS
48.7
44.7
47.0
NS
NS
62.2
57.3
58.9
NS
NS
*
NS, , *,
**, LNot significant or significant at P=0.05, 0.01, 0.001, or linear, respectively.
followed by different letters significantly different at P=0.05 (DMRT).
'Based on 2 sample areas of 6.1 x 1.7 m (2 rows) each.
Means
122
Table 5.14. Effect of year and N-rate
interactions on the total number of tubers,
desert site.
Year
N-rate
(kg. ha-1)
1992
1993
tubers ha-1 (x1000)
220
390
560
NS,
'''
531
495
501
NS
975
***
938 ***
663
*
L***
**' ***' 1Not significant or significant
linear,
at P=0.05, 0.01, 0.001, or
respectively.
zSignificance across rows.
Table 5.15. Interaction of year and irrigation rate on tuber yields.
Size class (g)
<116
114-340
>340
US#1
Irrigation
rate (%)
1992
1993
1992
1993
1992
1993
Total
1992
1993
1992
1993
14.0
40.2
48.9
L***
52.5
54.5
50.0
NS
23.4
48.7
56.4
L***
67.2 ab
71.9 a
65.9 b
mt*lia-1
70
100
130
NS,
13.7
10.7
9.7
L*
12.4
15.3
14.5
NS
9.7
33.3
39.7
L***
50.9
51.9
48.4
NS
0.2
4.7
7.0
L***
1.6
2.6
1.6
NS
**.' *' LNot significant or significant at P=0.05, 0.01, 0.001, or linear, respectively.
Means followed by different letters significantly different at P=0.05 (DMRT).
'''
*
124
Table 5.16. Interaction of year and
irrigation frequency on tuber yields of
tubers >340 g.
Year
Irrigation
frequency (days)
1992
1993
mt ha-3­
1
2
3
4.1
4.0
7.2
NS
3.8 a
2.1 b
2.2 b
NS
**
NS,
**,Not significant or significant at
P=0.05, or 0.01, respectively.
Means followed by different letters
significantly different at P=0.05 (DMRT).
At the pivot site, more tubers were produced in 1993 than 1992
(Table 5.17).
More tubers (by weight) in the 116-340 g and >340 g
size classes were produced in 1993 than 1992, but more <116 gram
tubers were produced in 1992.
There was no difference in the weight
of culls or US#2 tubers produced in 1992 and 1993, but there were more
US#1 produced in 1993 than in 1992. N-rate did not affect tuber
numbers at the pivot site (Table 5.17).
The weight of 116-340 g size
class tubers decreased linearly with increasing N-rate at the pivot
site, as did total tuber weight.
Year and N-rate interacted to affect
total weight of tubers in the <116 g size class and those greater than
340 g.
The total weight of tubers <116 g each decreased linearly with
increasing N-rate in 1993, but was not affected by N-rate in 1992
(Table 5.18), while the total weight of tubers >340 grams decreased
linearly with N-rate in 1992, but increased with N-rate in 1993.
Table 5.17. Effect of year and N rate on number and yield of tubers, pivot site.
Size class (g)
Number
Sitez
total
Culls
<116
116-340
>340
tubers. ha-1 (x1000) z
US#2
US#1
Total
mt. ha-1 z
Year
1992
1993
N-rate (kg. ha-1)
220
390
560
Year*N-rate
NS,
560
762
***
0.52
0.69
NS
14.5
13.5
726
592
671
NS
0.60
0.52
0.69
NS
NS
NS
30.7
41.2
***
2.4
4.1
***
1.9
1.6
NS
35.0
56.9
***
45.7
74.6
14.1
13.5
14.1
NS
43.9
41.2
37.5
L*
3.6
4.1
4.8
NS
1.3
2.0
1.9
48.0
46.3
43.4
NS
62.9
60.1
57.6
*
NS
*
NS
NS
NS
***
**' ***' LNot significant or significant at P=0.05,
0.01,
YBased on 2 sample areas of 6.1 x 1.7 m (2 rows) each.
'',
0.001,
NS
or linear, respectively.
***
L*
126
Table 5.18. Effect of year and N-rate interactions on the weight of
tubers <116 and >340 g, pivot site.
<116 g
>340 g
N-rate
(kg-ha-1)
1992
1993
1992
1993
3.71
2.33
1.29
L**
3.53
5.69
8.28
mt ha-1
220
390
560
12.2
11.8
13.7
NS
16.6
15.2
14.4
L*
**z
**
NS
NS
*
*
L*
NS,
* *, LNot significant or significant at P=0.05, 0.01, or linear,
respectively.
ZSignificance across rows.
Specific Gravity
Specific gravities of tubers were higher in 1992 than 1993
(Table 5.19), and the tubers from the desert site had a higher
specific gravity than the tubers from the pivot site.
Gravities were
not affected by N-rate either the desert (Table 5.20) or pivot
(Table 5.21) sites, nor were they affected by irrigation rate, or
irrigation frequency.
Visual Internal Defects
The percent of tubers with visual internal defects was higher in 1993
than in 1992 (Table 5.19), and did not differ significantly between
the two sites.
The percentage of tubers with hollow heart was not
affected by N-rate at either the desert site (Table 5.20) nor the
pivot site (Table 5.21). The percentage of tubers with internal
discoloration (ID) decreased linearly with increasing N-rate at both
sites in 1993 but was not affected in 1992 (Table 5.22). This effect
was observed in both freshly harvested and stored tubers from the
pivot site but only in freshly harvested tubers from the desert site.
