AN ABSTRACT OF THE THESIS OF in
Title:
Susan M. Kauffman
Soil Science for the degree of presented on
Master of Science
4 March 1994
Inorganic Nitrogen and Soil Biological Dynamics in Cover Crop Systems
Abstract approved:
Richard P. Dick
Potential leaching of nitrate (NO3 ") into groundwater is of concern in the
Willamette Valley of Oregon. Knowledge of seasonal trends in the soil biology can aid in understanding soil system NO3- dynamics. Biological trends and seasonal leaching patterns in three cover crop systems were compared in plots selected from a long-term rotation study initiated in fall 1989 at North
Willamette Research and Extension Center near Canby, on a Willamette silt loam (fine-silty, mixed, mesic Pachic Ultic Argixeroll). This part of the study was set up as a randomized split plot block with four replications. The main plot was cropping system, represented by a conventional winter wheat/fallow/ vegetable rotation and two alternative vegetable/cover crop rotations. Winter wheat (Triticum aestivum) was in production in the conventional rotation from fall 1991 through summer 1992. Broccoli (Brassica oleracea) was produced in all three rotations in summer 1991 and 1993, and sweet corn (Zea mays) was produced in only the alternative rotations in summer 1992. Winter cover crops in the alternative rotations were cereal rye (Secale cereale L.) and a mix of rye/Austrian winter pea (Pisum sativum ssp. arvense). Subplots were amended with urea fertilizer at zero (No), medium (NI), or high (N2) rates: 0, 67, and 179 kg ha-' for wheat; 0, 140, and 280 kg ha-` for broccoli; and 0, 56, and 224 kg ha' for sweet corn. Soil samples collected monthly during the first year and quarterly during the second were analyzed for ammonium (NH4+) and NO3- at 0 to 20, 20 to 40, and 40 to 80 cm and assayed for protease, P-glucosidase, and microbial biomass at the surface depth.

Up to 25% more N was available to corn or broccoli in the plots with rye/pea cover than in the rye or conventional plots. Net mineralization of incorporated cover crop residue continued through the summer seasons.
In general, significantly more NO3- (up to 100%) was found between 40 and 80 cm under the rye/pea plots than under the conventional or rye plots. The estimated average loss of NO3- in the fall was as high as 60 kg ha-1, but cover crops recovered as much as 65 kg ha-' of NO3 that mineralized during the mild portions of the winters.
Crop and N treatment effects on biological parameters were not significant except when they reflected incorporation of plant residues. Abrupt changes in moisture and temperature appeared to have the greatest effect on soil biology and N mineralization.

Inorganic Nitrogen and Soil Biological Dynamics in
Cover Crop Systems by
Susan M. Kauffman
A THESIS submitted to
Oregon State University in partial fulfillment of the requirements for the degree of
Master of Science
Completed 4 March 1994
Commencement June 1994

APPROVED:
Redacted for Privacy
Associate Professor of Soil Science in charge of major
Head of Department of Crop and Soil Science
Redacted for Privacy
Dean of Graduate Sc
Date thesis is presented
Typed by researcher for
4 March 1994
Susan M. Kauffman

ACKNOWLEDGEMENTS
number of people deserve thanks for making the final product possible.
My major professor, Dr. Richard Dick, is among those responsible for designing the rotation plots of which this study is a part.
thoughtful experimental design and for his help in interpreting the data.
The assistance of Joan Sandeno has been invaluable.
emotional as well as technical support (not to mention M&M's in times of need).
Dr. Steve Petrie of the Unocal Agricultural Services Division helped to obtain funding from Unocal and also provided constructive feedback.
Dr. Neil Christensen and Dr. Delbert Hemphill offered helpful information both before and during my thesis defense, and I thank them for their attention to detail.
Mary Fauci saved me from having to reconstruct methods from the original papers. I thank her for the time she spent developing protocols for many assays, and for her willingness to share information.
Morten Miller, Bob Christ, Kendall Martin, and Nancy Baumeister all provided willing technical and computer assistance, and I especially thank
Morten for his "hang loose" style and the way he kept me from losing my mind during my first year here. Break another flask, Morten- -you deserve it!!
John Burket, Mujibul Islam, Faustin Iyamuremye, and Helene Murray all periodically reminded me that the world extends beyond enzyme assays. I thank them for the collective sense of humor they've brought to the place.
Leigh Cimino and Dave D 'Amore were both welcome companions on the road to statistical understanding, and Leigh, Tad Buford, and Joe Federico were understanding and enjoyable office mates. Thank goodness Leigh and I simultaneously admitted our cluelessness in Soil Physics!!
Carle and I enjoyed many evenings and wee hours of mornings together.
He may be a little square, but inside, he's a real machine.

Many field workers and lab helpers dug holes, hauled soil, weighed samples, ran assays, washed glassware, steamed, labeled, sieved, and did other not-necessarily-enjoyable tasks. I thank Zachary Lee, Ann Vanderpool, Bryan
Coyle, Hung Phan, Scott Avila, Phil Landis, Randall Trox, Evan Day, Jason
Ewert, Eric and Heidi Sandeno, Krishna Rauniyar, Rowdy, and Gregg Baird.
I thank them from the bottom of my heart.

TABLE OF CONTENTS
INTRODUCTION
CHAPTER 1 Literature Review
Soil N Dynamics
Soil Biological Properties
Cover Crops
Literature Cited
CHAPTER 2 Nitrogen Availability and Leaching
Abstract
Introduction
Materials and Methods
Results and Discussion
Conclusions
Literature Cited
CHAPTER 3 Biological Parameters
Abstract
Introduction
Materials and Methods
Results and Discussion
Conclusions
Literature Cited
CHAPTER 4 Summary and Perspectives
BIBLIOGRAPHY
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TABLE OF CONTENTS, continued
APPENDICES
Appendix
Appendix
Appendix
Appendix
Appendix
Appendix
Appendix
Appendix
Appendix
A:
B:
C:
D:
E:
F:
G:
H:
I:
Appendix J:
Appendix K:
Appendix L:
Appendix M:
Data files for biological parameters
Data files for inorganic N
Enzyme activities after harvest
Microbial biomass after harvest
Ammonium after harvest
Nitrate after harvest
Analysis of variance for nitrate-N in year one
Analysis of variance for nitrate-N in year two
Analysis of variance for nitrate-N with time as a factor for September 1991, 1992, and 1993
Analysis of variance for MBc, CO2 respiration and
N flush at 0 to 20 cm depth
Analysis of variance for MBc, CO2 respiration and
MBN with time as a factor for September at 0 to
20 cm depth
Analysis of variance for enzyme activity in year one at 0 to 20 cm depth
Analysis of variance for enzyme activities with time as a factor for September 1991 and 1992
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LIST OF TABLES
Table
2.1.
Baseline soil information from North Willamette Research and
Extension Center Vegetable Rotation Plots, 19 Sept. 1989.
2.2.
Crop rotation plan, North Willamette Research and Extension
Center Vegetable Rotation Plots.
2.3.
Sampling dates in this study.
2.4.
Uptake of N in cover crops, Spring 1993.
3.1.
Meteorological data from North Willamette Research and
Extension Center
3.2.
Microbial biomass related parameters from both summers of the study, averaged over crop and N treatments.
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LIST OF FIGURES
Figure
2.1
Crop rotation sequence.
2.2
2.3
2.4
2.5
2.6
Distribution of NO3 in the soil profile as of 16 Sept. 1991.
Distribution of NO3 in the soil profile as of 31 Oct. 1991.
Distribution of NO3 in the soil profile as of 3 Dec. 1991.
Distribution of NO3in the soil profile as of 3 Jan. 1992.
Distribution of NO3in the soil profile as of 1 Feb. 1992.
2.7
2.8
Distribution of NO3in the soil profile as of 29 Feb. 1992.
Distribution of NO3in the soil profile as of 30 Mar. 1992.
2.9
2.11
Distribution of NO3 in the soil profile as of 16 May 1992.
2.10
NO3 in 0-20 cm depth on 3 July (Rye and Rye/pea) and 29 July
1992.
Distribution of NO3- in the soil profile as of 4 Sept. 1992.
2.12
Distribution of NO3- in the soil profile as of 14 Nov. 1992.
2.13
Distribution of NO3- in the soil profile as of 13 Feb. 1993.
2.14
Distribution of NO3 in the soil profile as of 22 May 1993.
2.15
Distribution of NO3 in the soil profile as of 4 Aug. 1993.
2.16
Distribution of NO3 in the soil profile as of 3 Sept. 1993.
2.17
Distribution of NH4+ in the soil profile as of 4 Aug. 1993.
2.18
Distribution of NH4+ in the soil profile as of 3 Sept. 1993.
2.19
Total kg ha-1 NO3- in 80-cm profile, year 1.
2.20
Total kg ha-` NO3- in 80-cm profile, year 2.
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LIST OF FIGURES, continued
Figure
3.1
3.2
3.3
3.4
Effect of cropping system and N rate on microbial biomass carbon, year 1.
Effect of cropping system and N rate on microbial biomass carbon, year 2.
Effect of cropping system and N rate on microbial biomass nitrogen, year 1.
Effect of cropping system and N rate on microbial biomass nitrogen, year 2.
3.5
3.6
3.7
Effect of cropping system and N rate on microbial biomass C:N ratio, year 1.
Effect of cropping system and N rate on microbial biomass C:N ratio, year 2.
Effect of cropping system and N rate on specific respiration, year 1.
3.8
Effect of cropping system and N rate on specific respiration, year 2.
3.9
Effect of cropping system and N rate on f3- glucosidase, year 1.
3.10
Effect of cropping system and N rate on protease, year 1.
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Inorganic Nitrogen and Soil Biological Dynamics in
Cover Crop Systems
INTRODUCTION
Potential leaching of nitrate (NO3) into groundwater is of concern in the
Willamette Valley of Oregon (Pettit, 1988). Little is known about the temporal and spatial behavior of NO3- in the agricultural systems of this area, and such information is needed to make sound recommendations and decisions about nitrogen (N) management.
Estimations of biological activity and measurements of available N made simultaneously may provide information about how N is made available in various cropping systems. Granatstein et al. (1987) speculate that the microbial biomass (MB) in a system may be a slow-release source of N for growing plants.
Soil samples were collected monthly during one year and quarterly during a second, from 0-20, 20-40, and 40-80 cm depths, in plots that were part
vegetable rotation study at North Willamette Research and Extension Center near
Canby, Oregon. The plots were arranged as a randomized split-plot block with four replications; three crop rotations (one winter fallow and two vegetable/ cover crop) were the main plots and three N fertilization rates (0-280
applied as urea) were the subplots. Ammonium and nitrate were quantified in samples from all three depths, and MB and enzyme activities were estimated in surface samples. Inorganic N and biological parameters will be discussed in
Chapters 2 and 3, respectively.

CHAPTER 1
LITERATURE REVIEW
2

SOIL N DYNAMICS
Soil N Fractions
Nitrogen (N) exists in soil in both organic and inorganic forms. In general, microorganisms are responsible for the transformation of N from its organic to its inorganic forms, and higher plants transform inorganic forms, of which they use only ammonium (NH4+) and nitrate (NO3-), into organic forms
(Richards, 1987).
The organic fraction in soil is divided into four general categories. These comprise plant and animal residues, microbial biomass (MB; functioning, dormant, or dead), partially stabilized decayed organic matter, and the humus fraction. The first three are available to microbes for energy and cell synthesis
humification, it is in a very recalcitrant form and only very slowly decomposed
(Stevenson, 1986).
Inorganic N comes ultimately from the atmosphere as N2. Higher plants have no access to this form and must rely on biological fixation by either symbiotic or free-living organisms to transform the N2 into plant-available forms.
The Rhizobium-legume relationship, by which the bacteria fixes N2 in the form of NH3 and exchanges it for carbon (C) energy from the photosynthetic plant, is a major source of N in agricultural soils. Fixation by rain and lightning constitute a negligible portion of the atmospheric N made available (Richards,
1987).
Soil N processes
3
Microorganisms transform N in four main biochemical processes: ammonification, nitrification, denitrification, and immobilization.
Ammonification, the transformation of organic compounds to NH4+, is a facultatively anaerobic process, and thus is carried out regardless of oxygen

4 availability and moisture conditions. Nitrification, the oxidation of NH4+ into
NO3-, is performed by obligate aerobes, so that availability of oxygen determines whether there will be an accumulation of NO3- or of NH4+ (Stevenson, 1986).
4.0, but is negligible below pH 5.0 (Richards, 1987). Denitrification, the conversion of NO3 to gaseous forms, occurs only under anaerobic conditions and represents a loss of N from the system (Stevenson,1986).
even in well-drained soils, anaerobic conditions can exist in the centers of soil aggregates so that denitrification occurs to some extent in almost every soil
(Tiedje, et al., 1984). Immobilization is the synthesis of N into microbial tissue, a form that is five times more available to other microbes than is native soil organic N (Stevenson, 1986).
If the C:N ratio of crop residues is greater than 30, microorganisms will assimilate all available N, bringing about net immobilization. If residue C:N ratio is below 30, net mineralization will occur because microorganisms cannot utilize all of the N. Net mineralization eventually occurs when microbial death makes more N available to survivors. Residue factors other than C:N ratio that influence decomposition include lignin:N ratio, age and particle size, and microflora indigenous to the residue itself. Moisture and the availability of oxygen are soil factors that influence decomposition (Parr and Papendick, 1978;
Richards, 1987).
N losses from soil
Several chemical phenomena exist by which N can be lost from the internal soil cycle. NH4+ can be fixed by certain clay minerals, and NH3 can be immobilized in organic matter (Stevenson, 1986). Loss by NH3 volatilization is also a concern if a cover crop is left on the soil surface for erosion control or snow catching (Janzen and McGinn, 1991). Denitrification, as mentioned above, can be a major loss from poorly-aerated or waterlogged soils. Finally, there is the loss by leaching of NO3 that occurs because both NO3- and soil particles are

negatively charged and the NO3- does not adsorb to soil particles as do cations such as NH4 + and Ca++.
5
Leaching and related issues
Nitrate leaching is of concern in many agricultural areas because nitrate in groundwater supplies can be a health and pollution hazard. In a survey in the
Willamette valley of Oregon, water in 28 out of 126 wells tested was found to exceed the 10 mg L-' limit of NO3- N, and 60 wells contained greater than 5 mg
L-1 (Pettit, 1988). Agricultural sources of N may not be entirely to blame for the problem, as seasonal variations in soil NO3- for the same land use can be greater than those between wooded, agricultural, and grassland soils (Trudgill et al.,
1991). Whitmore et al. (1992) estimated that half of the potentially-leachable
NO3 from a newly-plowed grassland is already gone in five years, and suggests that fertilizer restrictions may be misplaced. Most Oregon soils have been under cultivation for over one hundred years, but since N is one of the highest energy inputs in agriculture (Keeney, 1982), it should be managed as efficiently as possible.

