AN ABSTRACT OF THE THESIS OF
Machelle A. Nelson for the degree of Master of Science in Soil Science presented
on December 3, 2002.
Title: N Processing in Grass Seed Crops Differing in Soil Drainage and
Disturbance in West n Oregon, U.S.A.
Abstract
Redacted for privacy
approved:
Stephen M. Griffith
A better understanding of grass seed crop and soil fertility is necessary to
improve fertilizer practices and preserving water quality in Willamette Valley,
Oregon, where 55% of land-use is in grass seed production that directly impacts
adjacent waterways containing native protected fish species. I determined tillage
effects on soil N mineralization processes at two sites contrasting in soil drainage
(moderately well drained, MWD) and well drained, WD)) and studied the
relationship between temporal changes in soil N, N mineralization, crop N uptake
and biomass accumulation, and microbial biomass carbon MBC). Net
mineralization was determined using the in- situ buried bag method and MBC by
fumigation extraction. Nitrate was the dominant inorganic-N form at both sites.
Annual net nitrification was significantly (a=O.05 level) different between tillage
treatments for fallow and seed years 1 and 2 at the WD site (fallow no till (NT) 75
kg N/ha/yr; conventional till (CT) 153 kg N/halyr; first seed year NT 202 kg
N/halyr; CT 243 kg N/halyr; second seed year NT 51 kg N/halyr; CT 79 kg
N/halyr). Annual net nitrification was significantly (a=0.05 level) different
between tillage treatments for seed year 2 at the MWD site (year NT 46 kg
N/halyr; CT 63 kg N/ha/yr). MWD had higher rates of nitrification in the fall,
compared to the WD site where nitrification rates were greatest in the spring.
Tillage had no effect on fine fescue and tall fescue seed yield during the three
years of production. MBC under NT was significantly (ct=0.05 level) higher by
20-30% irrespective of soil drainage or time of year. WD had twice the amount of
MBC compared to MWD. Crop N was directly related to the amount of crop
biomass produced. Across all seed years tall fescue accumulated 300 kg N h&' yr
'and fine fescue approximately 200 kg N ha1 yf'. Each grass seed crop was
fertilized in the spring with 134 kg N hi'. Crop N uptake was lowest during the
fall crop re-growth period and highest when soil N was elevated in the spring.
Spring mineralization., supplemented with fertilizer N, seemed to efficiently meet
crop N demand for biomass and seed production. Overall, findings indicate that
soil NO3-N loss occurs during the high precipitation winter months of late-fall and
winter. The fall-winter NO3 flush is exacerbated by.
© Copyright by Machelle A. Nelson
December 3, 2002
All Rights Reserved
N Processing in Grass Seed Crops Differing in Soil Drainage and Disturbance in
Western Oregon, U.S.A..
by
Machelle A. Nelson
A THESIS
submitted to
Oregon State University
In partial fulfillment of
the requirements for the
degree of
Master of Science
Presented December 3, 2002
Commencement June 2003
Master of Science thesis of Machelle A. Nelson presented on December 3, 2002
APPROVED:
Redacted for privacy
Major Professor,
Soil Science
Redacted for privacy
Chair of Department of Crop and Soil Science
Redacted for privacy
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
Machelle A. Nelson, Author
ACKNOWLEDGEMENTS
I would like to express my sincere thanks to my major advisor, Dr. Stephen
M. Griffith, for his interest, support, help and encouragement with this research
project. His help and input was greatly appreciated.
I would like to thank the Oregon Seed Council and the USDA Agricultural
Research Service in Corvallis, Oregon for funding my research project.
Several people helped me in the lab and the field. I would like to express
my sincere gratitude to each and every one of them.
I would also like to thank my committee members, Dr. David Myrold, Dr.
John Selker, and Dr. Kenneth Johnson, for all of their helpful suggestion and
criticisms.
In particular, I would like to acknowledge Don Streeter, Bill Gavin, and
Kristine Reid at the USDA-ARS for their continued encouragement, and Dr.
Jeffery Steiner for sharing his statistical knowledge with me.
Additionally, I would like to thank my family (Mom, Dad, Linda, and
Chris) and Cliff's family for all of their encouragement and support.
Many thanks to all of my wonderful friends Jenny Davis and Nan Posavatz
for making graduate school a very delightful memory.
And finally, to Cliff, my loving husband, for being the wind beneath my
wings. Thank you for giving me love, inspiration, and encouragement; I am
forever thankful.
TABLE OF CONTENTS
General Introduction and Literature Review .............................................. 1
References ..................................................................................... 7
N Processing in Grass Seed Crops Differing in Soil Drainage and Disturbance in
Western Oregon, USA ........................................................................ 9
Abstract ............................................................................... 9
Introduction .......................................................................... 11
Materials and methods ............................................................. 13
Results and discussion ............................................................ 19
Precipitation ............................................................... 19
SeedYield .................................................................. 19
Soilwater .................................................................. 24
Microbial biomass carbon ................................................ 26
SoilN ....................................................................... 29
N mineralization .......................................................... 33
Crop biomass, Nitrogen Accumulation ................................ 38
Conclusions ........................................................................ 45
References ...................................................................................47
LIST OF FIGURES
Page
Figure
Effects of no till (NT, open symbols) and conventional till (CT,
closed symbols) on soil microbial biomass carbon in a moderately
well drained soil (0-30 cm) located in Benton County, Oregon,
U.S.A ............................................................................... 27
2. Effects of no till (NT, open symbols) and conventional till (CT,
closed symbols) on soil microbial biomass carbon (MBC) in a
well drained soil (0-30 cm depth) located in Marion County,
Oregon, U.S.A ...................................................................... 28
3.
Effects of no till (NT, open symbols) and conventional till (CT,
closed symbols) on soil nitrate in a moderately well drained soil
(0-30 cm depth) located in Benton County, Oregon, U.S.A ............... 30
4.
Effects of no till (NT, open symbols) and conventional till (CT,
closed symbols) on soil ammomum in a moderately well drained
soil (0-30 cm depth) located in Benton County, Oregon, U.S.A ......... 31
5.
Effects of no till (NT, open symbols) and conventional till (CT,
closed symbols) on soil nitrate in a well drained soil (0 30 cm
depth) located in Marion County, Oregon, U.S.A ............................. 32
6.
Effects of no till (NT, open symbols) and conventional till (CT,
closed symbols) on soil ammonium in a well drained soil (0 30
cm depth) located in Marion County, Oregon, U.S.A ........................ 33
7.
Effects of no till (NT, open symbols) and conventional till (CT,
closed symbols) on soil net nitrification in a moderately well drained
soil (0-30 cm depth) located in Benton County, Oregon, U.S.A .......... 35
8. Effects of no till (NT, open symbols) and conventional till (CT,
closed symbols) on soil net nitrification in a well drained soil
(0-30 cm depth) located in Marion County, Oregon, U.S.A ................ 36
9. Effects of no till (NT, open symbols) and conventional till (CT,
closed symbols) on soil net mineralization in a moderately well drained
soil (0-30 cm depth) located in Benton County, Oregon, U.S.A .......... 37
LIST OF FIGURES (CONTiNUED)
Figure
Page
10. Effects of no till (NT, open symbols) and conventional till (CT,
closed symbols) on soil net mineralization in a well drained soil
(0-30 cm depth) located in Marion County, Oregon, U.S.A ................ 38
11. Effects of no till (NT, open symbols) and conventional till (CT,
closed symbols) on tall fescue (Festuca arundinaceum S.J. Dartyshire
cv. Hounddog) above ground biomass accumulation during the
1999-2000 and 2000-2001 growing seasons ................................... 40
12. Effects of no till (NT, open symbols) and conventional till (CT,
closed symbols) on fine fescue (Festuca rubra L. cv. Bridgeport)
above ground biomass accumulation during the 1999-2000 and
2000-2001 growing seasons ....................................................
