AN ABSTRACT OF THE THESIS OF
Dost Mohammad Ba loch for the degree of Doctor of Philosophy in Crop Science
presented on July 31, 1998. Title: Evaluation and Use of a Soil Mineralizable
Nitrogen Test to Determine the Fertilizer Nitrogen Needs of Winter Wheat Grown
in Western Oregon
Abstract approved:
Russell S. Karow
The assessment of optimum nitrogen (N) fertilizer need for winter wheat (Triticum
aestivum L.) is important for economic and environmental sustainability. A comprehensive
understanding of fertilizer N requirement depends on estimation of the quantity of N
needed by the crop versus that supplied by soil.
The objectives of this study were: to assess the potential of using short-term
anaerobic incubation test values in developing nitrogen fertilizer recommendations for the
region; to evaluate the suitability of a nitrogen balance model for predicting N fertilizer
needs of winter wheat; and to document the N uptake patterns of spring and winter wheat.
Field experiments were conducted in the Willamette Valley of western Oregon in
1994-1997 and included both on-farm trials and small research plot trials. An array of
rotations, crop types and nitrogen fertilizer rates were evaluated.
Mineralizable nitrogen in soil samples taken prior to spring fertilization was
estimated by a 7-day anaerobic incubation method and results were compared with
estimations of soil supplied nitrogen from field experiments. Lab and field estimations
were well correlated. A more than four fold increase in soil supplied N values, 20 to 110
kg N III, was observed when mineralizable N test values increased from 14 to 29 mg N
kg'. Results indicate that soil mineralizable N values satisfactorily predict approximate soil
N availability and that results can be used to adjust fertilizer N requirements in the region.
A Feekes growth stage 5 spring soil and tissue test based model was developed
and evaluated for predicting the need for additional N fertilizer on winter wheat. Optimum
N rates predicted by the model were closely related to N rates required to obtain
maximum economic yield. Model validation experiments also gave promising results.
Nitrogen uptake patterns for spring and winter wheat were similar. Maximum N
uptake for spring wheat was at approximately 1100 accumulated growing GDD, before
Feekes 10. The maximum N uptake rate, 0.038 kg N GDD-1, occurred at 750 GDD.
Nitrogen uptake in winter wheat was significantly affected by rotations. Maximum N
uptake for fertilized winter wheat was at approximately 1400 GDD, also before Feekes
10. The maximum N uptake rate, 0.5 and 0.2 kg N GDD-1, for wheat following clover and
oat occurred at 1100 and 1300 GDD, respectively.
Evaluation and Use of a Soil Mineralizable Nitrogen Test to Determine the Fertilizer
Nitrogen Needs of Winter Wheat Grown in Western Oregon
by
Dost M. Baloch
A THESIS
submitted to
Oregon State University
in partial fulfillment of
the requirements for the
degree of
Doctor of Philosophy
Completed July 31, 1998
Commencement June 1999
Doctor of Philosophy thesis of Dost Mohammad Baloch presented on July 31, 1998
APPROVED:
Major professor, representing Crop Science
Head of Department of Crop and Soil Science
Redacted for privacy
Dean of Grad
e School
I understand that my thesis will become part of the permanent collection of Oregon State
University libraries. My signature below authorizes release of my thesis to any reader upon
request.
Redacted for privacy
Dost Mohammad Baloch
ACKNOWLEDGMENT
I would like to express my deep gratitude and sincere appreciation to my advisor,
friend and supervisor, Dr. Russell S. Karow, for his generous advice, incredible support,
and encouragement through all aspects of the study. His constant assistance and academic
advice made it possible to complete this dissertation. It has been a great pleasure and pride
to work under his supervision. I will never forget his extreme devotion, dedication and
willingness to helping others with smiling face.
I am grateful to the members of my committee, Dr. Neil W. Christensen and Dr.
John Hart for their availability, interest and incredible guidance. I am also thankful to my
minor professor Dr. William Braunworth and graduate representative Dr. Frederick
Obermiller for their valuable advice and review of my dissertation.
Sincere gratitude to Ernie Marx for not only helping me conduct field
experiments, but also discussing social, economical and political issues. Special thanks to
Barbara Reed for her cooperation throughout my course of study. I am also thankful to
Bruce and Helle Ruddenklau, James Van Leeuwen, Lincoln Volker and Chris Chipman for
their help in conducting field experiments on their farms. My appreciation is also extended
to Steve Petrie, agronomist, UNOCAL chemical company for grants and for supplying
fertilizer. Mark Mellbye, Linn-Benton-Lane field crop extension agent, for his help during
on-farm experiments. I am also very appreciative of the research funding provided by the
Oregon Department of Agriculture Groundwater Research and Development Grant
Program.
I owe great thanks to my home friends, Maqsood Hassan Qureshi, Yousaf Hussain
Bangash, Sami Molvi, Syed Navid Raja and Atta-a- Kareem for their emotional, material
and moral support. Their companionship, compassion, and mutual admiration made
possible my stay at Oregon State University.
My appreciation from the bottom of my heart goes to Christy M. Haarsma, whose
heartfelt support, encouragement and inspiration reinforced my personal desire to
complete my degree.
Words would never be enough to express my heartfelt gratitude to my affectionate
father and loving mother whose love not only for me but for knowledge as well, was the
sole inspiration that enabled me to get such an achievement. I am also grateful to my
brothers, sisters and all members of my family, whose love, support, and encouragement
helped me overcome problems and difficulties, I ever experienced in my life.
Above all Thanks 0! Allah, The Allmighty.
TABLE OF CONTENTS
Page
CHAPTER I. INTRODUCTION
CHAPTER 2. VALIDATION OF SOIL MINERALIZABLE NITROGEN TEST
1
.
.
11
.
Abstract
11
Introduction
13
Materials and Methods
21
On-Farm Trials
Small-plots Rotation Trials
Unfertilized On-farm Mini-plots
Laboratory Analysis
Anaerobic Incubation
21
23
24
25
26
26
27
Soil Supplied N Mineral N Balance Method
Soil Supplied N Unfertilized Plots
Results and Discussion
28
Conclusions
36
References
37
CHAPTER 3. A MODEL FOR MAKING FIELD-BASED NITROGEN
RECOMMENDATIONS FOR WINTER WHEAT IN WESTERN OREGON.
.
.
.
43
Abstract
43
Introduction
45
Materials and Methods
51
Nitrogen Balance Model
On-Farm Trials
Small Plot Research Station Trials
Model Validation Trial
Maximum Economic Yield Equations
Soil Analysis
Anaerobic Incubation
51
52
55
56
58
59
60
TABLE OF CONTENTS (Continued)
Page
Results and Discussion
Grain Yield Response
Determination of Nitrogen Rates for Optimum Grain Yield
Model Validation
61
63
69
72
Conclusions
75
Further Recommendations
77
References
78
CHAPTER 4. EVALUATION OF NITROGEN UPTAKE PATTERN IN SPRING
AND WINTER WHEAT IN WESTERN OREGON
83
Abstract
83
Introduction
85
Materials and Methods
89
Spring Wheat Rotation Experiment
Small Plot Research Station Trials
N uptake from Unfertilized Plots
Statistical Analysis
Results and Discussion
Spring wheat
Winter wheat
89
91
91
92
94
94
100
Conclusions
105
References
108
CONCLUSIONS
111
BIBLIOGRAPHY
113
APPENDIX
125
LIST OF FIGURES
Figure
Page
1-1. Soil mineralizable N (closed symbols) and soil residual N (NO3-N
and NH4-N, open symbols) taken throughout winter from three rotations
in 1994 growing season
29
1-2. Relationship between mineralizable N test values and soil supplied N. Each
value is an individual check plots from: on-farm experiment over three years,
small research plots over two years, and on-farm mini plots over one year.
Soil supplied N values were obtained by two methods (A) N uptake (B) N
balance method
33
1-3. Relationship between mineralizable N test values and soil supplied N across
four rotations. Each value is an individual check plots from: on-farm
experiment over three years, small research plots over two years, and
on-farm mini plots over one year. Soil supplied N values were obtained
by using N balancing method
35
2-1. Yield response of (a) Clover-wheat (b) Corn-wheat (c) Grass-wheat rotations
to fertilizer N rates of on-farm trials for the 1994-96 growing season.
65
2-2. Yield response of clover-wheat and oat-wheat( A) 1996 (B) 1997 of small
research plots.
73
2-3. Total biomass, grain yield and protein content as influenced by fertilizer N
for wheat following grass in 1996 growing season..
76
3-1. Comparison of five spring wheat cultivars for biomass accumulation in
1997 growing season
3-2. Comparison of five spring wheat cultivars for nitrogen uptake in 1997
growing season.
96
98
3-3 Average nitrogen uptake and biomass accumulation rates of spring wheat
in 1997 growing season
99
3-4 Nitrogen uptake in winter wheat as influenced by different rotations and
fertilizer N rates in (A) 1996 and (B) 1997 at Hyslop Farm..
101
3-5 Nitrogen uptake rate in winter wheat receiving 100 kg N ha -1 as influenced
by different rotations in (A) 1996 and (B) 1997 at Hyslop Farm
102
LIST OF FIGURES (Continued)
Figure
3-6. Accumulated biomass yield and nitrogen uptake of winter wheat from
unfertilized plot during 1996 growing season
Page
106
LIST OF TABLES
Table
Page
1-1. Location, previous crop, variety and soil series for experimental sites
1-2.
Ammonium, nitrate and mineralizable nitrogen measured in top 30 cm of
soil at spring fertilization in February during 1995-96 growing season
22
30
1-3. Mean values of mineralizable soil N measured in top 30 cm of soil at spring
fertilization and after harvesting over three years and rotations
31
2-1. Location, previous crop, variety and soil series for experimental sites.
53
2-2. Assessment of optimum N rates for each rotation using the N balance
model
62
2-3. Mean grain yield of on-farm trials for the 1994-96 growing season.
64
2-4. Regression equations for nitrogen response curves of on-farm trials for the
1994-1996 growing season
2-5. Comparison of recommended and actual N rates for maximum economic
yield
67
71
2-6. Main yield and protein content for model validation trials conducted during
1996-97 winter wheat growing season
74
3-1. Sampling dates and corresponding Feekes growth stages, and accumulated
growing degree days for spring and winter wheat experimental sites
3-2 Accumulative biomass yield and nitrogen uptake of five spring wheat
cultivars for 1997 growing season.
90
95
3-3. Biomass yield, nitrogen uptake, and carbon to nitrogen ration of winter wheat of
small plot research experiment for 1996 and 1997 growing seasons
104
LIST OF APPENDIX TABLES
Table
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
Page
Agronomic data of wheat following clover for 1994-95
Agronomic data of wheat following clover for 1995-96
Agronomic data of wheat following corn for 1994-95.
Agronomic data of wheat following corn for 1995-96
Agronomic data of wheat following grass for 1994-95
Agronomic data of wheat following grass for 1995-96
Soil test results through winter months for 1994-95
End of season soil test results of wheat following clover
End of season soil test results of wheat following corn
End of season soil test results of wheat following grass
Soil test results of wheat following clover 1995-96
End of season soil test results of wheat following clover
Soil test results of wheat following corn 1995-96
End of season soil test results of wheat following corn
Soil test results of wheat following grass 1995-96
End of season soil test results of wheat following grass
Agronomic data for Hyslop Farm for 1995-96
Agronomic data for Hyslop Farm for 1995-96
Biomass and N uptake of five spring wheat varieties
Data from on-farm-mini plots 1995-96
Agronomic data for wheat following corn.
Agronomic data for wheat following grass.
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
147
148
148
Dedicated to my father
SHAH MIR KHAN
EVALUATION AND USE OF A SOIL MINERALIZABLE NITROGEN TEST TO
DETERMINE THE FERTILIZER NITROGEN NEEDS OF WINTER WHEAT
GROWN IN WESTERN OREGON
CHAPTER 1
INTRODUCTION
The importance of a quick, reliable soil N mineraliztion test becomes ever greater
due to economic and environmental concerns. Currently, recommendations for nitrogen
fertilizer are mainly based on crop requirements. It is assumed that the nitrogen
mineralized during the growing season is either not important or closely related to the
initial soil N content. Not taking account of the soils potential for N mineralization often
leads to the excess use of N fertilizer resulting in ground and surface water pollution.
The availability of nitrogen is the prerequisite for agroecosystem productivity. On
a large scale, the cyclic nature of this essential element provides sufficient supply for plant
growth without depleting the soil. On a global basis, within natural and agricultural
terrestrial system, soils are the major N reservoirs, containing 2.4 x 1011 tons of N
(Stevenson,
1982).
Fertilizer addition, dry deposition, biological fixation and precipitation
are the main N input sources for soils. From 95 to
occurs as a part of organic molecules (Jansson,
99
1971;
percent of the nitrogen in a soil
Tisdale et al.,
1985).
This protects it
from loss but also leaves it unavailable to plants. In order to be utilized by plants, soil
organic N compounds have to be changed to an inorganic form. Conversion of organic N
2
into inorganic N is carried out by soil microorganisms through a process called
mineralization. Parnas (1975) described N mineralization as a by-product of microbial
activity.
Researchers have long been aware that a small percentage of organic N is
mineralized in the course of the growing season and can significantly contribute to
nitrogen requirements of the crop. Forth and Ellis (1988) reported that in a well-drained
mineral soil about two percent of the organic N is mineralized annually. Harper (1984) and
Power and Doran (1984) reported that the mineralization process converts from one to
three percent of total organic N in a soil to inorganic N annually. Marumoto et al. (1982)
argued that microorganisms may provide up to 40 percent of crop N need through
mineralization.
Soil N mineralization is profoundly influenced by temperature within the range
normally encountered under field conditions. Temperature greatly influences the microbial
population, substrate composition, nutrient cycling and transport processes in the soil. The
majority of soil micro-organisms are mesophllic and prefer moderate temperatures with an
optimum activity between 25 °C and 37 °C and a base temperature of 5 °C. Unlike
mesophiles, psychrophiles become active at lower temperature and play a significant role
in N mineralization during low temperature periods of the year (Jarvis et al., 1996). Since
mineralization ceases near the freezing point, the temperatures of greatest interest in soil
biology generally occurs in the range of 0 to 35° C. Stanford et al (1973) found that the
mineralization rate doubled with each 10 °C increase in temperature up to 35 °C. Soil
water availability and distribution are prominent factors regulating N mineralization in
3
soils. The water status of soil affects biological activities and the products of microbial
activity by controlling diffusion and mass flow. Linn and Doran (1984) found that
optimum N mineralization occurred when 60 percent of pore space was water filled.
Drying the soil below the optimum moisture content reduces mineralization and ultimately
affects the amount of available N in the soil. Soil drying to -100 kPa increased subsequent
N mineralization under optimum conditions (Seneviratne and Wild, 1984). Stanford and
Epstein (1974) reported that optimum net mineralization rates have been achieved
between -0.33 and -0.1 bar where water occupied 80 to 90 percent of the pore space.
It is well known that drying and wetting increases N mineralization (Lund and
Goksoyr, 1980; Orchard and Cook, 1983; Sparling and Ross, 1988), but the mechanisms
involved are poorly understood. Marumoto et al. (1982) stated that physical disruption or
increased accessibility of degradable organic materials, especially readily available
materials from freshly killed biomass cells, are the main cause of the flush of mineral N
after drying and wetting. Soil microbial biomass (SMB) is a potential source of labile N
and constitutes a significant proportion of the total soil N which remains constant
throughout the year (Holmes, 1994).
In spite of the fact that N mineralization can occur in deeper soil horizons (Casman
and Munns, 1980; Hadas et al., 1986), most research has been limited to the upper layers.
Soil layers vary in temperature, moisture, bulk density, aeration and organic matter
content, all of which may affect N mineralization at different depths. Federer (1983)
examined the dependence of mineralization and nitrification on horizons through a soil
profile by incubating soil in situ in buried bags. He reported that net mineralization of
4
nitrogen decreased with depth.
Change in crop sequence changes soil temperature, soil moisture, crop rooting and
residue inputs. Crops grown in rotation often produce more and higher quality plant dry
matter than those grown in monoculture (Copeland and Crookston, 1992). Crop rotation
helps balance the carbon-nitrogen ratio of the organic matter by adding different C:N ratio
residues to the soil. Cereal crops grown after a legume often have a higher yield as
compared to a non-legume crop (Wani et al., 1990). This is because legume residues
generally have a low C:N ratio and large fraction of readily available N. Thicke et al.
(1993) found that the decomposition of incorporated legume residues can a have
significant, but extremely variable, impact on total N mineralization. McKenney et al.
(1995) concluded that legume residues can provide a definite advantage compared with
grass and corn residue in term of N conservation depending on the aeration status of the
soil. Legume residues not only provide a great source of readily available N to other crops
(Azam, 1990), but can also increase long-term soil fertility (Palm and Sanchez, 1991).
This increase is mainly because of the conversion of a portion of biologically-fixed N into
the stable humus form (Azam et al., 1993). In addition to the enhancement of N fertility,
legumes also affect soil properties such as water holding capacity. cation exchange
capacity, buffer capacity, soil porosity and infiltration (Cook, 1988; Fyson and Oaks,
1990). Many legumes have deep root systems which allow exudates to exist at greater soil
depth. These exudates may serve as solubilization or chelating agents of plant nutrients
fixed in the unavailable form.
5
Choice of cropping and management practices used within a given crop production
system play an important role in the utilization of soil N. Physical disturbance of the soil
surface horizon with tillage greatly affects the soil micro environment (Doran and Power,
1983). Changes in tillage and residue management systems directly affect the temperature
and water status of the soil. Tillage also increases the accessibility of organic N to the
microbes. Breaking up of soil aggregates and exposing previously protected organic N by
tillage commonly stimulates short term N mineralization (Gupta and Germida, 1988). On
the other hand, no-till soils tend to be wetter, have different temperature regimes, and are
more compact than conventionally tilled soils and favor microbial activity. Dalai (1989)
compared the effect of 13-years of conventional tillage vs. no-tillage, crop residue retained
vs. burned, and no fertilizer N vs. N fertilizer. His results indicate that total N and
biologically mineralizable N in the soil can be increased by no-tillage and crop residue
retention with a moderate rate of N fertilizer (23 kg ha4 year-1).
Though factors and conditions determining N mineralization have been intensively
investigated, the development of a quick, easy and reliable soil N mineralization test has
not been accomplished. Several methods for quantifying N mineralization have been
proposed including, laboratory, field and modeling techniques. Each method has its own
unique criteria of implementation with advantages and disadvantages. The aim of all these
methods has been to provide a more precise basis for estimating N mineralization potential
of soil so that better N fertilizer recommendations can be made. Because of the complex
nature of N mineralization processes, none of the procedures have proven to be totally
adequate.
6
A great number of laboratory methods have been suggested including aerobic and
anaerobic incubations. The aim of such incubations has been to quantify the available
organic N pool for microbial decomposition under optimal conditions. The advantages of
these procedures are that they are relatively quick, offer control over certain limiting
factors and are relatively inexpensive. But the correlation between laboratory indices and
field studies is very poor because the laboratory methods do not include environmental
factors that regulate mineralization rate. Although good correlations often exist between N
released during incubation and uptake in green house studies (Stanford, 1982), incubation
test results do not necessarily reflect the actual N mineralization capacity of the soil (Fox
and Piekielek, 1984).
Field measurements of N mineralization are the most time consuming and
expensive way of estimating N mineralization. But they are also the most promising
technique which provide a degree of reality that may be difficult to achieve with either
laboratory procedures or computer simulations. Field approaches have the potential of
including the effect of regulatory factors on mineralization rate. Hence, assessment of net
mineralization under field conditions is the best and most accurate way of assessing the N
supplying power of the soil (Binkley and Hart, 1989). Numerous filed approaches to
estimate mineralization have been developed in recent years including nonfertilized
cropped plots, covered fallow plots, uncovered fallow plots, mineralization bags and PVC
tubes.
The Pacific Northwest has very unique climatic conditions with humid winters and
dry summers. Most of the precipitation, 60 to 70 percent annually, occurs from the first
7
week of October to the last week of March. Topography varies from nearly level valleys
to steeply sloping uplands. These situations make it very easy for soil nitrogen to
disappear from the system and very difficult for researchers to trace mineralizable N as
well.
Winter wheat is grown in rotation with grasses, legumes, grains and vegetables in
western Oregon. The residual N level differs significantly in these rotations and is strongly
influenced by weather pattern and specific site. Growers in the region are interested in
knowing how much residual N will be available form the proceeding crop and how best to
adjust their fertilizer rates to optimize yield while reducing risk of nitrogen pollution and
losses.
The goal of this research was to establish the specific nitrogen status and
requirement of winter wheat crops grown in various rotations in western Oregon.
The main objectives of the study were:
1
To investigate the use of soil testing and tissue analysis as a means of predicting
nitrogen fertilizer needs of winter wheat.
2 - To measure the effect of crop rotation on residual soil nitrogen level and yield of a
subsequent wheat crop.
3
To examine the dynamics of spring and winter wheat N uptake.
8
References
Azam, F. 1990. Comparative effect of organic and inorganic nitrogen sources applied to a
flooded soil on rice yield and availability. Plant Soil. 125:255-262.
Azam, F., F. W. Simmons, and R. L. Mulvaney. 1993. Mineralization of plant residues
and its interaction with native soil N availability. Soil Biol. Biochem. 25:1787­
1792.
Binkley, D., and S. C. Hart. 1989. The components of nitrogen availability assessment in
forest soils. Adv. Soil Sci. 10:57-112.
Cassman, K. G., and D. N. Munns. 1980. Nitrogen mineralization as affected by moisture,
temperature and depth. Soil Sci. Soc. Am. J. 44:1233-1237.
Cook, R. J. 1988. Biological control and holistic plant-health care in agriculture. Am. J.
Alt. Agri. 3:51-62.