6
SOIL BIOLOGICAL PROPERTIES
Microbial Biomass
Microorganisms in soils are an important source and sink for nutrients and play a critical role in nutrient transformations. Microbial biomass is being proposed as a measure of soil health and productivity, and has been called a good indicator of the intensity of soil life and soil microbial activity (Perucci,
1992).
Several methods have been used to quantify MB in soils. Direct counting can be useful in understanding population structures, but can also be cumbersome and inaccurate in that dead organisms are often counted as part of the functioning biomass. Several variations of CHC13 fumigation, with or without addition of glucose or reinoculation with soil organisms, are the most widely used. Another method, ATP determination, is not commonly used because of high cost and complicated lab procedures (Parkinson and Paul, 1982).
Greater cropping intensity appears to increase soil microbiological activity. Comparing adjacent farms in eastern Washington, Bolton et al. (1985) found that microbial populations and enzyme activities were higher in the organic system that utilized legumes as its N source than in an adjacent system that received anhydrous ammonia annually as its N source. Likewise, biological measurements were significantly lower in wheat-fallow systems than in annuallycropped systems in eastern Oregon (Collins et al., 1992), and MB and potentially mineralizable N reserves were greater in systems including legumes in southeastern Pennsylvania (Doran et al., 1987).
Immobilization of N by the microbial community upon incorporation of crop residue can be a problem, but
Allison and Killham (1988) found that systems apparently adapt to regular inputs of organic matter by increasing their fungal populations, so turnover of organic matter becomes progressively more rapid.
Whereas Doran et al. (1987) found differences due to cropping systems,
Amato and Ladd (1992) concluded from lab incubations that soil charge and

structure may be more influential in the accumulation of MB than are substrate type and concentration. Angers et al. (1992) found that microbial biomass carbon (MBc), taken as a percent of total soil organic matter (SOM), was not affected by cropping system during the first year in which their rotations were in place.
Microbial biomass N accumulated during fallow periods may be a gradual source of plant-available N during subsequent crop growing seasons.
Bremer and van Kessel (1992a), in an 151\1-partitioning study, found that the residue 15N in MB decreased, but that the net 15N mineralization increased during a growing season, and determined that the MB was the source of the mineralized
15N. Doran et al. (1987) also found that when NO3 was high, microbial biomass
N (MBN) was low, and vice versa. A major source of leachable NO3 ", according to Martinez and Giraud (1990) is dead MB that has been desiccated during the summer and is mineralized by survivors when fall rains revive them from dormancy. Granatstein et al. (1987) found that the no-till rotations they studied may approach an ideal situation in which a large MB during fallow captures nutrients and releases them slowly to subsequent crops. In contrast, Bonde et al.
(1988) concluded from a lab incubation study that MBN was not a major source of plant-available N, but rather that it processed other SOM fractions and made
N available from those. Yaacob and Blair (1980) found that the addition of organic residues stimulated the release of native organic N and referred to this as a positive priming effect, the magnitude of which increased with longer cropping histories, on each of several soils.
The C:N ratio of the MB is of interest in studies that monitor seasonal changes. Fungi generally have larger C:N ratios than do bacteria, so changes in the ratio can be a sign of population shifts (Jenkinson, 1976; Anderson and
Domsch, 1980)
One more microbially-related quantity is specific respiration (SR = CO2-
C flush / MBc). Campbell et al. (1991) calculated SR once during a growing season and concluded that there was greater SR in systems with a smaller MB.
Insam et al. (1991) found a negative correlation between SR and soybean yield
7

and expressed concern that systems receiving the least input of organic matter lose the most CO2 to the atmosphere.
8
Enzymes
Soil enzymes are excreted by microbial cells to obtain energy and cell constituents from the soil environment (Burns, 1982), and are thus crucial in the cycling of soil nutrients.
Extraction and purification of enzymes from soils has proved difficult, so most studies on soil enzymes have measured the rates of enzyme activities. The major problem in designing an assay of enzyme activity is the dinstinction between intracellular and extracellular activity. There are several methods for retarding or minimizing microbial growth and activity during these assays (Tabatabai, 1982).
Enzymes may be indicators of soil quality (Kiss et al., 1978) or of MB
(Ladd, 1978) and are known to be sensitive to long-term residue practices (Dick, et al., 1988), being not as sensitive to tillage alone as to tillage plus incorporation of crop residues (Martens et al., 1992). Khan (1970) found that activities of several enzymes were significantly greater in soils from a five-year grain and legume rotation than in those from a wheat-fallow rotation. Both rotation systems had been in place for forty years. Dick (1984) observed significantly higher enzyme activities in the surface 7.5 cm of soils under no-till management than in conventionally- tilled soils. Speir et al. (1980) monitored the activities of sulfatase, urease, and protease in planted and unplanted pots and observed that the presence or absence of plants significantly affected sulfatase and urease activities.
13-glucosidase is an important part of the soil C cycle.
Its end product is a simple sugar that is a major source of energy for microbes (Tabatabai, 1982).
Although it functions extracellularly, it is relatively long-lived because of complexation with humic materials (Ladd, 1978). It may also be colonized and/or protected by extracellular polymers (Martens and Frankenberger, 1991).

It is thought to be produced primarily by fungi (Hayano and Katami, 1977;
Hayano and Tubaki, 1985).
The activity of 13-glucosidase has been found to increase, although not significantly, with greater rates of N fertilizer (Dick et al., 1988; Kirchner et al.,
1993). This observation concurs with that of Eivazi and Tabatabai (1990), who found that P-glucosidase, among several soil enzymes, was one of those least inhibited by the addition of KNO3 and (NH4)2SO4.
Proteases play a part in the N cycle by degrading organic residues into energy, nutrients, and humic matter (Niskanen and Eklund, 1986). They tend to be short-lived in the soil because they are attacked by other enzymes (Ladd and
Butler, 1975) or adsorbed onto soil colloids and rendered inaccessible and thus inactive toward high molecular weight substrates (Rowell et al., 1973). Ross and
McNeil ly (1975) found no correlation between protease and N mineralization activities. They observed no clear sequence of trends in activity over time, confirming that the duration and function of soil protease is unpredictable.
9

10
COVER CROPS
General attributes
Cover crops have a long history of use, both to provide N for the succeeding crop and to recover N to reduce leaching. Long-term research on cover crops was conducted prior to the widespread use of synthetic N fertilizers.
the primary focus of this research was to determine the potential of legumes to fix N2 and of grasses to conserve N. It was found that certain legumes can make substantial N available and certain grasses can significantly reduce leaching (Morgan et al., 1942; Chapman et al., 1949; Karraker et al., 1950).
Cover crops can also reduce soil erosion, improve moisture-holding capacity, and increase the availability of other nutrients (Pieters and McKee, 1929; Lewis and
Hunter, 1940; Rodgers and Giddens, 1957). Greater cropping intensity has potential to reduce NO3- leaching because it leaves less NO3- in the soil profile.
It also provides for higher equilibrium levels of organic C and N (Wood et al.,
1991).
Grasses
A cover crop of rye has been shown capable of reducing leaching by
67% (Martinez and Giuraud, 1990). Shipley et al. (1992) observed a recovery
to summer crops.
Rye has been found to significantly reduce corky root, a lettuce pathogen
(Van Bruggen et al., 1990). More research is needed concerning the positive and negative effects of cover crops on plant pathogens.

11
Legumes
Among the many benefits of legume cover crops is that improvement in soil physical properties such as water-stable aggregate (WSA) size and infiltration rate (McVay et al., 1989). Badaruddin and Meyer (1989) found that
N uptake and N use efficiency were higher following a legume cover crop than following a period of fallow or fertilized wheat. They suggested that this was because there was more mineral N in the legume systems. Austrian winter pea
(AWP) has been capable of scavenging up to 40% of available soil N at 30° C
(Power and Zachariassen 1993) and has proved to be effective in competing against weeds (Biederbeck et al., 1993). AWP has been found to contribute up to 30 kg N ha-1 to a succeeding crop (Mahler and Auld, 1989). Wagger (1989) found that the time of desiccation of a legume affected the rate of N release to the soil.
Legume cover crops have been estimated to contribute up to 123 kg ha-1 to a succeeding crop (Ranells and Wagger, 1992; Mitchell and Teel 1977;
McVay et al., 1989; Mahler and Auld, 1989) using subtraction from original residue in mesh bags, subtraction of N available in fallow treatments, and fertilizer replacement estimates.
Many investigators have attempted to quantify this ability to contribute N to the system, and knowledge of comparative benefits of N fertilizer and green manure crops is essential to growers weighing cost effectiveness of both treatments. Janzen et al. (1990) found that the biggest addition by green manure to the soil N cycle was to the stable organic N pools; it was several times greater than that of the N fertilizer applied. The magnitude of the contribution depended on the N yield of the green manure and on the percentage of the N yield obtained by N2 fixation (N new to the system). Green manure was used less efficiently than the fertilizer by subsequent plants. Although crop uptake of green manure N may be low, it is important to consider that any residual soil N becomes less available as time passes and it becomes converted to stable humus.
This higher level of organic matter ensures the continual turnover of the

12 mineralization-immobilization cycle and promotes biological activity (Stevenson,
1986).
Hairy vetch, when used in combination with N fertilizer, has been found in Kentucky to possibly enhance grain yields beyond what can be obtained using
N alone. Rye, on the other hand, may reduce yield compared to fallow (Blevins et al., 1990). Both can provide better weed control, increased water conservation, and avoidance of nitrate losses through leaching (Blevins, et al.,
1990). Although hairy vetch enhances the effects of fertilizer N, it is suggested that for maximum corn yield, N fertilizer use should not be decreased following a cover crop of hairy vetch (Utomo et al., 1990).
Legumes and water quality
The use of legume cover crops, while it generally contributes N to the farming system, may not reduce nitrate leaching (Russel le and Hargrove, 1989).
But Janzen et al. (1990) found that 57% of fertilizer N, applied in spring, and
72% of green manure N, from flatpea or lentil, turned under in spring, were recovered in organic matter or microbial biomass (MB) in soil cropped to spring wheat, probably in forms resistant to leaching and denitrification. The wheat recovered 14% of green manure N and 36% of fertilizer N. Immobilization of cover crop N by the MB in the system can temporarily deplete plant-available N
(Karlen and Doran, 1991) and release it after the succeeding crop has completed most of its N uptake. Therefore, it is important to manage cover crops in such a way that the N they make available is in synchrony with the N needs of the succeeding crop (Huntington et al., 1985).
Current issues in cover cropping
The actual fate of N from cover crops in the soil is still poorly understood. Since the use of 15N has become widespread, a discrepancy has arisen between the "N benefit" (the yield response) of legume cover crops and

the cover crop N actually taken up by the succeeding crop (Bruulsema and
Christie, 1987). Several researchers have found that 25% or less of cover crop
N is actually taken up by the next crop (Janzen et al., 1990; Ta and Faris, 1990;
Muller and Sundman, 1988; Bremer and van Kessel, 1992a), and this reduces to around 5% in second seasons (Ladd et al., 1983). Harris and Hesterman (1990) reported that 96% of 15N applied in alfalfa remaining in soil was in the organic fraction and MB N was 15% of that. The discrepancy between estimates of N contribution from 15N and non-15N methods was attributed by Yaacob and Blair
(1980) to a "priming effect", wherein addition of organic residues stimulates the release of native soil organic N. It is therefore difficult to determine the fate of all N in the system, including N from legumes, native organic matter, and fertilizer, and decide whether the N gain by the use of legume cover crops outweighs the loss of N (possibly not mineralized at the right time) through leaching, and through mineralization of native SOM.
13

14
LITERATURE CITED
Allison, M.F., and K. Killham. 1988. Response of soil microbial biomass to straw incorporation. J. Soil Sci. 39:237-242.
Amato, M., and J.N. Ladd. 1992. Decomposition of HC-labelled glucose and legume material in soils: properties influencing the accumulation of organic residue C and microbial biomass C. Soil Biol. Biochem. 24:455-
464.
Anderson, J.P.E., and K.H. Domsch. 1980. Quantities of plant nutrients in the microbial biomass of selected soils. J. Soil Sci. 130:211-216.
Angers, D.A., A. Pesant, and J. Vigneux. 1992. Early cropping-induced changes in soil aggregation, organic matter, and microbial biomass. Soil Sci. Soc.
Am. J. 56:115-119.
Badaruddin, M. and D.W. Meyer. 1989. Forage legume effects on soil nitrogen and grain yield, and nitrogen nutrition of wheat. Agron. J. 81:419-24.
Biederbeck, V.O., O.T. Bowman, J. Loomen, A.E. Slinkard, L.D. Bailey, W.A.
Rice, and H.H. Janzen. 1993. Productivity of four annual legumes as green manure in dryland cropping systems. Agron. J. 85:1035-1043.
Blevins, R.L., J.H. Herbek, and W.W. Frye. 1990. Legume cover crops as a nitrogen source for no-till corn and grain sorghum. Agron. J. 82:769-772.
Bolton, H., Jr., L.F. Elliot, R.I. Papendick, and D.F. Bezdicek. 1985. Soil microbial biomass and selected soil enzyme activities: effect of fertilization and cropping practices. Soil Biol. Biochem. 17:297-302.
Bonde, T.A., J. Schniirer, and T. Rosswall. 1988. Microbial biomass as a fraction of potentioally mineralizable nitrogen in soils from long-term field experiments. Soil Biol. Biochem. 20:447-452.
Bremer, E. and C. van Kessel. 1992. Plant-available nitrogen from lentil and wheat residues during a subsequent growing season. Soil Sci. Soc. Am. J.
56:1155-1160.
Bruulsema, T.W., and D.R. Christie. 1987. Nitrogen contribution to succeeding maize from alfalfa and red clover. Agron. J. 79:96-100.
Burns, R.G. 1982. Enzyme activity in soil: location and a possible role in microbial ecology. Soil Biol. Biochem. 14:423-27.