41
13. Effects of no till (NT, open symbols) and conventional till (CT,
closed symbols) on tall fescue (Festuca arundinaceum S.J. Dartyshire
cv. Hounddog) above ground biomass nitrogen accumulation during
the 1999-2000 and 2000-200 1 growing seasons............................... 42
14. Effects of no till (NT, open symbols) and conventional till (CT,
closed symbols) on fine fescue (Festuca rubra L. cv. Bridgeport)
above ground biomass nitrogen accumulation during the 1999-2000
and 2000-200 1 growing seasons ................................................. 43
LIST OF TABLES
Page
Table
1.
Average precipitation and temperature for growing seasons 1999-2000
and 2000-200 1 at Benton County, OR,
......................................... 20
2. Average precipitation and temperature for Silverton Hills, Marion Co.
OR .................................................................................... 21
3. Mean (± s.c.) fine fescue (Feshica rubra L. cv. Bridgeport) and tall
fescue (Festuca arundinaceum S.J. Dartyshire cv. Hounddog) seed yield
for the 1999-2000 and 2000-200 1 growing seasons as affected by no till
(NT) and conventional till (CT) treatments .................................... 22
4. Plant development stages and growing degree-days for moderately well
drained (Benton site) and a well drained (Marion site) soil located in
Willamette Valley, Oregon, U.S.A.............................................. 23
5.
The effects of no till (NT) and conventional tillage (CT) on percent soil
water content for a moderately well drained (Benton) and a well drained
(Marion) site located in Willamette Valley, Oregon, USA................... 25
6.
The effects of tillage on annual net mineralization (kg N hi' yr), plant
shoot N accumulation and fertilizer input (kg hi1) for moderately well
drained (Benton site) and a well drained (Marion site) soils located in
Willamette Valley, Oregon, U.S.A.............................................. 44
N PROCESSiNG iN GRASS SEED CROPS DIFFERING IN SOIL DRAINAGE
AND DISTURBANCE iN WESTERN OREGON, U.S.A.
GENERAL INTRODUCTION AND LITERATURE REVIEW
In western Oregon's Willamette Valley (U.S.A.). there is a need for site-specific
information that can be used to optimize N fertilization of grass seed cropping systems.
This will lead to greater economic sustainability and environmental protection. Research
has addressed grass seed crop nitrogen (N) fertility (Griffith Ct al., 1997a; Griffith et al.,
1997b; Young et al., 1999), but has not evaluated soil N mineralization inputs. Because
N mineralization can contribute significant amounts of inorganic N to the crop, one must
be able to quantify these inputs and understand the factors that regulate N-mineralization
processes in the field. Recently, N mineralization inputs from Willamette Valley poorly
drained soils have been estimated to be about 65 kg N ha y' (Griffith et al., 1997c).
Under some conditions, the highest economic yield of tall fescue seed in the Willamette
Valley was achieved without added fertilizer N, whereas under other conditions over 100
kg ha' y' of N fertilizer was required (Griffith, unpublished data). This could be
explained by site-specific spatial and temporal variation in soil N mineralization. Soil
drainage, crop history, residue inputs, and tillage practices all could be factors
influencing this variation. Rice et al. (1987) found greater amounts of N mineralized in
tilled well-drained soils but less in the poorly drained soils in no till (NT) treatments.
2
As soil drainage, tillage, and crop residue inputs have key influences on
mineralization processes, it is important to understand how inputs of mineralized N are
affected by grass seed crops under both conventional and conservation tillage and high
residue management conditions on different soil drainage classes. Currently, post-seed
harvest residue removal and conventional till (CT) are the most common grass seed
production practices used for residue handling and ground preparation in the Willamette
Valley, OR. In 2001, the total acreage planted with grass and legume seeds was 196,417
ha, of that 88.5% was by conventional tillage (Conservation technology information
center; 2000). These practices may not be sustainable with regard to farm resource
conservation.
Conventional practices remove a potential source of nutrients (N, P, K and C),
further intensify the decline in soil organic matter, and increase soil erosion. These
practices may also place more reliance of crop productivity on applied fertilizer N and
increase the risk of elevated NO3 contamination in ground and surface waters. A
management practice with large amounts of soil disturbance accelerates the loss of C,
promoting net N mineralization (Stewart and Bettany, 1982). Total N loss from the
surface 30 cm of soil was 3, 8, and 19% for NT, stubble-mulch, and CT treatments,
respectively, whereas organic C losses were 4, 14, and 16%, respectively, after 12 years
of wheat/fallow cultivation in western Nebraska (Lamb et al., 1985). Beacuse soil
erosion at the site was minimal it was concluded that leaching of NO3 was the
mechanism of N loss and oxidation, as CO2, the mechanism of increased C loss from CT
compared with NT soils. Elliott et al. (1986) found that NO3 mineralized from CT soils
under field conditions was more subject to leaching than was NO3 produced under NT
management. In winter wheat, it appeared that cultivation affected mineralization,
immobilization, and subsequent movements of nutrients mineralized from organic matter.
Previous work has demonstrated that NT management increases microbial
biomass N in agricultural soils (Doran,
1987;
Gravatstein et al.,
well as the closely related content of active N (McCarty et al.,
Carter,
1987;
1995).
1991)
as
Soils under NT
often accumulate crop residue on the surface, resulting in wetter, cooler, and greater
concentrations of organic C and N than those under CT (Belvins et al.,
1985;
Havlin et a!,
1990).
1977;
Lamb et al.,
Greater amounts of surface soil organic C and N with NT
have been attributed to slower, less oxidative microbial metabolism under NT (Doran.
1980).
CT systems, when compared with NT, have been shown to decrease potentially
mineralized C and N (Woods and Schuman,
conserve mineral N (Follet and Schimel,
under NT than CT in the upper
biomass (Doran,
7.5
1988)
1989).
and the soils ability to immobilize and
Greater potentially mineralizable N
cm of soil has been associated with a larger microbial
1980).
In field conditions, soil moisture affects N mineralization both directly and
indirectly. The direct effect is related to water availability for microbial activity (Orchard
and Cook,
1983).
Water also affects N mineralization by controlling 02 diffusion within
the soil and the volume of soil supporting aerobic microbial activity (Skopp et al.,
1990).
Temperature directly controls N mineralization by affecting the biochemical
processes by microorganisms and the aerobic volume of the soil. For soil moisture and
El
temperature factors, N mineralization increased continuously with the increase of
temperature and the decrease of water potential (Renault and Sierra, 1994).
Nitrogen undergoes a wide variety of transformations in soil, most of which
involve the organic fraction. Although considered individually, each process is affected
by others occurring sequentially; in some cases, opposing processes operate
simultaneously.
An internal N cycle exists in soil apart from the overall cycle of N in nature.
Even if N gains and losses are equal the N cycle is not static. Continuous turnover of N
occurs through mineralization-immobilization, with incorporation of N into microbial
cells. Whereas much of the newly immobilized N is recycled through mineralization,
some is converted to relatively stable humus forms. The processes involved in
mineralization-immobilization turnover are not filly understood, and as a result there is
considerable confusion regarding interpretation of tracer data about soil N
transformations.
Current research in the Willamette Valley, OR has concentrated on minimum-
tillage vegetable production systems. According to Luna et al. (1997), strip-tillage
systems for sweet corn production using cover crops were shown to be more profitable
than CT treatments in on-farm trials. Several experiments have been conducted at
research stations and on-farm sites involving sweet corn, squash, and broccoli. In some
experiments, strip-till and CT produced comparable yields (Luna et al., 1997).
Tillage incorporates crop residue into the soil, making it more available to soil
microorganisms. Incorporating residue exposes more soil to the sun and lowers the soil
albedo, resulting in higher soil temperatures. Tillage also aerates and dries the soil.
Under NT, crop residue is made available to soil microorganisms at a slower rate for a
longer duration, soil is moister, and the soil is in a less oxidative condition with time
(Doran,
1980).