Copeland, P. J., and R. K. Crookston. 1992. Crop sequence affects nutrient composition
of corn and soybean growth under high fertility. Agron. J. 84:503-509.
Dalal, R. C. 1989. Long-term effect of no-tillage, crop residue, and nitrogen application
on properties of a vertisol. Soil. Sci. Soc. Am. J. 53:1511-1515.
Doran J. W., and J. F. Power. 1983. Effect of tillage on the nitrogen cycling in corn and
wheat production. In nutrient cycling in agriculture ecosystem. University of
Georgia. Athens. Special publication No. 23:441-455.
Federer, C. A. 1983. Nitrogen mineralization and nitrification: Depth variation in four
New England forest soils. Soil Sci. Am. J. 47:1008-1014.
Forth, D. H., and B. G. Ellis. 1988. The soil nitrogen cycle. In Soil Fertility. John Wiley &
Sons. Ins. p. 69-73.
Fox, R.H., and W. P. Piekielek. 1984. Relationship between =aerobically mineralized
nitrogen, chemical indexes, and nitrogen availability to corn. Soil Sci. Soc. Am. J.
48:1087-1090
Fyson, A., and A. Oaks. 1990. Growth proportion of maize by legume soils. Plant Soil.
122:259-266.
9
Gupta, V. R., and J. J. Germinde, 1988. Distribution of microbial biomass and its activity
in different soil aggregate size classes as affected by cultivation. Soil Biol.
Biochem. 17:517-523.
Hadas, A., S. Feigenbaum., A. Feigin, and R. Portnoy. 1986. Nitrogen mineralization rate
in profile of differently managed soil types. Soil Sci. Am. J. 50: 314-319
Harper, J. E. 1984. Uptake of Organic Nitrogen Forms by Roots and Leaves. In R. D.
Hauck(ed.) Nitrogen in Crop Production. Am. Soc. Agron. Madison, WI.
Holmes, W. E. 1994. Soil microbial biomass dynamics and net mineralization in northern
hardwood ecosystems. Soil. Sci. Soc. Am. J. 58:238-243.
Jansson, S. L. 1971. Use of15N in studies of soil nitrogen. Soil Biol. Biochm. 2:129-166.
Jarvis, S. C., A. S. Elizabeth., M. A. Shepherd,. and D. S. Powlson. 1996. Nitrogen
mineralization in temperate agriculture soils: Processes and measurement.
advances in agronomy. Vol. 57. Acadamic Press. pp 187-230.
Linn D. M., and W. Doran. 1984. Effect of water filled pore and space on CO2 and NO2
production in tilled and no-tilled soils. Soil Sci. Soc. Am. J. 48:1272-1276.
Lund, V., and B. Goksoyr. 1980. Effects of water fluctuations on microbial mass and
activities. Micro. Eco. 6:115-123.
Marumoto, T., J. P. Anderson, and K. H. Domsch. 1982. Mineralization of nutrients from
soil microbial biomass. Soil Biol. Biochem. 14:469-475.
McKenney, D. J., S. W. Wang., C. F. Drury., and W. I. Findlay. 1995. Denitrification,
immobilization, and mineralization in nitrate limited and non limited residueamended soil. Soil Sci. Soc. Am. J. 59:118-124.
Orchard, V. A., and Cook, F. J. 1988. Relationship between soil respiration and soil
moisture. Soil Biol. Biochem. 15:447-453.
Palm, C. A., and Sanchez, P. A. 1991. Nitrogen release from some tropical legumes as
affected by lignin contents. Soil Biol. Biochem. 23:83-88.
Parnas, H. 1975. Model for decomposition of organic material by microorganisms. Soil
Biol. Bioch. 7:161-169.
Power. J. F., and J. W. Doran. 1984. Nitrogen Use in Organic Farming. In R. D.
Hauck(ed.) Nitrogen in Crop Production. Am. Soc. Agron. Madison, WI.
10
Seneviratne, R., and A. Wild. 1984. Effect of mild drying on the mineralization of soil
nitrogen. Plant and Soil. 84:175-179.
Sparling, G. P., and D. J. Ross. 1988. Microbial contributions to the increased nitrogen
mineralization after air-drying of soils. Plant and Soil. 105:163-167.
Stanford, G. 1982. Assessment of soil N availability. p. 651-688. in F. J. Stevenson (ed).
Nitrogen in agriculture soils. Agron. Monogr. 22. ASA. CSSA, and SSSA,
Madison, WI.
Stanford, G., and E. Epstein. 1974. Nitrogen mineralization-water relations in the soils.
Soil Sci. Soc. Am. Proc. 38:103-107.
Stevenson, F. J. 1982. Origin and distribution of nitrogen in soils. In Nitrogen in
Agricultural Soils. ASA, CSSA, SSSA, Madison. 1-42.
Thicke, F. E., M. P. Russelle,. 0. B. Hesterman, and C. C. Sheaffer. 1993. Soil nitrogen
mineralization indexes and corn response in crop rotation. Soil Science. 156:322­
334.
Tisdale, S. L., W. L. Nelson, and J. D. Beaton. 1985. Soil fertility and fertilizers. New
York. Macmillan Publishing Company.
Wani, S. P., W.B. McGill, and L.A. Robertson. 1991. Soil N dynamics and N yield of
barley grown on Breton loam using biological fixation or fertilizer. Bio. Ferti.
Soils. 12:1018.
11
CHAPTER 2
VALIDATION OF SOIL MINERALIZABLE NITROGEN TEST
Abstract
Precise fertilizer N recommendations for a crop require an accurate assessment of
soil N availability. Several indices have been identified to estimate soil N availability.
Biological indices provide a sound relative measure of the soil N availability since they
involve microbial processes similar to those active under field conditions. However, in
order to check the validity of these tests, it is imperative that these indices be compared
with values for soil supplied nitrogen obtained under field conditions.
Our objective was to investigate the utility of short-term anaerobic incubation as a
tool to be used in making N fertilizer recommendations for the region. Data used in this
study were acquired from three sets of winter wheat (Triticum aestivum L.) nitrogen
response experiments: (1) on-farm rotation trials, (2) small plot rotation trials, and (3)
unfertilized on-farm mini-plots. On-farm experiments were conducted in growers' fields at
three different locations across the Willamette Valley of western Oregon during 1994­
1996 growing seasons. Three rotations - wheat following corn, wheat following clover,
and wheat following grass were considered. Small plot rotation trials were conducted
during 1996-1997 growing seasons and two rotations - wheat following oat and wheat
following clover were used. Unfertilized-mini plots were established during the 1995-96
12
growing season in 11 grower fields by leaving an unfertilized, randomly selected 15m X
15m area.
Mineralizable nitrogen in soil samples taken prior to spring fertilization was
estimated by an anaerobic incubation method and results were compared with estimation
of soil supplied nitrogen from field experiments. Soil supplied nitrogen was estimated by
two different methods; nitrogen balance and aboveground N uptake of check plots. Soil
mineralizable nitrogen estimated by the 7-day anaerobic incubation method correlated well
with field-measured N availability. The highest correlation for soil mineralizable N test
values was observed when soil supplied N was measured by the N budgeting method ( r2
=0.78). However, the correlation with soil supplied N estimated by N uptake of check
plots was also high (r2 = 0.69). A linear relationship was found between soil mineralizable
N test results and soil supplied N. A more than four fold increase in soil supplied N values,
20 to 110 kg N 11-1, was observed when the soil mineralizable N test values increased from
14 to 29 mg N kg-1. No consistent rotation effect was observed for wheat following clover
or corn while rotation effects were obvious for wheat following oat and wheat following
grass. Wheat following oat had very low soil mineralizable N test values while wheat
following grass had comparatively high soil mineralizable N test values. Our results
indicate that soil mineralizable N test values estimated by the 7-day anaerobic incubation
method satisfactorily predict approximate soil N availability in western Oregon soils and
that results can be used to adjust fertilizer N requirements in western Oregon.
13
Introduction
One of the primary goals of current soil fertility research is to improve the
efficiency of (N) fertilization, thereby improving the profit margin and reducing risk of
ground and surface water contamination by NO3-N. The potential for lodging, diseases,
yield losses and N contamination of surface and ground water increases as excessive N
fertilizer rates are applied. On the other hand, low rates of N fertilizer can cause
considerable yield reduction. Determination of the precise fertilizer N requirement of the
crop depends on an estimation of the quantity of N needed by the crop and an estimate of
both inorganic and organic soil N sources (Rice and Havlin, 1994).
Soil mineral N (NH4-N + NO3-N) testing before spring fertilization has been
proven a useful tool for adjusting N fertilizer requirements in the semi-arid and semihumid regions of the U.S. (Maples et al. 1977; Westfall, 1984; Rauschkolb et al., 1984;
Cox, 1985). A soil nitrate test before planting appears to be well related to the crop N
needs in sub-humid areas in the western US and Canada (Dahnke and Johnson, 1990).
Low annual precipitation in these regions usually limits leaching or denitrification of
profile NO3-N, resulting in significant carryover of NO3-N ( Bundy and Malone, 1988).
Despite complications such as mobility, leaching, and nitrification, soil tests for residual
NO3-N have been found to be useful in determining N fertilizer needs of crops (Gelderman
et al., 1988). In a study conducted on the Eastern Shore of Maryland, Meisinger et al.
(1987) found that the N requirement of a wheat crop could be effectively adjusted by
measuring residual spring N status of the soil.
14
In the humid regions of United States, including the Pacific Northwest, the amount
of mineral N at the time of spring fertilization has generally not been taken into account
when adjusting N fertilizer needs for winter wheat. This is because heavy precipitation
during the winter months causes losses of soil NO3-N by denitrification and leaching.
Ower (1980) reported that the estimated variable losses of nitrogen from wheat fields
within watershed boundaries in western Oregon were 14 to 63 kg N haTI. This typically
results in low and uniform mineral N level at the time of spring fertilizeration (Roth,
1987). In a study carried out in western Oregon, Sebastian (1995) found minimal amounts
of soil mineral N (NH4-N and NO3-N), 5 to 24 kg N ha-1, in the upper 60 cm of soil at the
time of spring application. He suggested that these amounts were not useful in predicting
N fertilizer requirements. Broadbent and Carlton (1978) and Sarrantonio and Scott (1988)
reported that the NO3-N concentration in soil after winter losses was only 5 to 10 mg N
kg-1 .
But other researchers have shown that measuring pre-plant soil profile NO3-N in
humid climates can be useful in adjusting crop N needs (Bock and Kelly, 1992). In humid
areas, researchers have reconfirmed that substantial amounts of NO3-N can remain in
medium-to fine-texture soils during the winter period and can contribute substantial
amounts of N to subsequent crops (Roth and Fox, 1990; Liang et al., 1991).
The cool, humid conditions during winter favor the decomposition of crop residues
and, as temperatures increase during the early spring, mineralization of organic N can
supply a significant portion of the total N requirement for subsequent crops. Therefore,
15
assessment of mineralizable N at the beginning of the growing season could be helpful in
improving fertilizer N recommendations.
Conversion of organic N into inorganic N is carried out by soil microorganisms.
Researchers have long been aware that a small percentage of organic N is mineralized in
the course of the growing season and can significantly contribute to nitrogen requirements
of the crop (Foth and Ellis,1988; Harper, 1984; Power and Doran, 1984). Nitrogen
mineralization has been shown to provide 3 to 100 percent of the N-nutritional
requirements of non-legume crops (Smith et al., 1993). Marumoto et al. (1982) argued
that microorganisms may provide up to 40 percent of crop N need through mineralization.
Biological immobilization of soil inorganic N occurs simultaneously with
mineralization. A significant portion of mineralized N is immediately assimilated by soil
microbial biomass and transformed into organic cell constituents (Mary and Recous,
1994). During mineralization-immobilization, soil microbial biomass itself temporarily
serves as source and sink of easily mineralizable nitrogen (Smith, 1994). Soil microbial
biomass predominantly assimilates NH4-N during the immobilization process, but in the
absence of N114-N, may use NO3 -N as an energy source ( Recous et al., 1988; Azam and
Malik, 1986). The difference between gross rates of mineralization and immobilization is
net mineralization. Net mineralization is strongly dependent on the C:N ratio of organic
matter (Whitmore and Groot, 1994; Neve et at., 1994). The amount of N returned to the
soil by crop residues depends on the quality and quantity of the substrate.
Crops grown in rotation often produce more and higher quality plant dry matter
than those grown in monoculture (Copeland and Crookston, 1992; Collins et al., 1992).
16
Change in crop sequence changes soil temperature, soil moisture, crop rooting and residue
inputs. Fertilizer N requirement for optimum grain yield is often reduced in rotation
compared to monoculture (Franzluebbers et al., 1994). Cereal crops grown after a legume
often have a higher yield as compared to those grown after a non-legume crop (Wani et
al., 1991). This is because legume residues generally have a low C:N ratio and large
fraction of readily available N. McKenney et al. (1995) concluded that legume residues
can provide a definite advantage compared with grass and corn residue in term of N
conservation depending on the aeration status of the soil. Legume residues not only
provide a great source of readily available N to other crops (Azam, 1990), but can also
increase long-term soil fertility (Palm and Sanchez, 1991). This increase is mainly because
of the conversion of a portion of biologically-fixed N into the stable humus form (Azam et
al., 1993).
Being a biological process, N mineralization is highly affected by complex
interactions among biological, chemical and physical components of the soil and
environmental factors (Loiseau et al., 1994; Hassink, 1994; Stanford and Smith 1972;
Linn and Doran, 1984; Sparling and Ross, 1988; Ellen and Bettany, 1992). Though
factors and conditions determining N mineralization have been intensively investigated, the
development of a quick, easy and reliable soil N supply predicting method has still been
unsolved. Several methods for quantifying N mineralization have been proposed including
laboratory (Keeney, 1982; Gianello and Bremner, 1986; Aiman, 1992; McTaggart and
Smith,1993), field (Eno, 1960; Magdoff, 1991; Qian et al., 1993), and modeling (Stanford
and Smith, 1972; Campbell et al., 1988; Jones, 1984; Beauchamp, 1986; Houot et al.,
17
1989) techniques. Each method has its own unique criterion of implementation with
advantages and disadvantages. The aim of all these methods has been to provide a more
precise basis for estimating N mineralization capability of soil so that better N fertilizer
recommendations can be made.
There are two groups of N mineralization indices widely used to provide reference
values for soil N mineralization capacities of soil - chemical indices and biological indices.
A rapid, convenient and relatively inexpensive way of estimating N release from labile soil
organic matter is through use of chemical extractants. It is assumed that the amount of N
extracted from a soil sample during the procedure will represent the actual N release to a
plant during the growing season. Unfortunately, mineralizable N determined through
chemical extractants is not well correlated to N uptake estimated from field experiments.
McTaggart and Smith (1993) found that chemical extraction methods did not predict
changes due to the recent addition of crop residue. Bremner (1965) and Serna and
Pomares (1992) argued that N release by chemical indices can not represent the same
fraction(s) of N that would be released in situ by microorganisms. Many chemical
extractants such as strong acids or bases, neutral salts and water are being used to assess
N mineralization in laboratory procedures. These procedures also vary in extractant
concentration and extraction time and temperature.
Since living organisms are used in biological incubation methods, such methods are
assumed to be more reliable then chemical tests. Biological methods supply a satisfactory
measure of soil N potential but are laborious and time-consuming (Keeney, 1982).
Incubation techniques may be either long-term or short-term. Short-term incubations are
18
done under aerobic or anaerobic conditions, long-term generally under aerobic. The
advantage of short-term procedures are that they are relatively quick, offer control over
certain limiting factors and are relatively inexpensive.
A short-term anaerobic incubation method described by Keeney (1982) is the most
widely used laboratory technique to assess N mineralization capacity of soils. In this
method, initial NH4-N content of the soil is determined. Distilled water is added to each
sample so that the soil is completely saturated. Samples are covered tightly and incubated
for 7 days at 40 °C in an incubator. Final N114-N content of the extract solution is
determined from incubated samples. Initial NH4-N values are subtracted from the final
values to obtain the N amount mineralized during the 7 day incubation period. Rice and
Havlin (1994) recommended use of this method. Wilson et al. (1994) used the method
proposed by Keeney (1982) to estimate N mineralization potential of soils and compared
the values with a chemical extraction method and found good correlation. In contrast, Fox
and Piekielek (1984) found a very poor correlation between mineralizable N values
obtained from incubation tests and N mineralized in the field.
Biological indices are often highly correlated with greenhouse N uptake. In both
cases, measurements are being made under controlled conditions. Although good
correlation often exists between N released during incubation and uptake in greenhouse
studies (Stanford, 1982), incubation tests results do not necessarily reflect the actual N
mineralization capacity of a soil (Fox and Piekielek, 1984). Michrina et al. (1981) found
no correlation between relative N uptake in a greenhouse study and relative N uptake in
the field. The best way to check the validity of N mineralized through chemical or
19
biological tests is to compare the results with N uptake by plants in the field. The
feasibility of N mineralization indices to predict N-suppling capacity of soil has not been
well tested under field conditions (Fox and Piekielek, 1978; Thicke et al., 1993). Binldey
and Hart (1989) stated that assessment of net mineralization under field conditions is the
best and most accurate way of assessing the N supplying power of the soil, since
environmental effects are included in the assessment.
Using a crop as a sink for N released by soil microbe decomposition of soil organic
matter and coupling the results with measurements of mineral N in the soil profile is one of
the simplest and the most effective ways of measuring net mineralization. The advantage
of this approach is that the study can be carried out without alteration of the system and
yet this method also takes into account the environmental and soil factors which regulate
N mineralization in the soil. This is also a very labor intensive method and requires a series
of plant and soil analyses. Rice and Havlin (1994) argued that plant sampling is the most
precise way of estimating N mineralization and is the standard by which other procedures
should be compared. Rees et al. (1994) argued that determining plant N uptake and at the
same time measuring changes in the pool of soil N and losses from the plant/soil system is
the most appropriate way of measuring net mineralization. Net mineralization is simply
estimated by the difference between total N uptake and the change in inorganic N in the
soil profile over time:
N min = (N2 - NO+ Nup
[1]
where N1 and N2 are the amount of inorganic N in the soil at the beginning and end of the
season and Nup is total plant N uptake. In nonfertilized cropped plots, a net mineralization
20
rate is usually high because plant roots compete with microbial populations for mineral N
and effectively remove N from the soil and reduce the risk of immobilization. Wang and
Bakken
(1989)
conducted an experiment to examine the effect of spatial distribution of N-
rich and N-poor plant residue on N mineralization. They found that in a N-poor plot, net
mineralization rates were highest. They argued that it is because plants more effectively
competed with microbes for mineral N. Jarvis et al.
(1996)
argued that this method
carefully be considered during the interpretation of the data. Potential problems include:
(1) this approach accounts for only above ground biomass while, roots, stubble and
senesced leaves may contain a significant portion of N,
(2)
there may be significant losses
through leaching, denitrification or volatilization, (3) the impact of plant exudates on
microbial population and on their activities is unknown, and (4) the information is only
applicable for a specific soil/crop/environment combination.
The objective of this study was to assess the potential of using an anaerobic
incubation test value to adjust N fertilizer recommendations in the Willamette Valley of
western Oregon. Soil mineralizabe N test values were obtained by using a modified
anaerobic incubation method proposed by Keeney (1982), while N supplying capacities
were determined through N balancing and measuring N uptake of unfertilized plots.
21
Materials and Methods
Data were obtained from unfertilized plots from three sets of nitrogen response
experiments (1) on-farm trials, (2) small plot rotation trials and, (3) unfertilized on-farm
mini-plots.
On-Farm Trials
On-farm trials were conducted in growers' fields at three different locations across
the Willamette Valley of western Oregon during 1994-1996 growing seasons. The 1993­
94 experiment was part of fellow graduate student Kevin Sebastian's (1995) MS Thesis.
Each site of this experiment represented a crop rotation system that is commonly used in
the Willamette Valley. Rotations considered were soft white winter wheat following grass
seed, sweet corn or a legume. The experimental design was a randomized complete block
with three replications at each site. Plot size varied site-to-site depending on size of
machinery used by the grower. An average 90m X 10m plot size was used. Nitrogen
fertilizer was applied as urea (45-0-0) at approximately Feekes 5 in one application. Four
treatments, including a check receiving no nitrogen, were used at each site during the
1993-94 and 1994-95 growing seasons. At corn and legume rotation sites, N was applied
at the rate of 0, 56, 112, and 168 kg N ha-1. Since less residual nitrogen was expected for
wheat following grass in rotation, slightly higher rates- 0, 67, 134, and 201 kg N ha'­
were used. During the 1995-96 growing season, five N rates - 0, 56, 112, 168 and 224 kg
N ha-1- were used in all three rotations. The location, soil series, cropping history and
wheat varieties used in the experiments are listed in Table 1-1.