The percentage of tubers with hollow heart was not affected by
irrigation rate (Table 5.20). ID in freshly harvested tubers increased
linearly with increases in irrigation rate, but no increases were
observed in tubers stored for 3 months (Table 5.20). HH and ID were
127
Table 5.19. Effect of site location on specific gravity, hollow heart
(HH), internal discoloration (ID), and fry color after storage.
At Harvest
Specific
gravity
HH
ID
After 3 months storage
HH
ID
4 C
9.5.y
10 C
Fry color'
Year
1992
1993
1.077
1.062
1.0
7.8
***
2.3
28.3
***
4.9
2.9
NS
0.0
15.2
15.6
NS
***
0.0
6.8
***
1.2
37.5
***
5.9
7.9
***
17.9
22.7
***
7.3
6.1
20.8
19.1
*
**
Sitez
Desert
Pivot
1.069
1.061
s-plot
1.069
***
0.0
4.4
4.9
NS
0.0
24.8
26.6
NS
0.0
NS, *-**-*"Not significant,
or significant at P=0.05, 0.01, or 0.001,
respectively.
zDesert site means included N-rate, irrigation rate, and irrigation
frequency plots;
Pivot site means included N-rate plots.
S-plot included for comparison purposes only.
YHH and ID after 3 month storage is average of values for 4 and 10 C.
"Potato Chip/Snack Food Association "Fry color standards for potatoes
for chipping", converted from measured Agtron values using formula
IPC=(Agtron)(-0.13285) + (5.3223).
not affected by irrigation frequency (Table 5.20)
.
Fry Color from 4 and 10 C Storage
Fry color after 3 months of storage at either 4 or 10 C was darker
(i.e., higher number value) in 1992 than in 1993 (Table 5.19). The
desert site produced lighter-colored chips than the pivot site from
both storage temperatures.
Fry color was not affected by either N-
rate for tubers grown in either the desert (Table 5.20) or the pivot
(Table 5.21
sites, nor was fry color affected by irrigation
)
frequency.
Fry color decreased linearly with increasing irrigation
rate from both storage temperatures (i.e. fry color darkened)
(Table 5.20).
128
Table 5.20. Effect of year, N rate, and irrigation rate and frequency
on tuber specific gravity, hollow heart (HH), internal discolorations
(ID), and fry color after storage, desert site.
Specific
Site
gravity
Harvest
HH
56.
ID
of tubers
After 3 months storage
HH
ID
% of tubers'
4 C
10 C
Fry colorY
Year
1992
1993
1.080
1.064
***
N-rate (kg-ha-1)
220
1.069
390
1.069
560
1.070
NS
Year*N-rate
NS
Irrigation rate (IR)
70
1.069
100
1.070
130
1.067
NS
Year*IR
NS
1.3
8.6
***
2.6
27.6
***
0.0
6.6
***
1.1
36.7
***
4.50
4.21
***
2.84
2.27
***
3.3
4.5
8.8
NS
25.4
12.9
16.7
NS
*
3.3
4.3
5.9
NS
NS
33.4
22.8
26.7
NS
NS
4.42
4.34
4.37
NS
NS
2.69
2.55
2.48
NS
NS
3.8
4.5
4.1
NS
NS
15.1
26.6
25.8
NS
NS
3.94
4.43
4.42
L***
NS
2.23
2.59
2.76
L***
4.1
4.6
3.7
NS
20.3
25.1
28.1
NS
4.49
4.30
4.45
NS
2.48
2.60
2.74
NS
*
(%-)
5.0
4.2
8.8
NS
NS
3.3
16.3
21.7
L**
Irrigation frequency (days)
1
1.070
3.3
11.3
2
1.069
5.8
16.3
3
1.070
2.1
14.2
NS
NS
NS
NS,
NS
* **
**'
iNot significant or significant at P=0.05, 0.01, 0.001, or
linear, respectively.
'HH and ID after 3 month storage is average of values for 4° and 10°C.
YPotato Chip/Snack Food Association "Fry color standards for potatoes
for chipping", converted from measured Agtron values using formula
Fry Color=(Agtron)(-0.13285) + (5.3223).
129
Table 5.21. Effect of year and N-rate on specific gravity, hollow
heart (HH), internal discoloration (ID), and fry color after storage,
pivot site.
Harvest
Specific
gravity
HH
After 3 months storage
HH
ID
of tubers
ID
4 C
% of tubersz
10 C
Fry colorY
Year
1992
1993
1.070
1.057
***
0.3
5.6
1.1
30.0
***
0.0
7.3
**
1.3
39.3
***
4.62
4.41
3.21
2.37
**
***
2.9
25.4
2.5
12.5
3.3
8.8
NS
L***
3.7
6.4
4.4
NS
35.8
25.6
18.6
L*
4.55
4.49
4.49
NS
2.78
2.78
2.78
NS
***
NS
NS
NS
NS
*
N-rate (kg-ha-1)
220
390
560
1.063
1.060
1.060
NS
Year*N-rate
NS
NS
ns,
**' *"' LNot significant or significant at P=0.05, 0.01,
linear,
respectively.
0.001, or
9IH and ID after 3 month storage is average of values for 4 and 10 C.
YPotato Chip/Snack Food Association "Fry color standards for potatoes
for chipping", converted from measured Agtron values using formula
Fry color=(Agtron)(-0.13285) + (5.3223).
Table 5.22. Effect of year and N-rate on internal discoloration (ID)
of tubers at harvest and after 3 months in storage.