Soil conditions under NT results in an increase in microbial numbers and
activity near the soil surface and no change or decline in microbial numbers and activity
at lower depths (Doran,
1980;
Carter and Rennie,
1982;
Franzluebbers et al.,
1994). A
common observation is that after NT practices have been utilized for a few study years,
the N supplying potential of the soil increases (Franzluebbers et al.,
closely related content of active N (McCarty et al.,
1995).
1994),
as well as the
These studies suggest that
tillage plays a key role in soil N availability.
In situ soil N
mineralization is rarely measured in agricultural field studies.
Estimates of N mineralization, when measured, are often solely based on laboratory
incubations of soil under a constant controlled condition of 28°C and have little
significance to environmental conditions in the field and thus does not provide
information of when mineralization occurs and how it relates to crop N demand. In
contrast, methods for measuring soil N mineralization in situ have been used in forest and
natural ecosystem studies (Binkley and Hart,
1989).
It was hypothesized that: (1) during the first year establishment of perennial grass
seed crops using direct seeding (NT), net N mineralization would be lower compared to
rates found .for CT soil; (2) MBC would be greater under direct seeded management; and
(3) following the crop establishment year, perennial grass seed production fields would
return to a more N conserving system. resulting in reduced annual N mineralization
losses and enhanced sequestration of N.
7
REFERENCES
Belvins, RI., G.W. Thomas, and P. L. Cornelius. 1977. Influence of no-tillage and
nitrogen fertilization on certain soil properties after 5 years on continuous corn.
Agron. J. 69: 383-386.
Binkley, D. and S.C. Hart. 1989. The Components of nitrogen availability assessments in
forest soils. Adv. Soil Sci. 10: 57-112.
Carter, M.R. 1991. The influence of tillage on the proportion of organic carbon and
nitrogen in the microbial biomass of medium-textured soils in a humid climate.
Biol. Fertil. Soils 11: 135-139.
Carter, M.R. and D.A. Rennie. 1982. Changes in soil quality under zero tillage farming
systems: Distribution of microbial biomass and mineralizable C and N potentials.
Can. J. Soil. Sci. 62: 587-597.
Conservation Technology Information Center, Core 4, Crop Residue Management.
Available URL "http://www.ctic.purdue.edu"
Doran, J.W. 1980. Soil microbial and biochemical changes associated with reduced
tillage. Soil Sci. Soc. Am. J. 44: 765-771.
Doran, J.W. 1987. Microbial biomass and mineralizable nitrogen distributions in no
tillage and plowed soils. Biol. Fertil. Soils 5: 68-75.
Elliott, E.T., P.W. Tracy, G.A. Peterson, and C.V. Cole. 1986. Leaching of mineralized N
is less under no-till cultivation. p.53-56. In Trans. Tnt, Congr.Soil
l3
Hamburg, W. Germany. Vol. 6. Congr. Centurum, Hamburg.
Follett, R.F. and D.S. Schimel. 1989. Effects of tillage practices on microbial biomass
dynamics. Soil. Sci. Soc. Am. J. 53: 1091-1096.
Franzluebbers, A.J., F.M. Hons, and D.A. Zubere. 1994. Long-term changes in soil
carbon and nitrogen pools in wheat management systems. Soil Sci. Soc. Am. J.
58: 1639-1645.
Granatstein, D.M., D.F. Bezdicek, V.L. Cochran, L.F. Elliot, J. Hammel. 1987. Longterm tillage and rotation effects on soil microbial biomass carbon and nitrogen.
Biol. Fertil. Soils 5: 265-276.
Griffith, S.M., S.C. Alderman, and D.J. Streeter. 1997a. Italian ryegrass and nitrogen
source fertilization in western Oregon in two contrasting climatic years. I. Growth
and seed yield. J. Plant Nutr. 20: 419-428.
Griffith. S.M., S.C. Alderman, and D.J. Streeter. 199Th. Italian ryegrass and nitrogen
source fertilization in western Oregon in two contrasting climatic years. II. Plant
nitrogen accumulation and soil nitrogen status. J. Plant Nutr. 20: 429-439.
Griffith, S.M., J.S. Owen, W.R. Horwath, P.J. Wigington Jr., J.E. Baham, and L.F.
1997c. Nitrogen movement and water quality at a poorly-drained agricultural and
riparian site in the Pacific Northwest. Soil Sci. Plant Nutr. 43: 1025-1030.
Havline, J.L., D. E. Kissel, L.D. Maddux, M. M. Clausen, and J.H. Long. 1990. Crop
rotation and tillage effects on soil carbon and nitrogen. Soil Sci. Soc. Am. J. 54:
448-452.
Lamb, J. A., G.A. Peterson, C.R. Fenster, 1985. Wheat fallow system's effect of a newly
cultivated grassland soil's nitrogen budget. Soil Sci. Soc. Am. J. 49: 352-356.
Luna, J.M., M. L., and T. J. O'Brien. 1997 Integration of cover crops and strip-tillage
systems for vegetable production in the Pacific Northwest. National Meeting,
Amer. Soc. Hort. Sci., Salt Lake City, UT.
McCarty, G.W., J.J. Meisinger, F.M. Jenniskens. 1995. Relationships between total-N,
biomass-N and active-N in soils under different tillage and fertilizer treatments.
Soil Biol. Biochem. 27: 1245-1250.
Orchard, V.A. and F.J. Cook. 1983. Relationship between soil respiration and soil
moisture. Soil Biol. Biochem. 15: 447-453.
Renault, P.J., and J. Sierra. 1994. Modeling oxygen diffusion in aggregated soils: II.
Anaerobiosis in topsoil layers. Soil Sci. Soc. Am. J. 58: 521-530.
Rice, C.W., J.H. Grove and M.S. Smith. 1987. Estimating soil net nitrogen mineralization
as affected by tillage and soil drainage due to topographic position. Can. J. Soil.
Sci. 67: 513-520.
Skopp, J., Jawson, M.D., Poran, J.W. 1990. Steady state aerobic microbial activities as a
function of soil water content. Soil Sci. Soc. Am. J. 54: 1619-1625.
Stewart, J.W.B., and J.R. Bettany. 1982. Dynamics of soil organic phosphorus and sulfur.
In Trans. mt. Congr. Soil Sci., 12th New Delhi, India. p.8-16 Feb 1982. Vol. 6.
Indian Soc. Soil Sci. Agric. Chem., New Delhi.
Woods, L.E. and G.E. Schuman. 1988. Cultivation and slope position effects on soil
organic matter. Soil Sci. Soc. Am. J. 52: 1371-1376.
Young, W.C. III. DO. Chilcote, and H.W. Youngberg. 1999. Spring-applied nitrogen and
productivity of cool-season grass seed crops. Agron. J. 91: 339-343.
N PROCESSING IN GRASS SEED CROPS DIFFERING IN SOIL DRAINAGE
AND DISTIJRBANCE IN WESTERN OREGON, U.S.A.
ABSTRACT
A better understanding of grass seed crop and soil fertility would lead to
improving fertilizer practices and preserving water quality in Willamette Valley, Oregon
where 55% of land-use is in grass seed production that directly impacts adjacent
waterways containing native protected fish species. This study determined tillage effects
on soil N mineralization processes at a moderately well drained (MWD) and a well
drained (WD) site and studied the relationship between temporal changes in soil N, N
mineralization, crop N uptake and biomass accumulation, and microbial biomass carbon
(MBC). Net mineralization was determined using the in situ buried bag method and MBC
by fumigation extraction. Nitrate was the dominant inorganic-N form at both sites.