22
Table 1-1: Location, previous crop, variety and soil series for experimental sites
Grower
County/City
Previous
crop
Wheat
variety
1994
Jones
Polk/Amity
Clover
Madsen
Amity
Fine-silty, mixed mesic,
Argiaquic Xeric Argialbolls
Volker
Benton/Monroe
Corn
Gene
Malabon
Fine, mixed, mesic Pachic Ultic
Argixerolls
Van Leeuwen
Linn/Halsey
Tall
Fescue
Gene
Malabon
Fine, mixed, mesic Pachic Ultic
Argixerolls
1995
Ruddenklau
Polk/Amity
Clover
Gene
Amity
Fine-silty, mixed mesic,
Argiaquic Xeric Argialbolls
Volker
Benton/Monroe
Corn
Gene
Chehallis
Fine-silty, mixed, mesic Cumulic
Ultic Haploxerolls
Van Leeuwen
Linn/Halsey
Tall
Fescue
Stephens
Woodburn
Fine-silty, mixed, mesic Aquultic
Argixerolls
1996
Ruddenldau
Polk/Amity
Clover
Gene
Amity
Fine-silty, mixed mesic,
Argiaquic Xeric Argialbolls
Volker
Benton/Monroe
Corn
Gene
Malabon
Fine, mixed, mesic Pachic Ultic
Argixerolls
Chipman
Benton/Albuny
Perennial
Raygrass
Madsen
Willamette
Fine-silty, mixed mesic Ultic
Haploxeralfs
Mulkey
Polk/Monmouth
Annual
Raygrass
Madsen
Willamette
Fine-silty, mixed mesic Ultic
Haploxeralfs
Jones
Benton/Corvallis
Corn
Stephens
Chehallis
Fine-silty, mixed, mesic Cumulic
Ultic Haploxerolls
Soil Series
1997
23
Samples were collected at approximately one month intervals from each site during
the 1993-94 and 1994-95 growing seasons. Samples were taken at four depths- 0-30, 30­
60, 60-90 and 90-120 cm. A single composite sample representing the entire plot area was
used prior to spring fertilization. Approximately ten cores were taken to make this
composite sample. Analysis of soil N data from the two growing seasons indicated that a
30 cm depth sample was adequate to assess soil N status (data not shown). During the
1995-96 growing season, pre-fertilization soil samples were collected from individual plots
to a depth of 30 cm. Each sample was a composite of approximately 10 cores. Intensive
soil sampling was performed just after harvest at each site on each plot in all years.
To calculate total N uptake, plant tissue samples were taken at Feekes 5 (prior to
fertilizer application) and at maturity. At Feekes 5, ten representative samples of 30 cm of
row were collected from each plot by cutting the plants at soil level. Whole plant samples
were weighed, ground and analyzed for nitrogen content. At maturity, nine one-meter row
sections were cut at soil level from each plot to determine dry matter. Heads from plants
were removed and threshed separately. Representative subsampling was performed for
each sample. Subsamples of grain, straw and chaff were analyzed for nitrogen content.
Small-plot Rotation Trials
The small plot rotation trials were established during the 1993-94 growing season.
The intent was to continue these trials over an extended period of time. The experiment
was arranged as a spilt plot design with four replications having rotation as main plots and
fertilizer treatments as sub-plots. Rotation plots were 6.4m X 45m in size, while N
24
fertilizer sub plots were 6.4m X 9m. Five fertilizer treatments - 0, 50, 100, 150 and 200 kg
N
- were used. Rotations included winter wheat following clover and winter wheat
following oat. The site had been fallow in 1993. Crimson clover was planted on all plots
in fall 1994. In spring 1995, two plots per replication were fallowed, one was planted to
oat and the fourth was left in clover. Clover and oat were allowed to mature, were
harvested and crop residue was incorporated. Wheat was planted on the clover and oat
stubble plots in fall 1995, crimson clover on one of the fallowed plots to establish the next
rotation cycle. Data were collected for 1995-96 and 1996-97 growing seasons.
Soil samples were collected pre-plant and post-harvest. An intensive pre-plant
sampling was done in fall 1995 by taking soil at 30 cm increments to a depth of 150 cm
from individual plots. This was done to assess the residual nitrogen status of the
experimental site. Post-harvest sampling was performed in 0, 150 and 200 kg N
treatment plots. Samples were analyzed for ammonium and nitrate concentrations.
Aboveground plant tissue samples were taken at both Feekes 5 and at maturity for
dry matter yield and nitrogen uptake. At maturity, four aboveground plant samples of 1.5
meter of row were cut from drill strips in each sub-plot. Heads were cut, threshed and
weighed. Grain and straw were analyzed separately for their nitrogen content.
Unfertilized On-farm Mini-plots
Unfertilized-mini plots were specifically designed to determine the correlation
between the lab incubation test for mineralizable N and the amount of nitrogen released in
the soil through the growing season. This study was done during the 1995-96 growing
25
season with the cooperation of growers and county extension agents. Growers were asked
to randomly select an area of 15m X 15m in one of their fields and leave it unfertilized.
Soil samples were taken to a 30 cm depth at Feekes 5 and just after harvesting. Soil
samples were analyzed for ammonium, nitrate and mineralizable N. Aboveground plant
tissue samples were taken at Feekes 5 and just before harvesting from one 0.90 m of row.
Tissue samples were analyzed for nitrogen content.
Laboratory Analysis
Soil and plant tissue samples were analyzed in the Central Analytic lab (CAL) at
Oregon State University, Corvallis, Oregon. Plant samples were dried at 70 °C in a forced
air oven, weighed and ground in Wiley mill to pass 1 mm mesh. The N content of wheat
grain and straw was determined by Leco CNS 2000 (Leco corporation, St. Joseph, MI)
combustion analysis.
Soil inorganic N (NH4-N and NO3-N) was determined using the modified KC1
extraction method described by Keeney and Nelson (1982). Twenty-gram soil samples
were placed in 250 mL extracting bottles and 75 ml of extracting solution (2 MKCI) was
added. Vessels were shaken on a mechanical shaker for one hour. The extraction solution
was filtered through Whitman No. 42 filter paper. The NH4-N and NO3-N content of the
extract was determined with an ALPKEM rapid flow analyzer (RF-300) which complexes
NI-14-N with salicylate to form indophenol blue. This color was intensified with sodium
nitroprusside and measured at a wavelength of 660 nm. The NO3-N concentration were
determined with the same equipment used for NH4-N analysis by reducing nitrate via a
26
cadmium reactor and complexing the NO3-N with sulfanilamide and N-(1-Napthyl)­
ethylenediamine dihydorchlwide to form a red-purple color. The color intensity was
measured at a wavelength of 540 nm.
Anaerobic incubation
Soil mineralizable N was determined using a short-term anaerobic incubation
method described by Keeney (1982), slightly modified by increasing the sample size.
Through use of a sample splitter, a 20 g soil sample was obtained and placed in a 250 ml
extraction bottle. Fifty mL of distilled water was added to each bottle so that the soil
become completely saturated. Bottles were made air tight by putting a plastic cover under
their lids. Samples were placed in an incubator for 7 days (168 h) at 40 °C plus or minus
0.5 °C. After incubation, samples were carefully removed from the incubator and 50.0 mL
of KCl was added. Vessels were shaken on a mechanical shaker for one hour. The
extraction solution was filtered through Whitman No. 42 filter paper. Final NH4-N content
of the extract solution was determined from incubated samples. Initial Nat-N values are
subtracted from the final values to obtain the amount of N mineralized.
Soil supplied N Mineral N Balance Method
The net amount of N mineralized under field conditions was estimated through use
of a equation proposed by Cabrera and Kissel (1988) modified to exclude root fractions.
N
= (N2-N1) + (Nup2-Nup1)
[2]
where N1 and N2 are the total amount of soil inorganic N (NH4-N + NO3-N) at
Feekes 5 and the end of the season, respectively, and N p1 and Nup2 are plant N uptake at
27
Feekes 5 and at maturity, receptively. It was assumed that N gain through atmospheric
fixation and N losses through denitrifiction and leaching were minimal given the
environmental situation of the region.
Soil Supplied N-unfertilized Plots
Nitrogen uptake values for aboveground tissue were obtained from unfertilized
plots and soil N availability was estimated as the N taken up by the crop during the
growing season. It was assumed that plants exhibited maximal N uptake and that N losses
from soil during the growing season were minimal.
28
Results and Discussion
Measurements of soil mineralizable N (SMN) on soil samples taken from the upper
30 cm of soil consistently showed a drop in SMN levels from fall to mid-winter but
showed little variation from late December to early February (Fig. 1-1). It was also
observed that mineral N (NH4-N and NO3-N) concentration in the soil at the time of
spring fertilization was minimal and uniform through all rotations (Fig. 1-1). This is likely
because heavy precipitation leached NO3-N and cold weather during winter months
slowed down decomposition of previous crop residue.
There was no significant difference for mineralizable N values among individual
plots at pre-fertilization sampling within each rotation (Table 1-2). There were, however,
differences among rotations. Wheat following grass had a higher SMN compared to wheat
following clover, 33.7 and 16.5 mg ke, respectively (Table 1-2).
Similar results were observed for soil samples taken at the end of season for all
rotations (Table 1-3). The effect of spring applied N on the amount of soil mineralizable
Nat the end of season for three rotations and years of on-farm experiment are shown in
Table 1-3. It is apparent that fertilizer N rates did not significantly (p>.05) affect
mineralizable nitrogen at the end of the season across rotations or years.
Soil mineralizable N as estimated by the 7-day anaerobic incubation method was
quite well correlated with field-measured N availability calculated by two different
methods - N balance [equation 2] and by using the aboveground N uptake of check plots
(Fig. 1-2). The highest correlation ( r2 = 0.78) for soil mineralizable N was observed when
29
40
30
bu
oA
20
10
0
9/22/93
I-- Grass-wheat
12/22/93
Sampling date
2/02/94
Corn-wheat A-- Clover-wheat
Fig. 1-1 Soil mineralizable N (closed symbols) and soil residual N (NO3-N and
NH4-N (open symbols) taken throughout winter from three rotations in 1994
growing season.
Table 1-2: Ammonium, nitrate and mineralizable nitrogen measured in top 30 cm of soil at spring fertilization in February
during 1995-96 growing season
Clover-wheat Rotation
Treatment
NO3-N
NH4-N
Min N
Corn-wheat Rotation
NO3-N
NI-14-N
Min N
Grass-wheat Rotation
NO3-N
NH4-N
Min N
mg kg1
1Xt
2,5
4.3
16.0
2.0
4.2
17.5
2.7
3.9
33.6
2X
2.3
3.9
15.7
2.1
4.8
20.7
2.4
4.4
36.6
3X
2.6
4.6
18.3
2.8
6.9
17.9
2.4
3.5
33.5
4X
2.2
3.6
16.0
1.7
5.7
22.8
2.7
3.5
32.7
5X
2.5
4.0
16.6
2.2
5.7
23.0
2.6
4.2
38.8
Average
2.4
4.0
16.5
2.1
5.4
20.0
2.5
3.9
33.7
11
8
CV (%)
15
11
23
14
8
15
20
t Table values are averages across three plots assigned to a particular N rate treatment. Treatments were not yet applied when
soil samples were taken hence data document field variation only. When analyzed as if plot groups represented treatments,
there were no differences among treatments.
Table 1-3: Mean values of mineralizable soil N measured in top 30 cm of soil at spring fertilization and after harvesting over
three years and rotations.
Corn-wheat
Clover-wheat
1994
1995
1996
1994
1995
Grass-wheat
1996
1994
1995
1996
mg kg''
Pre-fertilization*
16.2
19.8
16.1
30.0
14.6
17.5
23.1
25.1
33.7
1Xt
14.8
29.3
13.4
34.2
19.6
15.6
18.7
27.4
24.8
2X
15.4
28.3
12.4
34.0
17.5
18.2
21.8
30.0
32.8
3X
14.4
32.4
12.1
37.5
23.6
19.7
19.1
17.0
23.6
4X
17.0
31.2
15.1
35.3
24.8
19.0
19.9
29.4
30.0
After harvesting
5X
Average
12.7
15.4
30.1
13.1
19.3
35.3
21.4
18.4
41.1
19.9
25.9
30.3
CV
17.3
8.2
17.6
12.2
11.6
8.3
17.2
26.8
0.6
* Mean values of mineralizable N measured in top 30 cm of soil from check plots at spring fertilization
Fertilizer N applied rates. Fertilizer N was applied at 56 kg N ha'. For grass-wheat rotation, during 1994 and 1995 growing
seasons, N was applied at the increment of 67 kg N
32
N suppling capability was measured by the N balance method. This is likely because the N
balance method takes into account N taken up by the plant and initial inorganic N (NH4-N
and NO3-N) in the soil at the time of spring fertilization. The nitrogen balance method
also estimates N mineralization over a short period of time - from fertilization to harvest ­
which makes it more comparable with the SMN test taken at fertilization. By considering
these factors, better assessment of net N mineralization for the duration of the growing
season can be expected by N balance method. Fiez et al. (1995) used a N balance method
to calculate net nitrogen mineralization in a N use efficiency experiment and found
satisfactory results. Broadbent and Carlton (1978) and Meisinger (1984) also suggested
that determining the N uptake and an estimate of the change in soil mineral N of a field
crop receiving no N fertilizer is the most satisfactory method of estimating the soil N
supply in a given soil-crop-climate system.
The soil supplied N (SSN) values obtained by the two different methods were
plotted against soil mineral N test values to determine whether SSN could be expressed as
a function of SMN test values (Fig. 1-2). To better examine the relationship between
results obtained from anaerobic incubation method and SSN, we combined the individual
data from small research plots, on-farm experiments across all years and the data obtained
from mini plots conducted in the 1996 growing season. Soil supplied nitrogen increased as
SMN test values increased. As shown in Fig. 1-2 (A and B), a linear relationship was
found between SMN test and SSN calculated by the two methods The best linear
correlation (R2 = 0.78) between SMN test values and SSN was obtained when the N
budgeting method was used to estimate the N suppling capacity of the soil. However, total
33
10
15
(A)
20
25
Soil min N test (mg/kg)
30
Y = -46.2 + 5.42X
SE = 0.4
RA2 = 0.78
10
(B)
0 On-farm Plots
15
20
25
Soil min N test (mg/kg)
30
0 Small research Plots v On-farm mini Plots
Fig. 1-2: Relationship between mineralizable N test values and soil supplied N. Each
value is an individual check plots from: on-farm experiment over three years, small
research plots over two years, and on-farm mini plots over one year. Soil supplied N
values were obtained by two methods (A) N uptake (B) N balance method
34
N uptake was also highly correlated with SMN (r2 = 0.69). Nitrogen uptake showed
higher values typical of N uptake method. Mary and Recous (1994) argued that the
problem in comparing a N index to only N uptake is that N uptake not only depends on N
mineralization but also the amount of mineral N present in the rooting zone.
Figure 1-2 shows more than a four fold increase in SSN, 20 to 110 kg N11-1, was
observed when the SMN values increased from 14 to 29 mg N kg-1. While there is
considerable variation in SSN values related to SMN values in the 17-25 mg N kg-1 range
there is less variation in extreme values. This suggests that at a minimum, the SMN test
can be used to predict low or high potential SSN values. It should also be noted that all
three types of experiments exhibited a similar range of SMN and SSN values.
To examine the effects of rotation, SSN data obtained from individual check plots
from on-farm and small plot research experiments were plotted against SMN test values.
Significant differences were found among rotations. As shown in Fig. 1-3, no consistent
rotation effect was observed for wheat following clover or corn, but there was a pattern
for wheat following grass and oat. Great variability for SMN test and SSN values was
observed for wheat following both corn and clover while oat and grass rotations showed
less variation (Fig. 1-3). Wheat following grasses had relatively high and uniform SMN
test and SSN values across all years. The values ranged from 23 to 29 mg kg-i and 90 to
110 kg N ha-' for SMN test and SSN, respectively. Wheat following oats had the lowest
SMN test and SSN values ranging from 11 to 17 mg kg1 and 12 to 39 kg N ha-1,
respectively.
35
140 -
A
A
:120
'&)
4
-'5-'Q.,
0
100
o
o
80
0
2
0A
o
60
C4
.-_-,
0
o
C
6?
x
40
cA
X
20
o
X
x 0 1°I
0
1
10
I
15
I
I
1
I
25
20
Soil min N test (mg/kg)
0 Clover A Corn
o Grass
1
1
30
X Oat
Fig. 1-3: Relationship between mineralizable N test values and soil supplied N
across four rotations. Each value is an individual check plots from: on-farm
experiment over three years, small research plots over two years, and on-farm mini
plots over one year. Soil supplied N values were obtained by using N balancing
method.
36
Conclusions
Soil mineralizable N estimated by the 7-day anaerobic incubation method
correlated well with field-measured N availability. We concluded that the short-term
anaerobic incubation method can satisfactorily predict the approximate soil N availability
in western Oregon soils. This suggests that the results of a mineralizable N test could be
used in making real-time N fertilizer recommendations for the region. Mineralizable N
tests can be run on soil samples taken ahead of spring fertilization and results incorporated
into N fertilizer recommendations for the following wheat crop.
37
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43
CHAPTER 3
A MODEL FOR MAKING FIELD-BASED NITROGEN RECOMMENDATIONS
FOR WINTER WHEAT IN WESTERN OREGON
Abstract
Early determination of crop N status allows for greater options in N fertilizer
management. Incorporating information about crop N requirements, soil testing, and plant
analysis at early growth stages will be very helpful towards optimizing the fertilizer N
recommendations for winter wheat.
A model based on early spring soil and tissue analysis was developed and
evaluated for predicting the need for additional N fertilizer on winter wheat. On-farm N
response trials were established over three years to develop the model. Two field-scale
validation trials were run in another year. On-farm trials were conducted in growers' fields
at three different location across the Willamette valley of western Oregon during the 1994­
1996 growing seasons. Each site of these experiments represented a crop rotation system
that is commonly used in the valley. Rotations were soft white winter wheat following
grass seed, sweet corn or a legume. Four treatments, including a check receiving no
nitrogen, were used at each site during the 1993-94 and 1994-95 growing seasons. In
1996-97, two trials were conducted to further check the validity of the proposed model.
Rotations were soft white winter wheat following grass seed or sweet corn. Three
treatments were used at each site. At the site where wheat followed corn, the predicted
44
optimum N rate was 168 kg N ha-1. A low (84 kg N ha-1) and intermediate (140 kg N ha-1)
rate were selected as other treatments in this trial. At the site where wheat followed grass
seed, N was applied at the rate of 84, 112, and 140 kg N ha-1. The 112 kg N ha-1 rate was
the optimum rate predicted from our model. The 84 kg N ha-1 and 140 kg N ha.-1 rates
were selected to bracket the recommended rate (± 28 kg N ha-1).
Response of winter wheat to fertilizer N varied greatly among rotations and years
in this study. Wheat following corn was highly responsive to added fertilizer N while
wheat following grass seed was less responsive. Wheat following grass seed had high soil
supplied N which depressed the yield even at moderate fertilizer N rates. This finding
contradicts conventional wisdom suggesting that higher N rates are needed following
grass. This study documents a difference between perennial grasses and cereal grain crops
in rotation. The average yield with no fertilizer for wheat following corn and wheat
following legumes were about the same.
Optimum N rates predicted by our proposed model were closely related to the N
rates required to obtain maximum economic yield. This study overall shows that the model
appears to accurately assess field-specific optimum fertilizer N status and that it can be
used to make fertilizer N recommendations for the region.
45
Introduction
The assessment of optimum N fertilizer rates for winter wheat (Triticum aestivum
L.) is important for economic and environmental sustainability. Nitrogen alters plant
growth more than any other mineral nutrient. In wheat a suboptimal supply of N can
dramatically reduce dry matter and subsequently grain yield (Power and Allessi, 1978;
Robinson et al., 1979; Donohue and Brann, 1984; Nielsen and Halvorson, 1991), while
oversupply of N may cause lodging, disease and lower grain quality (Boquest and
Johnson, 1987; Beuerlein et al., 1992; Memon and Jamro, 1988).
The determination of optimum N fertilizer rates for winter wheat is a major
unsolved problem in most humid region of the world (Stanford, 1982). Determining
precise N fertilizer rates requires the consideration of yield goals, N requirement of the
crop, soil N tests, and plant analysis. The amount of fertilizer N necessary will vary
depending on yield desired, residual N and the N supplying capacity of the soil.
Fertilizer N recommendations are mostly influenced by yield goals. Nearly 80 % of
wheat growers in the great plains overestimate their yield goals and apply excess N
fertilizer (Goos and Prunty, 1990; Schepers et al., 1986). Realistic yield goals for each
field are crucial in determining optimum fertilizer N rates.
An estimate of the fertilizer N needs of a particular crop cannot be determined
quantitatively without knowledge of the crop's requirement for this element. Crop N
requirement is a function of yield potential and the amount of N required per unit of yield.
Stanford and Legg (1984) defined the N requirement as the minimum amount of N in the
46
above ground portion of crops associated with maximum production. Nitrogen rate
experiments are the most effective way of determining N requirements for a crop. Yield
will continue to increase as N is supplemented when N is a limiting factor in plant growth.
There is essentially no further increase in yield with increasing N content once the crop
requirement for N is met.
Soil mineral N (NI-14-N + NO3-N) testing before spring fertilization has proven a
useful tool for adjusting N fertilizer requirements in the semi-arid and semi-humid regions
of the U.S. (Maples et al., 1977; Westfall, 1984; Rauschkolb et al., 1984; Cox, 1985).
Despite complications such as mobility, leaching, and nitrification, soil tests for residual
NO3-N have been found to be useful in determining N fertilizer needs of crops (Gelderman
et al., 1988). A soil nitrate test before planting appears to be well related to the fertilizer
requirements of spring wheat in the Northern Plains (Fox and Piekielek, 1978). In a study
conducted on the Eastern Shore of Maryland, Meisinger et al. (1987) found that the N
requirement of a wheat crop could be effectively adjusted by measuring residual spring N
status of the soil.
Soil tests for residual N can improve prediction of crop N fertilizer requirements in
humid regions of U.S., but their adaptation in fertilizer recommendation depends on the
frequency of significant profile NO3-N carryover (Vanotti and Bundy, 1994). In the humid
Midwest, measurements of NO3-N in the soil profile before corn (Zea mays L.) planting
effectively predicted N response and the amount of supplemental N needed for profitable
production (Schmitt et al., 1991; Bundy et al., 1992). Usefulness of a soil N test in a
humid region was also reported by Vanotti and Bundy (1994). Their results illustrated that
47
large variations, 32 to 106 kg N ha-1, in N carryover made soil testing for NO3-N an
important tool to optimize N fertilizer use in the humid region of Wisconsin. Wehrmann
and Scharpf (1979) found a strong correlation between optimum fertilizer rates and soil
mineral N. They developed a predictive system (the Nmin method) from this relationship
which not only predicts the optimum fertilizer N rate but also identifies fields not needing
fertilization. Many researchers used their approach to optimize fertilizer N for winter
wheat (Baethgen and Alley, 1989; Bundy et al., 1992).