Harvest
N-rate
220
390
560
NS,
1992
1993
1.8
2.9
1.3
NS
49.2
22.8
24.2
L**
Storagez
1992
1993
2.0
1.3
0.0
NS
50.9 ***
34.1 ***
33.9 ***
L***
(kg. ha-1)
***Y
***
**
**' ***' Iliot significant or significant at P=0.01, 0.001,
respectively.
zAverage of ID after 3 month storage at 4 and 10 C.
YSignificance across rows.
or linear,
130
Summary of Results
Petiole NO3-N concentrations varied among sites and years somewhat
randomly. NO3-N concentrations increased with increasing N-rate on
all but the first sampling date when petiole nitrates for all
treatments were in the "excess" range. Petiole NO3-N concentrations
decreased with increasing irrigation rates but were largely unaffected
by irrigation frequencies. Tissue NO3-N concentrations were
"excessive" at the first and last sampling dates and "inadequate" for
the two mid-season dates, indicating a need to improve N availability
throughout the season.
Mid-season aerial biomass increased with increasing N and water at
both sites as expected, but was not significantly affected by
irrigation frequency. The weight of aerial biomass was greater on the
pivot site than the desert site; however, the desert site produced
higher tuber yields and numbers at mid-season than did the pivot site.
This increase in tuber yield was evidently not related to N
availability, because tuber yields were not significantly effected by
N-rate at either site.
Site selection had only minor affects on crop response to N-rate.
Exceptions were that tuber numbers decreased with increasing N-rate on
the desert site but not the pivot site, while tuber yields decreased
with increasing N-rate at the pivot site but not the desert site.
Tuber yields, both early and late, increased with irrigation rate, but
were not significantly affected by either N-rate or irrigation
frequency. Tuber numbers at mid-season were not affected by N-rate,
irrigation rate, or irrigation frequency, but decreased with
increasing N and increased with increasing irrigation at final
harvest.
Minor differences in tuber specific gravity and fry color occurred
between years and sites; however, tuber hollow heart and internal
discoloration were more severe in 1993 than 1992. Tuber specific
gravity and hollow heart were not affected by N-rate, irrigation rate,
or irrigation frequency. However, internal discoloration decreased
with increasing N and increased with increasing irrigation rates.
Fry color darkened linearly with increasing irrigation.
131
Discussion and Conclusions
Petiole NO3-N concentrations increased with increasing nitrogen
application rate, and decreased with increasing water amounts.
Decreases in response to increased irrigation were evidently not
caused by reduced soil N levels associated with increased leaching
beyond the rooting zone, because differences in soil NO3-N
concentrations were not effected by irrigation rates (Table 3.4).
Above ground biomass did increase with increased moisture, thus the
decrease in petiole NO3-N with increasing irrigation rates was
probably due to a "dilution effect" in plant tissues caused by
increased plant growth with higher moisture (Marschner, 1990).
Varying irrigation frequency from 1 to 3 days evidently did not affect
the water content of the soil enough to increase leaching of NO3-N out
of the rooting zone or to increase NO3-N "dilution" in plant tissues
from increased growth.
Based on petiole results, and the recommended ranges of Jones and
Painter (1975), even the lowest N-rate was adequate early and late in
the season but all three treatments were inadequate during mid-season.
This suggests a need to improve N availability throughout the growing
season by applying less at planting, more during the early part of the
season, and less near the end of the season. All three N complements
would probably have maintained petiole NO3-N levels in the "adequate"
range throughout the season if optimally applied.
Larger yields and tuber numbers observed in 1993 compared to 1992
were due to relatively favorable growing conditions and moister soils
in 1993
(Table 2.6).
The data show that tuber yields can be reduced
by N rates greater than 220 kgha-1, and increased by higher moisture;
however, these responses would depend on climatic conditions and
initial soil NO3-N concentrations.
The decrease in tuber size in
response to higher N-rates at the pivot site in 1992, and increase in
response to higher N-rates in 1993 probably are a result of both
higher soil N and favorable weather in 1993.
Favorable growing
conditions in 1993 allowed plants to grow larger and use more soil
nitrogen, thus reducing both petiole and soil NO3-N levels. Plants
advanced out of the vegetative stage to initiate tuber production
earlier, and thus grow larger tubers. In 1992, however, the less
favorable growing conditions resulted in less uptake of applied N and
reduced plant growth; an excessive buildup of NO3-N in soil and plant
132
tissues resulted, especially in plots receiving higher N-rates,
causing these plants to remain in the vegetative stage longer and not
produce tubers as early.
Irrigation frequency apparently has little effect on tuber numbers or
weights in the absence of moisture stress.
As expected, irrigation rates are only effective in increasing yields
when soil moisture is limiting at one or more rates. Even though
replacement amounts of water were applied each year, the initial soil
moisture level was much lower in 1992 than 1993, and yields increased
with increasing irrigation in 1992 but not in 1993.
Specific gravities seem to be influenced by climatic conditions during
tuber growth. Very mild growing conditions in 1993 afforded
continuous tuber growth, with late skin sets, and lower specific
gravities.
In 1992, however, the hotter drier climate probably
resulted in more moisture stress and earlier tuber maturity, resulting
in higher specific gravities in that year.
It is unclear why the
specific gravities recorded for 1993 are so much lower than normally
encountered for Russet Burbank potatoes.
The lighter fry colors of
tubers from the desert site than the pivot site, and for tubers
produced in 1992 vs. 1993, may be linked to the same factors that
increased specific gravity.
The fact that fry color decreased
(darkened) with increased irrigation rate would seem to support this
claim.