Annual net nitrification was significantly (P = 0.05) different between tillage treatments
for fallow and seed years 1 and 2 at the WD site (fallow no till (NT) 75 kg N ha1
conventional till (CT)
153
kg N ha1 yr'; first seed year NT 202 kg N ha
yf';
yf'; CT 243
kg
N ha' yf1; second seed year NT 51 kg N ha' yr; CT 79 kg N ha' yf'). Annual net
nitrification was significantly (P = 0.05) different between tillage treatments for seed year
2
at the MWD site (NT 46 kg N ha' yr'; CT 63 kg N ha yf') The MWD site had higher
rates of nitrification in the fall, compared to the WD site where nitrification rates were
greatest in the spring. Tillage had no effect on fine fescue and tall fescue seed yield
10
during the three years of production. MBC under NT was significantly (P = 0.05)
higher by 20 to 30% irrespective of soil drainage or time of year. WD had twice the
amount of MBC compared to MWD. Crop N was directly related to the amount of crop
biomass produced. Across all seed years, tall fescue shoots accumulated 300 kg N hi' yr
'and fine fescue shoots approximately 200 kg N
ha1
yr4. Each grass seed crop was
fertilized in the spring with 134 kg N hi'. Crop N uptake was lowest during the fall crop
re-growth period and highest when soil N was elevated in the spring. Spring
mineralization, supplemented with fertilizer N, seemed to efficiently meet crop N
demand for biomass and seed production. Overall, findings indicate that soil NO3-N loss
occurs during the high precipitation winter months of late-fall and winter. The fall-winter
NO3 flush is exacerbated when tillage is implemented over no till methods.
11
INTRODUCTION
In western Oregon's (U. S.A) Willamette Valley, there is a need for site-specific
information that can be used to optimize N fertilization of grass seed cropping systems.
This will lead to greater economic sustainability and environmental protection. N
mineralization can contribute significant amounts of inorganic N to the crop, one must be
able to quantify these inputs and understand the factors that regulate N-mineralization
processes in the field. Recently, N mineralization inputs from poorly drained Willamette
Valley, OR soils have been estimated to be about 65 kg N ha1 y' (Griffith, unpublished).
Under some conditions, the highest economic tall fescue seed yield in Willamette Valley
was achieved without added fertilizer N (Griffith, unpublished), whereas under other
conditions over 100 kg N ha1 y' of N fertilizer is required. This could be explained by
site-specific spatial and temporal variation in soil N mineralization. Soil drainage, crop
history, residue inputs, and tillage practices all could be factors influencing this variation.
As soil drainage, tillage, and crop residue inputs have key influences on
mineralization processes, it is important to understand how mineralized N inputs are
affected by grass seed crops under both conventional and conservation tillage and high
residue management conditions on different soil drainage classes. Currently, post-seed
harvest residue removal and conventional tillage (CT) are the most common grass seed
production practices used for residue handling and ground preparation in the Willamette
Valley. In 2001, the total acreage planted with grass and legume seeds was 196,417 ha, of
which 88 % was by CT (Conservation technology information center, 2002).
12
Conventional practices remove a potential source of nutrients (N, P. K and C);
further intensify the decline in soil organic matter, and increase soil erosion. These
practices may also place more reliance of crop productivity on applied fertilizer N and
increase the risk of elevated NO contamination in ground and surface waters. A
management practice with large amounts of soil disturbance accelerates the loss of C,
promoting net N mineralization (Stewart and Bettany, 1982).
Previous work has demonstrated that no till (NT) management increases microbial
biomass in agricultural soils (Doran 1987; Gravatstein et al., 1987; Carter, 1991) as well
as the closely related content of active N (McCarty et al, 1995; Belvins Ct al., 1977; Lamb
et al., 1985; Havlin et al., 1990). CT systems, when compared with NT, have been
shown to decrease potentially mineralized C and N (Woods and Schuman, 1988) and the
soils ability to immobilize and conserve mineral N (Follet and Schimel, 1989). Greater
potentially mineralizable N under NT than CT in the upper 7.5 cm of soil has been
associated with a larger microbial biom ass (Doran, 1980). A common observation is that
the N supplying potential of the soil increases after NT practices have been utilized for a
few growing seasons (Franzluebbers et at., 1994), as does the closely related content of
active N (McCarty et at., 1995). These studies suggest that tillage plays a key role in soil
N availability.
An internal N cycle exists in soil apart from the overall cycle of N in nature.
Even if N gains and losses are equal, the N cycle is not static. Continuous turnover of N
occurs through mineralization-immobilization, with incorporation of N into microbial
cells. Whereas much of the newly immobilized N is recycled through mineralization,
13
some is converted to stable humus forms. The processes involved in mineralizationimmobilization turnover are not fully understood.
In situ soil N mineralization is rarely measured in agricultural field studies.
Estimates of N mineralization, when measured, are often solely based on laboratory
incubations of soil under a constant controlled condition of 28°C and have little
significance to environmental conditions in the field, and thus does not provide
information of when mineralization occurs and how it relates to crop N demand. In
contrast, methods for measuring soil N mineralization in situ have been used in forest and
natural ecosystem studies (Binkley and Hart, 1989).
It was hypothesized that: (1) during the first year establishment of perennial grass
seed crops using direct seeding (NT), net N mineralization would be lower compared to
rates found for tilled soil; (2) microbial biomass carbon (MBC) would be greater under
direct seeded management; and (3) following the crop establishment year, perennial grass
seed production fields would return to a more N conserving system, resulting in reduced
annual N mineralized NO3 losses and enhanced sequestration of N.
MATERIALS AND METHODS
Research plots were located in the Willamette Valley of western Oregon (U.S.A.),
at two locations contrasting in soil drainage classification and grass species grown. One
site was located on a private grass seed production farm located in the Silverton Hills
region of eastern Marion County (N 44° 56' W 122° 45'); herein referred to as the well
drained (WD) site. The second site was located on the valley floor at the Oregon State
14
University Hyslop Research Farm in Benton County, OR (N 440 38' W 123° 12');
herein referred to as the moderately well drained (M\\TD) site. Sites were established in
1992 by the USDA-ARS National Forage Seed Production Research Center as part of a
long-term integrated agricultural systems study (Gohlke et al., 1999). The USDA-ARS
project contrasted alternative tillage, crop rotation, and residue management practices.
The treatments imposed in this study were direct seeding versus tillage and a subtreatment of seed year. All plots were replicated with four blocks measuring 560 m2 each.
The plots were planted with fine fescue (Festuca ru/ira L. cv. Bridgeport) (WD site) and
tall fescue (Festuca arundinaceum S.J. Dartyshire cv. Hounddog) (MWD site) in the
spring of 1999. First, second, and third year stands were included in this study.
The crop management at the WD site was as follows: The first, second, and third
seed-year stands were in a three-year continuous grass rotation since 1992. The first and
second year stand of CT plots were last tilled September 1998 and planted April 1999
and NT plots were last tilled September 1992 and planted April 1999. The third-year CT
plots were last tilled May 1995 and planted late April 1997. The fallow year plots were
planted in a three-year red clover (Trifolium prcuense L.)-grass rotation. The fallow CT
plots were last tilled October 2000 and planted Februaiy 2001 and the fallow NT plots
were last tilled May 1995. All plots were fertilized in the spring each year with 134 kg N
ha', with urea 46-0-0-0.
Crop management at the MWD (Benton) site consisted of a first and second year
tall fescue seed crop in continuous three-year rotations since 1992. The CT plots were
tilled September 1998 and planted March 1999. The NT plots were last tilled October
15
1994 and planted March 1999. The third seed year plots were in a three-year red clover
(T pratense
L.)-meadow foam (Limnanthes
a/ba Harfw.ex
Benth.)-tall fescue rotation.
The CT plots were tilled October 1998 and planted November 1998. The fallow year
plots were in red clover 1998 to 2000. The CT plots were tilled October 2000 and planted
March 2001. The NT plots were last tilled October 1994 and planted March 2001. All
plots were fertilized in the spring each year with 134 kg N ha', with urea 46-0-0-0.
The WD Marion Co. soil was representative of soils in the north Willamette
Valley foothills compared to the MWD site in Benton Co. that was typical of some the
southern Valley Benton) soils. At both locations soil water flow was by percolation. At
the Marion site the soil was well drained. The available water capacity was 10 to 18 cm.
Permeability is moderately slow.
The depth to which roots can penetrate ranges from
51 to 102 cm, but it was more than 76 cm in most places. At the Benton site the soil was
moderately well drained. The available water capacity was 28 to 33 cm. Permeability
was moderate in the upper part of the subsoil, and it was slow in the lower part. Depth to
which roots could penetrate was restricted by a seasonal perched water table These soils
were chosen for the study for their extensive presence in the area and contrasting physical
and chemical characteristics, which are thought to influence N mineralization processes.