Soil supplied N is derived either from residual inorganic N or from organic N that
becomes converted to inorganic N by soil microbes. Researchers have long been aware
that a small percentage of organic N is mineralized in the course of the growing season
and can significantly contribute to nitrogen requirements of the crop (Foth and Ellis,1988;
Harper, 1984; Power and Doran, 1984; Marumoto et al.,1982). Biological immobilization
of soil inorganic N occurs simultaneously with mineralization. A significant portion of
mineralized N is immediately assimilated by soil microbial biomass and transformed into
organic cell constituents (Mary and Recous, 1994). During mineralization-immobilization,
soil microbial biomass temporarily serves as source and sink of easily mineralizable
nitrogen (Smith, 1994). Soil microbial biomass predominantly assimilates NH4-N during
the immobilization process, but in the absence of NH4-N, can use NO3 -N as an energy
source (Recous et al., 1988; Azam et al., 1986). The difference between gross rates of
mineralization and immobilization is net mineralization. Net mineralization is strongly
dependent on C:N ratio of the organic matter (Whitmore and Groot, 1994; Neve et at.,
1994). The amount of N returned to the soil by crop residues depends on the quality and
48
quantity of the substrate.
Crops grown in rotation often produce more and higher quality plant dry matter
than those grown in monoculture (Copeland and Crookston, 1992; Collins et al., 1992).
Change in crop sequence changes soil temperature, soil moisture, crop rooting and residue
inputs. Fertilizer N requirement for optimum grain yield is often reduced in rotation
compared to monoculture (Franzluebbers et al., 1994). Cereal crops grown after a legume
often have a higher yield as compared to those grown after a non-legume crop (Wani et
al., 1991). This is because legume residues generally have a low C:N ratio and large
fraction of readily available N. Breland (1994) studied the decomposition dynamics of
white clover in a controlled environment. Net mineralization was estimated as the
difference between that in amended and unamended soil, respectively. He found that 38-56
percent of the nitrogen in clover shoot dry matter was mineralized during the initial period
(52 days) of rapid mineralization. Thicke et al. (1993) found that the decomposition of
incorporated legume residues can have significant, but extremely variable, impact on total
N mineralization. McKenney et al. (1995) concluded that legume residues can provide a
definite advantage compared with grass and corn residue in term of N conservation
depending on the aeration status of the soil. Legume residues not only provide a great
source of readily available N to other crops (Azam, 1990), but can also increase long-term
soil fertility (Palm and Sanchez, 1991). This increase is mainly because of the conversion
of a portion of biologically-fixed N into the stable humus form (Azam et al., 1993). In
addition to the enhancement of N fertility, legumes also affect soil properties such as
water holding capacity, cation exchange capacity, buffer capacity, soil porosity and
49
infiltration (Burnett, 1975; Cook, 1988; Fyson and Oaks, 1990).
In western Oregon, a variety of crop rotations create large differences in soil N
supplying capacity which are not reflected in soil tests for inorganic N. In a study carried
out in western Oregon, Sebastian (1995) measured N recovery by unfertilized winter
wheat ranging from 96 to 192 kg ha 1. Assessment of mineralizable N at the beginning of
the growing season and coupling the results with soil mineral and plant analysis could be
helpful in improving fertilizer N recommendations in the region.
Plant tissue analysis at early growth stages are another important method of
estimating optimum fertilizer N rates and have successfully been used as an indicator of N
fertilizer requirements for wheat by many researchers (Engel and Zubriski, 1982; Donohue
and Brann, 1984; Becker and Authammer, 1982). In regions were soil testing for N has
been impractical due to heavy precipitation, plant tissue testing could be a promising
method of estimating fertilizer N requirements for winter wheat (Fox and Piekielek, 1984).
Many fertilizer N recommendations are based on the analysis of plant tissue samples taken
at Feekes 5 (Large, 1954) in the spring. Vaughan et al. (1990) found that late tillering
(Feekes 5) is the most appropriate and usable growth stage for plant sampling in order to
make tissue-based N recommendations. They also suggested that total N should be
calculated from whole plant samples. Roth et al. (1989) reported that whole plant N
concentration at Feekes 5 rather than N uptake is the most accurate method of predicting
N deficiency. Scharf (1993) found tissue N content a useful tool in adjusting optimum N
rate in Virginia.
50
A method for making field-specific N rate recommendations for winter wheat at
early growth stages was reported by Baethgen and Alley (1989). Their method used crop
N uptake or plant N concentration at Feekes 5 as the basis of the N rate recommendations.
Strong correlation was found between uptake or plant N concentration at Feekes 5 and
optimum N rates. Similar results were reported by Batey (1977). He also found a high
correlation between crop uptake in spring and the rate of fertilizer N required to obtain
maximum grain yield. Peter et al. (1993) used this approach and also found a good
relationship between tissue N and optimum fertilizer N rates. Economic analysis indicated
that tissue-based N rate recommendation increased profit by an average of $36 hat
relative to traditional N applications.
Application of fertilizer N is often necessary to supplement soil supplied N in
commercial cropping systems. Efficient N management utilizes soil N as much as possible,
adding fertilizer N to enhance crop growth only when necessary (Sebastian, 1995). The
amount of fertilizer N required will vary depending on yield desired, residual N and the N
suppling capacity of the soil. Incorporating information about crop N requirements, soil
testing, and plant analysis at early growth stages will be very helpful towards optimizing
the fertilizer N recommendations for winter wheat.
The objective of this study was to evaluate the suitability of a N balance model for
predicting the need for additional N fertilizer on winter wheat under western Oregon
conditions.
51
Materials and Methods
Nitrogen Balance Model
A model similar to that proposed by Rice and Hav lin (1994) was developed to
calculate optimum fertilizer N rates. Recommended nitrogen rates were determined by this
model:
Recommended N = 300 - (Nr + Nmin N p)
[1]
Where,
N,.
= Residual inorganic N (NH4 -N + NO3-N) kg ha' at Feekes 5
Nrith, = Soil mineralizable N kg ha' at Feekes 5
1\cp = Plant N uptake kg ha' at Feekes 5
The 300 kg N ha.-1 is the total N (residual N + mineralizable N + fertilizer N) estimated to
be required for maximum yield in Willamette Valley of western Oregon. Analysis of
nitrogen response data for soft white winter wheat by Neil Christensen and John Hart, Soil
Scientists, Department of Crop and Soil Science, Oregon State University, suggested that
this total quantity of N maximized yield over an array of environmental and production
conditions. Data from over twenty years and dozens of trials were analyzed. Total N
requirement was estimated by adding the amount of N recovered in unfertilized plots (an
estimate of mineralized N) to the amount of applied fertilizer N that gave maximum yield
in each trial. The average total N requirement was about 300 kg N ha' (unpublished data)
and showed little variation across an approximately 2X range in grain yield. This
uniformity in N needed to maximize yield under an array of environmental conditions
52
suggested that it may be possible to model N need. Nitrogen response trials were
established in three years to develop model and two validation field-scale trials were run in
one year. Each type of trial is discussed below.
On-farm Trials
On-farm trials were conducted in growers' fields at three different locations across
the Willamette Valley of western Oregon during the 1994-1996 growing seasons. The
1993-94 experiment was part of fellow graduate student Kevin Sebastian's (1995) MS
Thesis. Each site of these experiments represented a crop rotation system that is
commonly used in the Valley. Rotations were soft white winter wheat following grass
seed, sweet corn or a legume. The experimental design was a randomized complete block
with three replications on each site. Plot size varied site-to-site depending on size of
machinery used by the grower. An average plot size of 90m X 10m was used. Nitrogen
fertilizer was applied as urea (46-0-0) at approximately Feekes 5 in one application with
drop or spinner spreader. Four treatments, including a check receiving no nitrogen, were
used at each site during the 1993-94 and 1994-95 growing seasons. At corn and legume
rotation sites, N was applied at the rate of 0, 56, 112 or 168 kg N ha-1. Since less residual
nitrogen was expected following grass in rotation, slightly higher rates- 0, 67, 134, or 201
kg N ha'- were used in the first two years. During the 1995-96 growing season, five N
rates - 0, 56, 112, 168 or 224 kg N ha-1- were used in all three rotations. The location, soil
series, cropping history and wheat varieties used in the experiments are listed in Table 2-1.
53
Table 2-1: Location, previous crop, variety and soil series for experimental sites.
Grower
County/City
Previous
crop
Wheat
variety
1994
Jones
Polk/Amity
Clover
Madsen
Amity
Fine-silty, mixed mesic,
Argiaquic Xeric Argialbolls
Volker
Benton/Monroe
Corn
Gene
Malabon
Fine, mixed, mesic Pachic Ultic
Argixerolls
Van Leeuwen
Linn/Halsey
Tall
Fescue
Gene
Malabon
Fine, mixed, mesic Pachic Ultic
Argixerolls
1995
Ruddenklau
Polk/Amity
Clover
Gene
Amity
Fine-silty, mixed mesic,
Argiaquic Xeric Argialbolls
Volker
Benton/Monroe
Corn
Gene
Chehallis
Fine-silty, mixed, mesic Cumulic
Ultic Haploxerolls
Van Leeuwen
Linn/Halsey
Tall
Fescue
Stephens
Woodburn
Fine-silty, mixed, mesic Aquultic
Argixerolls
1996
Ruddenklau
Polk/Amity
Clover
Gene
Amity
Fine-silty, mixed mesic,
Argiaquic Xeric Argialbolls
Volker
Benton/Monroe
Corn
Gene
Malabon
Fine, mixed, mesic Pachic Ultic
Argixerolls
Chipman
Benton/Albuny
Perennial
Raygrass
Madsen
Willamette
Fine-silty, mixed mesic Ultic
Haploxeralfs
1997
Mulkey
Polk/Monmouth
Annual
Raygrass
Madsen
Willamette
Fine-silty, mixed mesic Ultic
Haploxeralfs
Jones
Benton/Corvallis
Corn
Stephens
Chehallis
Fine-silty, mixed, mesic Cumulic
Ultic Haploxerolls
Soil Series
54
Soil samples were collected at approximately one month intervals from each site
during the 1993-94 and 1994-95 growing seasons. Samples were taken at four depths- 0­
30, 30-60, 60-90 and 90-120 cm. A single composite sample representing the entire plot
area was used prior to spring fertilization. Approximately ten cores were taken to make
this composite sample. Analysis of soil data for NH4-N and NO3-N from these two
growing seasons indicated that sample from 0-30 cm depth taken at Feekes 5 was
adequate to assess soil N status (data not shown). During the 1995-96 growing season,
pre-fertilization soil samples were collected from individual plots to a depth of 30 cm.
Each sample was a composite of approximately 10 cores. Intensive soil sampling was
performed just after harvesting at each site on each plot in all years to three depths- 0-30,
30-60, and 60-90 cm.
To calculate total N uptake, plant tissue samples were taken at Feekes GS 5 ( prior
to fertilizer application) and at maturity. At Feekes 5, ten representative samples of 30 cm
of row were collected from each plot by cutting the plants at soil level. Whole plant
samples were weighed, ground and analyzed for nitrogen content. At maturity, nine one-
meter row sections were cut at soil level from each plot to determine dry matter. Heads
from plants were removed and threshed separately. Representative subsampling was
performed for each sample. Subsamples of grain, straw and chaff were analyzed for
nitrogen content. Plant N uptake (kg N ha') was calculated by multiplying the N
concentration in the tissue by dry matter production (kg DM ha-1). Plant height and
lodging measurements were taken prior to harvest. Grain yield was obtained from
individual plots. Growers used their equipment to harvest the plots. Grain yield was
55
determined on site through use of a weigh wagon accurate to ± 1 kg. A grain sample was
saved for test weight, protein and 1000 kernel weight determination.
Small Plot Research Station Trials
Fertility trials were established during the 1993-94 growing season at the Hyslop
Experimental Station of the Department of Crop and Soil Science, Oregon State
University, Corvallis, Oregon. Work continues on these trials. The experiment was
arranged as a spilt plot design with four replications having rotation (clover or oat) as
main plots and fertilizer treatments as sub-plots. Rotation treatment (main plots) size was
12m X 45m, while fertilizer treatment (sub plots) size was 12m X 9m. Five fertilizer
treatments - 0, 50, 100,150 or 200 kg N ha.-1 - were used. Rotations include winter wheat
following clover and winter wheat following oat. The site had been fallow in 1993.
Crimson clover was planted on all plots in fall 1994. In spring 1995, two plots per
replication were fallowed, one was planted to oat and the fourth was left in clover. Clover
and oat were allowed to mature, were harvested and crop residue was incorporated.
Wheat was planted on the clover and oat stubble plots in fall 1995 and crimson clover on
one of the fallowed plots to establish the next rotation cycle. Oats were planted in spring
1996. Data were collected for 1995-96 and 1996-97 growing seasons.
Soil samples were collected pre-plant and post-harvest. An intensive pre-plant
sampling was done in fall 1995 by taking soil at 30 cm increments to a depth of 150 cm
from individual plots. This was done to assess the residual nitrogen status of the
experimental site. Post-harvest sampling was performed on 0, 150 and 200 kg N ha-1
56
treatment plots within each rotation. Samples were analyzed for ammonium and nitrate
concentrations.
Plant tissue samples were taken at Feekes 5 and at maturity for dry mater yield and
nitrogen uptake. Four above ground plant samples of 1.5 meter of row were cut from drill
strips in each sub-plot. Heads were cut, threshed and weighed. Grain and straw were
analyzed separately for their nitrogen content by combustion analyzer. Plant N uptake (kg
N ha') was calculated by multiplying the N concentration in the tissue by day matter
production (kg DM ha'). Plant height and lodging were measured prior to harvest. Plots
were harvested with a small plot combine harvester. Harvested grain was cleaned and
analyzed for yield, test weight, protein content by whole grain NIR analyzer and 1000
kernel weight.
Model Validation Trial
In 1996-97, two trials were conducted to further check the validity of the
proposed model. Trials were conducted in growers fields at two location in the Willamette
Valley. Rotations were soft white winter wheat following grass seed and sweet corn. The
experimental design was a randomized complete block with three replications at each site.
Plot size varied depending on size of machinery used by the grower. An average
90mX10m plot size was used. Nitrogen fertilizer was applied as urea (46-0-0) at
approximately Feekes 5. Three treatments were used at each site. We were not interested
in N response per se but bracketing N rates were used at each site. At the wheat following
corn rotation site, the predicted optimum N rate was 168 kg N ha'. Previous corn rotation
57
trials had not shown an economic yield respond beyond this rate hence a low (84 kg N
ha-1) and intermediate (140 kg N ha-1) rate were selected as other treatments in this trial.
The cooperating grower was interested in lower N rates. Spreader calibration error
resulted in an intermediate rate of 132 kg N ha-1 At the wheat following grass seed
rotation site, N was applied at the rate of 84, 112, and 140 kg N ha-1. The 112 kg N ha-1
rate was the recommended rate from our model. The 84 kg N ha-1 and 140 kg N ha-1 rate
were selected to bracket the recommended rate (± 28 kg N ha-1). The location, soil series,
cropping history and wheat varieties used in the experiments are listed in Table 2-1.
Soil samples were collected before fertilizer application and after harvest. At prefertilization, soil samples were taken from a 0-30 cm depth while after-harvest samples
were taken at three depths- 0-30, 30-60, and 60-90 cm from individual plots. Each sample
was a composite of approximately 10 cores.
Plant tissue samples were taken at Feekes GS 5 ( prior to fertilizer application) and
at maturity to calculate total N uptake. At Feekes 5, ten representative samples of 30 cm
of row were collected from each plot by cutting the plants at soil level. Whole plant
samples were weighed, ground and analyzed for nitrogen content. At maturity, nine one-
meter row sections were cut at soil level from each plot to determine dry matter. Heads
from plants were removed and threshed separately. Representative subsampling was
performed for each sample. Subsamples of grain, straw and chaff were analyzed for
nitrogen content. Nitrogen uptake (kg N ha-1) was calculated from day matter production
(kg DM ha-1) and corresponding plant N concentration.
58
Maximum Economic Yield Equations
The validity of the N balance model was checked by comparing the recommended
N rates determined by the model with N rates determined in 1996-97 trials to obtain
maximum economic yield. To calculate the fertilizer rate required for maximum economic
yield, regression equations were developed to describe wheat grain yield response to N
fertilizer applied at Feekes 5 (Baethgen and Alley, 1989). The relationship between grain
yield and fertilizer was quadratic in shape for each rotation (Mason, 1987). The quadratic
equation used is as follow:
Y = a + biN - b2N2
[2]
Where,
Y = Grain yield (kg ha-1)
a = Intercept
b1 = Linear regression coefficient
b2 = Quadratic regression coefficient
N = Fertilizer N rate (kg ha-1)
The maximum economic N rate for any given response curve is the N fertilizer rate
value that makes the first derivative of the response function equal to the price ratio of N
fertilizer to wheat ($kg N to $ kg wheat)( Heady et al. 1955). The fertilizer rate for
maximum economic response was calculated as follows:
Y = a + biN - b2N2
Setting the first derivative equal to N price/wheat price
[2]
59
dY/dN = bi - 2 b2 N = PN/Py = r
r = bi - 2 b2N
2 b2N = bl - r
N = (bi - r)/ 2b
[3]
Where,
r = price ratio of N fertilizer to wheat ($ 0.60 per kg N to $ 0.14 and 0.16 per kg wheat)
b1 and b2 are regression coefficients.
Soil Analysis
Soil and plant tissue samples were analyzed in the Central Analytical Lab (CAL) at
Oregon State University, Corvallis, Oregon. Plant samples were dried at 70 °C in a forced
air oven, weighed and ground in a Wiley mill to pass a 1 mm mesh screen. The N content
of wheat grain and straw was determined by a Leco CNS 2000 (Leco corporation, St.
Joseph, MI) combustion analyzer.
Soil inorganic N (NH4-N and NO3-N) was determined using the modified KCI
extraction method described by Keeney and Nelson (1982). Twenty-gram soil samples
were placed in 250 mL bottles and 75 mL of 2 N KC1 extracting solution was added.
Vessels were shaken on a mechanical shaker for one hour. The extraction solution was
filtered through Whatman No. 42 filter paper. The NH4-N and NO3-N content of the
extract was determined with an ALPKEM rapid flow analyzer (RF-300) which complexes
NH4-N with salicylate to form indophenol blue. This color was intensified with sodium
nitroprusside and measured at a wavelength of 660 nm. The NO3-N concentration were
60
determined with the same equipment used for NH4-N analysis by reducing nitrate via a
cadmium reactor and complexing the NO3-N with sulfanilamide and N-(1-Napthyl)­
ethylenediamine dihydorchloride to form a red-purple color. The color intensity was
measured at a wavelength of 540 nm.
Anaerobic Incubation
Soil mineralizable N was determined using a short-term anaerobic incubation
method described by Keeney (1982) slightly modified by increasing the sample size.
Through use of a sample splitter, a 20 g soil sample was obtained and placed in a 250 mL
extraction bottle. Fifty mL of distilled water was added to each bottle so that the soil
became completely saturated. Bottles were made air tight by putting a plastic cover under
their lids. Samples were placed in an incubator for 7 days (168 h) at 40 °C plus or minus
0.5 °C. After incubation, samples were carefully removed from the incubator and 50.0 mL
of KCl was added. Vessels were shaken on a mechanical shaker for one hour. The
extracting solution was filtered through Whatman No. 42 filter paper. Final NH4-N
content of the extract solution was determined from incubated samples. Initial NI14-N
values were subtracted from the final values to obtain the amount of N mineralized.
61
Results and Discussion
Optimum fertilizer N rates for winter wheat were estimated by the following N
balance model.
Recommended N = 300 - (N, + Nuun + N 1,)
[1]
Where N, and Nmu, are the soil inorganic N (NH4 -N + NO3-N) and soil mineralizable N kg
ha-' at Feekes 5 before fertilizer application, respectively, and Nup is the total N (kg ha-1)
taken up by the crop at Feekes 5 prior to fertilization. The 300 N kg ha-1 is the total N
(residual N + mineralizable N + fertilizer N) assumed to be needed for maximum yield in
Willamette Valley of western Oregon. The parameters used in the model were determined
at the time of spring fertilization in order to assess optimum N rates. Parameter values and
predicted fertilizer N need for the various trials conducted as part of this study are shown
in Table 2-2.
At on-farm sites, the amount of soil inorganic N in the top 30 cm of soil at the time
of spring fertilizer application was low and similar through all rotations over years. The
average inorganic N across all rotations over years was only 27 kg N ha.-1 (Table 2-2).
This is likely because of leaching and/or denitrification losses due to heavy precipitation
during winter months (Sebastian, 1995). Soil mineralizable N in the top 30 cm of soil
varied greatly among rotation over years. Amount measured prior to spring fertilization
ranged from 53 kg N ha"' in wheat following corn in 1995 to 116 kg N ha-' in the wheat
following grass seed in 1996. In 1995 and 1996, wheat following grass had relatively high
soil mineralizable N. The amount of N taken up by the crop at the point of fertilization
was also comparatively high in wheat following grass in 1995 and 1996 which indicates
62
Table 2-2:
Assessment of optimum N rates for each rotation using the N balance model
Rotation
Mineralizable
Soil N 11
Nt
Plant N
uptake ¶
Recommended
N rate
kg ha-1
On-farm Trials
1994
Clover-wheat
Corn-wheat
Grass-wheat
94.9
22.9
106.5
84.4
18.4
19.0
18.0
38.8
20.0
163
157
157
36.1
25.8
24.9
25.6
31.1
38.6
166
190
145
60.4
74.4
116.0
26.6
26.1
Oat-wheat
Clover-wheat
1995
Clover-wheat
Corn-wheat
Grass-wheat
72.2
53.2
91.6
1996
Clover-wheat
Corn-wheat
Grass-wheat
33.3
15.1
26.7
42.8
187
177
114
55.1
33.7
17.6
193
59.7
43.1
14.3
179
Oat-wheat
63.2
13.1
6.5
217
Clover-wheat
85.3
14.4
31.7
168
Small Plot Trials
1996
1997
1. Soil mineralizable N kg ha' at Feekes 5 before fertilizer application
11 Residual N (NH4 -N + NO3-N) kg ha' at Feekes 5 before fertilizer application
11 Whole plant N uptake kg ha' at Feekes 5 before fertilizer application
ImiRecommended N rate obtained by using model: N = 300 (N, + Nur, + N p) [1]
63
high N availability in grass rotation (Table 2-2).