Optimal tuber yield and quality are obtained with N fertilization and
irrigation practices described as "best management practices" herein,
(specifically 390 kgha-1 N, irrigation at recommended replacement rate
applied every other day). Tuber yields on the long-term cultivated
site, which had higher soil NO3-N levels throughout the season,
decreased with increasing N-rate. Therefore, N levels above the BMP
rate of 390 kgha' are not recommended. N-rates below 390 kgha' N
may have resulted in reduced yields if the crop had grown an
additional month, as is typical in this area.
Irrigation rates higher
than recommended promoted yields, but also increased hollow heart and
darkened fry color. Although irrigation frequencies did not affect
any of the measured yield and quality parameters, the 2 day frequency
is recommended because of convenience and insurance against damaging
watering delays caused by failure of the watering system.
If
necessary, however, watering frequencies as long as three days could
133
be used under normal weather conditions if needed to help control
diseases associated with wet foliage, such as late blight or white
mold.
References
Jones, J.P. and C.G. Painter. 1975 Tissue analysis, a guide to
nitrogen fertilization of Idaho Russet Burbank Potatoes. Current
Info. Series No. 240 Univ Idaho, Moscow, ID.
.
Marschner, H. 1986. Mineral nutrition of higher plants.
Press. New York, NY.
Academic
134
CHAPTER 6
RELATIONSHIP AMONG NITRATE CONTENT OF SOIL, SOIL SOLUTION,
AND PETIOLE TISSUES, AND OVERALL CONCLUSIONS OF STUDY
Comparison of Values and Significant Effects
Relationship Among NO3-N Values Obtained from Soil, Petiole and
PCL Samples
The coefficient of variation (CV) is a measure of experimental
variation not attributable to treatment effects (i.e., degree of
randomness).
When CV values for the NO3-N monitoring methods (soils,
petioles, and soil solution) are compared, petiole analysis provided
the most consistent readings with CV values averaging one-fourth and
one-sixth of those for soil and lysimeter samples, respectively
(Table 6.1).
Soil sample analysis varied less than the analysis of
lysimeter samples, but direct comparison was not possible because soil
samples were a composite of five 2-cm cores, while PCL samples were
single samples drawn from an undetermined volume of soil.
Soil and Petiole NO3-INT Values and Analyses
Petiole and soil NO3-N values for the 0-0.6 m of the soil profile
followed similar seasonal trends in response to N-rate (Table 6.2,
Figure 6.1, Figure 6.2). However, a very poor statistical correlation
existed between the two in 1992 (Figure 6.3), or 1993 (Figure 6.4).
Regression values were 0.14 in 1992 and 0.44 in 1993. Regression of
petiole NO3-N levels on soil NO3-N concentration from the same sampling
dates throughout the season did not yield higher regression values,
indicating that petiole nitrate content is a rather poor indicator of
soil NO3-N levels, and vice-versa.
There are many factors that can
influence petiole nitrate content that have little on effect on soil
NO3-N levels, such as rapid plant growth during favorable growing
Table 6.1. Comparison of soil, lysimeter, and petiole estimates of plot variation in NO3-N
concentrations.
Weeks from planting
Sampling
method
Pre-plant
6
8
10
12
Coefficient of Variation,
14
16
18
Post-harvest
Avg
36
37
59
47
61
%
Soil
Desert site
Pivot site
S-plots
40
87
14
Petioles
Desert site
Pivot site
S-plots
Lysimeter
raw
Desert site
Pivot site
S-plots
Lysimeter
converted
Desert site
Pivot site
S-plots
51
62
76
50
81
84
49
44
6
25
20
19
15
18
22
17
16
12
9
8
3
8
-
7
58
55
27
52
106
85
73
50
83
82
56
88
77
60
99
79
77
97
67
53
88
75
67
77
70
59
87
71
44
85
78
64
65
77
79
93
85
123
115
92
74
31
83
75
67
73
69
114
41
-
-
88
75
67
Table 6.2. Effects of N-rate on petiole and soil (0.0-0.6 m) NO3-N content.
Petiole NO3-N
Weeks from planting
N-rate
(kgha-1)
6
10
Soil NO 3 -N
Weeks from planting
14
18
6
NO3-N (ppmx100)
1992
Desert
220
390
560
1992
Pivot
220
390
560
1993
Desert
220
390
560
1993
Pivot
220
390
560
NS,
*,
*,
102
148
142
NS
214
227
231
NS
119
160
167
NS
344
348
368
NS
133
197
L**
50
174
253
L***
299
300
294
NS
118
138
193
L*
51
62
148
162
L***
139
174
L**
78
87
157
188
L***
14
18
Post-harvest
NO3-N (ppm)
296
286
307
NS
71
143
156
L**
10
99
189
238
L***
116
189
214
L***
53
169
202
L***
LNot significant, or significant at P=0.05,
9
-
5.5
7.1
10.5
NS
5.6
9.9
12.3
NS
0.01,
3.4
3.9
4.6
7.8
5.7 10.2
NS
L*
2.7
6.9
11.0
L***
7.1
6.0
10.8
15.6
10.3
20.4
26.2
L*
L*
22.7
14.2
NS
1.7
2.6
6.2
L***
2.5
3.4
5.0
L*
0.001,
1.4
2.3
2.4
4.5
3.0
7.7
L** L***
14.9
L***
1.8
2.7
4.5
L**
3.8
8.8
18.6
L**
2.3
3.7
7.9
L**
4.5
8.8
or linear, respectively.
Figure 6.1. Petiole vs. soil NO3-N values, 1993 desert site.
400
16
, 350
14
300
12
E- 250
10
z 200
8
0
0
g
1
rn
o
z 150
6
a)
-5 100
4
t.)
cl-
50
2
0
10
14
18
postharvest
Sample dates (weeks from planting)
petiole low N
%//
soil low N
ET soil control N
petiole control N
petiole high N
--m soil high N
0
a
a
Figure 6.2. Petiole vs. soil NO3-N values, 1993 pivot site.