The Marion site (WD) contained a Nekia-Jory Association soil classified as fine, mixed,
active, mesic Xeric Palehumult. This soil had 7% organic matter and 3.8% total carbon.
The Benton site had a Woodburn soil series classified as fine-silty, mixed, superactive,
mesic Aquultic Argixeroll. This soil had 4% organic matter and 1.3% total carbon.
16
The Willamette Valley has a Pacific Northwest marine climate, with hot, dry
summers and cool, wet winters. The mean annual precipitation is 1114 mm (30-year
average) with 90% occurring between October and June. The annual mean air
temperature is 12°C.
The in situ buried bag method (Eno, 1960) was used to quantify net N
mineralization using 24 incubations, September 1999 to June 2001, with an average
incubation period of 26 days. Three pairs of intact soil cores measuring 5 cm in diameter
by 15 cm were taken within each plot. One of the core-pairs (N- final) was sealed within
a self-sealable polyethylene bag (approximately 27 by 28 cm; 1.75 MIL thickness) and
replaced in its original position in the ground. The bag was covered with loose soil and
litter to reduce exposure. Nai was collected approximately 26 days later. The other
core-pair (Ninitiai) was transported to the laboratory sealed in a sealable polyethylene bag
for analyses of baseline soil properties.
Three separate sub-samples from the main sample core were extracted with 100
mL of 0.5 M K2SO4, shaken for 30 mm on a rotary shaker at 350 rpm and filtered through
a Whatman # 1 filter. The filtrate was then analyzed for NO3 and NH using a Lachat
Quick Chem 4200 analyzer. An additional set of three soil sub-samples were taken for
determination of soil moisture by gravimetric methods. Soil pH was measured using a
glass electrode (1:2, soil: water ratio).
Soil microbial biomass carbon (MBC) was determined by chloroform (CHCI3)
fumigation extraction method (Horwath, 1994). This method measures total organic
carbon (TOC) in extracts of CHC13-flimigated and non-fumigated soils. Six sub-samples
17
from each soil core were used for this analysis. Three 20 g (d.wt. equivalent) field
moist soil samples were fumigated with chloroform for 48 h and three left unfumigated.
Soil samples were fumigated by placing sample cups of soil in a large vacuum desiccator
lined with moist paper. A beaker containing 50 mL of ethanol free CHC13 and boiling
chips were placed in the desiccator. The desiccator was evacuated three times until the
CHC13 boiled vigorously. The samples were exposed to CHC13 for 48 h. The beaker of
CHC13 and the moist paper were removed from the desiccator and the residual CHC13
vapor was removed from the soils by repeated evacuation. The unflimigated soils were
extracted when fumigation began. Soil samples were extracted with 100 mL of 0.5
K2SO4, shaken for 30 mm at 350 rpm, and filtered through a Whatman #1 filter. The
extracts were analyzed using a Tekmar-Dorhmann Phoenix 8000 UV-Persulfate TOC
analyzer.
The above ground crop biomass was collected on 30 January, 29 February, 30
March, 27 April, 25 May, 26 June and 30 October 2000 and 13 February, 13 March, 13
April, 29 May, and 25 June 2001. Biomass was taken from three 30 cm2 randomly
selected areas in each replicated treatment and were forced-air dried at 70°C for 24 h,
then weighed. Plant material was ground using a Tecator Cyclotec 1093 sample mill and
analyzed for total C and N using a Perkin Elmer 2400 Series II CFINS/O analyzer. Plant
development was also recorded using the following phenologic terminology: number of
tillers, boot, elongation, and anthesis.
18
Calculation of N Mineralization and Nitrification
The amount of N mineralized or immobilized was calculated by:
[1
Net mineralization
NH4
Kg, J
[
NO3
Kg
final
1
NO3
[1 NH4
Jj
kg
initial
)
Kg initial jj
Time
Net nitrification=
NO3
Kg.final
NO3
Kginitial
Time
Calculation of Microbial Biomass Carbon
Microbial Biomass Carbon (MBC) in the soil was calculated from the amounts of
CO2 carbon extracted from the fumigated and unfumigated soil samples:
MBC F-NF/k
Where,
F = extractable C from fumigated samples;
NF = extractable C from unfumigated samples;
k factor = 0.41
Statistical Analysis
The results were analyzed using an ANOVA to determine if there were significant
differences between plots and if no differences, data was pooled and an ANOVA was
used to determine if there were significant differences between the two treatments for
each sample date. Main effects were direct tillage (NT) and sub treatments were year of
stand (fallow, first year, and second year). All values were expressed as the mean of four
replications ± one standard error and significance determined at the P = 0.05 level.
19
RESULTS AND DISCUSSION
Precipitation
Annual precipitation dramatically contrasted between study-years (Tables 1 and
2). The total precipitation for 1999-2000 growing season was near normal 1068 mm at
MWD (Benton) and 1135 mm at WD (Marion). During 2000-2001, the annual
precipitation was 563 mm at MWD (Benton) and 756 mm at WD (Marion), 48% and
36%, respectively, below the 30-year mean.
Seed Yield
During both study years and at both locations, for seed years one and two, tillage
(CT vs. NT) had no effect on fine fescue and tall fescue seed yield; there was no
significant difference in seed yield between tillage and seed year (Table 3). This
substantiates previous findings of Steiner et al. (2002). The time of seed harvest for both
grass species occurred earlier in the drier year compared to the normal precipitation year
(Table 4). The accumulated growing degree day difference to time of seed harvest,
between the normal (1999-2000) and drier (2000-200 1) precipitation years, was earlier by
417 GDD at the WD site and 397 GDD at the MWD site.
20
Table 1. Average precipitation and temperature for study years 1999-2000 and 20002001 at Benton County, OR, U.S.A.
1999-2000
Precipitation
Average Monthly Temperature
Month
Soil 10 cm depth
Soil 5 cm depth
mm
26.6
September
2
31.5
October
74
17.8
20.2
11.4
November
228
12.4
December
151
7.3
8.1
January
207
6.3
6.7
February
161
8.4
9.9
March
93
13.9
11.4
April
41
19.9
16.7
May
76
20.4
23.8
June
31
26.8
31.6
July
4
31.1
36.1
Total
1068
September
October
November
December
January
February
March
April
May
June
July
Total
7
563
30 yr average
1085
16
75
70
112
41
31
72
59
28
51
2000-2001
29.8
19.4
9.7
7.5
8.1
9.9
14.3
17.7
27.3
29.1
34.8
25.5
16.8
8.4
6.5
6.7
8.0
11.7
14.7
23.0
24.8
30.2
21
Table 2. Average precipitation and temperature for study years 1999-2000 and 20002001 at Marion County, Oregon, U.S.A.
1999-2000
Precipitation
Month
September
October
November
December
January
February
March
April
May
June
July
Total
Average Monthly Temperatures
Soil 5 cm depth Soil 10 cm depth
°C
26.1
30.4
16.8
19.5
10.8
11.9
3.2
3.5
3.5
4.4
8.1
8.9
7.2
7.9.
14.6
14.9
9.9
10.2
26.7
31.5
31.0
35.9
mm
1
85
232
127
196
189
100
70
105
27
2
1135
2000-200 1
September
October
November
December
January
February
March
April
May
June
July
26
28.4
24.6
101
18.7
9.4
6.9
6.1
9.1
15.3
8.9
26.5
15.2
8.1
6.1
94
104
65
45
128
78
41
59
16
Total
756
30 yr average
1180
28.9
34.7
5.6
7.8
12.9
8.7
22.9
24.5
30.1
22
Table 3. Mean (± S.E.) fine fescue (Festuca rubra L. cv. Bridgeport) and tall fescue
(Festuca arundinaceum S.J. Dartyshire cv. Hounddog) seed yield for the 1999-2000 and
2000-2001 study years as affected by no till (NT) and conventional till (CT) treatments.