In small plots in 1996 and 1997, the soil inorganic N in the top 10 cm of soil at
Feekes 5 was similar in oat and clover rotations (Table 2-2). In 1996, the soil
mineralizable N in the top 10 cm of soil was also same for two rotations with average of
57 kg N ha-1. In 1997, however, wheat following clover had a higher soil mineralizable N
compared to wheat following oat. A similar pattern was found for plant N uptake at
Feekes 5 where in 1996 the N uptake was not significantly different between rotations but
in 1997, clover-wheat had a significantly higher N uptake 32 kg N ha-' compare to 6 kg N
ha1 for wheat following oat (Table 2-2). Based on the proposed model recommended N
rates ranged from 114 to 217 kg N
Grain Yield Response
The grain yields for each site-year are summarized in Table 2-3. There was a
significant yield response to fertilizer N in every trial. In all rotations, a significant yield
increase occurred with the first increment of N fertilizer. The effects of additional N varied
among rotations and years. This variation in yield response to added fertilizer N among
rotations and years may have been due to the factors such as soil types and texture, water
availability, soil nutrient levels and weather. Grain yield responded curvilinearly to applied
N fertilizer as illustrated in Figs 2-1. Similar observations have been reported by Entz and
Flower (1989) and others. The regression equations that best described grain yield
response to N fertilizer at each site are given in Table 2-4.
In the 1994, yields were high across all rotations (Table 2-2). The average yield
across all rotations with no fertilizer was 6824 kg ha-I- a yield above the long term yield
Table 2-3: Mean grain yield of on-farm trials for 1994-96 growing seasons.
Previous crop
Total NI
applied
Clover
1994
1995
Corn
1996
1994
kg ha"'
Grass
1995
1996
1994
1995
1996
kg ha-1
0
5842a
4950a
4697a
7880a
5207a
4559a
6752a
3191a
4520a
56
7082b
5731b
6518b
9147b
6295b
6178b
9165b
5499b
5704b
112
7020bc
6138bc
7987c
9742c
7549c
7897c
9180bc
5853bc
6331bc
168
8076d
6258cd
8794d
10315d
7957cd
8111cd
10272d
6288cd
5915bcd
224
9082de
8251cde
5551bcde
PLSD
949
517
513
493
975
690
935
925
720
CV %
6
4
3
2
7
6
5
9
5
P-value
0.008
0.004
0.000
0.008
0.009
0.003
0.001
0.000
0.00
I In 1994 and 1995 wheat following grass fertilizer N rates were 0, 67, 134, 201 kg N
65
11000
10000
9000
et
8000
7000
:T.
a)
6000
5000
4000
3000
A
1994 0 1995 -X-
1996
2000
50
100
150
200
250
N rate (kg/ha)
11000
10000
9000
b
1
8000
7000
6000
I
5000
4000
3000
A-- 1994 0 1995 -- 1996
2000
0
50
100
150
200
250
N rate (kg/ha)
Fig. 2-1 Yield response of (a) Clover-wheat (b) Corn-wheat (c) Grass-wheat
rorations to fertilizer N rates of on -farm trials for the 1994-95 growing season
66
11000
10000
C
9000
t
8000
7000
6000
;--:
5000
4000
3000
A 1994 0 1995 X-- 1996
2000
0
50
100
150
200
250
N rate (kg/ha)
Fig. 2-1 (cont.) Yield response of (a) Clover-wheat (b) Corn-wheat
(c) Grass-wheat rotations to fertilizer N rates of on -farm trials for
the 1994-96 growing season
67
Table 2-4: Regression equations for nitrogen response curves of on-farm
trials for the 1994-1996 growing season
Rotation
Regression equation
R2
On-farm Trials
1994
Clover-wheat
G = 5963 + 14.34 * N - 0.11 * N2
.66
Corn-wheat
G = 7913 + 23.40 * N - 0.05 * N2
.78
Grass-wheat
G = 6925 + 30.50 * N - 0.73 * N2
.98
Clover-wheat
G = 4955 + 16.59 * N - 0.53 * N2
.77
Corn-wheat
G = 5156 + 26.07 * N - 0.05 * N2
.84
Grass-wheat
G = 3324 + 35.61 * N - 0.10 * N2
.92
Clover-wheat
G = 4674 + 38.75 * N - 0.85 * N2
.82
Corn-wheat
G= 4499 + 39.40 *N - 0.10 *N2
.77
Grass-wheat
G = 4359 + 24.08 * N - 0.09 * N2
.67
Oat-wheat
G = 2193 + 40.77 * N - 0.06 * N2
.97
Clover-wheat
G = 4027 +36.80 * N - 0.07 * N2
.89
Oat-wheat
G = 1171 + 43.38 * N 0.06 * N2
.97
Clover-wheat
G= 3566 + 51.61 *N - 0.14 * N2
.94
1995
1996
Small Plot Trials
1996
1997
68
average for the region. The USDA Agriculture Statistics Service reported yields 15%
above the long term average in western Oregon during 1994 (Sebastian, 1995). In the
wheat following corn rotation, each increment of N fertilizer significantly increased yields
(p < 0.05). The high response to N fertilizer for wheat following corn could be because
corn provided a large quantity of a residue with a high C:N ratio. Echeverria et al. (1992)
also found that wheat after corn responded most to N fertilizer as compared to wheat
following soybean or sunflower. Wheat following clover in 1994 had lowest overall mean
yields ranging from 5842 kg ha with no fertilizer to 8076 kg ha"1 with 168 N kg ha'. No
significant difference was observed between the 56 and 112 kg N ha-1- treatments (Table
2-3). Current western Oregon fertilizer recommendations for wheat following clover are
less than for wheat following row crops, but varies depending on how vigorous the clover
crop was. A less than average stand of clover would result in less available N for the
subsequent wheat crop. The check yield for wheat following grass in 1994 was 6752 kg
ha' (Table 2-3). As was observed for the wheat following clover rotation, there was not a
significant difference between treatments of 56 and 112 N kg ha."1 (Table 2-2).
In 1995, response to N fertilizer for wheat following corn was similar to 1994
observations. Yield increased significantly with each increment of N fertilizer except at the
highest N rate. Mean grain yields were, in general, greater in wheat following corn
compared to wheat following clover or grass. The wheat following grass rotation had the
lowest check yield (3191 kg ha-1) and the largest response to initial N increment. Adding
68 N kg ha-1 increased the yield by over 2300 kg ha-1. At the highest N fertilizer rate, the
mean yield of wheat following clover and grass were the same, 6258 kg ha-1 and 6288 kg
69
ha-i, respectively. In addition, the yield increase from 56 to 112 N kg ha-1 was not
significant for clover-wheat and grass-wheat rotations.
As 1994-95 data suggested there many be a response to a higher N rate, a 224 N
kg ha rate was included in 1995-96 experiments. No additional yield response was
obtained for this higher rate in any rotation. Interestingly, the check yield for all three
rotations was similar with an average value of 4592 kg ha-1. At higher N rates, mean yields
of wheat following clover and corn were about the same, while yields of wheat following
grass were less. In fact, the highest yield of wheat following grass was achieved with 112
N kg ha"'. Yield dropped when the fertilizer N was applied at the rates of 168 and 224 N
kg ha-1 (Fig. 2-1 c). This reduction in yield at high N rates may be due to increase disease
incidence, water stress, or to physiological reactions by the plant itself (Blade and Baker,
1991). No lodging occurred in any rotation. It was observed throughout the study that
wheat following grass had relatively higher soil N availability (Table 2-2) and higher N
uptake (data not shown) as compared to wheat following clover and wheat following
corn.
Determination of Nitrogen Rates for Optimum Grain Yield
Figures 2-1 show yield as a function of applied fertilizer N for wheat following
clover, corn and grasses. The yield data fit a quadratic model using applied N as an
independent variable. Regression equations for yield response curves and their
corresponding correlation coefficient (R2) are given in Table 2-4.
70
The amount of N fertilizer required at Feekes 5 to produce maximum yield
(NMAX) in each rotation and years was determined using the N balance model. The
NMAX rates predicted by this model were compared with actual N rates required to
obtain maximum economic yields (NMEY). The amount of fertilizer N required for
maximum economic yield were calculated from each response curve at each rotation site.
The NMEY for any given response curve is the fertilizer rate where the first derivative of
the response function equals the price ratio of N fertilizer to wheat [3]. Two N
fertilizer/wheat price ratios were used in this study to calculate NMEY (Table 2-5). The
difference between the two ratios was the price of wheat 0.14 $ per kg Ni and 0.16 $ kg
for N2. The price of N was held constant at $ 0.60 per kg. The difference between the
NMEY values (N1 and N2) was not significant (p > 0.8), consequently N1 is used in further
comparisons.
In 1994, the NMEY rates for wheat following clover and wheat following corn
exceeded the largest N fertilizer rate used in study, therefore, the highest N rate of 168 N
kg ha-1 was considered as NMEY rate. The comparison of NMAX and NMEY values are
given in Table 2-5.
At on-farm sites in 1994, the model underestimated NMEY by 5 N kg ha-1, 11 N
kg ha-1 and 18 N kg ha-1 for wheat following clover, corn and grass, respectively. In 1995,
the model overestimated N need in the clover rotation by 54 N kg ha-1. This was the
largest difference observed in this study. In 1995, corn and grass rotation NMAX and
NMEY rates were very close. In 1996, good agreement was found between NMAX and
NMEY values for all three rotations with the largest difference only 7 N kg ha-1.
71
Table 2-5.Comparison of recommenced and actual N rates for maximum economic yield
Rotation
Yield at
N t rate
Actual N /trate for
recommended
recommended
Max. Econ. Yield
N rate
by model
NI
N2
kg ha"'
On-farm Trials
1994
Clover-wheat
7994
163
168
168
Corn-wheat
10216
157
168
168
Grass-wheat
9908
157
175
182
Clover-wheat
6258
166
112
121
Corn-wheat
8007
190
196
200
Grass-wheat
6287
145
147
152
Clover-wheat
8951
187
190
196
Corn-wheat
8290
177
170
175
Grass-wheat
5956
114
107
112
Oat-wheat
7953
193
200
200
Clover-wheat
9154
189
179
200
Oat-wheat
7915
217
200
200
Clover-wheat
8145
168
162
165
1995
1996
Small Plot Trials
1996
1997
t Recommended N rate calculated by using equation [1].
II N rate to obtain maximum economic yield. Ni and N2 are the rates where the price of wheat
was set equal to $0.14 and $0.16 per kg, respectively, and price of N fertilizer was $0.60 per kg.
72
Average NMAX and NMEY rates, 174 and 178 N kg ha-1, respectively, were highest for
wheat following corn. Due to high soil N, low average NMAX and NMEY rates (141 and
143 N kg ha-1) were observed for wheat following grasses. A good correlation between
NMAX and NMEY ( r = 0.77) was observed across rotations and years.
In small plot trials the N fertilizer rates predicted by the model were also fairly
closed to the N rates required to obtain maximum economic yields. In 1996 and 1997, due
to high response of grain yield to N fertilizer (Fig. 2-2), the NMEY rates for wheat
following oat exceeded the largest N fertilizer rate, therefore, high rate of 200 was
considered as NMEY rates. In 1997, NMAX and NMEY rates were very similar for both
rotations. Wheat following oat had higher NMAX and NMEY rates- 35 kg N ha.-1 more.
Model Validation
In 1996-97, N rate trials were conducted to further check the validity of the
proposed model. Recommended N rates and subsequent yield and grain protein
concentration are given in Table 2-6. The recommended fertilizer N rates were 112 N kg
ha-1 and 168 kg N haTI for wheat following grass and corn, respectively. Cooperating
growers assisted in selecting other N treatments in these trials. Bracketing treatments were
chosen at the grass site, while lower rates were considered at the corn site.
In both rotations, the mean yield for the recommended rate was higher than the
other two treatments used in the experiment (Table 2-4). In the grass rotation, mean yield
dropped at the higher fertilizer N rate and there was no significant difference in yield
between the high and low fertilizer N rate treatments. Soil analyses also revealed high
73
10000
9000
8000
7000
6000
5000
4000
3000
2000
1000
50
0
100
150
200
150
200
N rate (kg/ha)
10000
9000
(B)
1997
8000
t
7000
-c:
5000 -7)1
---Nct
6000
4000
3000
2000
1000
-r
0
50
100
N rate (kg/ha)
mr Oat-wheat
--c Clover-wheat
Fig. 2-2 Yield response of clover-wheat and oat-wheat rotations to fertilizer N
rates (A) 1996 and (B) 1997 of small research plots trials
74
Table 2-6: Main yield and protein content for model validation trials
conducted during 1996-97 winter wheat growing season
N rate
Yield
(Kg ha -1)
(Kg ha-1)
Protein content
Grass-wheat rotation
84
4651a
9.8a
112 t
5168b
9.7ab
140
4875ab
10.5c
0.15
CV (%)
381
2
P-value
.004
.000
84
6476a
8.0a
132
7237b
8.7b
168 t
7946c
9.5c
577
0.56
PLSD
1
Corn-wheat rotation
PLSD
CV (%)
P-value
3
.005
3
0.01
1. Recommended N rate by using model [1]
residual N (NI-14-N and NO3-N) at the end of the season (data not shown). The plant N
uptake at the end of the season was also higher for wheat following grass compared to
wheat following corn (data not shown). Similar results were observed for wheat following
grass on-farm trials in 1996 where mean yield dropped at higher fertilizer N rates, while
total biomass and grain protein content increased significantly as higher fertilizer N was
added (Fig. 2-3). Costa and Kronstad (1994) reported that the redistribution of N from
75
vegetative plant growth accounted for at least 50 % of grain protein N. Higher levels of
biomass observed in the study due to higher levels of N, could potentially increase the
amount of N to be redistributed which contributes to a higher grain protein N
concentration. In the wheat following corn rotation each increment of N fertilizer
significantly increased grain yield. These results are similar to observations for wheat
following corn in 1994-96 in on-farm trials (Table 2-2).
Conclusions
Optimum N rates predicted by our proposed model were closely related to the N
rates required to obtain maximum economic yield. In 1996-97, the model validation
experiment also gave promising results. This study overall shows that the model appears
to accurately assess field-specific optimum fertilizer N status and that it can be used to
make fertilizer N recommendations for the region.
The response of winter wheat to fertilizer N varied greatly among rotations and
years in this study. Wheat following corn rotation was highly responsive to added fertilizer
N while wheat following grass was less responsive. Wheat following grasses had high soil
supplied N which depressed the yield even at moderately high fertilizer N rates. This
finding contradicts conventional wisdom that suggests higher N rates are needed following
grasses. This study documents a difference between perennial grasses and cereals grain
crops in rotation. The average yield with no fertilizer for wheat following corn and wheat
following legumes was about the same.
76
25000
12.5
-12
20000
11.5
11
to 15000
-10.5
10000
10
9.5
5000
-9
1
0
50
100
I
150
8.5
I
200
250
N rate (kg/ha)
Biomass 0-- Grain
0--- Protein
Fig 2-3: Total biomass, grain yield and protein content as influenced
by fertilizer N for wheat following grass in 1996 growing season.
77
Further Recommendations
Research efforts should be directed to further evaluate the validity of the model
over a range of soil and crops. Further research on N mineralization in soils following
grasses is also needed.
78
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83
CHAPTER 4
EVALUATION OF N UPTAKE PATTERNS IN SPRING AND WINTER WHEAT
IN WESTERN OREGON
Abstract
An understanding of the above ground nitrogen uptake pattern for wheat (Triticum
aestivum L.) is needed to facilitate nitrogen management. Evaluation of crop N uptake
pattern is critical for high N fertilizer use efficiency. Maximum efficiency should be
expected when plant N availability is synchronized with the period of rapid N uptake by
the crop.
The purpose of this study was to determine the N uptake pattern of spring and
winter wheat grown in western Oregon. Data used in this study were obtained from three
different trials: spring wheat rotation trials, small plot rotation trials, and unfertilized plots.
In spring wheat rotation trials five spring wheat cultivars; Alpowa (soft white; SW),
Pennawawa (SW), Treasure (SW), WB936R (hard red; BR), and Whitebird (SW) were
used. Fertilizer N (16-16-16-4) at the rate of 140 kg ha-1 was shanked into the soil at the
time of planting (April 4, 1997). An additional 194 kg ha' of fertilizer (46-0-0-0) was
broadcast on Aril 27, 1997. Small plot rotation trials were established during the 1993-94
growing season at the Hyslop Experimental Farm of the Department of Crop and Soil
Science, Oregon State University, Corvallis, Oregon. Five fertilizer treatments - 0, 50,
100,150 and 200 kg N ha' were used. Rotations include winter wheat following clover
84
and winter wheat following oat. In 1996, N uptake and dry matter yield of winter wheat
were determined from unfertilized plots of Stephens wheat in a trial at Hyslop
Experimental Station. Three 30 cm rows of above-ground plant tissue were randomly cut
at approximately 15 days interval starting a Feekes 5 and continuing until maturity.
In examining the N uptake pattern of spring and winter wheat it was observed that
maximum N uptake for spring wheat was at approximately 1100 accumulated growing
GDD, before Feekes 10. The maximum N uptake rate, 0.038 kg N GDD-1, occurred at
750 GDD. The peak N uptake was observed at May 30, approximately 35 days after
Feekes 2. Nitrogen uptake in winter wheat was significantly affected by rotations.
Significant differences for rate and time of maximum uptake between rotations were
observed. The maximum rate of N uptake (0.4-0.5 kg N GGD-1) for wheat following
clover was observed at approximately 1100 accumulated GDD, while the maximum rate
of N uptake (0.1-0.2 kg N GGD-1) for wheat following oats was at 1300 GDD.
85
Introduction
Evaluation of crop N uptake pattern is critical for high N fertilizer use efficiency.
Timing of fertilizer N application to coincide with specific growth stages can maximize
efficiency. High fertilizer N use efficiency is a key factor in achieving optimum cereal grain
yield and reducing the opportunities for N losses by denitrification, leaching and
volatilization. Maximum efficiency should be expected when plant N availability
synchronizes with the stage of crop development that permits rapid N uptake (Olson and
Kurtz, 1982). Better understanding the crop N uptake pattern for wheat in a particular
environment is critical for improving N fertilizer management and adjusting timing of
fertilizer application (Harper et al., 1987; Papastylianou et al., 1984). In the humid midAtlantic region of the US, Baethgen and Ally (1989) conducted a study to determine the
pattern of winter wheat N uptake through the spring growing season and found that
maximum daily N uptake rates were obtained in the period immediately after Zadoks GS
30 (Feekes 5), suggesting that this is when the highest efficiency of N fertilizer use could
be expected.
Nitrogen uptake by plants depends on several factors including nitrogen use
efficiency of the plant (yield per unit of N supply), N application rate and timing,
availability of N in the soil solution at the root surface, the state and morphology of roots,
temperature and other climate-related factors (Karrou and Maranville, 1994; Bock, 1984).
Total nitrogen content (the amount of nitrogen present in the aboveground portion
of a plant) shows the plant's capability to accumulate nitrogen. Fiez et al. (1995) argued
86
that N use efficiency can be divided into two multiplicative components - N uptake
efficiency and N utilization efficiency. Nitrogen efficiency illustrates the ability of a plant
to take up supplied N while utilization efficiency shows the capability of plant to utilize N
by increasing yield.
Application of N fertilizer stimulates early vegetative growth. The addition of
fertilizer N can increase vegetative growth and the amount of dry matter and N in crop at
anthesis (McDonald, 1992). In wheat, nitrogen content per plant is positively correlated
with total dry matter (Desai and Bhatia, 1978). Nitrogen uptake per unit N applied is
greatest where yield response to N is high (Gauer, et al. 1992). Increase in N uptake due
to fertilizer mainly depends on the N supplying capacity of the soil and the plants' ability
to use available N.
Time of fertilizer N application greatly affects the N uptake efficiency in wheat
production systems. In high precipitation regions, spring applied N is superior to fallapplied N (Doll, 1962). Spring-applied N was more available to winter wheat and more
profitable than fall or split-applied N in a semi-arid climate (Vaughan et al., 1990). In
Kansas, Kelly (1995) found no significant yield increase from split N (fall + late winter)
and split-spring N (fall + late winter + early spring) applications compared with single
preplant or late winter topdress applications, regardless of previous crop. Johnston and
Fowler (1991) observed that early N uptake and early growth was prevented by delaying
spring N fertilization of winter wheat under dryland conditions. Type of fertilizer N also
influences the N uptake and total dry matter yield of a wheat crop. Xingting and Below
(1992) argued that the growth and yield of wheat is enhanced when plants are provided a
87
mixture of NO3-N and NH4-N compared to either form alone. They suggest that the
growth and yield increase due to mixed N was because the mixed N increased the root
number and branches which enhanced N uptake.