300
,
o
20
-18
250
-16
0
7-< 200
-14
-12
150
10
100
50
10
14
postharvest
18
Sample date (weeks from planting)
petiole low N M petiole control N
soil low N
--ta soil control N
petiole high N
NI soil high N
Figure 6 . 3 .
Regression of petiole NO3-N on soil NO3-N, 1992.
220
r squared=0.14
200
0o 180
IN
E 160
.
m
I...
.I
so
.
IN
m
= NE lal
IN
=IN
NI
a_
140
I.
amm
=
ow
. .
EP
Wil .
=
im
=
0 120
100
se
iir
=
se
a
80
as
60
0
m
5
so
se
NI
.
.
10
15
.
20
25
30
soil NO3 N (ppm)
35
40
45
50
Figure 6 . 4 .
Regression of petiole NO3-N on soil NO3-N, 1993.
450
400
i
o
0 350
.
1,
El
El
NM
NI
INI
MN
MI
NM
x 300
MK
mg
r squared=0.44
= IN
ON um
MI
IN
iINI.
111.
El es
E
R 250
z
I
V)
0
Z
a)
a=
mi
200
150
-5
i 100
Ns
.
NI
.m
No
NI
all
its m si. ..
IN
50
.
El
I. =
w
IN
0
5
10
15
soil NO3 N (ppm)
20
25
30
141
conditions diluting absorbed tissue NO3-N, or cold soil conditions
restricting NO3-N uptake by roots, thus this poor correlation is not
surprising.
Soil and Lysimeter Solution Analysis
Estimated differences in NO3-N levels among years, sites, and depths
were generally similar for PCL extracts and soil samples, though the
actual values (ppm) differed (Table 6.3).
PCL extracts contrasted
poorly to soil samples in estimating effects of N-rate and irrigation
treatments on soil NO3-N (Table 6.4).
Soil samples taken from 0.6 m on
week 6 had higher NO3-N levels than those taken from 1.2 m, while the
PCL showed an opposite trend with the 0.6 m extraction having a lower
NO3-N than the 1.2 m extract. However, in other cases differences were
related more to magnitude than direction; while response trends for
the two methods were similar, soil samples produced significantly
different treatment means more often.
Soil and Lysimeter Estimates of NO,,N on a Dry Soil Basis
In general, data showed a rather poor correlation between PCL
estimates of soil NO3-N levels and estimates obtained from soil samples
for year or site effects (Table 6.3), or treatments at the desert
(Table 6.4) or pivot (Table 6.5) sites.
Significant effects of site
and year on NO3-N levels shown by soil samples were not apparent when
converting PCL estimates; however, significant treatment effects shown
by soil samples were verified by PCL.
One exception to this trend
occurred in week 6 at the desert site when converted lysimeter NO3-N
levels showed a linear decrease with increasing irrigation rate while
soil samples did not.
Table 6.3. Comparison of soil and lysimeter estimates of year, site, and depth effects on soil NO3-N.
Weeks from planting
10
6
Soilz
Ly-RY
Ly-S
Soil
Ly-R
14
Ly-S
Soil
Ly-R
3.3
3.2
NS
4.9
2.0
64.0
34.5
***
***
5.3
1.9
***
Ly-S
NO3-N (ppm)
Year
1992
1993
3.8
4.0
NS
52.7
31.9
***
3.8
3.8
NS
5.1
2.1
***
42.6
26.6
3.9
4.0
NS
5.1
23.0
87.9
2.2
7.7
***
8.2
2.4
6.4
***
3.2
16.6
77.4
***
30.0
1.6
7.3
***
3.9
3.1
4.3
***
4.6
27.5
93.4
***
45.8
2.2
10.8
***
9.7
4.1
3.5
NS
37.9
46.3
3.8
3.7
NS
3.6
3.7
NS
32.0
36.2
NS
3.1
3.3
NS
3.6
3.2
49.5
46.1
NS
4.2
3.8
NS
***
Site
Desert
Pivot
S-plot
Depth
0.6
1.2
NS,
***
53.8
(m)
**
NS
**'
***' LNot significant, or significant at P=0.05, 0.01, 0.001, or linear, respectively.
zSoil sample from 0.3-0.6 m = 0.6 and 0.9-1.2 = 1.2 m.
YLy-R = ppm NO3-N in extracted soil water sample ("raw" values); Ly-S = Ly-R values converted to a ppm dry
soil basis.
'''
Table 6.4.
Comparison of soil and lysimeter estimates of year, depth, N-rate, and irrigation rate, on
soil NO3-N, desert site.
Weeks from planting
6
Soil'
Ly-RY
10
Ly-S
Soil
Ly-R
14
Ly-S
Soil
Ly-R
Ly-S
NO3-N (ppm)
Year
1992
1993
Depth
N-rate (kg.ha-1-)
220
390
560
Irrigation rate
100
130
NS,
28.7
17.8
***
2.5
2.0
4.2
3.3
NS
20.8
25.1
NS
3.4
3.7
5.7
L*
3.1
1.7
***
17.6
15.8
NS
1.4
1.7
NS
4.3
1.9
***
30.4
25.3
NS
2.4
1.9
NS
2.2
2.3
NS
2.4
2.4
NS
14.6
18.6
NS
1.5
1.7
NS
3.3
2.8
29.5
25.8
NS
2.5
1.9
NS
27.8
22.0
23.1
NS
2.6
2.2
2.2
NS
1.9
2.3
3.2
L***
14.5
17.1
16.4
NS
1.3
1.7
1.3
NS
1.9
3.2
4.2
18.1
28.2
34.7
NS
1.3
2.5
1.7
17.4
23.8
24.1
NS
1.3
2.4
2.5
L*
14.6
17.0
16.5
NS
1.3
1.6
1.8
NS
25.9
27.8
27.5
NS
2.1
2.1
2.4
NS
* *
(m)
0.6
1.2
70
3.5
3.9
NS
NS
L***
NS
(%)