Seed
1999 2000 Species
Year Tillage 2000
2001
(kg ha1) (kg ha1)
Fine Fescue
1
NT 357±56
1
CT
233±74
2
NT
1422±204
2
CT
1296±55
3
CT 290± 46
Tall Fescue
1
NT 1136±167
1
CT
2
2
NT
CT
CT
3
1295±187
2271±160
1720±264
1203±334
23
Table 4. Plant development stages and growing degree-days for moderately well
drained (Benton site) and a well drained (Marion site) soil located in Willamette Valley,
Oregon, U.S.A.
Day of
Growing Degree
Site
Benton
Marion
Date
Year
Days
Plant Development Stage
02/07/00
38
186
2 leaf 3rd emerging
2/29/2000
60
312
3or4leafstage
3/30/2000
90
517
4 leaf stage
4/27/2000
118
825
Emergence out of the boot
5/24/2000
145
1168
Early stamen emergence
6/26/2000
178
1688
Seed harvest
2/13/200 1
44
196
2-3 leaf stage
3/19/2001
78
426
3-4 leaf stage
4/24/2001
114
719
Emergence out of boot
5/29/200 1
149
1189
Head fully emerged
6/25/2001
176
1584
Seed ready
2/15/2000
46
228
3 lcaf 4th emerging
3/20/2000
80
440
4 leaf stage
4/13/2000
104
678
Emergence out of the boot
5/1 1/2000
132
979
30% FLOWERING
7/6/2000
188
1871
Seed harvest
1/30/2001
30
140
2-3 leaf stage
3/6/2001
65
318
4 leaf stage
4/10/2001
100
598
Emergence out of boot
5/15/2001
135
981
Headfull emerged
6/18/2001
169
1474
Seed ready
24
Soil Water
Throughout the season soil water content was greater at WD (Marion) than at
MWD (Benton) (Table 5). Tillage and seed year did not affect percent soil water during
the normal rainfall year (1999-2000), but during the drier study year (2000-200 1), the
tilled plots had significantly (P = 0.05) higher soil water than the direct seeded plots
during fallow (year-0). This might be explained from the breakdown of soil aggregates by
tillage operations thus reducing the porosity and causing surface sealing during the winter
under higher rainfall amounts. During both
study
years, soil water content was very
responsive to precipitation events (data not shown); soil water rapidly increased with
increasing rainfall and diminished with decreasing rainfall. Soil water for the WD
(Marion) site was 4% higher, on average, compared to the MWD (Benton) site (Table 5)
and was probably due to greater organic matter in the WD (Marion) soils. WD (Marion)
had significantly (P = 0.05) more organic matter; 3.9 1% higher than soils at MWD
(Benton) (see materials and methods). Soil organic matter (SOM) can hold up to 20
times its weight in water (Stevenson 1994). Another factor would be the percent clay
content. It is well documented that generally the higher soil clay content the higher the
soil's capacity to retention water. Soil at the WD (Marion) site had 18% more clay than
the MWD (Benton) site; there was no significant difference in soil water for tillage or
year of stand. This could be attributed to the return of the post harvest straw on the soil
surface across all treatments and the fact that CT treatments were tilled every 3 to 4 years
25
Table 5. The effects of no till (NT) and conventional tillage (CT) on percent soil water
content for a moderately well drained (Benton) and a well drained (Marion) site located
in Willamette Valley, Oregon, U.S.A.
Site
Benton
Seed Year
°ct
1
Ont
lfl
2
2nt
% Soil Water
Date
Seed Year
Site
Marion
°ct
1
Ont
2nt
% Soil Water
Date
11/02/99
23 22
11/02/99
25
12109199
25 25
11/27/99
28**28**
12131/99
24 24
12/27/99
26
01/31/00
26 26
01/20/00
29**28**
02/29/00
26 25
02/15/00
30**29**
03/30/00
23 23
03/20/00
29**29**
04/27/00
19
04/13/00
28**27**
05/11/00
28
19
2ct
lfl
24
26
28
10/30/00
20
20
20 19
10/16/00
23
23
22
22
12/04/00
27*
23
24 23
11/20/00
25
24
24
25
01/05/01
27*
22
24 23
12/18/00
29* 25
26
27
02/13/01
27
24
25 26
01/30/01
30* 27
27
27
03/19/01
26
24
25 25
03/06/01
27* 24
25
26
04/24/01
22
21
23 23
04/10/01 29***26**
27**27**
05/29/01
14
14
14
13
05/15/01 28** 26**
25**26**
06/25/01
11
12
12
11
06/18/01 22** 20**
21**21**
= 0.05 level for tillage
= 0.05 level for site
26
Microbial Biomass Carbon
At both sites, for all sampling times, tillage decreased MBC on average (Figs. I
and 2). MBC content, under direct seeding was significantly (P
0.05) higher; being 20
to 30 % greater than under tillage establishment the fallow and first year and this result
corroborates, in general, the numerous reports of other investigators that MBC was
increased under direct seeding (Doran, 1980; Carter and Rennie, 1982; Franzluebbers et
al., 1994).
There was a significant (P == 0.05 level) difference between MBC among sites,
with WD (Marion) having twice as much MBC as MWD. At the WD site MBC trend
was constant for all treatments, but at the MWD site fluctuated little for all treatments,
compared to the MWD site where MBC steadily declined. This could be explained by
the differences in percent organic matter and total C, as well as differences in soil water
holding capacity and aeration. The WD site had twice as much percent of organic matter
and total C, and had higher soil water content, on average, than the MWD site. Moore et
al., (2000) found systems with higher organic matter inputs, and easily available organic
matter compounds, tend to have higher microbial biomass contents.
27
--- Fallow CT
0-- Fallow NT
7-- Year 1-CT
v---
300
Year 1-NT
- Year 2-CT
-0-- Year 2-NT
--- Year 3-CT
200
II
100
:ii
10/99
2/00
6/00
10100
2101
6101
Mouth/Year
Figure 1. Effects of no till (NT, open symbols) and conventional till (CT, closed symbols)
on soil microbial biomass carbon (MBC) in a moderately well drained soil (0 30 cm
depth) located in Benton County, Oregon, U.S.A. for study years 1999-2000 and 20002001. Tall fescue (Festuca arundinaceum S.J. Dartyshire cv. Hounddog) was grown for
seed at this site. The error bars indicate ± 1 S.E. (n = 4). Arrow denotes when fertilizer
was applied.
28
-IIIu
300
0
200
Fallow-CT
0 Fallow-NT
y Year 1-CT
v Year 1-NT
100
1
Year2-CT
0 Year 2-NT
Year 3-CT
II
10/99
2/00
6/00
10/00
2/01
6101
Month/Year
Figure 2. Effects of no till (NT, open symbols) and conventional till (CT, closed
symbols) on soil microbial biomass carbon (MBC) in a well drained soil (0-30 cm
depth) located in Marion County, Oregon, U.S.A. for study years 1999-2000 and 20002001. Fine fescue (Festucci rubra L. cv. Bridgeport) was grown for seed at this site. The
error bars indicate ± 1 S.E. (n = 4). Arrow denotes when fertilizer was applied.
Soil N
Common among all seed crop production years and study sites, fall soil NO3
levels declined appreciably from November to January (Figs. 3-6); the months of highest
annual precipitation (Tables 1 and 2). Initial fall soil NO3 levels ranged from
approximately 5 to almost 50 kg N ha'. During the winter months of January through
most of March, soil NO3 concentrations reached their lowest levels, maintaining soil
NO3 concentrations of I to 10 kg N ha'. Soil NO3 begin to increase in April and May
and was attributed to both fertilizer-N application of urea and the simulation of microbial
mineralization and nitrification of soil organic matter. Unlike some poorly drained
Willamette Valley, OR soils, where N}T was the dominant N-form for much of the
winter (Griffith et al., 1997a), NO3 was the dominant N-form at the fine fescue (WD)
and tall fescue sites (MWD) sites.