One of the primary factors affecting N uptake is root morphology (Xingting and
Below,1992). Luxova (1988) argued that even though the entire root system is involved in
uptake, the majority of uptake occurs in the apical zones or axes of branches in young
roots. Moorby and Besford (1983) found that the growth of lateral roots increased the
rate of N uptake. Similarly, addition of fertilizer N affects growth and morphological
development of roots. Tennant (1976) found that root length increased when N was
applied to either part or all of a cereal root system.
Nitrogen uptake closely follows the growth pattern and at a certain developmental
stage, N uptake ceases and remobilization of N within the plant starts. Bauer et al. (1987)
measured N uptake in hard red wheat aerial parts from three-leaf to kernel-stage and
found that peak N uptake in leaves occurred during flag-leaf-extension through the boot
stage. They also reported that about 70 % of the 112 kg N ha' found in spikes was
translocated from leaves and stems. Baethgen and Alley (1989) observed that the total
amount of N found in leaves and stems decreased with time during the spring, while spike
N increased from the earliest stages of development until harvest. McNeal et al. (1968)
reported that under an irrigation system, 64 % of N translocated from leaves, stems and
chaff to grain of seven heard winter wheat varieties. Waldren and Flowerday (1979)
evaluated the concentration of N in leaves, stems, and spikes and found that translocation
accounted for over 70 % of N in grain of hard red winter wheat. Lal et al. (1978) also
88
reported that 58 % of grain N translocation from other parts of wheat crop.
Among environmental factors, temperature is the most important element that
affects N uptake in plants by regulating growth. Many researchers have reported a close
relationship between accumulated heat unit (growing degree days) and phenological
development in cereals (Buxton and Marten; 1989; Bauer et al., 1984; Klepper et al.,
1982). Because of its precision as in estimator of growth rate, growing degree days
(GDD) has been incorporated into N fertilizer management practices and crop
development models. Bauer et al. (1984) investigated the utility of GDD to estimate
spring wheat growth rate and stages and reported that precision of estimating growth rate
and stages by GDD was superior to calendar days.
The objective of this study was to determine the N uptake pattern of spring and
winter wheat grow in western Oregon. This information will be summarized in a bulletin
format for use by growers and field representatives in making decisions about wheat
fertilization.
89
Materials and Methods
Data were obtained from three different trials. Information about sampling dates,
Feekes growth stage, and accumulated growing degree days (GDD) for each trial are
shown in Table 3-1.
Spring Wheat Rotation Experiment
Nitrogen uptake and dry matter production in spring wheat were measured in an
on-going rotation study in 1997. The experiment was conducted at the USDA-ARS
Sustainable Grass Seed Production Research Project Coon Farm site located in Linn
county, Oregon. This site is an untiled, poorly drained, low pH Dayton soil that is
intermittently flooded during much of winter and early spring. The purpose of the this on­
going experiment is to determine the effect of perennial ryegrass residue management on
rotation crops. In 1997, spring grains were grown in rotation. The five spring wheat
cultivars used in this study were: Alpowa (soft white; SW), Pennawawa (SW), Treasure
(SW), WB936R (hard red; HR), and Whitebird (SW). The wheat cultivars were planted
on a 17 cm row spacing on April 4, 1997 using a conventional John Deere double disk
opener drill as a no till planter. A seeding rate of 40 seeds/30 cm of row was used.
The experimental design was a randomized complete block with four replications.
Two 10-row wide strips of each cultivar were planted in each of four replicated blocks.
Fertilizer N (16-16-16-4) at the rate of 140 kg ha.-1 was shanked into the soil at the time of
planting. An additional 194 kg ha-1 of fertilizer (46-0-0-0) was broadcast on Aril 27, 1997.
Aboveground plant samples were taken from randomly selected 1 m sections of row
90
Table 3-1: Sampling dates and corresponding Feekes growth stages
and accumulated growing degree days for spring and winter wheat
experimental sites.
Experiment
Sampling Date
Feekes Stage
GDD
April 25
F2
218
May 13
F3
466
May 31
F6
764
June 22
F 10
1126
July 11
F 10.5
1432
August 1
F 11
1784
March 4
F4
961
May 5
F8
1455
July 25
F 11
2763
February 22
F4
999
May 2
F9
1614
July 25
F 11
3020
Spring Wheat
1997
Winter Wheat
1996
1997
approximately every 250 growing degree days starting from Feekes GS 1 and continuing
until maturity. One sample was taken from each of the treatment subplots in a block and
combined. Plant samples were dried at 70 °C in a forced air oven. Samples were then
weighed and ground in a Wiley mill to pass a 1 mm mesh screen. Total N content was
determined by combustion analysis. Nitrogen uptake in kg N ha."1 was calculated as
product of total N content (%) in plant tissue times the biomass in kg ha.-1 divided by 100.
91
Small Plot Research Station Trials
Nitrogen uptake and biomass data for winter wheat were obtained from fertility
trials established during the 1993-94 growing season at the Hyslop Experimental Farm of
the Department of Crop and Soil Science, Oregon State University, Corvallis, Oregon.
The experiment is arranged as a split plot design with four replications having rotation as
main plot and fertilizer treatments as sub-plots. Main plots are 12m X 45m, while sub plot
fertilizer treatment size is 12m X 9m. Five fertilizer treatments - 0, 50, 100,150 and 200
kg N ha-1 - are used. Rotations include winter wheat following clover and winter wheat
following oat.
Plant tissue samples were collected at three different growth stages in 1996 and
1997 and used for dry matter yield and nitrogen uptake determination. Data used in this
study were obtained from two N rate treatments; 0 and 100 kg N ha."1. Plant samples were
collected at Feekes 5 (spring fertilization), at Feekes 9 (flag leaf), and at Feekes 11
(maturity). At Feekes 5 and Feekes 9, plant samples were taken from one m of row. At
maturity, four plant samples of 1.5 meter of row were cut from drill strips in each plot.
Heads were cut, threshed and weighed. Grain and straw were analyzed separately for their
nitrogen content by combustion analysis. Plant N uptake (kg N ha.-1) was calculated by
multiplying the N concentration in the tissue by dry matter production (kg DM ha-1).
N uptake from Unfertilized Plots
In 1996, N uptake and dry matter yield of winter wheat were determined from
unfertilized plots of Stephens wheat in a trial at Hyslop Experimental Farm of the
92
Department of Crop and Soil Science, Oregon State University, Corvallis, Oregon. Three
30 cm rows of above-ground plant tissue were randomly cut at approximately 15 days
intervals starting a Feekes 5 and continuing until maturity. All three plant samples were
mixed. All plant samples were dried at 70 °C in a forced air oven. Plant samples were than
weighed and ground in a Wiley mill to pass a 1 mm mesh screen. Total N content was
determined by combustion analysis. Nitrogen uptake (kg ha') was calculated as product of
total N content (%) in plant tissue times the biomass kg ha-1 divided by 100.
Statistical Analysis
In the spring wheat trial, sampling date was treated as a as main plot and cultivars
as subplots. In the Hyslop Farm rotation trial, treatment variables included rotation as
main plot and fertilizer N treatments as subplot. No statistical analysis was used for the
unfertilized wheat trial.
A logistic model was used to describe biomass accumulation and N uptake as a
function of time. The model used for fitting the plant growth and nitrogen uptake is given
in equation [1]. The parameters of the model describing dry matter accumulation and
accumulative N uptake were estimated by using Statgraphic Dos ver. 2.0.
K
1+ [
(K No)]
No
[I]
exp rt
93
Where:
Nt = Biomass accumulation or N uptake at time t
K = Maximum Biomass accumulation or N uptake
No = Initial or minimum biomass accumulation or N uptake
r = Rate of increase (slope factor) in biomass accumulation or N uptake
t = Time (growing degree days)
exp = Base of natural log, 2.71828
The first derivative of equation [1] was taken to determine a rate function dN/dt
[2]. The time of maximum biomass accumulation and maximum N uptake were estimated
by plotting dN/dt.
dN
dt
-
rN (1- N)
K
[2]
Growing degree days were calculated from daily maximum and minimum
temperatures by Eq. [3]:
GDD = [(T mix + Tmto)/2]
Where,
T
= Daily maximum temperature ( °C)
Ttnti, = Daily maximum temperature ( °C)
Tb = Based temperature with 0 °C
Tb
[3]
94
Results and Discussion
Spring wheat
Significant interaction between biomass accumulation and sampling date was found
(p< 0.002) which indicates that the pattern of biomass accumulation of five cultivars
varied with date of sampling. The mean values for biomass accumulation, Feekes growth
stages and their corresponding accumulated GDD are shown in Table 3-2. Biomass
accumulation followed a sigmoidal response (Fig. 3-1). Maximum biomass yield for all
five cultivars was observed at approximately 1432 GDD or Feekes 10.5. Biomass
accumulation leveled off beyond 1432 GDD. Each of five cultivars accumulated
approximately the same amount of dry matter until 1125 GDD or Feekes 10. A difference
in biomass yield among cultivars was observed at 1432 and 1784 GDD, Feekes 10.5 and
Feekes 11, respectively (Fig. 3-1). At 1432 GDD, the difference for biomass yield between
Pennawawa and Alpowa was 2595 kg ha' (Table 3-2).
The interaction effects of cultivar and sampling date for N uptake were not
significant (p> 0.2) indicating that the pattern of N uptake for all cultivars was the same
and the magnitude of N uptake of all cultivars was independent of sampling date.
Significant differences among cultivars were observed for N uptake (p < 0.001). The mean
values of N uptake for each cultivar are given in Table 3-2. Sampling dates and their
corresponding GDD are shown in Table 3-1. N uptake pattern also showed a sigmodal
response (Fig. 3-2). The coefficient of determination (R2) for the model ranged from 0.93
to 0.96 indicating a highly significantly fit of the model.
Table 3-2:
Accumulative biomass yield and nitrogen uptake of five spring wheat cultivars for 1997 growing season.
Sampling Time (Growing Degree Days)
218
467
763
1125
1433
1784
F2
F3
F6
F10
F 10.5
F 11
Variety
Biomass N uptake Biomass N uptake Biomass N uptake Biomass N uptake Biomass N uptake Biomass N uptake
kg ha'
Alpowa
52
2.5
618
25
3130
76
9126
115
11379
113
11264
117
Pennawawa
66
3.2
668
30
3573
93
8588
152
13797
155
13859
155
Treasure
68
3.2
790
28
3297
79
7935
146
13560
151
14167
152
WB963R
80
3.9
909
35
4653
105
9729
134
12427
129
12433
134
White Bird
58
2.7
697
27
3229
73
8682
119
11939
129
12122
128
96
16000
14000
03
-a) 12000
..­
i'd 10000
E
.2
..c.
a)
8000
i 6000
tE 4000
U
2000
0
100
m
Alpowa
400
700
1300
1000
Time (GDD)
-IN- Pennawawa v Treasure
1600
-0- VVB963R
1900
v
White Bird
Fig 3-1: Comparison of five spring wheat cultivars for biomass accumulation in
1997 growing season
97
The N uptake of all cultivars was rapid at early growth stage of the crop until the
crop accumulated 1000 GDD (Fig 3-2). After accumulation of 1000 GDD, N uptake
become slow and virtually there was no N uptake from 1120 to 1784 accumulated GDD,
Feekes 10 to Feekes 11, respectively, for all cultivars. Rapid N uptake at early growth
stages was associated with increase in biomass since it is well known that in wheat N
uptake and dry matter accumulation is positively correlated (Austin et al., 1977).
Maximum N uptake for all cultivars except WB963R was observed at approximately 1100
GDD, before Feekes 10. For WB963R, maximum N uptake was obtained at
approximately 900 GDD (Fig. 3-2). Similar results were reported by Bauer et al. (1987)
were they found that for spring wheat peak N uptake occurred during flag-leaf extension
(Feekes 10) to boot stage (Feekes 10.1). At Feekes 10, greatest N uptake was observed
for Pennawawa and Treasure, 152 and 146 kg N ha', respectively. The lowest plant N
uptake at Feekes 10 was observed for Aplowa and White Bird, 115 and 119 kg N ha-1
(Table 3-2). Over all, Pennawawa had the highest and Alpowa had the lowest N uptake
throughout the growing season.
Average N uptake rate (kg/ha/GDD) of all five cultivars is shown in Fig. 3-3. Plant
N uptake was very high from 218 GDD (first sampling date) to 750 GDD. The maximum
N uptake rate, 0.038 kg N GDD-1, occurred at 750 GDD (Fig. 3-3). After accumulation of
750 GDD, the rate of plant N uptake declined and the crop almost stopped taking N at
1100 GDD.
The window of N uptake for spring wheat on a calendar day basis was about 50
days, starting April 25 and ending June 15. However, the peak N uptake was compressed
98
160
Tzi
---al" 140
x
x0 120
sa,100
Z 80
0
>
i 60
5 40
U
100
1=
Alpowa
400
700
1000
1300
Time (GDD)
1600
--m Pennawawa ---nz-- Treasure 0 WB963R
1900
v White Bird
Fig 3-2 Comparison of five spring wheat cultivars for nitrogen uptake
in 1997 growing season.
99
0.25
0.04
-0.20
e0.03
g
Pr
-0.15 t
0.02
-0.10
= 0 01
c--1-
-0.05
Z
0.00
0.00
100
10
500
900
1300
1700
Time (ccumulative GDD from planting)
40
65
90
110
Time (calender days from planting)
Fig 3-3: Average nitrogen uptake and biomass accumulatoin rates of spring
wheat in 1997 growing season
rn
100
into a 30 days period.
Winter Wheat
A similar pattern for N uptake in winter wheat was observed for both 1996 and
1997 growing years. Nitrogen uptake was significantly affected by rotations. Wheat
following clover had greater N uptake at all sampling dates for both levels of N over two
years as compared to wheat following oat (Fig. 3-4). Nitrogen uptake of wheat following
clover receiving 100 kg ha"' was very rapid at early growth stages compared to wheat
following oat. In wheat following clover, maximum N uptake, 130 kg N ha.-1, was
observed at approximately 1350 GDD, prior to Feekes 9 growth stage. There was no
change in N uptake was observed after 1350 GDD. In wheat following oat, the crop
continued N uptake after Feekes 9 growth stage in both years. In 1996, maximum N
uptake, 105 kg N ha-1, was observed at approximately 1750 accumulated GDD, while in
the 1997 growing season, the peak N uptake of 100 kg N ha' for wheat following oats
was at 2180 GDD.
The first order derivative sigmoidal curve describing N uptake rate clearly shows
the significant differences for rate and time of maximum uptake between rotations where
100 kg ha-1 N fertilizer was applied (Fig. 3-5). The wheat following clover had
significantly higher N uptake rates in both growing years compared to wheat following
oat. The maximum N uptake rate of both rotations dropped in the 1997 growing year. In
wheat following clover, maximum rates of N uptake of 0.5 and 0.4 kg N ODD' were
observed in 1996 and 1997 growing seasons, respectively, at approximately 1100 GDD.
101
z
(L)
80
60
40
(..)
20
0
900
(A)
1400
2900
2400
1900
Time (GDD)
160
100-N
_1140
-61)
a
120
100-N
-g 100
z
80
60
0 -N
40
0 0-N
e) 20
0
(B)
1
900
1400
1900
2400
Time (GDD)
--cr Clover-wheat
I
2900
3400
Oat-wheat
Fig 3-4 Nitrogen uptake in winter wheat as influenced by different rotations
and fertilizer N rates in (A) 1996 and (B) 1997 at Hyslop Farm.
102
0.5
1996
A 0.4
t 0.3
a)
0.2
F4
'Alt
0.1
Fll
F8
0
800
1200
1600
2000
2400
2800
114
160
196
224
249
266
(A)
0.5
0.4
Clover-wheat
t 0.3
a)
Oat-wheat
0.2
u.
z 0.1
0
800
(B)
107
1200
1600
2000
2400
2800
Time (ccumulative GDD from planting)
168
209
235
259
283
Time (calendar day from planting)
Fig 3-5 Nitrogen uptake rate in winter wheat receiving 100 kg N ha -1 as
influenced by different rotations in (A) 1996 and (B) 1997 at Hyslop Farm
103
After accumulation of 1100 GDD, the rate of plant N uptake declined sharply and crop
almost stopped taking N at 1400 GDD. The maximum rate of N uptake of 0.2 and 0.1 kg
N GDD-1 for wheat following oats was observed in 1996 and 1997 growing seasons,
respectively, at approximately 1300 GDD. The rate of N uptake decreased after 1300
GDD and ceased at 2000 GDD. Though uptake rates varied by years, growing degree
days to maximal uptake was similar for each rotation over years.
The effect of added fertilizer N on N uptake and biomass yield of winter wheat
was also examined in this study. The mean values of each variable are given in Table 3-3.
N uptake by winter wheat was significantly influenced by rotations and added fertilizer (p
< 0.01). In 1996, the interaction effects of rotation and N fertilizer treatments for N
uptake were not significant (p> 0.2), but in 1997, significant interaction was observed
between rotation and N fertilizer treatments. In 1997, the influence of previous crop on N
uptake was greater relative to 1996 especially for wheat following clover where N uptake
increased in 1997 compare to wheat following oats. This indicates that N was more readily
available following clover over time. Nitrogen uptake was significantly higher following
clover than following oats at each level of applied N fertilizer, Over all, in both rotations,
N uptake increased almost linearly with added fertilizer N.
No significant interaction between rotation and fertilizer N treatments was found
for biomass yield. In 1996, the rotation effect was not significant, but in 1997 the
difference between the two rotations for biomass yield was significant (p< 0.04) perhaps
indicating that with time the difference between the two rotation is becoming more
pronounced. A significant increase in biomass yield was observed at the first increment of
Table 3-3 Biomass yield, nitrogen uptake, and carbon to nitrogen ration of winter wheat of small plot research experiment for 1996
and 1997 growing seasons.
Previous crop
Fertilizer N
Oat-wheat
Biomass
kg ha-1
1996
N uptake
1997
1996
1997
Clover-wheat
C:N ratio
1996
1997
Biomass
1996
kg ha'
N uptake
1997
C:N ratio
1996
1997
1996
1997
kg ha-1
0
5660
2965
44
20
171
181
7140
9420
59
57
175
274
56
9292
10047
64
54
201
336
15951
16726
120
94
194
282
112
15836
17245
109
101
209
284
15979
20814
133
143
160
189
168
16734
18620
131
140
152
262
17603
21776
135
168
165
153
224
19741
19525
156
174
125
139
21976
21479
215
225
103
104
4506
3151
38.4
25.5
24.4
64.0
4506
3151
38.4
25.5
24.4
64.0
21
13
22
14
10
19
21
13
22
14
10
19
PLSD (0.05)
CV (%)
105
N fertilizer for both rotations over years (Table 3-3). In 1996, increasing N fertilizer from
100 to 150 kg N ha-1 did not increased the biomass yield in either rotation. In 1997,
biomass yield of wheat following clover was significantly higher than wheat following
oats. In wheat following clover, increasing N fertilizer from 100 to 200 kg ha-1 did not
significantly increased biomass yield (Table 3-3). The biomass 1997 yield of wheat
following clover with no fertilizer N was 6500 kg ha1 higher than the biomass yield of
wheat following oats.
Nitrogen uptake and biomass yield in the 1996 unfertilized Stephens plots showed
the same pattern as it was observed in the Hypslop farm rotation experiment (Fig. 3-6). At
early growth stages, Feekes 3 to Feekes 5, N uptake was rapid. Maximum N uptake was
achieved at Feekes 8 (May 8). There was litte change in total N uptake from Feekes 8 to
maturity. Biomass yield increased linearly from Feekes 3 to Feekes 8. Highest increase in
biomass yield was observed at Feekes 8 to Feekes 10.1. Maximum biomass yield was
obtained at Feekes 10.1 and beyond that biomass accumulation leveled off.
Conclusions
The amount of N taken up by spring wheat was different among cultivars. The
pattern of plant N uptake was same for all five spring cultivars. Maximum N uptake for all
five cultivars was observed at approximable 1100 accumulated growing GDD, before
Feekes 10. The maximum N uptake rate, 0.038 kg N GDD-1, occurred at 750 GDD. On
calendar day bases, the range of N uptake was about 50 days, starting from April 25 and
ending at June 15. The peak N uptake was observed at May 30, approximable 35 days
106
10000
80
70
8000
60
50
6000
'Ia.' 40
4000
too 30
..4A1 20
2000
10
0
0
3-8
3-23
4-8
4-25 5-13
6-2
6-26 7-13
Sampling Date
o Biomass
N Uptake
Fig. 3-6: Accumulative biomass yield and nitrogen uptake of
winter wheat from unfertilized plot during 1996 growing season.
107
after Feekes 2.
Nitrogen uptake in winter wheat was significantly affected by rotations. Wheat
following clover had greater N uptake at all sampling dates for both levels of N over two
years as compare to wheat following oat. Significant differences for rate and time of
maximum uptake between rotations were also observed. The maximum rate of N uptake
for wheat following clover was observed at approximable 1300 accumulated GDD, while
the maximum rate of N uptake for wheat following oats was at 2000 GDD.
108
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rates and anthesis from air temperature. Agron. J. 76: 829-835.
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Nitrogen and phosphorus concentration and content by plant development stages.
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111
CONCLUSIONS
Soil mineralizable nitrogen estimated by the 7-day anaerobic incubation method
correlated well with field-measured N availability. A linear relationship was found between
soil mineralizable N test results and soil supplied N. A more than four fold increase in soil
supplied N values, 20 to 110 kg N 11', was observed when the soil mineralizable N test
values increased from 14 to 29 mg N kg"'. No consistent rotation effect was observed for
wheat following clover or corn while rotation effects were obvious for wheat following
oat and wheat following grass. Wheat following oat had very low soil mineralizable N test
values while wheat following grass had comparatively high soil mineralizable N test
values. Our results indicate that soil mineralizable N test values estimated by the 7-day
anaerobic incubation method satisfactorily predict approximate soil N availability in
western Oregon soils and that results can be used to adjust fertilizer N requirements in
western Oregon.