4.7
3.9
3.3
NS
2.1
2.5
2.1
NS
2.5
3.1
4.1
L*
**' ***' LNot significant, or significant at P=0.05, 0.01, 0.001, or linear, respectively.
'Soil sample from 0.3-0.6 m = 0.6 and 0.9-1.2 = 1.2 m.
YLy-R = ppm NO3-N in extracted soil water sample ("raw" values); Ly-S = Ly-R values converted to a ppm dry
soil basis.
Table 6.5.
Comparison of soil and lysimeter estimates of year, depth, and N-rate, on soil NO3-N,
pivot site.
Weeks from planting
10
6
Soil'
Ly-RY
Ly-S
Soil
Ly-R
14
Ly-S
Soil
Ly-R
Ly-S
8.1
6.7
NS
6.4
2.3
***
136.8
56.0
11.7
2.2
NO3-N (ppm)
Year
1992
1993
4.0
4.1
NS
113.3
64.7
4.1
4.0
NS
77.5
99.8
NS
***
7.7
7.8
NS
9.9
3.0
109.0
52.0
***
***
7.4
8.1
6.3
6.7
NS
74.1
80.8
NS
7.1
7.5
NS
4.4
4.1
NS
3.6 a
9.3 a
6.4 ab
93.1
62.7
77.9
NS
8.2
5.9
7.9
NS
3.1
3.4
6.1
L***
***
***
91.4
95.5
NS
10.2
11.5
NS
Depth (m)
0.6
1.2
NS
N-rate (kg. ha-1)
220
390
560
2.8
4.1
5.9
L*
NS,
110.2 a
74.9 b
80.0 b
*
9.6
6.6
7.1
NS
**
88.2
83.7
106.8
NS
10.8
10.6
11.1
NS
**'
***' LNot significant, or significant at P=0.05, 0.01, 0.001, or linear, respectively.
Means followed by different letters are significantly different at P=0.05 (DMRT).
'Soil sample from 0.3-0.6 m = 0.6 and 0.9-1.2 = 1.2 m.
YLy-R = ppm NO3-N in extracted soil water sample ("raw" values); Ly-S = Ly-R values converted to a ppm dry
soil basis.
'',
145
Estimates of NO3-N Changes in the Soil
Significant changes in soil NO3-N concentrations occurred between
sample dates at both desert and pivot sites in response to N-rate as
shown in Tables 22 and 25 of Chapter 3. With the minor exception of
week 14, changes in soil NO3-N between sample dates were not affected
by irrigation rates or frequencies. The amount of NO3-N in kgha-1 for
these soils can be roughly calculated by multiplying the NO3-N
concentrations (ppm) by a conversion factor of 4.48 (Schepers and
Mosier, 1991). When this value is subtracted from the value for the
previous sampling date, changes in kgha-1 N are derived for desert
site (Table 6.6) and pivot site (Table 6.7).
In the desert site, seasonal soil NO3-N concentrations did not increase
at any depth with 220 kgha-1 N-rate, increased to 1.2 m at the 390
kgha-1 N-rate, but only to 0.9 m at the 560 kgha-1 N-rate.
Failure of
the 560 kgha-1 N-rate to also produce significant responses in NO3-N
to 1.2 m may have been due to large experimental error (MSE).
Seasonal soil NO3-N levels for the 560 kgha-1 N were about double
those for the 390 kg-ha-1 N treatment at 0.9 m. On the pivot site,
soil NO3-N increases in response to N-rate were limited to 0.3 m for
the 220 and 390 kgha-1 N-rate, but extended to 0.9 m for the 560
kgha-1 N treatment.
Estimates of NO3.41 Leaching
Nitrate concentration changes in a cultivated, fine sandy loam are
primarily caused by fertilizer additions, plant uptake, leaching,
immobilization or mineralization of soil organic matter and crop
residues. Denitrification, is not considered to be significant in
aerated sandy loams
(Meisinger and Randall, 1991). The amount of
nitrogen removed with a Russet Burbank potato crop varies with
cultural practices, tuber yields, and harvest techniques. Some
"standard values" or estimates of tuber N contents include 0.7 %,
0.40, 0.17% of the tuber fresh weight (SICCFA, 1985; Meisinger and
Randall, 1991; Doerge et. al., 1991).
Using the 0.4% estimate, the
harvest values can be multiplied by 0.004 to estimate N removed with
the crop for each of the N treatments.
146
Table 6.6. Change in soil NO3-N between sampling dates in response to N
rate and depth, desert site.
Sample depth (m)
and
N-rate (kgha-1)
Weeks from planting
10
14
Post-harvest
SeasonalY
NO3-N (kg ha-1)
0.0-0.3
220
390
560
20.6
55.6
0.0
15.2
0.0
0.3-0.6
220
390
560
0.0
2.2
10.8
0.6-0.9
220
390
560
0.0z
0.0
15.7
34.8
51.5
113.0
0.0
5.4
0.0
0.0
15.2
25.1
22.9
41.2
0.0
0.0
0.0
0.0
0.0
0.0
0.0
9.0
24.6
0.0
13.9
32.7
0.9-1.2
220
390
560
0.0
0.0
0.0
0.0
0.0
0.0
0.0
6.3
0.0
0.0
7.2
0.0
0.0-1.2
220
390
560
0.0
32.5
132.8
0.0
0.0
20.6
46.2
84.5
0.0
95.5
189.9
0.0
0.0
0.0
'0.0=not statistically changed from previous sampling date, only
changes significant at P=0.05 or less are shown.