100
Fallow-CT
0 Fallow-NT
y Year 1-CT
v---
80
o--
Year 1-NT
Year 2-CT
Year 2-NT
b-- Year 3-CT
60
0,
0
z
0,
E
20
0
10/99
02/00
LVrrTLr
06/00
10/00
02/01
06/01
Month/Year
Figure 3. Effects of no till (NT, open symbols) and conventional till (CT, closed
symbols) on soil nitrate in a moderately well drained soil (0 30 cm depth) located in
Benton County, Oregon, U.S.A. for study years 1999-2000 and 2000-2001. Tall fescue
(Festuca arundinaceum S.J. Dartyshire cv. Hounddog) was grown for seed at this site.
The error bars indicate ± 1 S.E. (n = 4). Arrow denotes when fertilizer was applied.
31
0
(I)
C)
I
z
C)
E
2
10/99
02/00
06/00
10/00
02/01
06/01
Month/Year
Figure 4. Effects of no till (NT, open symbols) and conventional till (CT, closed
symbols) on soil ammonium in a moderately well drained soil (0-30 cm depth) located
in Benton County, Oregon, U.S.A. for study years 1999-2000 and 2000-2001. Tall
fescue (Fesluca arundinaceum S.J. Dartyshire cv. Hounddog) was grown for seed at this
site. The error bars indicate ± 1 S.E. (n = 4). Arrow denotes when fertilizer was applied.
32
100
-- Fallow-CT
-0- Fallow-NT
-.y--. Year 1-CT
-v- Year 1-NT
80
-0---
Year 2-CT
Year 2-NT
-+- Year 3-CT
0
U)
C)
.
0
C)
40
E
20
0
10/99
02/00
06/00
10100
02/01
06/01
Month/Year
Figure 5. Effects of no till (NT, open symbols) and conventional till (CT, closed
symbols) on soil nitrate in a well drained soil (0 30 cm depth) located in Marion
County, Oregon, U.S.A. for study years 1999-2000 and 2000-2001. Fine fescue (Festuca
rzibra L. cv. Bridgeport) was grown for seed at this site. The error bars indicate ± 1 S.E.
(n = 4). Arrow denotes when fertilizer was applied.
33
[1
[j
0
(I)
I
z
0
10/99
02/00
06/00
10/00
02/01
06/01
Month/Year
Figure 6. Effects of no till (NT, open symbols) and conventional till (CT, closed
symbols) on soil ammonium in a well drained soil (0-30 cm depth) located in Marion
County, Oregon, U.S.A. for study years 1999-2000 and 2000-2001. Fine fescue (Festuca
rubra L. cv, Bridgeport) was grown for seed at this site. The error bars indicate ± I S.E.
(n = 4). Arrow denotes when fertilizer was applied.
N Mineralization
The WD site had higher rates of nitrification in the spring (Fig. 7) compared to the
MWD site, where nitrification rates were greatest in the fall (Fig. 8). Nitrification was
enhanced by tillage. The total annual net nitrification was significantly (P = 0.05) greater
in tilled soil at WD site but not for tilled soils at MWD (Table 4).
34
N mineralization varied with soil drainage class (Fig. 9-10). Tilling of the WD
soil resulted in greater amounts of N mineralized than that observed for NT. In contrast,
M\\TD soil resulted in greater amounts of N mineralized in the NT treatments than in the
CT treatments. Rice Ct al. (1987) found that, in general, the trend was that more poorly
drained soils mineralized a smaller amount of N, particularly in tilled treatments.
At the MWD and WD sites, during the first seed year, N mineralization rates in
the spring, prior to urea fertilizer application, were greater in direct seeded plots
compared to the previously tilled established plots. Other field studies have shown that
mineralization rates in spring were similar or higher in direct drilled or reduced tilled
soils, compared with cultivated soils (Kohn et al., 1966; Reeves and Ellington 1974; Stein
etal., 1987).
There was a difference between study years, during the first year of the study the
precipitation was near normal and the second year was drier (Tables 1 and 2). At the
MWD site precipitation in the fall, winter, and spring were 47, 65, and 24%, respectively,
less than a normal year. At the WD site the differences were 31,58, and 11%,
respectively, less. There was no difference in soil temperatures. Soil water content was
lower in the dry year, at the M\ATD site was different in the fall, and at the WD site it was
different in the fall and spring. Nitrification rates were significantly (P = 0.05) less in the
dry year during the fall compared to the normal year at the MWD site. At the WD site in
the spring nitrification rates were significantly (P = 0.05) less. This could be explained
by the differences in precipitation amount. In the summer there was very little rainfall,
and soils were past wilting point, thus soil N remained in the upper surface of the soil,
35
when the rainfall began with the cooler temperatures in October there was an N flush,
the size of the flush would be affected by the amount of rainfall received.
10
Fallow-CT
0-- Fallow-NT
Year 1-CT
8
vYearl-NT
0
-
6
Year 2-CT
Year2-NT
4 Year 3-CT
z
a)
0
0
z
0
-2
10/99
2/00
6/00
10/00
2/01
6/01
Month/Year
Figure 7. Effects of no till (NT, open symbols) and conventional till (CT, closed symbols)
on soil net nitrification in a well drained soil (0 30 cm depth) located in Marion County,
Oregon, U.S.A. for study years 1999-2000 and 2000-2001. Fine fescue (Festuca rubra
L. cv. Bridgeport) was grown for seed at this site. The error bars indicate ± 1 S.E. (n = 4).
Arrow denotes when fertilizer was applied.
10
--- Fallow-CT
0 Fallow-NT
-it--
8
U
Year 1-CT
v-- Year 1-NT
Year 2-CT
0 Year 2-NT
6
-4 Year 3-CT
z
C
0
02
I,-
z
0
-2
10/99
I
2/00
6/00
10/00
2/01
6/01
MonthlYear
Figure 8. Effects of no till (NT, open symbols) and conventional till (CT, closed
symbols) on soil net nitrification in a moderately well drained soil (0 30 cm depth)
located in Benton County, Oregon, U.S.A. for study years 1999-2000 and 2000-2001.
Tall fescue (Festuca arundinaceum S.J. Dartyshire cv. Hounddog) was grown for seed at
this site. The enor bars indicate ± 1 S.E. (n = 4). Arrow denotes when fertilizer was
applied.
37
3
---- Fallow-CT
0--- Fallow-NT
yYearl-CT
2
I
V--Yearl-NT
I
--- Year 2-CT
0-- Year 2-NT
--- Year 3-CT
V
z
C
0
N
C)
C
-1
-2
10/99
2/00
6/00
10/00
2/01
6101
Month/Year
Figure 9. Effects of no till (NT, open symbols) and conventional till (CT, closed
symbols) on soil net mineralization in a moderately well drained soil (0 30 cm depth)
located in Benton County, Oregon, U.S.A. for study years 1999-2000 and 2000-2001.
Tall fescue (Fesluca arundinaceum S.J. Dartyshire cv. Hounddog) was grown for seed at
this site. The error bars indicate ± I S.E. (n 4). Arrow denotes when fertilizer was
applied.
11
3
--- Fallow-CT
0 Fallow-NT
Year 1-CT
Year 1-NT
2
-*- Year 2-CT
Ci-- Year 2-NT
4 Year 3-CT
z
0)
0
N
0
-1
-2
10/99
2/00
10/00
6/00
2/01
6/01
Month!Year
Figure 10. Effects of no till (NT, open symbols) and conventional till (CT, closed
symbols) on soil net mineralization in a well drained soil (0-30 cm depth) located in
Marion County, Oregon, U.S.A. for study years 1999-2000 and 2000-2001. Fine fescue
(Festuca rubra L. cv. Bridgeport) was grown for seed at this site. The error bars indicate
± I SE. (ii = 4). Arrow denotes when fertilizer was applied.