Response of winter wheat to fertilizer N varied greatly among rotations and years
in this study. Wheat following corn was highly responsive to added fertilizer N while
wheat following grass seed was less responsive. Wheat following grass seed had high soil
supplied N which depressed the yield even at moderate fertilizer N rates. This finding
contradicts conventional wisdom suggesting that higher N rates are needed following
grass. This study documents a difference between perennial grasses and cereal grain crops
in rotation.
112
In examining the N uptake pattern of spring and winter wheat it was observed that
maximum N uptake for spring wheat was at a approximately 1100 accumulated growing
GDD, before Feekes 10. The maximum N uptake rate, 0.038 kg N GDD-1, occurred at
750 GDD. The peak N uptake was observed at May 30, approximately 35 days after
Feekes 2. Nitrogen uptake in winter wheat was significantly affected by rotations.
Significant differences for rate and time of maximum uptake between rotations were
observed. The maximum rate of N uptake (0.4-0.5 kg N GGD-1) for wheat following
clover was observed at approximately 1100 GDD, while the maximum rate of N uptake
(0.1-0.2 kg N GGD-1) for wheat following oats was at 1300 GDD.
113
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APPENDIX
Appendix Table 1. Agronomic data of wheat following clover for 1994-95 growing season (Helle Ruddenklan site)
Maturity
Feekes 5
9-m samples
Treatment
Kg ha'
DM
N cont
Plant he
1000 Sw9
Tw
Kg ha'
(%)
(cm)
(g)
(kg ili3)
( %)
Plot
Yield
Grain
chaff
Straw
Protein
DM
N cont.
DM
N
Yield
N
Kg ha
%
Kg ha'
%
Kg ha'
%
Kg ha'
0
524
4.29
76
58.2
529
8.02
7666
0.29
1228
0.59
6194
1.38
5007
56
598
4.28
84
59.0
548
8.18
10247
0.39
1602
0.53
7325
1.37
6163
112
676
4.48
82
58.4
503
8.35
9782
0.39
1784
0.67
8376
1.60
6028
168
676
4.05
88
58.2
558
8.77
12436
0.49
2124
0.86
9581
1.62
6756
0
824
3.98
76
57.8
515
8.25
11086
0.30
1003
0.42
4837
1.37
5033
56
674
3.96
85
57.9
498
8.23
9283
0.36
1612
0.61
7510
1.43
5793
112
588
4.37
86
57.4
575
8.66
10503
0.41
1831
0.50
8001
1.49
6226
168
567
4.04
86
57.0
554
8.69
11587
0.33
2073
0.79
9413
1.58
6114
0
507
4.31
74
57.5
537
7.96
7518
0.35
1200
0.54
5546
1.33
4812
56
493
3.98
84
57.5
557
8.42
9002
0.36
1479
0.74
6912
1.36
5239
112
532
3.90
85
58.0
576
8.44
10050
0.51
1715
0.78
8271
1.44
6162
168
750
4.23
87
57.7
544
9.02
11512
0.43
1833
0.71
8622
1.70
5905
Plant height, 1111Seed weight,
Test weight
Appendix Table 2. Agronomic data of wheat following clover for 1995-96 growing season (Helle Ruddenklan site)
Maturity
Feekes 5
Treatment
Kg ha'
DM
Kg ha'
N
(%)
Plant htl
(cm)
1000 Swill
T«w§
(g)
(kg m-3)
(%)
Grain
Straw
Protein
DM
N cont.
Yield
N cont.
Kg ha'
%
Kg ha'
%
Yield
Kg ha'
0
737
3.99
80
55.2
746
7.73
5582
0.22
4745
1.24
4858
56
620
4.05
88
56.0
744
7.34
7751
0.20
6314
1.19
6161
112
710
3.61
88
58.4
749
8.44
8951
0.34
7801
1.73
7979
168
694
3.76
88
58.2
759
8.91
9026
0.31
7526
1.43
8905
224
741
4.16
91
56.4
757
10.24
11033
0.45
8295
1.81
9060
0
635
4.30
82
13:
746
7.65
5388
0.21
4676
1.28
4765
56
745
4.00
88
57.4
748
7.86
7045
0.21
5607
1.31
6680
112
631
4.01
93
57.0
746
8.27
10489
0.32
6901
1.34
7990
168
545
4.45
93
56.6
760
9.08
8120
0.44
7395
1.57
8654
224
502
4.00
93
57.5
767
9.96
10727
0.50
8676
1.84
9535
0
561
4.62
80
gN
747
7.69
5063
0.19
4876
1.30
4469
56
643
4.46
88
57.7
745
7.84
11414
0.22
6864
1.28
6715
112
467
4.42
96
56.3
753
8.52
11496
0.29
8283
1.41
7993
168
459
4.48
91
58.1
760
9.22
10589
0.36
8045
1.52
8823
224
737
4 25
93
54.3
752
9 91
13433
0 61
9977
1 99
8653
¶ Plant height, 7 Seed weight, § Test weight
Appendix Table 3. Agronomic data of wheat following corn for 1994-95 growing season (Volker site)
Maturity
Feekes 5
9-m samples
Treatment
Kg ha'
DM
N cont
Plant he
1000 swn
Tw*
Kg ha'
(%)
(cm)
(g)
(kg ni3)
Protein
(%)
Plot
Yield
Grain
chaff
Straw
DM
N cont.
DM
N
Yield
N
Kg ha
%
Kg ha'
%
Kg ha'
%
Kg ha'
0
951
4.38
76.7
45.7
725
7.53
12634
0.36
1190
0.63
4872
1.26
4199
56
577
4.21
86.6
44.1
735
7.47
13146
0.34
1756
0.41
6645
1.33
6261
112
833
3.46
90.2
41.9
738
8.11
14130
0.42
2023
0.8
8622
1.42
7150
168
879
4.56
90.7
38.3
744
9.23
17067
0.57
1061
1.11
10168
1.79
7970
0
682
5.50
74.4
44.8
737
7.86
6313
0.29
1537
0.53
6626
1.21
5367
56
708
4.19
87.1
41.6
735
8.10
10526
0.37
2112
0.45
8314
1.27
6611
112
689
4.24
92.2
39.2
734
8.99
13693
0.43
2101
0.73
9593
1.69
7578
168
485
3.53
90.9
41.0
749
9.99
14795
0.65
2193
0.76
9470
1.73
7707
0
761
3.97
79.5
44.3
728
8.71
9387
0.28
1222
0.68
5681
1.33
6056
56
833
5.17
86.9
44.5
745
8.37
12897
0.38
1915
0.57
6626
1.41
6013
112
551
4.34
92.7
40.0
747
9.14
15934
0.48
2379
0.77
9785
1.67
7920
93.0
3.37
833
168
Plant height, uu Seed weight, § Test weight
39.7
752
10.22
16643
0.7
2805
0.59
11187
1.78
8194
Appendix Table 4. Agronomic data of wheat following corn for 1995-96 growing season (Volker site)
Maturity
Feekes 5
Treatment
Kg ha-1
DM
Kg ha'
N
( %)
Plant htll
(cm)
1000 Sw"
TIO
(g)
(kg ni3)
(%)
Grain
Straw
Protein
DM
N cont.
Yield
Kg ha-1
%
Kg ha-1
Yield
N cont.
Kg ha'
0
302
4.99
80
50.7
753
6.4
6060
0.20
3760
1.10
3932
56
411
5.02
88
50.1
753
6.7
12295
0.23
6848
1.15
5642
112
363
5.03
90
51.2
760
7.6
15413
0.33
7790
1.41
8133
168
332
4.93
92
52.1
756
7.7
18859
0.42
7265
1.51
7811
224
341
5.39
96
51.4
769
9.0
17552
0.53
8681
1.87
7748
0
341
5.09
82
52.1
763
7.0
8900
0.22
4892
1.16
4858
56
428
5.24
88
51.1
756
7.0
11857
0.20
6440
1.21
6854
112
319
4.64
93
51.2
765
7.5
14975
0.25
7608
1.31
7503
168
315
5.45
96
52.1
772
8.1
13974
0.40
7214
1.51
8280
224
367
4.04
97
52.4
772
9.1
15208
0.63
7287
1.86
8505
0
428
5.23
80
55.7
758
6.8
9170
0.18
5089
1.11
4889
56
389
4.88
88
50.1
761
7.0
15274
0.20
5279
1.16
6039
112
354
4.78
96
51.2
771
8.1
15632
0.31
7498
1.39
8056
168
363
5.05
98
52.1
772
8.2
16179
0.49
6359
1.52
8242
98
5.11
Plant height, 111 Seed weight, § Test weight
51.4
774
9.0
14668
0.51
7097
1.82
8502
224
385
Appendix Table 5. Agronomic data of wheat following grass for 1994-95 growing season (Van Leeuwen site)
Maturity
Feekes 5
9-m samples
Treatment
Kg ha-1
DM
Kg ha'
N cont
Plant he
1000 SwIr
Tw
Protein
(%)
(cm)
(g)
(kg in-3)
(%)
Plot
Yield
Grain
chaff
Straw
DM
N cont.
DM
N
Yield
N
Kg ha
%
Kg ha'
%
Kg ha'
%
Kg ha'
0
735
3.14
71
56.8
483
8.52
7078
0.24
960
0.66
3967
1.43
3180
67
604
4.06
87
57.8
548
9.19
12372
0.45
1817
0.70
7240
1.44
4989
134
649
3.94
87
56.8
470
9.21
18121
0.66
2733
0.84
11574
1.69
5298
201
846
3.40
93
57.2
470
10.04
14786
0.51
2506
0.65
10870
1.70
5978
0
407
4.24
71
56.9
535
8.63
7448
0.43
1102
0.70
4614
1.43
3184
67
577
3.82
86
57.7
535
8.34
12446
0.43
1745
0.67
7522
1.38
5279
134
584
4.31
87
57.0
509
9.35
13319
0.62
1979
0.69
7028
1.69
5090
201
663
3.76
91
57.0
464
9.95
17150
0.65
2034
0.70
8698
1.63
5903
0
525
4.36
76
57.9
580
8.68
8060
0.32
1176
0.60
4824
1.32
3211
67
551
3.91
85
58.1
567
8.21
11316
0.49
1563
0.62
6341
1.42
6231
134
781
3.88
87
58.1
509
8.95
12882
0.62
1835
0.57
7544
1.58
7173
201
590
3.97
94
57.9
535
9.90
14537
0.64
2184
0.54
8928
1.75
6984
¶ Plant height, 1111 Seed weight,
§ Test weight
Appendix Table 6. Agronomic data of wheat following grass for 1995-96 growing season (Chipman site)
Maturity
Feekes 5
Treatment
Kg ha-1
DM
Kg ha-1
N
(%)
Plant he
(cm)
1000 swn
(g)
TNO
(kg in")
(%)
Grain
Straw
Protein
DM
N cont.
Yield
N cont.
Kg hal
°A
Kg ha-1
°A
Yield
Kg ha-1
0
907
3.79
87
745
8.7
9689
0.29
6564
1.45
4876
56
870
3.87
87
743
9,1
12946
0.32
8445
1.59
6140
112
1061
4.23
87
751
10.1
8658
0.56
7482
2.00
7285
168
1222
3.98
93
741
11.4
13640
0.59
7545
2.21
6322
224
1140
3.60
96
735
12.2
16053
1.11
6182
2.45
5763
0
1084
3.64
86
741
8.8
8345
0.27
5013
1.47
4212
56
1114
3.98
87
738
9.3
12039
0.31
6514
1.61
5445
112
1091
3.53
91
728
10.3
13990
0.53
7895
2.00
5620
168
971
3.44
95
730
11.0
13296
0.71
6426
2.24
5804
224
1234
3.72
95
702
12.4
16878
1.08
7995
2.51
4914
0
930
2.89
84
723
9.1
5995
0.31
4657
1.45
3874
56
979
3.66
87
731
9.1
11896
0.40
7132
1.64
4812
112
919
3.93
92
722
9.7
10789
0.53
6170
1.70
5209
168
821
3.16
98
684
11.2
10989
0.54
5482
2.05
4879
98
2 25
900
224
Plant height, 111 Seed weight, § Test weight
688
11.7
13658
0 81
7889
2 23
5238
132
Appendix Table 7. Soil test results through winter months of all on-farm
sites for 1994-95 growing season.
Mineralizable N
Date of
Soil depth
NO3-N
NH4-N
sampling
cm
mg kg-1
mg kg-1
mg kg-1
Clover-wheat rotation
1-05-95
2-25-95
0-30
30-60
60-90
36-48
2.7
2.9
0-30
30-60
60-90
36-48
5.5
3.4
3.5
3.7
3.5
1.6
4.5
11.6
10.1
9.6
5.6
0.4
1.9
11.8
9.1
3.7
2.1
2.1
2.3
16.1
4.9
2.4
3.3
19.8
6.5
1.9
2.6
Corn-wheat rotation
11-1-94
0-30
30-60
60-90
3.6
2.5
3.8
12-22-94
0-30
30-60
60-90
36-48
4.2
2.8
0-30
30-60
60-90
5.2
5.0
0-30
30-60
60-90
36-48
1-23-95
2-7-95
1.4
2.4
4.0
3.0
5.4
1.1
12.1
1.2
0.8
5.5
3.5
4.8
5.6
3.3
2.8
1.5
1.2
1.1
1.3
14.6
8.2
0-30
30-60
60-90
16.2
5.8
17.5
3.0
3.0
4.9
5.9
0-30
30-60
60-90
36-48
3.4
9.0
1.6
3.1
7.1
0-30
30-60
60-90
36-48
4.5
3.8
6.0
3.0
4.9
3.3
Grass-wheat rotation
11-1-94
12-22-94
2-6-95
2.4
1.8
23.7
5.7
6.7
5.6
1.6
1.7
25.1
7.5
133
Appendix Table 8. End of season soil test results of clover-wheat rotation for
1994-95 growing season.
NO3-N Mineralizable N
Block
Treatment
NH4 -N
Depth
mg kg'
mg kg-'
mg kg-1
1
1
3.4
1
1
2
3.5
1
1
3
2.8
1
2
1
2
2
2
3
2.1
1.6
1.2
1
3
1
1.8
1
3
2
0.8
1
3
3
1
1
2
1
4
4
4
2
1
1
1
1
2
2
1
3
1
2
1
3
2
2
2
1
2
2
2
2
3
2
2
2
2
2
2
3
1
3
2
3
3
4
4
4
2
3
1
1
3
1
2
3
1
3
3
2
3
2
2
2
3
3
1
3
3
2
3
3
3
3
4
4
4
2
3
3
3
Treatments
Depth
1
1
1
= 0 kg N hi
1
3
1
3
1
3
2 = 56 kg N hi
= 30 cm 2= 60 cm 3= 90 cm
1.3
4.3
2.9
4.1
4.1
3.2
2.6
4.9
3.2
2.7
4.4
2.8
2.8
4.1
3.3
3.2
4.0
3.6
3.0
4.4
4.0
3.8
3.9
3.9
2.9
3.8
2.9
2.6
3
4.6
0.4
0.4
3.6
0.4
0.4
4.4
0.4
0.4
4.2
0.4
0.4
4.7
0.5
0.4
4.3
0.4
0.4
4.9
0.4
0.4
4.4
0.4
0.4
3.6
0.6
0.4
5.1
0.5
27.3
8.6
23.7
10.4
29.8
9.2
25.7
9.3
29.5
14.6
29.1
11.4
32.2
9.5
34.1
12.6
31.2
17.3
32.2
16.3
0.4
7.1
35.2
0.7
0.4
5.0
0.6
0.4
17.8
33.8
15.3
= 112 kg N hi 4 = 168 kg N h-1
134
Appendix Table 9. End of season soil test results of corn-wheat rotation for
1994-95 growing season.
Treatment
Block
Depth
NOrN Mineralizable N
NH4 -N
mg kg-1
mg kg-1
mg kg-1
17.0
10.2
1
1
1
1
2
2.7
2.0
3.9
1
1
1
3
2.1
1
1
2.4
2
1.8
1
2
2
2
3
1
3
1
1
3
2
1
3
3
1
4
4
4
2
5.8
3.8
2.7
2.1
3.2
2.2
2.6
2.2
2.4
0.6
3.7
0.9
0.4
3.3
1
1
1
2
2
2
2
2
2
2
2
2
2
2
2
1
1
2
1
3
1.7
7.6
2.2
2
2
2
2
3
1.6
1
4.3
2
2.0
3
3
3
1
3
1.5
4
4
4
2
2.5
5.9
3
1.8
1
1
2.2
1
2
1.7
1
3
2
2
2
3
3
3
3
Treatments
Depth
3
1
3
3
3
3
3
3
3
3
3
3
1
1
1
2
3
1
2
1.5
2.0
2.6
1.5
2.2
2.2
2.3
2.3
1.0
15.5
9.4
26.7
10.0
1.2
0.5
3.1
24.7
1.1
15.8
0.5
3.1
1.0
19.8
14.6
0.4
3.4
1.0
0.5
3.3
1.0
0.4
3.9
17.2
12.4
21.4
14.4
24.7
1.2
16.2
0.4
2.2
0.4
0.4
22.1
13.2
1.5
19.9
0.7
0.4
18.1
1.0
1.0
22.6
12.7
0.4
25.1
4
0.4
1
16.9
4
0.9
2
2.1
4
3
2.1
0.4
1 = 0 kg N If' 2 = 56 kg N If' 3= 112 kg N WI 4= 168 kg N
1 = 30 cm 2= 60 cm 3= 90 cm
3
3
135
Appendix Table 10. End of season soil test results of grass-wheat rotation for
1994-95 growing season.
Block
Treatment
Depth
NO3-N Mineralizable N
NH4-N
mg kg'
mg kg-1
mg kg-1
2.8
7.9
1.4
21.3
11.7
1
1
1
1
1
2
1
1
3
1.9
6.1
1
2
1
3.2
0.4
0.8
2
2
2
1.8
1.3
3
1
2.4
2.0
0.6
3
3
3
2
1.5
3
2.1
1
1
1
1
1
1.0
1.0
0.5
2.1
10.6
9.7
29.3
7.7
1
4
4
2
1
4
3
1
1
2.4
5.9
2.4
5.5
1
2
1.8
10.5
1.7
1
3
1
2.3
2.7
0.7
9.4
2
1.9
1.6
3
2.6
5.6
0.5
1
2
2
2
2
2
2
2
2
2
1
2
2
2
3
3
3
1
2
3
2
2
4
4
4
2
3
1
1
3
1
2
3
1
3
3
3
2
2
2
2
3
3
3
3
3
3
3
Treatments
Depth
1
3
1.9
2.1
6.8
1.7
2
3.5
29.3
10.6
1.5
0.7
9
1.5
30.5
12.9
31.5
13.4
24.9
8.9
0.8
7
1.1
0.5
8.7
29.1
12.8
30.3
15.4
3
2.7
2.8
3.4
3.2
3.4
3
1
3.8
0.7
0.4
6.6
3
3
2
2.4
1.1
13.3
3
4
4
0.4
5.8
29.9
2
1.1
16.1
4
3
2.5
2.7
2.8
2.9
1
2
1
1 = 0 kg N hi
1 = 30 cm
2 = 67 kg N 11-1
2= 60 cm 3= 90 cm
1.3
0.5
4
29.2
6.8
24.1
0.5
3= 134 kg N hi 4 = 204 kg N
136
Appendix Table 11. Soil test results through winter months of clover-wheat
rotation for 1995-96 growing season.