Campbell, C.A., V.O. Biederbeck, R.P. Zentner, and G.P. Lafond. 1991. Effect of crop rotations and cultural practices on soil organic matter, microbial biomass and respiration in a thin Black Chernozem. Can. J. Soil Sci.
71:363-376.
15
Chapman, H.D., G.F. Leibig, and D.S. Rayner. 1949. A lysimeter investigation of nitrogen gains and losses under various systems of covercropping and fertilization, and a discussion of error sources. Hilgardia 19:57-128.
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Granatstein, D.M., D.F. Bezdicek, V.L. Cochran, L.F. Elliot, and J. Hammel.
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Harris, G.H., and O.B. Hesterman. 1990. Quantifying the nitrogen contribution from alfalfa to soil and two succeeding crops using 15N. Agron. J. 82:
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Hayano, K., and K. Tubaki. 1985. Origin and properties of (3- glucosidase activity of tomato-field soil. Soil Biol. Biochem. 17:553-557.
Huntington, T.G., J.H. Grove, and W.W. Frye. 1985. Release and recovery of nitrogen from winter annual cover crops in no-till corn production.
Commun. Soil Sci. Plant Anal. 16:193-211.

16
Insam, H., C.C. Mitchell, and J.F. Dormaar. 1991. Relationship of soil microbial biomass and activity with fertilization practice and crop yield of three ultisols. Soil Biol. Biochem. 23:459-464.
Janzen, H.H., J.B. Bole, V.O.Biederbeck, and A.E. Slinkard. 1990. Fate of N applied as green manure or ammonium fertilizer to soil subsequently cropped with spring wheat at three sites in western Canada. Can. J. Soil
Sci. 70:313-323.
Janzen, H.H., and S.M. McGinn. 1991. Volatile loss of nitrogen during decomposition of legume green manure. Soil Biol. Biochem. 23(3):291-7.
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Karlen, D.L., and J.W. Doran. 1991. Cover crop management effects on soybean and corn growth and nitrogen dynamics in an on-farm study. Am. J. Alt.
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Karraker, P.E., C.E. Bortner, and E.N. Fergus. 1950. Nitrogen balance in lysimeters as affected by growing Kentucky Bluegrass and certain legumes separately and together. Bulletin 557, Ky. Ag. Expt. Sta., Univ.
of Kentucky, Lexington.
Keeney, D.R. 1982. Nitrogen management for maximum efficiency and minimum pollution. p. 605-650. In F.J. Stevenson (ed.) Nitrogen in agriculture. Agron. Monog. 22. ASA and SSSA, Madison, WI.
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(ed.) Soil Enzymes. Academic Press, London.
Ladd, J.N., M. Amato, R.B. Jackson, and J.H. Butler. 1983. Utilization by wheat of nitrogen from legume residues decomposing in the field. Soil Biol.
Biochem. 15:231-238.

Ladd, J.N., and J.H.A. Butler. 1975. Humus-enzyme systems and synthetic organic polymer-enzymes analogs. p. 143-194. In E.A. Paul and A.D.
McLaren (ed.) Soil biochemistry. Vol. 4. Marcel Dekker, New York.
Lewis, R.D., and J.H. Hunter. 1940. The nitrogen, organic carbon, and pH of some southeastern coastal plain soils as influenced by green-manure crops. Agron. J. 32:586-601.
McVay, K.A., D.E. Radcliffe, and W.L. Hargrove. 1989. Winter legume effects on soil properties and nitrogen fertilizer requirements. Soil Sci. Soc. Am.
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17
Mahler, R.L., and D.L. Auld. 1989. Evaluation of the green manure potential of
Austrian winter peas in northern Idaho. Agron. J. 81:258-64.
Martens, D.A., and W.T. Frankenberger, Jr. 1991. Saccharide composition of extracellular polymers produced by soil microorganisms. Soil Biol.
Biochem. 23:731-736.
Martens, D.A., Johanson, J.B., and W.T. Frankenberger, Jr. 1992. Production and persistence of soil enzymes with repeated addition of organic residues.
Soil Sci. 153:53-61.
Martinez, J., and G. Guiraud. 1990. A lysimeter study of the effects of a ryegrass catch crop, during a winter wheat/maize rotation, on nitrate leaching and on the following crop. J. Soil Sci. 41:5-16.
Mitchell, W.H., and M.R. Teel. 1977. Winter anual cover crops for no-tillage corn production. Agron. J. 66:569-573.
Morgan, M.F., H.G.M. Jacobson, and S.B. LeCompte, Jr. 1942. Drainage water losses from a sandy soil as affected by cropping and cover crops.
Windsor Lysimeter Series C, Bulletin 466, Connecticut Ag. Expt. Sta.,
New Haven.
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Plant Soil 105:133-139.
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58:9-17.
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Agronomy, Madison, WI.
18
Perucci, P. 1992. Enzyme activity and microbial biomass in a field soil amended with municipal refuse. Biol. Feral. Soils 14:54-60.
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State of Oregon, Dept. of Environ. Qual., Portland, OR.
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19
Trudgill, S.T., T.P. Burt, A.L. Heathwaite, and B.P. Arkell. 1991. Soil nitrate sources and nitrate leaching losses, Slapton, South Devon. Soil Use
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Yaacob, 0., and G.J. Blair. 1980. Mineralization of '5N-labelled legume residues in soils with different nitrogen contents and its uptake by Rhodesgrass.
Plant Soil 57:237-248.

CHAPTER 2
NITROGEN AVAILABILITY AND LEACHING
20

21
ABSTRACT
Potential leaching of nitrate (NO3 -) into groundwater is of concern in the
Willamette Valley of Oregon. Seasonal leaching patterns in three cover crop systems were compared in plots selected from a long-term rotation study at
North Willamette Research and Extension Center near Canby, on a Willamette silt loam (fine-silty, mixed, mesic Pachic Ultic Argixeroll). This part of the study was set up as a randomized split plot block with four replications. The main plot was cropping system, represented by a conventional winter wheat/ fallow/vegetable rotation and two alternative vegetable/cover crop rotations.
Winter wheat (Triticum aestivum) was in production in the conventional rotation from fall 1991 through summer 1992. Broccoli (Brassica oleracea) was produced in all three rotations in summer 1991 and 1993, and sweet corn (Zea mays) was produced in only the alternative rotations in summer 1992. Winter cover crops in the alternative rotations were cereal rye (Seca le cereale L.) and a mix of rye/Austrian winter pea (Pisum sativum ssp. arvense). Subplots were amended with urea fertilizer at zero (No), medium (N1), or high (N2) rates: 0,
67, and 179 kg ha-1 for wheat; 0, 140, and 280 kg ha' for broccoli; and 0, 56, and 224 kg ha-Ifor sweet corn. Soil samples collected monthly during the first season and quarterly during the second were analyzed for ammonium (NH4+) and
Up to 25% more N was available to corn or broccoli in the plots with rye/pea cover than in the rye or conventional plots. Net mineralization of incorporated cover crop residue continued through the summer seasons. In general, significantly more NO3- (up to 100%) was found between 40 and 80 cm under the rye/pea plots than under the conventional or rye plots. The estimated average loss of NO3- in the fall was as high as 60 kg ha-1, but cover crops recovered as much as 65 kg ha-` of NO3 that mineralized during the mild portions of the winters.

22
INTRODUCTION
The leaching of NO3- is a concern in many agricultural areas because
NO3 in groundwater supplies can be a health and pollution hazard. In a survey in the Willamette Valley of Oregon, water in 28 out of 126 wells tested was found to exceed the drinking water standard of 10 mg L-1 for NO3--N, and 60 wells contained greater than 5 mg L-' (Pettit, 1988). In the Willamette Valley, the potential for NO3- leaching is particularly high because of the combination of intensive crop production and high fall and winter precipitation. Traditional management of these systems has left the soils fallow during the winter season.
Winter cover crops hold potential to both provide N for the succeeding
synthetic N fertilizers, considerable research on cover crops was done to evaluate their potential to provide N and maintain crop yields (Morgan et al., 1942).
With the pressing environmental concerns of agricultural systems, the focus of cover crops is now on their potential to reduce NO3- leaching to groundwater.
Cover crops recover residual fertilizer N applied in the summer and provide for higher equilibrium levels of organic carbon (C) and N (Wood et al.,
1991). Furthermore, cover crops as green manures help reduce soil erosion, improve moisture-holding capacity, and increase the availability of other nutrients (Lewis and Hunter, 1940; Pieters and McKee, 1929; Rodgers and
Giddens, 1957). Negative aspects of cover cropping include seed costs, additional operations such as establishment and incorporation of the cover crops, some potential for increased disease and pest problems, and reduced flexibility for planting the summer crop (Shennan, 1992).
Recent findings have shown that cereal rye can reduce leaching by 67%
(Martinez and Giuraud, 1990), and recover from 21% of N applied at a low rate to 48% of N applied at a higher rate (Shipley et al., 1992) .
Legume winter cover crops have several benefits. First, they can supply substantial amounts of N for subsequent crops. Estimates have been as high as
123 kg N ha-` (Ranells and Wagger, 1992; Mitchell and Teel 1977; McVay et al.

23
1989; Mahler and Auld, 1989). Also, legume cover crops can improve soil physical properties such as water stable aggregate (WSA) size and infiltration rate (McVay et al., 1989). Badaruddin and Meyer (1989) found that N uptake and N use efficiency were higher following a legume cover crop than following a period of fallow or fertilized wheat. They suggested that this was due to more mineral N in the legume systems. Austrian winter pea (AWP) is capable of scavenging up to 40% of available soil N at 30° C (Power and Zachariassen
1993) and has proved to be effective in competing against weeds (Biederbeck et al., 1993).
The use of legume cover crops, while it generally contributes N to the farming system, may not reduce nitrate leaching (Russel le and Hargrove, 1989).
The actual fate of N from cover crops in the soil is still not well understood. Since the use of '5N has become widespread, a discrepancy has arisen between the "N benefit" (the yield response) of legume cover crops and the cover crop N actually taken up by the succeeding crop (Bruulsema and
Christie, 1987). Recovery of cover crop N by subsequent crops has been found to be 25% or less the first year (Janzen et al., 1990; Ta and Faris, 1990; Muller and Sundman, 1988; Bremer and van Kessel, 1992a), and only 5% the second year (Ladd et al., 1983). The discrepancy between estimates of N contribution from '5N and non-'5N methods was attributed by Yaacob and Blair (1980) to a
"priming effect", wherein addition of organic residues stimulates the release of native soil organic N. It is therefore difficult to determine the fate of all N in the system, including N from legumes, native organic matter, and fertilizer, and decide whether the N gain by the use of legume cover crops outweighs the loss of N (possibly not mineralized at the right time) through leaching, and through mineralization of organic N fractions.
A further factor to consider for cover crop systems is synchronization of
N mineralization to uptake of N by summer crops and winter cover crops. This is because immobilization of cover crop N by the microbial biomass in the system can temporarily deplete plant-available N (Karlen and Doran, 1991) and release it after the succeeding crop is finished (Huntington et al., 1985).

24
Generally, studies exploring cover crop N availability throughout the season rarely include soil profile and leaching data. Cover crops are beginning to gain popularity and to be investigated in the Willamette Valley of western
Oregon, but to date few studies have been conducted in the area to aid in the understanding of NO3- dynamics as influenced by cover crops. Further, there are little or no data on the ability of grass/legume mixtures to affect groundwater quality (Meisinger et al., 1991). The present study compares N availability and
NO3 leaching in three vegetable cropping systems: two with winter cover crops
(a grass and a grass/legume mix), and one under the conventional winter fallow system, which includes winter wheat every third year.

25
MATERIALS AND METHODS
Soil
The plots sampled for this experiment were established in 1989 at the
OSU North Willamette Research and Extension Center near Canby, Oregon, on a
Willamette silt loam (Pachic Ultic Argixeroll), as part of a long-term study which was set up to compare traditional and alternative crop rotations. The
Willamette Valley, in which the study is located, has a Mediterranean climate with approximately 1000 mm annual rain, 650-700 mm of which falls between
November and April. The winters are mild, thus giving opportunity for leaching, and the summers tend to be warm and dry, sometimes necessitating irrigation.
For the previous four years, the plot area had been in a winter wheat-fallow rotation under locally recommended management practices. Baseline soil parameters are shown in Table 2.1.

Table 2.1.
Baseline soil information from North Willamette Research and
Extension Center Vegetable Rotation Plots, 19 Sept. 1989 (unpublished data, R.P. Dick, 1989).
26
Parameter pH
Total C 1
NO3 -N t
NH4+-N t
S042--S t
Extractable P042--P t
Histidase §
3- glucosidase 1
Sulfatase 1
Phosphatase 1
§ mg NH4+ kg soil" 48 hr-1
Depth
5.60
1.5
1058.0
14.6
9.8
81.3
9.4
2612.0
142.0
272.0
21.1
25.4
102.0
10 to 20 cm
6.18
1.5
1008.0
15.9
10.7
163.1
10.8
2632.0
140.0
260.0
30.9
29.0
118.0
Experimental Design
The experimental design was a randomized split plot block with four replications, in which crop treatment was the main plot. In fall 1991, the three crops were winter wheat, lye, and a mix of Austrian Winter Pea and rye (see
Fig. 2.1 and Table 2.2). All three were preceded by broccoli planted in spring
1991. The wheat, part of the traditional winter fallow rotation currently used in the area, was planted 17 Oct. 1991 and harvested 20 July 1992; these plots were

27 disked after harvest and not further disked until spring 1993. There was negligible growth of weeds and volunteer wheat during the fall and winter, so the conventional plots were essentially under bare fallow during the second year of the study. The two winter cover crops were part of the alternative system
corn was planted in these plots on 20 May 1992 at a spacing of 18 cm in 50-cm paired rows that were spaced 100 cm apart, and harvested 19 Aug. 1992.
Broccoli was seeded on 9 June 1993, thinned on June 28, and final-harvested on
30 Aug. 1993. All three plots received locally recommended pesticide and fertilizer treatments, with the exception of N.
Table 2.2. Crop rotation plan, North Willamette Research and Extension Center
Vegetable Rotation Plots.
Rotation
Conventional
Rye/pea
Rye S
F
S
F
St
Ft t spring t fall
§ cereal rye/pea
1989
Fallow
R/p §
Rye 1
1990
Corn
Fallow
Corn
R/p
Corn
Rye
Year
1991
Broccoli
Wheat
Broccoli
R/p
Broccoli
Rye
1992
Wheat
Fallow
Corn
R/p
Corn
Rye
1993
Broccoli
Fallow
Broccoli
R/p
Broccoli
Rye
Main plots were split into subplots for three urea-N fertilizer treatments of zero (No), medium (NI), and high (N2) N rates throughout the experiment.
Broccoli received zero, 140, or 280 kg N ha-I; in 1991, 140 kg N ha' was

28 applied to the NI and N2 plots on June 4, and the same rate was applied to only the N2 plots on July 1.
Jan. 1992), or 179 kg N ha4 (67 kg 24 January, 112 kg 15 Apr. 1992).
Field Methods
Samples were collected by hand on sixteen dates from September 1991 through September 1993 (exact dates Table 2.3) at depths of 0 to 20, 20 to 40, and 40 to 80 cm, using 2.5-cm diameter probes. Composite samples of ten cores per subplot were put into plastic-lined paper sample bags, transported at ambient temperature, and stored in the dark at 4°C. On 3 July 1992, the cover-cropped plots were sampled to 20 cm to estimate N availability midway through the corn
wheat harvest and stubble incorporation. In September 1991, 1992, and 1993, 0to 10- and 10- to 20-cm depth samples consisted of ten-core composites sampled by hand, and a Kauffman Soil Sampler (Marvin Kauffman, Albany, Oregon) was used to take composite samples of three cores per subplot at 20- to 40-, 40- to
sampled in Rep I only because of an underestimation of the number of workers required for the collection task.