Ynet change from pre-plant to post-harvest.
Uptake of soil N and incorporation into the non-harvested portion of
the potato plant (leaves, stems and roots) constitutes another
seasonal sink for soil NO3-N.
Doerge et al. (1991) estimated this
fraction to be approximately equal to the amount of N removed with the
tuber crop.
Westerman (1993) estimated that nitrogen makes up
approximately 4% of the foliage dry weight on average, and that the
average root/aerial biomass (AB) ratio is approximately 1/1 at
season's end. Thus, multiplying the accumulated mid-season AGB by
0.08, provides an estimate of the amount of N incorporated in plant
147
Table 6.7. Change in soil NO3-N between sampling dates in response to N
rate and depth, pivot site.
Sample depth (m)
and
N-rate (kgha-1)
Weeks from planting
10
14
Post-harvest
SeasonalY
NO3-N (kg-ha-1)
0.0-0.3
220
390
560
0.0z
0.0
71.2
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
60.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
34.5
34.9
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
71.2
0.0
0.0
0.0
36.3
66.3
219.9
49.0
118.7
305.5
36.3
66.3
125.4
49.0
118.7
207.4
0.3-0.6
220
390
560
0.0
0.0
63.2
0.6-0.9
220
390
560
0.9-1.2
220
390
560
0.0
0.0
0.0-1.2
220
390
560
'0.0=not changed from previous sampling date, only changes significant
at P=0.05 or less are shown.
Ynet difference from pre-plant to post-harvest.
tissues
However, Pumphrey and Rasmussen (1983) found that such plant
biomass rapidly decomposed after potato harvest to contribute to soil
NO3-N concentrations.
Meisinger and Randall (1991) suggested that 13.6 kgha-1 of N is
released for each 1% reduction in soil organic matter. Schepers and
Mosier (1991) noted that 2% of the total organic N in the surface 0.3
m of a soil is mineralized annually, meaning that a soil with 1% OM to
a depth of 0.3 m could mineralize about 45 kgha-1 N annually.
Schepers and Mosier (1991) further suggested that in irrigated fields,
148
mineralization of large amounts of recently added crop residue may
double estimates of N mineralized from soil OM to about 90 kgha-1 N.
Based on the assumption that all nutrient uptake into a potato plant
would occur within the 0.0-0.6 m soil zone, and the data collected,
estimates of the amount of N available for leaching with each of the
N-rate treatments were prepared for each site (Table 6.8, Table 6.9).
Although estimates for crop removal and accumulation, and
mineralization of crop residues and soil OM are inherently imperfect,
none of these activities occurred significantly below the 0.6 m depth.
Thus, increases in soil NO3-N at the 0.6-1.2 m zone can reasonably be
attributed to leaching of NO3-N from above, and decreases attributed to
leaching to the layers below (NH4 -N was not found to be leaching in
this soil based on analysis of PCL samples). Estimates of NO3-N
leaching from the 0.6-0.9 to 0.9-1.2 and beyond should be reasonably
creditable.
N availability for leaching is difficult to estimate. In the desert
site, 0, 7, and 60 kgha-1 were available for leaching from 0.9-1.2 m
in response to the 220, 380, and 560 kg-ha-1 N additions, respectively.
Data for the pivot site do not reflect reality.
Leaching must have
occurred from the 0-0.6 m layers to net a 16.9 and 43.9 kgha-1
increase in soil NO3-N at 0.3-0.6 m for the 390 and 560 kgha-1 N-rate
(respectively).
However, no NO3-N was "available" for leaching to the
0.3-0.6 m depth.
This error occurs despite N increases of 150 kgha-1
contributed by OM and biomass mineralization to account for a pre-
plant plow down of the winter wheat cover crop, and the inclusion of a
10% "misc" loss.
The source of the unaccountable N can not be
accurately determined from the data generated for this thesis and
points out the inherent difficulties in attempts to create accurate N
budgets predicting N leaching rates.
Table 6.8. Effects of N-rate on potential NO3-N leaching budget between successive soil layers,
desert site.
Potential additions
Sample depth (m)
and
N-rate (kgha-1)
Fert./
leaching'
Soil OM + BM
MineralizationY
Potential losses
Biomass"
Cropw
NO,-N
0.0-0.6
220
390
560
220
390
560
3.8 + 95
3.4 + 95
4.0 + 95
87
101
112
Miscv
Net change
in NO3-N
Available
for leaching
(kg ha-1)
200
219
217
32
0
49
66
45
110
0.0
74.4
154.2
0.6-0.9
220
390
560
0.9-1.2
220
390
560
0
18
89
0
4
36
0.0
0.0
0.0
0
0
0
0
0
0
5
4
0
11
56
0.0
0.0
0.0
0
0
0
0
0
0
0
0
3
-4
56
7
0
0.0
13.9
32.7
0.0
7.2
0.0
'fertilizer applications to 0.0-0.6 m, leaching additions to 0.0-0.9 and 0.9-1.2 m.
Y% change in soil OM x 13.6 (kg N / % change in OM) (Meisinger and Randall, 1991).