NO3-N Mineralizable N
Date of
Soil depth
NH4-N
sampling
cm
mg kg'
mg kg-1 mg kg'
10-27-95
2-16-96
0 Plots
0-30 cm
30-60 cm
60-90 cm
36-48 cm
6.6
0-30 cm
30-60 cm
60-90 cm
3.2
3.4
3.2
21.2
8.0
2.4
75.4
29.0
3.3
2.2
1.4
1.7
17.4
6.4
4.4
Before fertilizer was applied
2-16-96
Plot #
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
10/27/95
pH
5.1
0-30 cm
0-30 cm
0-30 cm
0-30 cm
0-30 cm
0-30 cm
0-30 cm
0-30 cm
0-30 cm
0-30 cm
0-30 cm
0-30 cm
0-30 cm
0-30 cm
0-30 cm
4.5
4.7
4.5
3.6
3.4
3.7
4.4
3.9
3.8
3.6
3.6
5.6
3.8
3.9
3.7
Sample depth 0-12"
P
Mg
ppm
meg/100g
46.0
1.4
3.2
3.1
2.8
2.4
2.4
2.8
2.6
2.3
2.2
2.5
2.0
2.3
1.9
2.1
2.3
Na
17.2
16.8
18.8
17.1
16.0
19.3
16.5
16.0
15.6
14.0
16.7
16.9
18.1
13.7
15.8
OM So4-S
meg/100g
0.08
5.77
10.4
137
Appendix Table 12. End of season soil test results of clover-wheat rotation for
1995-96 growing season
Block
Treatment
NO,-N Mineralizable N
Depth
NarN
1
1
1
1
1
2
1
1
3
1
2
1
1
2
2
1
2
3
mg kg-'
2.8
2.9
mg kg-'
mg kg'
3.2
0.9
0.4
11.0
3.1
3.5
2.1
10.7
0.4
4.0
0.0
2.3
2.7
1
3
1
1
3
2
1
3
3
1
4
1
1
4
2
1
4
3
1
5
1
3.1
1
5
2
3.8
1
5
3
2
1
1
1
2
1
3
2.7
2.3
2.5
3.6
2
2
2
2
2
2
2
3
1
2
2
2
2
2
2
2
2
3
2
3
3
4
4
1
3.1
2
2.6
4
3
5
5
5
2
3
3
3
1
1
1
2
3
3
3
2
2
2
3
2
3
3
3
1
3
3
2
3
3
3
3
4
4
4
5
3
3
3
3
2
2
1
5
1
2.9
2
3.1
3
1
3.1
3.9
2.3
2.8
3
1
1
2
2.8
2.9
2.3
4.0
2
3
1.1
0.2
3.6
1.1
0.2
2.8
0.6
0.0
3.0
0.9
0.2
2.9
0.8
0.3
4.8
1.5
0.0
10.4
4.4
0.0
13.8
5.9
0.0
17.2
5.9
0.0
12.9
7.0
0.0
11.3
4.4
0.0
16.4
6.9
0.0
11.5
6.2
0.0
11.9
6.1
0.0
3.3
13.7
5.5
1.1
2.4
2.8
3.5
2.4
1.0
3.3
1.4
3.2
3.5
12.9
7.1
0.5
0.3
3.3
1.2
0.4
2.6
0.8
3
1
0.5
2.6
0.6
0.1
2.0
0.5
0.1
3.0
0.9
0.2
3.9
6.4
0.0
0.0
12.1
8.0
0.0
18.4
6.3
0.0
12.7
8.5
0.0
0.4
Treatments 1 = 0 kg Nit' 2 = 56 kg N hi' 3 = 112 kg NW' 4 = 168 kg N11-15 = 224 kg N11-1
Depth
1 = 30 cm 2= 60 cm 3= 90 cm
3
5
138
Appendix Table 13. Soil test results through winter months of corn-wheat
rotation for 1995-96 growing season
Date of
Soil depth
NO3-N Mineralizable N
NH4-N
sampling
cm
mg kg-1
mg kg-1
mg kg-1
01/12/96
0-30 cm
30-60 cm
60-90 cm
36-48 cm
4.5
2.5
2.7
2.4
4.5
5.9
21.3
13.0
03-06-96
0 Plots
0-30 cm
30-60 cm
60-90 cm
12.9
12.9
14.5
4.5
8.8
7.2
45.6
16.8
24.1
Before fertilizer was applied
2-13-96
Plot #
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
0-30 cm
0-30 cm
0-30 cm
0-30 cm
0-30 cm
0-30 cm
0-30 cm
0-30 cm
0-30 cm
0-30 cm
0-30 cm
0-30 cm
0-30 cm
0-30 cm
0-30 cm
5.1
4.1
2.2
5.8
7.0
5.0
8.7
1.8
1.8
1.8
8.1
9.3
2.9
3.0
1.7
1.9
1.7
1.8
4.8
3.4
8.1
4.7
3.4
5.7
7.0
25.0
24.9
28.6
26.5
27.0
34.3
20.7
28.0
24.4
22.7
34.4
27.4
25.0
27.4
24.1
2.1
2.3
2.0
3.6
2.3
01/12/96
pH
6.0
Na
meq/100g
% OM
meq/100g
Mg
meq/100g
14.6
0.14
0.14
6.9
P
ppm
K
Ca
ppm
50.0
406
139
Appendix Table 14. End of season soil test results of corn-wheat rotation for
1995-96 growing season
Block
Treatment
Depth
1
1
1
1
1
2
1
3
2
1
2
2
2
1
3
1
1
3
2
1
3
3
1
2
1
4
4
4
1
5
1
1
5
5
2
1
1
1
2
1
3
2
2
2
2
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
2
2
2
2
1
NO,-N
mg kg-1
mg kg-1
mg kg-1
1.8
16.7
7.7
2.8
3.2
3.7
3.4
3
1
3.3
3.6
3.2
3.8
3
4.1
2.8
3
1
2.7
3.2
3.6
2.5
3
3
1
3
2
3
3
4
4
4
5
1
2.9
2.7
0.7
0.5
1.8
19.9
0.8
0.3
0.7
0.4
0.2
0.9
0.5
0.2
7.8
18
15.7
8.5
0.3
3
0.4
0.7
0.4
6.9
1
3.9
3.3
1
2
5
3
3
1
1
3
1
2
3.1
4.8
0.4
0.8
0.5
3
1
3
3
1
3
2
3.2
3
2
2
2
3
3
1
3
3
2
3
3
3
3
3
2.9
2.9
15.6
7.7
8.6
2
3
10.2
1.8
5
3.4
3.2
20.4
0.7
0.7
0.8
0.6
0.5
0.7
0.3
1.2
0.5
0.3
1.6
2
Mineralizable N
NH4 N
13.9
18
18
7.7
19.6
11.4
0
14.4
10.1
0.1
0.6
0.1
0
20.8
7.3
1
20.6
0.3
12.5
0.2
1.6
23.3
12.2
0.5
3
3
0.1
20.4
1
2.2
3
5
4.2
3
5
10.9
3.3
0.9
2
3
0.4
3
5
Treatments 1 = 0 kg N 11-1 2 = 56 kg N hi 3= 112 kg N11-1 4 = 168 kg N11-1 5 ---- 224 kg N If'
Depth
1 = 30 cm 2= 60 cm 3= 90 cm
3
3
4
4
4
1
2
4.5
4.6
140
Appendix Table 15. Soil test results through winter months of grass-wheat
rotation for 1995-96 growing season
Date of
sampling
10-27-95
Soil depth
cm
NH4-N
0-30 cm
30-60 cm
60-90 cm
36-48 cm
4.5
2.5
2.7
mg kg-1
NO3-N
mg kg-1
Mineralizable N
mg kg'
11.7
5.5
2.6
2.5
76.1
22.5
2.7
2.9
3.2
3.0
35.2
50.5
38.4
38.4
29.0
34.3
31.4
43.6
28.0
33.9
37.2
37.3
25.6
34.7
28.7
Before fertilizer was applied
2-14-96
Plot #
0-30 cm
0-30 cm
0-30 cm
0-30 cm
0-30 cm
0-30 cm
0-30 cm
0-30 cm
0-30 cm
0-30 cm
0-30 cm
0-30 cm
0-30 cm
0-30 cm
0-30 cm
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
pH
6
3.5
3.9
4.5
3.0
4.9
4.7
5.0
5.0
3.4
4.2
3.3
3.7
2.9
3.9
3.2
1.9
2.8
2.8
2.5
2.3
2.4
2.9
2.3
2.3
2.4
2.5
Na
ppm
ppm
Mg
meq/100g
meq/100g
61
172
1.3
0.07
% OM So4-S
5.58
7.1
141
Appendix Table 16. End of season soil test results of grass-wheat rotation for
1995-96 growing season.
Block
NO,-N Mineralizable N
Treatment
Depth
NI-14-N
mg kg'
mg lie
mg kg'
1
1
1
1
1
2
1
1
3
1
1
2
1
2
2
2
1
3
1
1
3
2
1
3
3
1
1
4
4
2
1
4
3
1
5
1
1
5.2
3.3
5.3
5.3
3
4.8
3.8
4.90
5.30
1.20
0.75
4.7
2
3.1
30.20
10.50
4.10
5.30
1
1
2
2
2
2
2
2
2
2
2
2
2
2
2
2
1
2
1
3
2
2
2
2
3
1
4.5
3.8
4.50
8.70
1.50
0.80
23.80
5.80
0.70
32.50
9.90
4.70
7.60
3
1
4.8
3
2
4
3
3
4
4
4
2
5.4
3.8
3
1
2
4.3
2.5
3
3.9
4.2
1
1
3
1
2
3
1
3
3
1
3
2
2
2
3
2
3
3
3
1
4.1
3
3
2
4
3
3
3
3
4
4
4
2
1
4.4
3.2
4.8
3.6
3
3
5
5
2
3
5
3
1
1.10
0.75
3.9
2.7
3
1
40.50
3.60
32.20
3.30
24.80
4.50
52.30
3.90
1.60
3
3
1.10
1
1
3
0.75
4.80
21.00
6.60
2
3
1.10
4.9
3.9
1
5
5
5
5
5
7.20
4.6
3.4
1.10
0.75
1.70
0.90
6.30
1.40
0.90
5.30
1.40
1.20
13.00
2.90
1.60
19.60
3.50
1.80
60.10
8.20
17.70
3.00
21.00
5.20
30.10
2.80
22.90
4.80
41.40
4.50
16.20
1.50
0.00
45.10
6.20
15.90
1.30
14.80
3.20
21.80
4.10
Treatments 1 = 0 kg N fil 2 = 56 kg N11-1 3 = 112 kg N 11-1 4 = 168 kg N hi 5 = 224 kg N Fr'
Depth
1 = 30 cm 2= 60 cm 3= 90 cm
142
Appendix Table 17. Agronomic data of Hyslop Farm small plot research site for 1995-96
growing season.
6-in sample
Block
Treatment Rotation
1
1
1
2
1
1
3
1
1
4
1
1
1
1
2
1
3
1
2
2
2
2
4
1
1
2
2
2
2
2
2
2
3
2
4
2
2
2
1
2
3
4
1
1
1
1
2
2
1
3
1
2
3
1
3
3
1
4
3
1
1
3
2
3
Straw
Kg/ha
N%
2591
4198
2460
3772
4986
2895
5855
2394
5437
5453
7470
2435
8905
9610
9553
9602
10562
8856
8446
9414
11160
0.29
0.25
0.23
0.29
0.26
0.28
0.26
0.23
0.25
0.21
0.22
0.23
0.22
0.25
0.23
0.24
0.25
0.19
0.24
0.21
10381
7191
0.27
0.28
0.29
0.35
0.34
0.25
0.29
0.35
0.26
0.25
0.27
0.43
0.33
0.38
0.33
0.53
0.5
0.41
0.36
3
3
2
2
2
4
3
2
7528
1
4
1
2
4
1
3
4
4
4
4
4
4
4
1
5
1
2
5
1
3
5
1
4
5
1
1
5
2
5
2
2
3
5
5
2
2
10545
11882
5166
10365
10652
8971
11037
11431
11136
9471
10758
15252
11603
9766
16064
11373
4
1
2
3
4
Rotation :
Treatment :
1
1
2
2
2
2
0.3
Grain
Kg/ha N %
1845
3067
2075
2632
2870
2132
4535
2895
3756
3985
4822
3813
6527
6084
6880
6642
7175
6199
5929
6765
8725
7708
5314
5912
7273
9299
4100
8307
5396
7060
6732
9135
8208
7396
7970
8774
8102
9733
12439
8823
Yield
Kg/ha
Hole plot
Protein
Tw
(g/qt)
(%)
1.30
1.83
1.75
1.57
2231
2375
2464
2119
3984
3034
4790
2978
4427
3375
3741
3830
4666
5361
5876
5537
5872
5853
6004
5439
6560
6613
6723
7823
7000
7449
7703
6272
7114
6844
7762
7176
7639
7821
8255
8094
9043
8748
8038
873
866
871
865
868
853
872
872
856
850
836
841
855
859
861
858
850
845
857
844
867
862
866
857
858
853
853
855
862
870
864
872
865
865
847
868
870
858
872
1.49
8343
859
1.43
1.51
1.47
1.57
1.53
1.53
1.56
1.68
1.31
1.24
1.28
1.27
1.57
1.51
1.40
1.56
1.40
1.28
1.33
1.40
1.56
1.63
1.50
1.46
1.32
1.44
1.42
1.42
1.54
1.43
1.47
1.54
1.48
1.47
1.54
1 = Oat-wheat
2 = Clover-wheat
1 =0 kgN11-1
4= 150 kg N
2 = 50 kgNlil 3 = 100 kg1\1111
5 = 200 kg N
8.43
8.58
8.61
8.13
8.45
8.64
8.46
8.86
8.12
7.36
7.76
7.17
8.30
8.51
7.94
8.36
7.98
7.71
7.90
7.20
8.56
8.49
8.12
8.39
8.03
7.91
7.84
7.62
8.17
8.23
8.10
8.34
8.37
8.25
8.47
8.41
8.91
9.07
8.44
8.25
143
Appendix Table 18. Agronomic data of Hyslop Farm small plot research site for 1996-97
growing season.
6-m sample
Block
Treatment Rotation
1
1
1
2
1
1
1
3
1
4
1
1
1
1
2
1
3
1
4
1
2
2
2
2
1
2
1
2
2
1
3
1
1
2
2
2
2
2
3
4
2
2
2
2
2
2
4
1
1
3
1
2
3
1
3
3
1
4
3
1
1
3
2
2
3
2
3
3
2
4
3
2
1
4
4
4
4
1
4
4
2
2
2
2
2
3
4
1
2
1
1
1
1
4
4
5
2
5
1
3
5
5
1
4
1
5
2
2
5
3
5
2
2
4
5
2
3
4
Rotation :
Treatment :
1
1
1 = Oat-wheat
Straw
Kg/ha
1673
1624
1591
1886
5807
6324
5643
4995
6389
5495
4446
7603
9129
14985
11713
7644
12680
8604
10187
9662
12352
11376
14321
11901
9613
10696
11393
9408
13739
13607
12156
12680
11138
11762
8661
12680
13148
13181
12393
N % Kg/ha
0.20
0.35
0.26
0.23
0.17
0.15
0.17
0.18
0.13
0.15
0.16
0.12
0.15
0.16
0.15
0.22
0.14
0.17
0.19
0.17
0.23
0.29
0.25
0.22
0.23
0.32
0.13
0.14
0.30
0.26
0.35
0.32
0.36
0.33
0.36
0.31
0.46
0.44
0.39
0.52
10843
2 = Clover-wheat
1 = 0 kg N hi' 2 = 50 kg N 11-'
4= 150 kg N hi 5 = 200 kg N h1
3
Hole plot
Tw
Protein
(%)
Kg/ha (g/qt)
Yield
Grain
N%
1288
1043
1024
1190
9621
9137
7439
8727
8612
7833
7308
10105
10220
10622
8801
1.14
1.34
1.25
1.27
1.22
1.26
1.31
1.40
1.09
1.15
1.10
1.20
1.19
1.25
1.30
1.50
1.16
1.17
1.26
1.28
1.38
1.33
1.37
1.48
1.31
1.63
1.29
1.46
1.55
1.48
1.51
1.59
1.46
1.80
1.50
1.72
1.77
1.73
1.71
2839
3756
3218
3815
3022
2833
2594
3025
4967
5517
5889
4851
4909
4464
4596
5398
6312
6849
7061
6179
5194
6188
6261
6675
7712
7997
7984
7780
6961
7209
7305
8070
7140
7843
7689
840
836
834
837
831
842
841
836
827
820
825
824
838
837
841
846
839
837
831
833
849
852
856
860
843
847
839
846
865
859
858
869
850
871
849
862
865
870
864
6709
1.87
6998
857
1083
1058
1468
1476
3781
4101
4101
2928
4158
3617
3150
5331
5307
6972
6767
4388
8514
6357
6660
6316
7882
8317
9719
7390
8432
8801
7767
8374
= 100 kg N 11-'
7.5
7.9
7.7
7.8
7.9
8.2
8.3
8.3
6.7
7.2
6.8
7.2
7.7
7.9
7.9
8.4
7.2
7.2
7.1
7.1
8.0
8.2
8.2
8.5
8.1
8.1
7.4
7.8
8.6
8.4
8.9
9.2
8.1
9.3
8.3
8.7
9.5
9.4
9.8
10.1
144
Apendix Table 19
Biomass and N uptake of five spring wheat varieties (1997)
Date : 1 = April 25 2 = May 13 3 = May 31 4 = June 22 5 = July 6 = 11 August 1
Variety : 1 = Alpowa 2 = Pennawawa 3 = Treasure 4 = WB963R 5 = White bird
1[GDD
218
218
218
218
218
218
218
218
218
218
218
218
218
218
218
218
218
218
218
218
467
467
467
467
467
467
467
467
467
467
467
467
467
467
467
467
467
467
"G Stage
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
Block
1
2
Date
Variety
1
1
1
1
1
1
4
1
1
1
1
2
1
2
2
3
1
2
4
1
2
1
1
3
2
1
3
3
1
3
4
1
3
1
1
2
1
3
1
4
1
4
4
4
4
1
1
5
2
1
5
3
1
4
1
5
5
5
1
2
1
5
2
3
5
4
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
1
5
1
5
2
5
3
5
4
5
1
5
2
5
3
5
4
5
1
5
2
5
3
5
4
5
1
5
2
N uptake
kg ha'
kg ha-1
63
3
5
Biomass
49
46
52
89
60
66
52
60
75
69
69
63
77
83
1
98
46
69
52
66
809
525
565
574
2
712
2
2
763
1
3
732
548
910
772
769
709
4
1065
4
832
887
852
784
594
2
3
3
3
4
4
5
5
3.3
2.1
2.3
2.2
4.8
2.9
2.7
2.5
3.3
3.4
3.3
2.9
3.7
3.4
4.4
4.0
2.7
3.2
2.3
2.4
31.7
20.3
24.2
22.4
30.4
36.7
28.5
22.9
33.4
28.7
27.5
23.4
45.9
30.8
34.4
27.1
29.8
26.5
145
Appendix Table 19 (continued)
1GDD
IIG Stage Block
Date
Variety
Biomass
N uptake
kg ha'
kg ha'
5
827
29.5
4
2
2
5
1
3
1
6
2
3
1
6
6
3
3
1
4
3
1
6
1
3
20.5
76.5
85.2
70.5
71.6
74.0
6
2
3
6
6
3
3
4
3
2
2
2
2
6
1
3
3
6
6
6
6
2
3
3
3
3
3
4
3
3
1
3
4
6
2
3
6
6
6
3
3
4
3
4
4
4
1
3
5
763
763
763
6
2
3
5
6
3
3
5
6
4
1125
1125
1125
1125
1125
1125
1125
1125
1125
1125
1125
1125
1125
1125
1125
1125
1125
1125
1125
1125
1433
10
10
10
10
10
10
10
10
10
583
2959
3499
2904
3160
3257
4156
2982
3900
3252
3381
3788
2767
4951
5266
4380
4018
3941
3369
2787
2821
9988
7376
10102
9041
7893
9815
8840
7806
6802
9098
7893
7950
467
5
3
467
763
763
763
763
763
763
763
763
763
763
763
763
763
763
763
5
6
763
763
3
5
4
4
1
1
2
4
4
4
4
3
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
1
5
1
2
3
4
1
1
10
10
10
10
2
10
10
10
2
10
10
10
10
10.5
3
4
1
3
4
1
2
3
1
1
2
2
2
2
3
3
3
3
4
4
4
4
5
5
5
5
1
10361
10189
9959
8409
7376
9902
8983
8467
12599
112.7
88.8
97.7
79.6
78.2
105.7
51.7
96.5
128.7
97.6
96.4
79.7
78.8
62.5
69.1
119.9
74.4
140.2
123.8
113.2
91.7
190.1
213.0
123.7
171.9
128.0
161.5
125.6
115.9
160.7
135.0
82.1
127.5
131.7
132.7
142.0
146
Appendix Table 19 (continued)
1GDD
"G Stage Block
1433
1433
1433
1433
1433
1433
1433
1433
1433
1433
1433
1433
1433
1433
1433
1433
1433
1433
1433
1784
1784
1784
1784
1784
1784
1784
1784
1784
1784
1784
1784
1784
1784
1784
10.5
10.5
10.5
10.5
10.5
10.5
10.5
10.5
10.5
10.5
10.5
10.5
10.5
10.5
10.5
10.5
10.5
10.5
10.5
1784
1784
1784
1784
1784
Date
Variety
2
5
1
3
5
1
4
5
1
1
5
2
5
3
5
4
5
2
2
2
2
1
5
3
2
5
3
3
5
3
4
5
3
1
5
2
5
3
5
4
5
4
4
4
4
1
5
5
2
5
5
3
5
5
4
5
5
11
1
2
11
3
11
4
11
1
11
2
6
6
6
6
6
6
1
11
11
3
6
11
4
11
1
6
6
11
2
11
11
1
1
1
2
2
2
2
3
3
3
6
6
4
6
3
11
1
6
11
2
6
11
3
11
4
6
6
6
6
6
6
4
4
4
11
1
11
2
11
3
11
4
1 Growing degree days
" Feekes growth stage
3
4
5
5
5
5
Biomass N uptake
kg ha'
kg ha-1
12800
10533
9586
15125
16474
11394
12198
12111
16158
11911
14063
11337
16158
10476
11738
11509
13001
11824
11423
11214
10590
12690
10562
13690
13000
14041
13805
13633
14723
14051
14264
11853
12341
12653
12886
14379
12838
10339
10935
109.1
110.4
92.1
167.0
152.3
140.0
160.3
130.7
183.9
136.7
153.4
132.5
145.6
130.5
132.3
126.4
134.9
118.9
134.5
117.4
108.0
130.3
111.6
154.6
143.0
163.8
159.0
150.0
148.7
151.7
156.9
118.5
146.4
127.8
141.8
138.5
125.8
122.0
126.9
Appendix Table 20 Data from on-farm-mini plots (1995-96)
Soil Minralizable ¶ Total Soil N at
Growers Name
Feeks 5
N at Feeks 5
Plant N uptake
at Feeks 5
¶ Total Soil N
at harvest
Plant N uptake
at maturity
kg ha -1
mg kg-1
Sam Sweeney
26.7
27.4
26.8
20.0
96
1
2
Hamlin Farms
28.0
25.8
36.7
33.9
110
Dalke Farms Wilco farm
22.0
25.8
13.6
25.8
87
3
Steve Vanger
15.1
47.0
20.2
16.8
59
4
Tom Cranford (Susan Aldrich)
25.2
26.6
22.9
16.4
82
5
Pat Peters
17.2
29.6
28.4
9.0
50
6
Dave Jossi
23.8
27.0
29.9
29.4
75
7
Forest Hills farms
23.2
31.9
21.4
20.8
86
8
Handrics Farm (Paul Camuso)
17.0
37.2
11.3
28.9
50
9
Mark Shmdlin Hard drough
17.2
42.1
30.1
15.1
42
10
11NO3-N and NH4-N