29
Table 2.3. Sampling dates in this study.
16 Sept. 1991
31 Oct. 1991
3 Dec. 1991
3 Jan. 1992
1 Feb. 1992
Year 1
29 Feb. 1992
30 Mar. 1992
16 May 1992
3, 29 July 1992
Year 2
4 Sept. 1992
14 Nov. 1992
13 Feb. 1993
22 May 1993
4 Aug. 1993
3 Sept. 1993
Laboratory Methods
Samples were air-dried for 48 h and put through a 2-mm sieve after grinding with a mortar and pestle. They were stored at ambient temperature and
in 2 M KC1, and NH4-' and NO3- in the extracts determined by steam distillation
(Keeney and Nelson, 1982).
Data Analysis
Inorganic N data were converted from mg kg' using bulk densities measured on soils from North Willamette Research and Extension Center (John
Hart, client of OSU Soil Physics Laboratory).
Data were analyzed by standard ANOVA techniques for repeated measures on randomized split-plot blocks with a statistical software package
(SAS Institute, Cary, NC) Main effect means were separated with Tukey's studentized range test at the p = 0.05 level.

30
RESULTS AND DISCUSSION
Soil Profile Inorganic Nitrogen by Date
Distribution of NO3 and NH4 4- in soil profiles tended to have similar shapes for all nine treatments except when winter fertilization of wheat and summer fertilization of corn or broccoli accounted for differences at the 0-20
in samples in which higher levels were noted. Each data point represents the amount of inorganic N (NH4 .4- or NO3-) present in the depth range in which it is centered; for example, points at 10 cm indicate the amount of inorganic N in the
0- to 20-cm depth.
Results obtained from samples collected 16 Sept. 1991 form the baseline soil profile of this study (Fig. 2.2). There were no significant effects due to cropping treatment, and N treatment effects were significant only in the 0- to 10cm depth, which contained 11(N0), 17(N1), and 35(N2) mg
13.5 mm of rain that fell between September 1 and September 15 were probably responsible for the NO3- bulge between 20 and 40 cm.
On 31 Oct. 1991 (Fig. 2.3), more NO3 was present in the N1 and N2 subplots in the 20- to 40-cm depth than on September 16, suggesting that leaching had occurred in those treatments between September 16 and October
31.
Differences in NO3- content were no longer significant at the N treatment level between 0 and 20 or between 20 and 40 cm on 3 Dec. 1991 (Fig. 2.4).
All plots contained between 20 and 30 mg kg-IN03--N at that depth. More NO3was present at the surface in the No plots than on October 31, suggesting that mineralization had occurred, but NO3 at the surface of the N2 plots had decreased, presumably because of uptake by wheat and cover crops, or because of leaching. In the 40- to 80-cm portion of the profile, differences between N treatment subplots were significant (p < 0.05). At that depth, No, NI, and N2 subplots contained approximately 3, 6, and 12 mg kg' NO3--N. An average of

31
On 3 Jan. 1992, an effect due to crop treatment appeared, and significantly more NO3 (around twice as much) was present between 40 and 80 cm in the rye/pea plots in all N treatments than in plots with the other two cropping histories (Fig. 2.5). This may relate to summer and fall net mineralization of that cover crop in 1991, resulting in excess N beyond what broccoli was able to utilize that year and susceptible to leaching, or it may indicate that the rye/pea combination did not recover as much NO3 as did the rye alone. About 22 mg kg' NO3--N remained in the 0-20 cm depth in all three crop treatments (averaged over N treatments) despite uptake of N by wheat, indicating that, especially in the wheat plots, N was still being mineralized from
SOM or broccoli residues.
The 1 Feb. 1992 profiles (Fig. 2.6) reflected fertilization of wheat on
January 24. Wheat plots, averaged over N treatments, contained significantly more NO3- than did cover-cropped plots at 0 to 20 and 20 to 40 cm, but rye/pea plots still contained significantly more NO3- between 40 and 80 cm. Profiles from February 1, February 29, and March 30 showed utilization of surface NO3by all three winter crops (Figs. 2.6, 2.7, and 2.8), and some leaching into the 20-
kg'
NO3--N were present in any of the nine treatments between 40 and 80 cm, indirect evidence that crops were taking up NO3 and the remainder had leached out of the soil profile. There was no seasonal effect in the biological parameters at that time, suggesting that no more or less N was present in the microbial biomass on March 30 than at other times (see Chapter 3).
On 16 May 1992, significantly more NO3- was in the rye/pea plots than in the rye plots, which in turn contained twice as much NO3 as did the wheat
taking up N at that time, whereas the cover crops had been incorporated three weeks earlier. Wheat in the N2 plots was fertilized on April 15, hence the larger amount of NO3- in those plots. It also appeared that more NO3- was made

32 available more quickly in the rye/pea plots than in the plots with rye alone upon incorporation of the cover crops. There was more NO3- in the 40-80 cm depth on this sampling date than on March 30. This is probably explained by the 30 mm of rain that fell between April 27 and May 16, which was sufficient to saturate the profile to roughly 65 cm.
The difference in NO3- concentration between rye/pea and rye plots continued to be significant on 3 July 1992 (Fig. 2.10), when the rye/pea N2 plots contained an average of 60 mg NO3 -N kg-1 (155 kg ha') and the rye N2 plots
received only 112 kg N ha' as urea on 21 May, and corn was actively growing in the plots. Apparently, cover crops were being actively mineralized, or there was a priming effect by which decomposition of organic N fractions was stimulated by addition of substrate (Yaacob and Blair, 1980). Only in the N2 plots was there NO3- at the soil surface on July 29 (ten days after wheat harvest).
On 4 Sept. 1992, conventional plots in all three N treatments contained more NO3- in the surface soil than they had in July (Fig. 2.11). There was evidence of some leaching into the 20- to 40-cm depth in the conventional plots, which were now fallow after the July 16 harvest. Around 10 mm of rain had fallen since harvest, enough to saturate the soil to roughly 20 cm. Cover crop plots (except in the No treatment) still contained more NO3- at the surface depths
(0- to 10- and 10- to 20-cm) than conventional plots, with rye/pea containing the most, suggesting that the 91-92 cover crop was still being mineralized. Also, more mineral N was present in the rye/pea plots throughout the corn season, possibly giving the corn residues in these plots a smaller C:N ratio and allowing them to mineralize more rapidly after harvest on August 19. No more than 5 mg kg' NO3- -N were present at the 40-80 and 80-120 cm depths.
Sufficient rain had fallen by 14 Nov. 1992 (assuming a dry profile as of
September 4) to saturate the soil profile to approximately 30 cm. As might be expected, most of the NO3- in the profile on that day was measured between 20 and 40 cm (Fig. 2.12). There was more NO3- at that depth in the rye/pea plots than in plots of the other two crop treatments. It is unclear whether the decrease

33 in NO3- in the surface of the cover-cropped plots is due entirely to leaching or may in part be due to cover crop uptake.
No more than 5 mg kg' NO3- -N were present in any of the plots at any depth by 13 Feb. 1993 (Fig. 2.13). However, uptake data in Table 2.4 clearly show that N treatments affected N uptake in cover crops. Furthermore, subsoil lysimeters in fallow and rye cover in these same plots showed significantly less
NO3 leaching under the rye cover crop (Brandi-Dorhn et al., 1994). The May 22 soil profile (Fig. 2.14) was similar to that of February 13. Cover crops were incorporated May 14, but eight days apparently were not sufficient to allow for as much net mineralization as on 16 May 1992 (Fig. 2.9).
No
Rye
Rye/pea
19.7
43.9
N1
24.2
59.3
N2
45.0
87.0
Data from surface samples collected 4 Aug. 1993 (Fig. 2.15) showed that, as in July 1992, plots under all three cropping treatments contained significantly different amounts of NO3- between 0 and 20 cm (p < 0.05), although all three treatments had been managed identically since preparation of plots for broccoli planting. Differences between amounts of NO3- in all three N treatments were also significant (p < 0.05). The rye/pea plots, under mid-season broccoli,
fallow the previous winter (100 % more at the No rate).
On 3 Sept. 1993 (Fig. 2.16), the NO3 profile appeared similar to that of
16 Sept. 1991, but more of the NO3" in the profile was present at the surface in
1993. In 1991, 13.5 mm of rain fell in the 16 days before sample collection, but

34
the profile in which the majority of the NO3- is left at the time of cover crop planting will influence the efficiency of cover crop uptake. Martinez and
Guiraud (1990) predict greater NO3 recovery in drier autumns, since the NO3- is accessible to young roots.
In both August and September of 1993, large flushes of NH4+ were evident, especially in the plots with a winter fallow history (Figs. 2.17 and 2.18).
This may relate to the phenomenon noted by Martinez and Guiraud (1990), in which the survivors of summer desiccation mineralized dead microbial biomass and other organic matter upon rewetting in fall. This may indicate that repeated application of inorganic N in the absence of cover crop C inputs has resulted in a more labile form of N that is rapidly mineralized after the summer crop.
However, more years of monitoring are required to determine if this is a consistent trend. The relationship of this large inorganic N flush to biological and meteorological parameters is discussed in more detail in Chapter 3. A cool, wet July coupled with a hot, dry August may have reduced the activity of nitrifying bacteria, resulting in atypical longevity of NH4 .1- in the soil. Large amounts of NH4+ measured at the 20- to 40- and 40- to 80-cm depths are difficult to explain.
In the first year of this study, most leaching appeared to occur between
December and February. Second year data appear to confirm this. Conversely,
Shipley et al. (1992), in an area with rainfall patterns similar to this study, found low leaching rates in the fall. This is likely due to differences in soil textural profiles. Their soil surface had a high clay content and overlaid a sand layer.
The clay layer held water until it was saturated, before releasing it into the sand.
In this study, a horizon of lesser bulk density overlaid one of greater bulk density, so water in the surface percolated more rapidly into the lower soil profile.

35
Total profile NO3-
When NO3 totals in the 0-80 cm profile are plotted against time (Figs.
2.19 and 2.20), it can be seen that no cropping history consistently contained the
Feb. 1992 because they were fertilized on January 24. In times following cover crop incorporation (16 May 1992 and 22 May 1993), plots with a history of rye/pea cover contained the most NO3- in all N treatments.
On 16 May 1992, three weeks after incorporation of cover crops, as much NO3 was present (ca. 70 kg ha
1) in the rye/pea No plots as in the rye/pea
N2 plots. The additional N added by the fertilizer was either being immobilized by the microbial community or had been leached out of the profile.
In both years, there was more NO3 in the total profile in all treatments three or four months after harvest of the summer crop than there was at harvest, even though no N had been applied as fertilizer after harvest. This indicates that there was a significant amount of N mineralization occurring in the fall which reflects net mineralization of the summer crop residue, soil organic matter, or dead microbial biomass resulting from the dry period in August (Martinez and
Guiraud, 1990). Also in both years, NO3 in all profiles (except where wheat was fertilized) had decreased by February and continued to decrease gradually until spring, indicating either utilization by the cover crops or leaching loss.
These two observations point to the importance of cover crops in NO3- recovery.
Although some NO3 may leach before cover crops are established, these data show that there was mineralization of N in the fall and early winter. The data presented here is not clear evidence of cover crop NO3 uptake, but Table 2.4
shows greater N uptake with greater fertilizer N application, suggesting that the cover crops were able to accumulate NO3 and reduce leaching. Clearer evidence of the cover crops' ability to recover NO3 would be obtained by comparing the leaching pattern of a true fallow such as in fall 1993 (see Table 2.2) with those of cover-cropped treatments. No fall 1993 data are presented here.

36
CONCLUSIONS
The rye/pea cover-cropped rotation made the most N available for the summer crops in both years of this study. Net mineralization, however, continued throughout both summers, leaving excess NO3 at the end of the summer that was susceptible to leaching. Most leaching occurred between
October and February, by which time NO3- that had not already passed out of the soil profile was being taken up by cover crops. The highest levels of NO3 were in the rye/pea plots. There was indirect evidence that cover crops reduced leaching in the fall and appeared to recover the inorganic N that mineralized throughout the late fall and winter at the surface of the plots.

Coll. Date
Wheat/Fall
Rye/pea
Rye
Sep 91 Feb 92 May 92 Aug 92 Dec 92 Apr 93 Aug 93
A: Rye/pea;
*: Corn; : Broccoli; v: Collection date.