"mid- season sampling of foliage (g/sample area) x 2 (g root+foliage/g foliage) x 0.033 (kg N / kg
(Doerge, et al. 1991).
biomass)
wharvest weight (mt/ha) x 0.004 (kg N/kg fresh tubers) (Meisinger and Randall, 1991).
"other sources of loss including denitrification, fixation as NH,-N, and unaccountable (10% of additions).
H
lo
Table 6.9. Effect of N-rate on potential NO3-N leaching budget between successive soil layers, pivot
site.
Potential Additions
Sample depth (m)
and
N-rate (kgha-1)
Fert./
leaching'
Soil OM + BM
MineralizationY
Potential Losses
Net change
Biomass"
Crop''
Miscv
in NO3-N
Available
for leaching
37
54
71
49
119
271
-12
43
59
NO3-N (kg. ha-1)
0.0-0.6
220
390
560
0.6-0.9
220
390
560
0.9-1.2
220
390
560
220
390
560
0
43
59
0
26
15
0.0 + 150
-1.0 + 150
-0.7 + 150
-1.0
0.4
0.0
0.0
0.0
0.0
116
144
150
252
240
230
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
43
15
0
0
44
-1
26
15
'fertilizer applications to 0.0-0.6 m, leaching additions to 0.0-0.9 and 0.9-1.2 m.
Yt change in soil OM x 13.6 (kg N / t change in OM) (Meisinger and Randall, 1991).
"mid- season sampling of foliage (g/sample area) x 2 (g root+foliage/g foliage) x 0.033 (kg N / kg
biomass).
(Doerge, et al. 1991).
"'harvest weight (mt/ha) x 0.004 (kg N/kg fresh tubers) (Meisinger and Randall, 1991).
'other sources of loss including denitrification, fixation as NH4 -N, and unaccountable (10t of additions).
151
Discussion and Conclusions
The basic "working hypothesis" of this study assumed that under best
management practices, there should be minimal NO,-N leaching under a
commercial potato field in the Lower Columbia Basin.
For this study,
"best management practices" called for the crop to be irrigated at
recommended replacement rates, every 2 days, and to receive 390 kgha-1
N.
The main study site included all three cultural variables and was
located on virgin desert soil to reduce the impact that spatial
variability in soil NO3 -N concentration would have on this study.
The
pivot site was chosen to determine how well data from the desert site
would transfer to extensively cropped center pivot fields. The side
plot was included to test the divergence between center pivot and set
line watering on the same field.
The term "minimal" as related to NO,­
N leaching was never clearly defined.
Under the defined "best management practices" (BMP) statistically
significant increases of 7 kgha-1 in soil NO3 -N concentrations were
found to 1.2 m at the desert site, but no significant changes were
found at the pivot site.
In fact, under the pivot statistically
significant increases in soil NO3 -N content in response to BMP were
limited to the surface 0.3 m, while increases in soil NO3 -N at higher
than BMP N levels reached the 0.9 m depth. The difficulty in
verifying the basic "working hypothesis" is associated with defining
what the term "minimal" means. Data generated during these
experiments, indicates that more replications per treatment may have
produced statistically significant increases in soil NO3 -N to much
greater depths than observed in this instance.
Because of very high
levels of soil spatial variability, especially under the pivot,
statistically significant increases in soil NO3 -N under BMP were
limited to the surface sampling depth on the pivot site. This does
not imply that increases in soil NO3 -N did not occur below this depth;
in fact, the data suggest this to be the case.
It simply means that
these increases were not statistically different from earlier sample
dates due to high means squares for experimental error (MSE). Not
being statically different, is not synonymous with being statistically
"the same".
Lack of statistical significance simply implies that one
can not assume to a P level of certainty that the "true" means of any
two groups are not different.
152
Additional replicates would have reduced the effect of random spatial
variability in soil NO3-N on statistical data analysis and thus aided
in detecting significant N-rate treatment effects.
Irrigation rates
and frequencies did not cause significant changes below the 0.6 m
depth, nor were there indications that they would have with more
replications.
Therefore, irrigation variables, at least at these
levels, need not be repeated in future studies.
PCL NO 3 -N data were
less precise than soil sample values, and far more difficult to
analyze and use;
PCL's are not recommended for further studies.
Experiments designed to better quantify effects of N-rate on nitrate
leaching under commercial potato fields in the Lower Umatilla Basin,
would require larger plot size than used herein to reduce vine damage
during sampling and at least 4 or 5 replicates of each N-rate to
reduce the MSE term and improve separation of means. N fertilizers
should be applied through the pivot if possible.
It is recommended
that soil samples be taken at three week intervals throughout the
growing period and be tested only for NO3-N in future trials.
Petiole
samples do not indicate the NO3-N status of the deeper soil layers of
interest in this study and thus would be deempathized in subsequent
trials.
It is evident that growers in the Lower Umatilla Basin, who irrigate
at 1 to 1.3 times the recommended replacement rates, and who apply no
more than 390 kgha-1 of fertilizer N dispersed throughout the season,
do not contribute substantial amounts of NO3-N to local aquifers.
There appears to be little risk of excessive NO3-N leaching below the
rooting zone as long as N-rates closely match plant uptake rates, even
with irrigation rates which exceed replacement requirements by as much
as 30 percent. This safety margin allows growers to leach salt from
the rooting zone as needed without co-leaching substantial amounts of
NO3-N.
However, growers must bear in mind that irrigating in excess
of replacement rates may increase hollow heart and affect other
quality factors such as fry color.
Results of this study tend to refute claims that responsible potato
producers in the Lower Umatilla Basin are contributing to increased
groundwater NO3-N levels.
153
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