Crop Biomass and Nitrogen Accumulation
During the
1999-2000
and 2000-200
1
study years, at both locations, for seed
years one through two, tillage had no effect on fine fescue and tall fescue shoot biomass
and N accumulation compared to the direct seeded treatment (Fig. 11-14). There was a
significant difference between year of stand and shoot biomass and N accumulation. The
first- and third-year stands were similar, but second-year had 50% (WD, Marion, fine
fescue) more shoot biomass than first- or third-year stands (Fig. 12). Second-year
shoots contained 30% more N (Fig. 14), Tall fescue at MWD during the second year had
35% more shoot biomass than first year (Fig. 11). Second year shoots contained the same
N amount (Fig. 13). Tall fescue shoots accumulated about 300 kg N ha'
y4
(Fig. 13),
while fine fescue shoots accumulated approximately 200 kg N ha" y' (Fig. 14).
Results suggest that tall fescue at the M.VD site was more efficient at utilizing
both fertilizer and mineralized soil N and that less excess N would be lost to ground and
surface waters (Table 6). During the fallow year, at the WD site both direct till and
conventional tillage had remaining nitrogen of2l 1 and 284 kg N ha"' and the MWD site
at 176 and 196 kg N ha"'. which could potentially be lost in the system during the fall and
winter high rainfall months. During the normal rainfall year, the WD site had an excess
of 167 ± 13 kgNha' and duringthedryyearanexcessofl4± 10 kgNha',theMWD
site was 64±45 kg N ha"' and 26±50 kg N hi'. This was determined by adding the
net annual mineralization and fertilizer N and then subtracting plant shoot N before
harvest. This does not take into account denitrification (not determined), which can
consume a fraction of the excess N when the soil is saturated (Horwath, 1998). Fine
fescue and tall fescue crop N uptake efficiency was very low during the fall season
resulting in significant (P = 0.05) soil N loss during the winter. In contrast, N uptake
efficiency during the spring was high, with soil N loss greatly reduced. This is further
evidence that fall fertilization would intensify N loss.
40000
-- Year I
0-- Year I
CT
NT
-y- Year 2- CT
vYear 2-NT
f 30000
B-- Year 3-CT
C
(I)
20000
E
4-
0
0
10000
0
10/99
1/00
4/00
7/00
10/00
1/01
4/01
7/01
Month/year
Figure 1 L Effects of no till (NT, open symbols) and conventional till (CT, closed
symbols) on tall fescue (Festuca arunthnaceum S.J. Dartyshire cv. Hounddog) above
ground biomass accumulation during the 1999-2000 and 2000-2001 study years. The
error bars indicate ± 1 S.E. (n = 4). Arrow denotes when fertilizer was applied.
41
20000
-0- Year 1 - NT
-- Year I - CT
-A-- Year 3- CT
-- Year2-NT
r 15000
-E'- Year2-CT
5000
0
10/99
1/00
4/00
7/00
10/00
1/01
4/01
7/01
M onthlyear
Figure 12. Effects of no till (NT, open symbols) and conventional till (CT, closed
symbols) on fine fescue (Festuca ru/ira L. cv. Bridgeport) above ground biomass
accumulation during the 1999-2000 and 2000-200 1 study years. The error bars indicate ±
1 S.E. (n = 4). Arrow denotes when fertilizer was applied.
42
500
400
z
300
z
0
0
.
U,
100
iI
10/99
2/00
6/00
10/00
2/01
6/01
Month/year
Figure 13. Effects of no till NT, open symbols) and conventional till (CT, closed
symbols) on tall fescue (Festuca arundinaceum S.J. Dartyshire cv. Hounddog) above
ground biomass nitrogen accumulation during the 1999-2000 and 2000-200 1 study years.
The error bars indicate ± 1 S.E. (n = 4). Arrow denotes when fertilizer was applied.
43
500
-- Yearl-CT
0-- Year 1 - NT
-y-- Year2-CT
vYear 2-NT
400
U-- Year 3- CT
300
0
200
(I)
100
0
10/99
1/00
4/00
7/00
10/00
1/01
4/01
7/01
Month/year
Figure 14. Effects of no till (NT, open symbols) and conventional till (CT, closed
symbols) on fine fescue (Festuca rubra L. cv. Bridgeport) above ground biomass
nitrogen accumulation during the 1999-2000 and 2000-200 1 study years. The error bars
indicate ± 1 S.E. (n 4). Arrow denotes when fertilizer was applied.
44
Table 6. The effects of tillage on annual net mineralization, plant (shoot + root) N
accumulation and fertilizer input for moderately well drained (Benton site) and a well
drained (Marion site) soils located in Willamette Valley, Oregon, U.S.A. Fine fescue
(Festuca rubra L. cv. Bridgeport) and tall fescue Festuca arundinaceum S.J. Dartyshire
cv. Hounddog) were grown for seed. The rate of N fertilizer applied for all treatments and
sites was 134 kg N h&' yf' applied as a split application in the spring. For both species,
root N was determined to be about 11% of the total plant N accumulated (Griffith,
unpublished).
Plant
Site
Season
Marion
2000-2001
Fallow
1999-2000
1st year
Remaining
N
Annual Net
Mineralization Accumulation Nitrogen
(kg N ha1yr1) (kg N ha1 yr') (kg N ha1)
211
284
NT
CT
77
150*
NT
CT
164
192*
147
161
NT
CT
32
89*
161
5
202
21
CT
187
166
155
NT
CT
42
62
NT
CT
83
NT
CT
60
CT
150
193
2000-200 1
2nd year
1999-2000
3rd year
Benton
2000-2001
Fallow
176
196
1999-2000
1St year
2000-2001
2nd year
2000-2001
3rd year
= 0.05 level
246
328
-29
-127
35
203
307
-9
-138
47
134
47
68
CONCLUSIONS
This research confirms previous findings that fine fescue and tall fescue seed
yield was not affected by conventional tillage and planting operations, compared to no till
directing seeding (Gohlke et al., 1999; Steiner et al., 2002). Findings here, though, were
first to show under in Oregon grass seed productions systems that tillage directly
impacted soil abiotic and biotic factors to the extent of reducing N retention. For
example, tillage enhanced mineralization resulting in more NO3 produced at a time when
the crop was less actively growing and plant N demand was lowest. Soil NO3 surplus
during this period had high leaching potential from future late-fall and winter rainfall.
This is especially true for fallow years as plant demand is very low. Data here indicated
that the magnitude of this response is enhanced in better-drained soils. These findings do
not support the practice of fall fertilization of grass seed crops grown in western Oregon
where the majority of the approximately 1100 mm of precipitation occurs late-fall and
winter. The lower recommended N fertilizer rates for fine fescue, 34 to 56 kg N ha',
compared to tall fescue, 101 to 151 kg N ha' (Young et al., 2002), seem reasonable
considering that the fine fescue site WD soils provided greater amounts of mineralized N
than the MWD soils in which tall fescue was grown. Growers should keep in mind that
mineralized N inputs can vary annually with changes in weather, so the optimum N
fertilizer rate might need to be adjusted. Data here indicate that drier years reduce
mineralized-N inputs; therefore adjustments in N rate may be necessary. It was found that
MBC was higher in direct tillage compared to conventional tillage. This result
corroborates, in general, the numerous reports of other investigators that MIBC was
increased under direct seeding (Doran,
et al.,
1994).
1980;
Carter and Rennie,
1982;
Franzluebbers
Microorganisms take part in the degradation of organic compounds and
nutrient cycling into elements that are assimilable by plants. Microbial biomass in one of
the most sensitive parameters, as a consequence, any change in environmental and
agronomic conditions will have an impact on microbial biomass.
Aside from the environmental impact of tillage on soil quality, another incentive
for farmers to convert to direct seeding, over conventional crop establishment, would be
the proven economic advantage and time saved during conventional field preparation
(Gohike et al.,
1999,
Steiner et al.,
2002).
Steiner et al.
(2002)
reported a savings of $593
(U.S.) per hectare for direct seeding establishment.
More research is needed under western Oregon climatic conditions to understand
N processes as influenced by tillage and soil drainage. Future studies could examine more
sites of differing soil drainage class.
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