38
80
100
120
00
20
40
60
--- 20
E
40
.46
60
10
NO3-
-N (mg kg-1)
20
I
30
I
40
I
50
1
N0
Cropping History
Conventional (Wheat)
Rye / Pea
Rye
"a 100
CO
120
20
40
60
80
100
120
Fig. 2.2. Distribution of NO3 in the soil profile as of 16 Sept. 1991.
N2
60

39
---20
40
..c
60-f-a
0
CD
80
7a 100
U)
120
20
40
60
80
100
120
00
20
40
60
80
100
120
10
NO3-
-N (mg kg-1)
20 i
30 40 50
N 0
Cropping History
Conventional (Wheat)
Rye / Pea
Rye i
I
Fig. 2.3. Distribution of NO3- in the soil profile as of 31 Oct. 1991.
-
N
1
N 2
60

40
-----
E
-i---)
_c
-4a.
0
CD
20
40
60
80
75 100
(/)
120
0
0
20
40
60
80
100
120
.
.
20
40
60
80
100
120
10
NO3-
-N (mg kg-1)
20
I
30
I
40 50
N0
Cropping History
Conventional (Wheat)
Rye / Pea
-- Rye
.
N1
N2
.
60

--- 20
E
-9--
40
60
0_ a) o
80
100 cn
120
0
0
20
40
60
80
100
120
* *
10
20
40
60
80
100
120
NO3- -N (mg kg-1)
20 30 40 50
I
N
0
Cropping History
Conventional (Wheat)
Rye / Pea
Rye
N
1
N
2
60
Fig. 2.5.
significant effect of crop treatment (p < 0.05).
41

42
----
E
-S.-)
20
40
60 a) o 80
74f5 100
CO
120
20
40
60
80
100
120
60
80
100
120
20
40 o
0 10
NO3"
-N (mg kg-1)
20 30 40 50
Fig. 2.6. Distribution of NO3- in the soil profile as of 1 Feb. 1992. * indicates significant effect of crop treatment (p < 0.05).
60

0
0
20
40
60
80-
100-
120
10 ii
NO3- -N (mg kg-1)
20 30 40 50
N
0
Cropping History
Conventional (Wheat)
Rye/ Pea
Rye
1
60
43
N
1 o
80
'c3 100
120
20
40
60
80 ii
100
120
N
2

44
--- 20
E
-(-%-)
40
_c
60 a_ a) o
80
100
U)
120
80
100
120
0
0
20
40
60
20
40
60
80
100
120
10
I
NO3-
-N (mg kg-1)
20
I
.
30
I
40
I .
50
1
N
0
Cropping History
Conventional (Wheat)
Rye / Pea
Rye
Fig. 2.8. Distribution of NO3 in the soil profile as of 30 Mar. 1992.
N
1
N
2
60

10
* i
NO3- -N (mg kg-1)
20 i
30 i
40
I
50
I i
N
0
Cropping History
Conventional (Wheat)
Rye / Pea
Rye
.
i
1
N
1
60
.----
20
40 p a)
-
60
0 80
Tb 100
(f)
120
60
80
100
120
00
20
40
1
20
40
60
80
100
120
N
2
significant effect of crop treatment (p < 0.05).
45

46
10
I
NO3-
-N (mg kg-1)
20 30 40
MIA
50
N
0
Cropping History
Conventional (Wheat)
Rye / Pea
-- Rye
N
1
60
--- 20
40
_c
460 a) o
80
100
120
00
20
40
60
80
100
120
A
20
40
60
80
100
120
N
2
(Wheat) 1992.
* indicates significant effect of crop treatment (p < 0.05).

10
1.40C)
2.0
-CA (nig kkg4)
30 40 50
20
S
40
60 o 0
(f)
100
120
0
100
12.0
2.0
40
60
2.0
40
60
60
100
1 20
Fig, 2.11. Distribution of N,; in the soil pcofile 26 of 4 Sept. 1992.
60

-2- 40
_c
60 a)
O
80
7j7, 100
120
60
80
100
00
20
40
120
10
NO3- -N (mg kg-1)
20 30 40 50
N0
Cropping History
Conventional (Fallow)
Rye / Pea
Rye
20
40
60
80
100
120 rQ
indicates significant effect of crop treatment (p < 0.05).
N1
60
48

00
20
40
60
80
100
120
--- 20
E
-2- 40
( a.
o 80
100 u)
120
.
100
120
20
40
60
80
(
10
NO3-N (mg kg-1)
20 30 40 50
N
0
Cropping History
Conventional (Fallow)
Rye / Pea
Rye
.
i
N
1
N 2
60
significant effect of crop treatment (p < 0.05).
49

60
80
100
120 o
0
20
40
--- 20
E
40
_c
-1-i
CL a)
60 o 80 c
7a. 100
(/)
120
10
1
.
NO3- -N (mg kg-1)
20 i
30
1 i
40
1
.
50
1
N
0
Cropping History
Conventional (Fallow)
Rye / Pea
Rye
N
1
60
120
100
20
40
60
80 f
N
2
significant effect of crop treatment (p < 0.05).
50

40
_c
60
0a) a 80
7-0j 100
C/)
120 o0
20
40
60
80
100
120
.
10
NO3- -N (mg kg-1)
20 30
.
40 i
50
.
60
N0
Cropping History
Conventional (Fallow)
A
Rye / Pea
Rye
N1
.
20
40
60
80
100
120
* indicates significant effect of crop treatment (p < 0.05).
51

52
00
20
40
60
80
100
120
10
NO3- -N (mg kg-1)
20 30 40 50
N 0
Cropping History
Conventional (Fallow)
Rye / Pea
Rye
----
E
(--:-%
20
40
60 a) o
80
"3 100
(/)
120
20
40
60
80
100
120
Fig. 2.16. Distribution of NO3- in the soil profile as of 3 Sept. 1993.
N
1
N
2
60

-----
E
20
,c----)
40
_c
4o_ a)
60 o 80
7c1 100
CD
120 oo
20
100
80
40
60
I
120
.
20
-N (mg kg-1)
40 60 80 100
N
0
Cropping History
Conventional (Fallow)
Rye / Pea
-- Rye
.
N
1
120
1
20
40
60
80
100
120
N
2
on x axis.
53

54
0
20
40
60
80
100
120
20
NH4 + -N (mg kg-1)
40 60 80 100
N
Cropping History
Conventional (Fallow)
Rye / Pea
Rye
120
20
-S% 40
6 a_ a) o
80
0
'Fj 100
120
N1
20
40
60
80
100
120
128.0
N2
Fig. 2.18. Distribution of NH4+ in the soil profile as of 3 Sept. 1993. Note scale on x axis.

240
120
0
0
00 240
120 z
00)
240
120
0
Sep 91 Nov 91 n 92
kg he
N031-iv in 8D-em profile, Year j
May
92

240
120
0 co
E
Q)
Li= 0
0
240 al c
0)
120 z
0
240
120
N0
N1
N2
Cropping History
Conventional (Fallow)
AA Rye / Pea
Rye
0
Sep 92 Nov 92 Feb 93 May 93
Aug 93
56

57
LITERATURE CITED
Badaruddin, M. and D.W. Meyer. 1989. Forage legume effects on soil nitrogen and grain yield, and nitrogen nutrition of wheat. Agron. J. 81:419-24.
Biederbeck, V.O., O.T. Bowman, J. Loomen, A.E. Slinkard, L.D. Bailey, W.A.
Rice, and H.H. Janzen. 1993. Productivity of four annual legumes as green manure in dryland cropping systems. Agron. J. 85:1035-1043.
Brandi-Dohrn, F.M., R.P. Dick, and J.S. Selker. 1994. Nitrate leaching under a cereal rye cover crop. J. Environ. Qual. (in review).
Bremer, E. and C. van Kessel. 1992. Plant-available nitrogen from lentil and wheat residues during a subsequent growing season. Soil Sci. Soc. Am. J.
56:1155-1160.
Bruulsema, T.W., and D.R. Christie. 1987. Nitrogen contribution to succeeding maize from alfalfa and red clover. Agron. J. 79:96-100.
Huntington, T.G., J.H. Grove, and W.W. Frye. 1985. Release and recovery of nitrogen from winter annual cover crops in no-till corn production.
Commun. Soil Sci. Plant Anal. 16:193-211.
Janzen, H.H., J.B. Bole, V.O. Biederbeck, and A.E. Slinkard. 1990. Fate of N applied as green manure or ammonium fertilizer to soil subsequently cropped with spring wheat at three sites in western Canada. Can. J. Soil
Sci. 70:313-323.
Karlen, D.L., and J.W. Doran. 1991. Cover crop management effects on soybean and corn growth and nitrogen dynamics in an on-farm study. Am. J. Alt.
Ag. 6:71-82.
Keeney, D.R., and D.W. Nelson. 1982. Nitrogen organic forms. p. 643-698. In
A.L. Page, R.H. Miller, and D.R. Keeney (ed.) Methods of Soil Analysis,
Part 2. ASA and SSSA, Madison, WI.
Ladd, J.N., M. Amato, R.B. Jackson, and J.H. Butler. 1983. Utilization by wheat of nitrogen from legume residues decomposing in the field. Soil Biol.
Biochem. 15:231-238.
Lewis, R.D., and J.H. Hunter. 1940. The nitrogen, organic carbon, and pH of some southeastern coastal plain soils as influenced by green-manure crops. Agron. J. 32:586-601.

McVay, K.A., D.E. Radcliffe, and W.L. Hargrove. 1989. Winter legume effects on soil properties and nitrogen fertilizer requirements. Soil Sci. Soc. Am.
J. 53:1856-1862.
58
Mahler, R.L., and D.L. Auld. 1989. Evaluation of the green manure potential of
Austrian winter peas in northern Idaho. Agron. J. 81:258-64.
Martinez, J., and G. Guiraud. 1990. A lysimeter study of the effects of a ryegrass catch crop, during a winter wheat/maize rotation, on nitrate leaching and on the following crop. J. Soil Sci. 41:5-16.
Meisinger, J.J. W.L. Hargrove, R.B. Mikkelsen, J.R. Williams, and V.W.
Benson. 1991. Effects of cover crops on groundwater quality. p. 57-68. In
W.L. Hargrove (ed.) Cover crops for clean water. Proc. Int. Conf.,
Jackson TN 9-11 Apr. 1991. Soil and Water Conserv. Soc. Am., Ankeny,
IA.
Mitchell, W.H., and M.R. Teel. 1977. Winter anual cover crops for no-tillage corn production. Agron. J. 66:569-573.
Morgan, M.F., H.G.M. Jacobson, and S.B. LeCompte, Jr. 1942. Drainage water losses from a sandy soil as affected by cropping and cover crops.
Windsor Lysimeter Series C, Bulletin 466, Connecticut Ag. Expt. Sta.,
New Haven.
Muller, M. M., and V. Sundman. 1988. The fate of nitrogen (15N) released from different plant materials during decomposition under field conditions.
Plant Soil 105:133-139.
Petit, G. 1988. Assessment of Oregon's groundwater for agricultural chemicals.
State of Oregon, Dept. of Environ. Qual., Portland, OR.
Pieters, A.J., and R.J. McKee. 1929. Green manuring and its application to agricultural practices. Agron. J. 21:985-993.
Power, J.F., and J.A. Zachariassen. 1993. Relative nitrogen utilization by legume cover crop species at three soil temperatures. Agron. J. 85:134-140.
Ranells, N.N., and M.G. Wagger. 1992. Nitrogen release from crimson clover in relation to plant groth stage and composition. Agron. J. 84:424-430.
Rodgers, T.H., and J.E. Giddens. 1957. Green manure and cover crops. p. 252-
257. In USDA Yearbook of Agriculture.
Russel le, M.P., and W.L. Hargrove. 1989. Cropping systems: Ecology and management. In R.F. Follett (ed.) Nitrogen management and groundwater protection. Elsvier, New York.

Shennan, C., 1992. Cover crops, nitrogen cycling, and soil properties in semiirrigated vegetable production systems. Hort. Sci. 27:749-754.
Shipley, P.R., J.J. Meisinger, and A.M. Decker. 1992. Conserving residual corn fertilizer nitrogen with winter cover crops. Agron. J. 84:869-876.
59
Ta, T.C., and M.A. Faris. 1990. Availability of N from 15N-labeled alfalfa residues to three succeeding barley crops under field conditions. Soil
Biol. Biochem. 22:835-8.
Wood, C.W., D.G. Westfall, and G.A. Peterson. 1991. Soil carbon and nitrogen changes on initiation of no-till cropping systems. Soil Sci. Soc. Am. J.
55:470-476.
Yaacob, 0., and G.J. Blair. 1980. Mineralization of '5N-labelled legume residues in soils with different nitrogen contents and its uptake by Rhodesgrass.
Plant Soil 57:237-248.

CHAPTER 3
BIOLOGICAL PARAMETERS
60

61
ABSTRACT
Knowledge of seasonal trends in the biology of a soil system can aid in the understanding of overall system dynamics. Temporal trends in enzyme activities and microbial biomass three cover crop systems were compared in plots selected from a long-term rotation study at North Willamette Research and
Extension Center near Canby, Oregon, on a Willamette silt loam (fine-silty, mixed, mesic Pachic Ultic Argixeroll). This part of the study was set up as a randomized split plot block with four replications. The main plot was cropping system, represented by a conventional winter wheat/fallow/vegetable rotation and two alternative vegetable/cover crop rotations. Winter wheat (Triticum aestivum) was in production in the conventional rotation from fall 1991 through summer 1992. Broccoli (Brassica oleracea) was produced in all three rotations in summer 1991 and 1993, and sweet corn (Zea mays) was produced in only the alternative rotations in summer 1992. Winter cover crops in the alternative rotations were cereal rye (Seca le cereale L.) and a mix of rye/Austrian winter pea (Pisum sativum ssp. arvense). Subplots were amended with urea fertilizer at zero (N0), medium (N1), or high (N2) rates:
140, and 280 kg ha-1 for broccoli; and 0, 56, and 224 kg ha-1 for sweet corn, respectively. Soil samples from the surface 0-20 cm of the study plots, collected monthly throughout one year, were assayed for protease and 13-glucosidase activities and microbial biomass.
Crop and N treatment effects on biological parameters were not significant except when they reflected incorporation of plant residues.
0glucosidase activity increased consistently with increasing N fertilization rates.
Abrupt changes in moisture and temperature appeared to have the greatest effect on soil biology, possibly altering the population structure of the microbial community.

62
INTRODUCTION
Microbial biomass in soils is an important source and sink for nutrients and plays a critical role in nutrient transformations. It is also being proposed as a measure of soil health and productivity, and has been called a good indicator of the intensity of soil life and soil microbial activity (Perucci, 1992).
Greater cropping intensity appears to increase biological activity.
In comparing adjacent farms in eastern Washington, Bolton et al. (1985) found that microbial populations and enzyme activities were higher in the organic system that utilized legumes as its N source than in an adjacent system that received anhydrous ammonia annually as its N source. Likewise, biological measurements were significantly lower in wheat-fallow systems than in annuallycropped systems in eastern Oregon (Collins et al., 1992), and microbial biomass and potentially mineralizable N reserves were greater in systems including legumes in southeastern Pennsylvania (Doran et al., 1987). Immobilization of N by the microbial community upon incorporation of crop residue can reduce crop productivity. However, Allison and Killham (1988) found that systems that receive regular organic amendments adjust by increasing their fungal populations, and turnover of organic matter becomes progressively more rapid.
Whereas Doran et al. (1987) found differences due to cropping systems,
Amato and Ladd (1992) concluded from lab incubations that soil structure may be more influential in the accumulation of microbial biomass than are substrate type and concentration. Angers et al. (1992) found that microbial biomass carbon, taken as a percent of total soil organic matter (SOM), was not affected by cropping system during the first year in which their rotations were in place.
Microbial biomass N accumulated during fallow periods may be a gradual source of plant-available N during subsequent crop-growing seasons.
Bremer and van Kessel (1992b), in an '5N-partitioning study, found that the residue '5N in microbial biomass decreased, but that the net '5N mineralization increased during a growing season, and determined that the microbial biomass was the source of the mineralized '5N. Doran et al. (1987) also found that when

63
NO3- was high, microbial biomass N was low, and vice versa. Granatstein et al.
(1987) found that the no-till rotations they studied may approach an ideal situation in which a large microbial biomass during fallow captures nutrients and releases them slowly to subsequent crops.
In contrast, Bonde et al. (1988) concluded from a lab incubation study that microbial biomass N was not a major source of plant-available N, but rather it processed other SOM fractions and made N available from those. Yaacob and Blair (1980) found that the addition of organic residues stimulated the release of native organic N and referred to this as a positive priming effect, the magnitude of which increased with longer cropping histories, on each of several soils.
Soil enzymes are found in viable cells and as extracellular entities. They catalyze innumerable reactions which are important for microbial cells in obtaining energy and performing cellular processes (Burns, 1982), and are thus crucial in the cycling of soil nutrients. Soil enzyme activity appears to be an indicator of soil quality (Dick, 1994) or of microbial biomass and activity
(Frankenberger and Dick, 1983) and are known to be sensitive to the effects of long-term residue practices (Dick, 1994).
0-glucosidase is an important part of the soil C cycle. Its end product is a simple sugar that is a major source of energy for microbes (Tabatabai, 1982).
Although it functions extracellularly, it is relatively long-lived because of complexation with humic materials (Ladd, 1978). It may also be colonized and/or protected by extracellular polymers (Martens and Frankenberger, 1991).
It is thought to be produced primarily by fungi (Hayano and Katami, 1977;
Hayano and Tubaki, 1985).
Proteases play a part in the N cycle by degrading organic residues into energy, nutrients, and humic matter (Niskanen and Eklund, 1986). They tend to be short-lived in the soil because they are attacked by other enzymes (Ladd and
Butler, 1975) or adsorbed onto soil colloids and rendered inaccessible and thus inactive toward high molecular weight substrates (Rowell et al., 1973).
Cover crops are an important stimulant of microbial activity, and promote soil health. However, they can reduce N for plant uptake by immobilizing N in

64 the microbial biomass (Doran et al., 1987). Various enzyme activities have been found to be associated with certain rotations (Khan, 1970), tillage practices
(Dick, 1984), or the presence or absence of plants (Speir et al., 1980), but few field studies have been conducted to explore seasonal trends. Cover crops are being investigated in the Willamette Valley of western Oregon as a means for recovery of residual N during mild, wet winters after heavily-fertilized summer vegetable crops. Until now there have been no studies to explore the effects of cover crops on the biological activity in soils of this area, nor has activity been monitored throughout full growing seasons. The objective of this study was to determine whether there was a relationship between biological activity and temporal N immobilization/mineralization patterns in a locally-used winter fallow rotation and in two rotations that included winter cover crops.

65
MATERIALS AND METHODS
Field Methods
Soil samples were taken from the field study described in Chapter 2.
Within 24 h of collection, samples from the 0-20 cm depth were put through a
2-mm sieve, except for very wet samples, which were spread out and dried at
4°C (<12 h) until moisture was low enough to facilitate seiving. The samples were stored at 4°C in their original sample bags.
Analytical Methods
Microbial Biomass Microbial biomass C (MBc) and N (MBN) were estimated in soil samples by a modified procedure of Jenkinson and Powlson (1976). Within
48 h of collection, 12-g samples (moist-sieved weight) of soil were weighed into glass scintillation vials. Duplicates for unfumigated controls were weighed into polyethylene tubes (21 cm x 22.5 mm diameter) fitted on one end with natural rubber septa (Aldrich, Z12, 439-7) that enabled sampling for gas chromatography after fumigation. The scintillation vials were placed in a desiccator containing wet paper towels and a 50-mL beaker containing 20 mL of ethanol-free chloroform and a few boiling chips. The desiccator was evacuated and the soil exposed to chloroform vapors for 24 h. Unfumigated controls were placed in the same fume hood as the desiccator, their open ends covered with wet paper towels. Fumigated soil was transferred into polyethylene tubes like those containing the controls. All tubes were fitted with septa on their upper ends.
No inoculum was added and soil moisture was not adjusted. Samples were incubated at 25° C in the dark for 10 d. Total CO2 produced after 10 d was determined with a thermal conductivity gas chromatograph.
Using the following formula, MBc was calculated:
MBc = CO2 C fun, / 0.41 (Voroney and Paul, 1984). The control was not subtracted.

66
After CO2 sampling, 50 mL of 2 M KC1 were added to each tube. The tubes were shaken lengthwise for 1 h and stored overnight at 4°C. Extracts were decanted off into Nalgene bottles and stored frozen pending further processing;
NH4+-N and NO3--N were determined in the extracts by Kjeldahl steam distillation (Keeney and Nelson, 1982).
Using the following formula, MBN was calculated:
MBN = (NH41--N1 + NO3--1\11) (NH4+-Nuf + NO3"-Nuf) / 0.68 (Shen et al.,
1984), where f denotes fumigated and of denotes unfumigated samples.
Enzyme Activities Enzyme activities were measured during the first year of the study, from September 1991 through September 1992. Within one week of collection, all samples were assayed for protease activity using the method described by Nannipieri et al. (1979) with the following modifications: No preassay incubation treatments were carried out. Samples, run in duplicate, had 1.0
15-mL polypropylene centrifuge tube (Corning, 25319-15). Rounded-end tubes are recommended for ease in cleaning. A control for each sample was prepared with 1.5 mL tris. A quick shaking by hand prior to incubation is recommended for even wetting-up of the soil. The tubes were shaken horizontally in a circular-shaking incubator-shaker. After shaking and the addition of TCA, 1 mL of pH 8.1 tris was added to each sample and 1 mL of 2.5% casein to the control.
Tubes were centrifuged and 1 mL of the supernatant from each tube was transferred to a tissue culture tube, to which CuSO4 and Na2CO3 were added.
After immediate mixing on a vortex mixer, the tubes were allowed to stand at room temperature for 15 min. Folin reagent was added and tubes were vortexed, then stood at room temperature for 35 minutes before absorbance of their contents was read at 700 nm. Activities are expressed in mmol tyrosine kg soil-1
WI.
Within two weeks of collection, samples were assayed for P-glucosidase activity after the method of Eivazi and Tabatabai (1988) with these

modifications: Samples were assayed moist, and P-D-glucopyranoside was used as the substrate. Activities are expressed in mg p-nitrophenol (PNP) kg soil-1
All results are expressed on a per kg oven-thy (105°C, 24 h) weight basis. The data were analyzed by standard ANOVA techniques for repeated measures on randomized split-plot blocks with a statistical software package
(SAS Institute, Cary, NC). Main effect means were separated with Tukey's studentized range test at the p = 0.05 level.
67

68
RESULTS AND DISCUSSION
Microbial biomass
Seasonal trends in MBc showed less variation with greater N fertilization
(Figs. 3.1 and 3.2). Generally, maximum levels were observed in the fall,
second year. The gradual decline in MBc from fall to summer during the first year of this study is in agreement with findings of Granatstein et al. (1987), who studied 10-year-old plots and observed a decrease during winter wheat and spring barley growing seasons.
MBc in conventional plots in this study, averaged over N treatments, increased by 29 July 1992, 10 days after shallow-incorporation of wheat straw, but by 11 Nov. 1992 it had dropped to a lower level than in cover-cropped soils.
There was a trend of the conventional plots having lower MBc than in the alternative plots throughout the fallow period in the second year of the study.
(Significance levels ranged from 0.07 to 0.30 during the fallow period.) This is in contrast to work by Granatstein, et al, (1987), who observed an increase in
MBc during the fallow period between July and October. McGill et al. (1986) found that annual C additions from a wheat-fallow system were not sufficient to account for annual microbial biomass turnover and reasoned that native SOM was being depleted to maintain the microbial population. Schniirer et al. (1985) found that MB estimates showed a significant correlation with SOM. Although the differences in this study are rarely significant, these data may be a preliminary indication that more SOM is accumulating in the cover-cropped plots, with annual C inputs, than in the winter fallow rotation. Maximum MBc values in this study corresponded to addition of substrates, in contrast to findings of Collins et al. (1992), who observed maximum MBc in February during both wheat and fallow years in 56-year-old plots. Schntirer et al. (1986), observed higher than mean value bacterial biomass during a summer growing season and decreased values during the winter, but generalized that there were no clear

69 seasonal trends in the 1-year-old plots they studied. Observations in this study are more similar to those in the study by Schniirer et al. (1986). The trend towards lower M13c in the conventional fallow plots is likely related to lower C inputs than the cover cropped plots.
Based on a lab study, Nannipieri et al. (1983) postulated that homeostatic mechanisms may exist that keep microbial populations at a certain level, thus diminishing seasonal changes. On the whole, MBN in this study followed this pattern (Figs. 3.3 and 3.4). MBN remained generally steady in all nine treatments throughout two seasons, decreasing slightly in July, until the end of the study when a dramatic decrease in MBN (Fig. 3.4) corresponded with a large increase in NH4+ (Fig. 2.20) and a small but consistent increase in M1 lic (Fig.
3.2). Between 22 May 1993 and 3 Sept. 1993, MBN decreased by 7.7 g kg' and
NH4+ increased by 27 g kg'. This is in agreement with findings of Doran et al.
(1987), who found decreases in MBN with a corresponding increase in inorganic
N.
A laboratory study by Cochran et al. (1988) provided evidence of two microbial populations, one C-limited and one N-limited. The fact that MBN decreased and MBc tended to increase in September 1993 suggests a shift in the microbial population in this study. September 1993 was the only time at which subtraction of evolved CO2 in the unfumigated control would have yielded a positive M13c, further evidence of a shift in microbial dynamics. Rather than being limited by nutrients, dominant populations in this study may have been limited by environmental conditions. One population may have been vulnerable and the other resistant to desiccation in this situation. Weather had been cool and wet (Table 3.1) through July in an area that is typically warm and dry at that time of year. Temperatures warmed to the long-term average in August and little rain fell. Warm and unusually moist conditions (residual moisture from
July rains) may have encouraged high net mineralization, explaining the large
NH4+ flush that was evident by 4 Aug. 1993. These unusual conditions may have caused a shift in dominant microbial populations, from one efficient in cool, moist situations, to one efficient in warm, moist environments. The

decrease in MBN that coincided with a large flush of inorganic N (Chapter 2) suggests that the microbial biomass may have been the source of the N mineralization.
70
Table 3.1. Meteorological data from North Willamette Research and Extension
Center.
Month
July 1992
July 1993
Historic July mean
August 1992
August 1993
Historic August mean
Mean temperature, °C
20.6
14.4
18.9
20.5
19.8
19.0
Rain, mm
33.3
62.0
17.8
12.7
7.6
23.9
Van Gestel et al. (1992) commented on the effect of field desiccation on microbial death, reasoning that with abrupt changes in moisture, cells have little time to adjust to changes in osmotic pressure. Continued warm soil temperatures through early September, combined with cessation of irrigation in mid-August (an abrupt decrease in moisture along with an increase in temperature), may have caused another microbial shift in this study, this time from moisture-adapted organisms to those that could quickly adjust to dry environments. Data from a field study by Schniirer et al. (1986) indicate that bacterial and protozoan biomass were more influenced by soil moisture than by crop growth. The dramatic changes in MBN and M13c in this study, along with the large NH4+ flush in late summer 1993, also may be more adequately explained by temperature and moisture than by cropping effects.
Crop Effects MBc was affected by cropping treatment on 30 Mar 1992 (Fig.
3.1), with more M1 3c in both cover crop plots than in the wheat plots,

71 presumably because the wheat was beginning to grow more actively with increasing spring temperatures, resulting in competition for nutrients. On 16
May 1992, three weeks after cover crop incorporation, MB was greater again in the cover cropped plots, probably in response to fresh substrate.
Cropping treatment affected MBN only on 22 May 1993 (Fig. 3.4), eight days after incorporation of the cover crops, when MBN in the rye plots was significantly greater than in the wheat but MBN in rye/pea plots was not significantly different from either.
N Treatment Effects The rate of N fertilization had no significant effect on either MBN or MBc. Drury et al. (1991) observed an effect of added N immediately after fertilization that disappeared after one month, but samples in this study were taken too long after fertilization to observe such an effect. Ocio et al. (1991a, b) concluded in two separate studies that N incorporated into MBN did not come from inorganic N added to the soil but from N in straw residues.
Knapp et al. (1983) postulated that the turnover of substrate and microbially associated N results in significant decompostion of crop residues even under presumably N-deficient conditions. It is in agreement with these findings that added fertilizer N had no effect at the times of sampling in this study.
Biomass C:N Ratio The estimates of MBA and MBN were consistent with estimates found in the literature (Bolton et al. 1985). In this study, MB C:N ratios were generally between 5:1 and 30:1, comparable to those referenced by
Bolton et al. (1985), but high compared with a mean of 4.7 reported by Ocio et al. (1991a). The soils studied by Ocio et al. (1991a) were from bare fallow plots at Rothamsted, in which a large fungal population would not be expected. High
C:N ratios are generally associated with fungal populations (Jenkinson, 1976;
Anderson and Domsch, 1980), so it can be reasoned that plots in this study, with some annual organic matter input, host a population higher in fungi than do bare fallow plots.

72
During the two years of the study, MB C:N ratio was not affected significantly by either cropping or N treatment Trends were not consistent (Figs.
3.5, 3.6), but the ratio was generally larger at warmer times of the year (July
1992, August 1993), or possibly at times when a previous crop was being decomposed (December 1991).
Specific Respiration In this study, there were no significant effects of either cropping or N treatment on SR. Insam et al. (1991) found lower specific respiration (SR) (CO2-C flush / MBc) in soil receiving full fertilization than in inadequately fertilized soil. They obtained a negative correlation between SR and soybean yield and expressed concern that more CO2 would be lost from systems with the least input of organic material. That study was in long-term treatments but they only sampled once in February, and SR might be different in other times of the year.
Seasonal trends in specific respiration were not predictable in this study,
(Figs. 3.7, 3.8), but SR decreased dramatically in all treatments in September
1993. This decrease, along with the concurrent increase in MBc, suggested that the microbial population was large but relatively inactive, probably dormant in the field, at that time.
Enzymes
The activities of both protease and 0-glucosidase most clearly reflected incorporation of plant material.
13-glucosidase followed some seasonal trends, and increased slightly between September 1991 and September 1992 (Fig. 3.9).
On 16 May 1992, three weeks after cover crop incorporation, its activity was significantly greater in the cover crop plots than in the conventional plots (in which wheat was still actively growing). On 3 July 1992, midway through the corn season, activity remained significantly greater in the cover crop plots than in the conventional plots, which were sampled on 29 July, ten days after wheat harvest and shallow-incorporation of stubble. This persistence of P-glucosidase

73 activity may reflect that it has been found to be catalytic outside of microbial cells as a humus-enzyme complex (Ladd, 1978). The overall trend in activity shows a reversal by cropping system 7 weeks after wheat harvest (on 4 Sept.
1992). Although it is not significant, the trend may reflect a delayed increase in activity due to incorporation of the wheat straw. It is possible that differences in enzyme activities were a result of differences in overall management between the conventional and alternative systems, but statistically different activities were observed only at times of residue incorporation, and no consistent response to fertilization.
The consistent peak in activity on 3 Jan 1992 is not explained by any particular trend in rainfall, soil temperature, or incorporation of organic residues.
It is possible that the peak is related to an unavoidable delay between spreading out and seiving the samples on that particular collection date. A cool-drying period of >12 h may have caused an increase in the activity of all samples
(Eivazi and Tabatabai, 1990).
J3- glucosidase activity was also consistently, although not significantly, greater with greater N fertilizer rate. This is consistent with reports by Dick et al. (1988) and Kirchner et al. (1993). It also supports the findings of Eivazi and
Tabatabai (1990) who reported less inhibition by KNO3 and (NH4)2SO4 of 13glucosidase activity than of other enzymes' activities.
General levels of activity (between 40 and 120 mg kg-' 11-') were low compared with findings of Martens et al. (1992), who reported mean 13glucosidase activities between 162 and 345 mg kg-111-'. Their soils were unprimed, though, and upon adjusting to repeated inputs, they exhibited activities at the lower end of the range. Otherwise, activity was comparable to most literature reports (Dick et al. 1988; Eivazi and Tabatabai 1988).
Protease activity was less consistent and predictable than that of 13glucosidase.
It was poorly correlated with soil NO3 (r = 0.53; p < 0.001, on 3
Jan. 1992 only), and showed only slight seasonal trends (Fig. 3.10). These data are in agreement with the findings of Ross and McNeil ly (1975) who found that protease activity was not correlated with N mineralization activity and did not

74 follow a clear trend. There was significantly greater protease activity, however, in the cover crop plots three weeks after incorporation than in wheat plots in which wheat was actively growing (16 May 1992). The trend continued, but not significantly, through the July 3 and July 29 collections (midway through the corn season and 10 d after shallow-incorporation of wheat residue). This may reflect the short-lived status of protease in soil (Ladd and Butler, 1975), but it is possible that available proteinaceous substrate had been depleted and was therefore limiting to activity (Tateno, 1988). As in 13-glucosidase, the trend in crop effects shows signs of a reversal in the ranking of cropping systems after wheat harvest, but not significantly.
The level of activity ranged from 0.2 and 0.8 mmol tyrosine kg', which is typical of what has been reported in the literature (Asmar et al., 1992;
Bonmati et al., 1991; Ladd and Butler, 1972).
The question might be asked whether increases in activity were the result of tillage itself as well as the addition of substrate. Martens et al. (1992) found that tillage alone had a much smaller effect on 13-glucosidase activity than did the combination of tillage and incorporation, suggesting that the addition of substrate was responsible for the increase.
Correlations
The correlations among various biological, chemical, and soil moisture parameters were generally not significant or were significant at unusual times of the year. MBc was correlated with CO2-C flush (r = 0.80, p<0.001) during the first year of the study, and SR correlated with CO2-C flush (r = 0.67, p<0.001) during the second year. Ross (1987) found that CO2-C flush was negatively correlated with field moisture, and suggested that CFIM might not be the appropriate method for measuring MBc in wet, compacted soils but on 1 Feb.
1992, when several of the research plots were under water, CO2-C flush in this study was positively correlated with soil moisture at r = 0.69 (p<0.001). Overall and within collection dates, there was no significant correlation in this study,

75 positive or negative, between MBN and NO3 -, but on 3 Sept. 1993, MBN was correlated with NH4 1- at 0-20 cm at r = 0.58 (p<0.001).
Nannipieri et al. (1983) observed that all microbial characteristics increased with increasing energy supplies, but eventually diminished to the same level as unamended soil.
It may be that biological systems in these rotations are responding similarly, or that the effect of each parameter on others may not have been measurable until several days later. Schrairer et al. (1986) concluded from their data that because of the ability of microorganisms to multiply rapidly in the proper environment, seasonal changes might be masked. They propose more intense sampling around meteorological or management events like rain, plowing, or irrigation. Given that activities in this study responded mainly to incorporation of crop residue, such intense sampling in these plots might have helped to differentiate between management and seasonal effects.
Another factor affecting results may be the age of the plots. The clearest differences due to crop treatments have been found in the studies on the oldest rotation plots (Bolton et al., 1985; McGill et al., 1986; and Collins et al., 1992, reporting on studies in 76-, 50-, and 56-year-old plots, respectively). In studies on recently-established plots or in the laboratory (Schniirer et al., 1985; Angers et al., 1992; Amato and Ladd, 1992), cropping and seasonal effects were not pronounced.
Perhaps the most revealing part of the study was that drastic changes in moisture affected several biological parameters in all nine treatments. In comparing data from both summers in the study (Table 3.1), it is clear that weather patterns in 1992 were different from those in 1993. Table 3.2 indicates that trends in all parameters related to MB, except MBc, were reversed from
1992 to 1993 as they moved from midsummer to early September. The information in Table 3.2 suggests that the composition of the microbial population changed in 1993, and the weather information helps explain why that may have occurred. The death of some microorganisms and their mineralization by those that became dominant helps explain the large flush of NH4+.

Table 3.2. Microbial biomass related parameters from both summers of the study, averaged over crop and N treatments.
76
Parameter July
MB 180
MBN
MB C:N
SR
163
1.67
.35
1992
Sept.
221
227
1.04
.45
Aug.
163
237
0.61
.43
1993
Sept.
207
150
1.31
.28
Mid to late summer change
1992
+41
+64
-0.63
+0.10
1993
+44
-87
+0.70
-0.15

77
CONCLUSIONS
Biological parameters in this study were more affected by residue incorporation and meterological changes than by crop or N treatments. Cover crop and wheat incorporation brought about the only significant differences between crop treatments in all biological parameters. The type of substrate
(wheat, rye or rye/pea) seemed not to affect these properties as much as did the fact that they had been incorporated, and there were no significant differences in biological activities between the rye and rye/pea plots. Differences may not have had enough time to become established. The general lack of change in enzyme activity and MB estimates throughout two years, coupled with overall changes in MB-related trends in September 1993, suggest that abrupt changes in soil moisture were most responsible for changes in the microbial population in this study.

Cropping History
Conventional (Wheat)
Rye/Pea
Rye
78
300
200
100
0
'0) 300 cm 200 co
0
2
0
C)
N
0
N1
300
200
100
N
2
C)
Sept 91 Nov 91 Jan 92 Mar 92 May 92 Jul 92
Fig. 3.1. Effect of cropping system and N rate on microbial biomass carbon, year 1. (* indicates significant crop treatment effect at p < 0.05).

300
200
100
,
..--, r3) 300
0
0 c:3) 200
I I
Cropping History
Conventional (Fallow)
Rye/Pea
Rye
N
0
2
0 1
300
200
1
N
1
100
1 0
Sept 92
1
Nov 92 Feb 93
N
2
May 93 Sept 93
Fig. 3.2. Effect of cropping system and N rate on microbial biomass _carbon, year 2. There was no significant treatment effect.
79

30
20
47.7
A
Cropping History
-- Conventional (Wheat)
Rye/Pea
Rye
10
N0
0
0) z 30
0
.c 20
E
`10 z
2
0
N1
30
20
10
0
Nov 91 Jan 92 Mar 92 May 92 Jul 92
Fig. 3.3. Effect of cropping system and N rate on microbial biomass nitrogen, year 1. There was no significant treatment effect.
80

30
20
10
Cropping History
Conventional (Fallow)
Rye/Pea
Rye
N
0
0) z 30
0
2)
0
.c 20
0)
E z
2
0
30
20
N
1
10
N2
0
Sept 92 Nov 92 Feb 93 May 93 Sept 93
Fig. 3.4. Effect of cropping system and N rate on microbial biomass nitrogen, year 2.
(* indicates significant crop treatment effect at p < 0.05-
81

40
30
_
N
20
Cropping History
Conventional (Wheat)
Rye/Pea
Rye
9
0
10
I I I I I
N1
4 0 u) 30
E
0 20 rz
1 0
02
0
I
,,........--:
I I .
40
N 2
52.2
30
20
10
0
I
Nov 91
I I I
Jan 92 Mar 92 May 92
I
Jul 92
year 1.
82

83
40
30
20
N
Cropping History
Conventional (Fallow)
Rye/Pea
Rye
0
10
(8
CC
40 u) 30
E
0 20
7610
2
0
40
30
20
10
N1
N2
*M11111.1111...mmn'--.111
C)
Sept 92 Nov 92 Feb 93 May 93 Sept 93
Fig. 3.6. Effect of cropping system and N rate on microbial biomass Ce-N ratio, year 2.

0.4
0.2
()
O
0.6
0.6
I
N
0 ft
lk"<:1
A
:I.
..............
Cropping History
Conventional (Wheat)
Rye/Pea
Rye
I
I
I
1
CC(L)
0 4 c)
:+-
0 a)
0 2 cn
0
N1
0.6
0.4
0.2
0
Nov 91
N2
Jan 92 Mar 92 May 92 Jul 92
Fig. 3.7. Effect of cropping system and N rate on specific respiration, year 1.
84

0.6
0.4
0.2
0
Ell 0.6
0 cc 0.4
2
N
a_ co
0
N1
Cropping History
Conventional (Fallow)
Rye/Pea
Rye
0'
Sept 92 Nov 92 Feb 93 May 93 Aug 93
Fig. 3.8.
Effect of cropping system and N rate on specific respiration, year 2.
85

*
80
40
0 I
Cropping History
Conventional (Wheat)
Rye/Pea
Rye
I
N
*
0) 80
40
0
0
_J
80
N1
40
N2
0
Sept 91 Nov 91 Jan 92 Mar 92 May 92 Jul 92 Sept 92
Fig. 3.9. Effect of cropping system and N rate on P-glucosidase activity, year 1.
(* indicates significant effect of cropping treatment at p < 0.05.)
86

0.6
0.4
-
0.2
Cropping History
Cony. (Wheat)
Rye/Pea
Rye
N0
C)
2
0.6
0
E 0.4
0 w
U) 0.2
w
0
0
CC
0
0.6
0.4
N1
0.2
N
2
0
Sept 91 Nov 91 Jan 92 Mar 92 May 92 Jul 92 Sept 92
Fig. 3.10. Effect of cropping system and N rate on protease activity, year 1.
indicates significant effect of cropping treatment at p < 0.05.)
87

88
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Kirchner, M.J., Wollum, A.G., and L.D. King. 1993. Soil microbial populations and activities in reduced chemical input agroecosystems. Soil Sci. Soc.
Am. J. 57:1289-1295.
Knapp, E.B., L.F. Elliot, and G.S. Campbell. 1983. Microbial respiration and growth during the decomposition of wheat straw. Soil Biol. Biochem.
15:319-323.
Ladd, J.N. 1978. Origin and range of enzymes in soil. p.51-96. In R.G. Burns
(ed.) Soil Enzymes. Academic Press, London.
Ladd, J.N., and J.H.A. Butler. 1972. Short-term assays of soil proteolytic enzyme activities using proteins and dipeptide derivatives as substrates. Soil Biol.
Biochem. 4:19-30.
Ladd, J.N., and J.H.A. Butler. 1975. Humus-enzyme systems and synthetic organic polymer-enzymes analogs. p. 143-194. In E.A. Paul and A.D.
McLaren (ed.) Soil biochemistry. Vol. 4. Marcel Dekker, New York.
McGill, W.B., K.R. Cannon, J.A. Robertson, and F.D. Cook. 1986. Dynamics of soil microbial biomass and water-soluble organic C in Breton L after 50 years of cropping to two rotations. Can. J. Soil Sci. 66:1-19.
Martens, D.A., and W.T. Frankenberger, Jr. 1991. Saccharide composition of extracellular polymers produced by soil microorganisms. Soil Biol.
Biochem. 23:731-736.
Martens, D.A., Johanson, J.B., and W.T. Frankenberger, Jr. 1992. Production and persistence of soil enzymes with repeated addition of organic residues.
Soil Sci. 153:53-61.

Nannipieri, P., L. Muccini, and C. Ciardi. 1983. Microbial biomass and enzyme activities: production and persistence. Soil Biol. Biochem. 15:679-685.
91
Nannipieri, P., F. Pedrazzini, P.G. Arcara, and C. Piovanelli. 1979. Changes in amino acids, enzyme activities, and biomasses during soil microbial growth. Soil Sci. 127:26-34.
Niskanen, R., and E. Eklund. 1986. Extracellular protease-producing actinomycetes and other bacteria in cultivated soil. J. Ag. Sci. Finland
58:9-17.
Ocio, J.A., P.C. Brookes, and D.S. Jenkinson. 1991a. Field incorporation of straw and its effects on soil microbial biomass and soil inorganic N. Soil
Biol. Biochem. 23:171-176.
Ocio, J.A., J. Martinez, and P.C. Brookes. 1991b. Contributions of straw-derived
N to total microbial biomass N following incorporation of cereal straw to soil. Soil Biol. Biochem. 23:655-659.
Perucci, P. 1992. Enzyme activity and microbial biomass in a field soil amended with municipal refuse. Biol. Fertil. Soils 14:54-60.
Ross, D.J. 1987. Soil microbial biomass estimated by the fumigation-incubation procedure: seasonal fluctuations and influence of soil moisture content.
Soil Biol. Biochem. 19:397-404.
Ross, Di., and B.A. McNeil ly. 1975. Studies of a climosequence of soils in tussock grasslands. 3. Nitrogen mineralization and protease activity. New
Zealand J. Sci. 18:361-375.
Rowell, M.J., J.N. Ladd, and E.A. Paul. 1973. Enzymatically active complexes of proteases and humic acid analogues. Soil Biol. Biochem. 5:699-703.
Schnurer, J., M. Clarholm, and T. Rosswall. 1985. Microbial biomass and activity in an agricultural soil with different organic matter contents. Soil
Biol. Biochem. 17:611-618.
Schniirer, J., M. Clarholm, and T. Rosswall. 1986. Fungi, bacteria, and protozoa in soil from four arable cropping systems. Biol. Fertil. Soils 2:119-126.
Shen, S.M., G. Pruden, and D.S. Jenkinson. 1984. Mineralization and immobilization of N in fumigated soil and the measurement of microbial biomass N. Soil Biol. Biochem. 16:437-444.
Speir, T.W., R. Lee, E.A. Pansier, and A. Cairns. 1980. A comparison of sulphatase, urease, and protease activities in planted and in fallow soils.
Soil Biol. Biochem. 12:281-291.

Tabatabai, M.A. 1982. Soil Enzymes. In A.L. Page et al. (ed.) Methods of
Analysis, Part 2, 2nd Ed. Agronomy 9:903-947.
Tateno, M. 1988. Limitations of available substrates for the expression of cellulase and protease activities in soil. Soil Biol. Biochem. 20:117-118.
Van Gestel, M., J.N. Ladd, and M. Amato. 1992. Microbial biomass responses to seasonal change and imposed drying regimes at increasing depths of undisturbed topsoil profiles. Soil Biol. Biochem. 24:103-111.
92
Voroney, R.P., and E.A. Paul. 1984. Determination of Kc and KN in situ for calibration of the chloroform fumigation-incubation method. Soil Biol.
Biochem. 16:9-14.
Yaacob, 0., and G.J. Blair. 1980. Mineralization of '5N-labelled legume residues in soils with different nitrogen contents and its uptake by Rhodesgrass.
Plant Soil 57:237-248.

CHAPTER 4
SUMMARY AND PERSPECTIVES
93

94
Chapters 2 and 3 presented biological and inorganic N data and discussed those data in relationship to literature findings. This chapter will summarize data from this study and present them in terms of their relationships to each other.
The biological parameters were not significantly altered by crop or N treatment throughout the course of two growing seasons. Effects of residue incorporation and meteorological events had an important effect on biological parameters.
There was seasonal variation in the amount of NO3- and NH4+, which was possibly related to incorporation of cover crop residue. In both years, NO3remained in the soil profiles of all treatments after harvest in late summer and was present in especially large amounts in late summer 1993.
The fact that N uptake by cover crops was related to the rate of N fertilizer applied and that rye cover crops with reduced NO3 recovered in subsoil lysimeters, indicates that cover crops are reducing NO3- leaching. However, sampling for NO3- and NH4+ were less conclusive in showing treatment effects between fallow plots and rye cover crops.
Throughout both years, N availability was generally highest in the rye/pea plots. There was no clear indication that MB was a source of inorganic N during crop seasons, but when inorganic N increased in September 1993, there was a concurrent decrease in MBN. Greater organic inputs did not appear to increase immobilization of N in the MB.
Enzyme activity correlated with N availability only on 1 Jan. 1992
(protease x NO3- at 0-20 cm r = 0.53, p < 0.001; f3- glucosidase r = 0.55, p <
0.001). Presumably, the mild winters in this area allow for mineralization throughout the year. This mineralization is evident in the NO3 profile data as well, and underscores the importance of cover crops for the recovery of NO3- as it becomes available.
The frequency of sampling in this study was adequate for assessing N availability throughout the growing season, but would need to have been done more frequently at critical times (e.g., residue incorporation) to develop potential relationships of microbial and enzyme activity with N availability.

95
The relationship of MB, SR, and MB C:N to available N during August and September 1993 was probably a result of meteorological events, which in turn brought about dramatic changes in the makeup of the microbial community.
The large inorganic N flush at that time has the strongest implications for the conventionally-managed system, which, entering a fallow period, offers no way of recovering excess N.
Perspectives
A dry late summer followed by a warm, rainy fall is common in the
Wilamette Valley. Fall conditions are optimal for biological activity and N mineralization rates can be high. Inorganic N can therefore be present in large amounts. In this study, the cover-cropped treatments did not contain as much inorganic N as did the conventional treatments in summer of 1993, although all treatments contained more than in 1992. Although differences between conventional and cover-cropped plots were not significant, these data suggest that a more labile form of N was produced in the conventional plots in 1993.
This observation is based on one year of data, but underscores the importance of cover crops in the recovery of N remaining in the soil in the fall. Inorganic N in the cover-cropped soil may be less susceptible to leaching because the cover crops will recover some portion of it.
This study was carried out on rotation plots that had been established relatively recently.
It is possible that clear differences due to treatments have not had a chance to develop in these plots, and that crop and N treatments will have significant effects in the future. Because the area had previously been cropped to a winter wheat/fallow rotation, the microbial community had adapted to deal with wheat residues biannually, usually during warm, dry weather.
Fertilizer application and tillage are timed differently in the vegetable/cover crop rotations, and the microbial community in those rotations needs to adjust its mechanisms in order to utilize different substrates twice annually and procure more N for itself. Mineralization of spring-incorporated cover crops may

96 proceed more rapidly in future years as the microbial population adjusts to fresh substrate additions in cooler, moister conditions.
These rotation plots will continue to be used to monitor NO3 leaching from the rye and winter fallow plots using lysimeters. Results from this study and from the lysimeter studies will be valuable in helping farmers to make decisions about N management.
Ferguson et al. (1990) were able to realize an $18.66 ha-' savings by taking NO3 in irrigation water and in spring surface soil into account before applying fertilizer in the spring. Their work and reports by Ranells and Wagger
(1992), who are estimating N potentially available in legume cover crops at various times of desiccation, bears continued attention.
Mike Strohm, a farmer in West Union, IL, disks or desiccates vetch in the fall, and claims that no decomposition occurs below 60°F so his system holds
N at the surface until it is needed (Bowman, 1993). The work of innovative farmers like Strohm should be taken into account, and their methods scientifically quantified.

97
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Yaacob, 0., and G.J. Blair. 1980. Mineralization of '5N-labelled legume residues in soils with different nitrogen contents and its uptake by Rhodesgrass.
Plant Soil 57:237-248.

APPENDICES
106

Appendix A. Data files for biological parameters.
Sample t
13-G
PR §
1.279
0.937
0.877
0.290
0.146
0.553
0.469
0.646
0.287
0.561
1.010
0.574
0.695
1.048
0.214
0.488
0.325
0.433
0.731
0.208
0.503
0.476
0.213
0.897
0.958
0.461
0.388
0.407
0.832
0.314
0.570
0.627
0.304
0.755
0.714
1.009
0.815
0.325
1.299
0.780
0.943
0.771
0.338
0.273
0.301
0.892
0.605
50.36
55.04
63.68
67.20
105.18
58.78
68.44
69.84
53.74
91.38
74.55
71.84
84.17
100.06
82.98
55.83
68.37
76.17
66.42
69.77
79.92
53.29
99.05
94.96
67.74
72.33
77.99
64.47
94.97
82.49
126.05
102.30
85.57
117.18
113.45
77.22
77.66
77.01
74.43
88.24
90.81
83.20
90.51
74.50
79.34
92.85
70.23
I0C33542
I1C33542
I2C33542
10Hr33542
I1Hr33542
I2Hr33542
10H133542
I1H133542
I2H133542
110C33542
II1C33542
112C33542
110H133542
II1H133542
II2H133542
II0Hr33542
II1Hr33542
II2Hr33542
III0C33542
1111C33542
III2C33542
1110H133542
III1H133542
III2H133542
III0Hr33542
III1Hr33542
III2Hr33542
1V0C33542
IV1C33542
IV2C33542
IV0Hr33542
IV1Hr33542
IV2Hr33542
IV0H133542
1V1H133542
1V2H133542
10C33575
I1C33575
I2C33575
I0Hr33575
I1Hr33575
I2Hr33575
I0H133575
11H133575
I2H133575
II0C33575
II1C33575
MBc
56.02
247.50
234.42
352.22
55.85
445.43
442.50
145.10
318.42
237.48
218.41
215.36
306.37
236.75
306.30
245.85
219.01
277.77
432.06
139.81
244.22
220.87
164.81
341.71
279.20
286.73
386.40
411.07
125.87
239.39
89.72
248.94
120.88
204.08
147.59
335.81
129.75
364.92
304.85
248.22
177.36
267.57
227.87
328.48
249.25
322.58
263.89
107
MBN tt
19.23
21.64
27.02
25.31
60.20
12.05
16.74
29.95
40.10
10.79
17.42
21.45
20.05
13.21
11.83
11.66
7.79
21.16
27.83
27.98
26.94
29.79
21.39
18.00
14.19
28.00
17.36
24.49
23.53
21.18
12.97
26.95
23.25
25.46
81.68
45.20
21.55
33.85
35.98
29.34
10.00
29.75
31.27
25.38
20.24
21.60
21.65
Resp #
125.73
101.99
115.92
95.21
103.92
127.21
160.46
38.28
119.05
117.59
37.05
124.19
110.56
133.91
80.90
187.73
122.55
52.30
106.92
77.05
143.21
159.14
158.08
154.55
89.91
91.24
115.00
122.64
73.61
128.15
127.86
88.62
127.85
122.90
70.38
73.50
199.02
91.96
110.69
77.52
111.19
63.04
124.10
54.13
122.04
55.93
110.47

Sample t
1110Hr33575
III1Hr33575
III2Hr33575
1V0C33575
1V1 C33575
IV2C33575
IV0Hr33575
IV1Hr33575
IV2Hr33575
1V0H133575
IV1H133575
IV2H133575
I0C33606
11C33606
12C33606
I0Hr33606
II Hr33606
I2Hr33606
10H133606
I1H133606
I2H133606
II0C33606
II1C33606
II2C33606
110H133606
II1H133606
112H133606
II0Hr33606
II1Hr33606
II2Hr33606
1110C33606
III1C33606
III2C33606
1110H133606
1111H133606
II2C33575
II0H133575
111H133575
II2H133575
II0Hr33575
II1Hr33575
II2Hr33575
III0C33575
III1C33575
III2C33575
1110H133575
III1H133575
1112H133575 f3-G 1
100.43
97.82
94.84
114.47
67.27
77.64
94.97
81.24
105.00
140.47
155.73
99.86
109.54
95.66
85.76
103.82
99.18
102.17
116.06
79.21
42.85
48.43
94.76
89.25
118.93
113.82
61.32
51.52
51.11
61.82
74.29
64.19
66.52
81.53
70.39
79.11
91.90
89.68
71.69
66.32
77.70
81.26
59.44
65.77
50.99
60.43
74.99
63.01
PR §
0.920
0.536
0.341
0.444
1.079
0.111
0.659
0.491
0.350
0.321
0.667
0.672
0.533
0.511
0.255
0.238
0.639
0.306
0.707
0.507
0.548
0.490
0.323
0.349
0.416
0.464
0.236
0.506
0.549
0.307
0.872
0.468
1.238
1.063
0.283
1.039
0.584
1.001
1.438
0.836
0.473
0.721
0.701
0.315
0.198
0.526
0.703
0.646
MBc cl[
55.95
426.29
297.25
268.27
81.40
277.68
258.99
114.01
71.50
378.88
437.12
126.55
113.55
357.58
186.50
250.73
69.02
146.53
291.61
89.99
335.85
314.64
255.06
99.51
67.53
235.68
281.38
466.96
197.28
198.70
172.29
167.75
196.40
221.19
98.10
74.51
98.12
251.35
292.98
225.35
171.99
233.92
260.50
202.76
236.12
270.88
281.09
213.93
108
MB, if
1.53
12.50
19.30
15.10
18.59
21.98
24.22
15.42
12.44
14.76
22.81
12.05
14.50
20.08
22.88
13.65
20.41
16.63
14.13
25.45
33.58
27.98
0.00
6.44
65.73
0.00
22.66
0.00
0.00
16.55
41.07
54.61
19.31
14.07
18.27
17.60
27.16
26.37
42.84
28.44
26.88
46.81
54.70
60.89
11.42
30.34
58.20
13.23
Resp #
143.96
129.20
119.63
94.32
72.98
75.42
80.85
99.88
76.04
94.99
82.44
77.09
87.27
101.88
86.46
107.56
120.46
102.13
147.02
36.58
33.54
59.47
34.98
33.58
33.98
113.62
128.57
32.39
170.84
129.80
140.31
47.20
124.02
145.90
43.46
166.60
33.33
116.94
134.67
120.07
43.99
134.94
156.46
63.80
33.81
178.67
222.56
81.07

Sample t
III2H133606
III0Hr33606
III1Hr33606
III2Hr33606
1V0C33606
1V1C33606
IV2C33606
IV0Hr33606
IV1Hr33606
IV2Hr33606
1V0H133606
1V1H133606
IV2H133606
I0C33635
I1C33635
12C33635
I0Hr33635
11Hr33635
I2Hr33635
I0H133635
II H133635
I2H133635
II0C33635
II1C33635
II2C33635
II0H133635
II1H133635
II2H133635
II0Hr33635
II1Hr33635
II2Hr33635
III0C33635
III1C33635
1I12C33635
1110H133635
III1H133635
III2H133635
III0Hr33635
III1Hr33635
III2Hr33635
IV0C33635
1V1C33635
IV2C33635
IV0Hr33635
IV1Hr33635
IV2Hr33635
1V0H133635
IV1H133635
P-G t
69.85
107.97
54.73
64.86
68.52
49.60
69.75
65.26
87.83
88.82
64.29
57.02
91.44
73.14
80.97
90.95
50.39
42.90
57.35
63.60
84.61
112.93
106.33
93.13
97.06
88.91
78.98
88.36
83.47
99.64
60.15
65.84
85.26
95.94
112.71
113.25
67.69
84.25
103.47
74.38
73.03
95.52
60.31
91.90
80.76
90.72
114.02
125.59
PR §
0.393
0.393
0.172
0.225
0.407
0.246
0.376
0.426
0.369
0.131
0.279
0.663
0.547
0.459
0.273
0.339
0.925
0.770
0.777
0.606
0.261
0.552
0.768
0.459
0.505
0.141
0.148
0.548
0.648
0.676
0.361
0.573
1.236
0.637
0.611
0.514
0.575
0.336
0.472
0.592
0.516
0.436
0.792
0.275
0.380
0.325
0.242
0.722
MBc ¶
229.64
228.83
232.03
199.79
221.31
228.74
186.55
83.56
102.75
98.45
73.44
210.83
216.55
285.07
335.42
209.60
306.64
421.57
337.97
247.33
209.46
246.87
228.79
283.11
181.14
217.75
267.52
181.01
202.79
190.97
120.18
162.69
188.04
212.99
229.56
229.48
196.06
178.70
230.04
188.33
146.47
136.65
165.98
215.99
110.09
140.02
160.71
156.34
109
MB, tt
47.42
36.60
0.00
25.95
19.11
26.32
22.27
6.57
26.41
37.74
41.08
5.08
33.27
19.85
17.45
37.17
25.86
16.81
16.45
21.25
29.01
12.06
0.00
29.01
0.00
25.80
13.30
25.02
12.10
20.02
17.69
10.02
20.16
29.09
0.00
15.46
27.59
32.22
56.29
23.06
0.00
37.83
29.11
36.78
8.16
30.27
0.00
13.89
Resp #
90.54
100.90
154.39
119.97
79.56
126.09
114.12
103.83
132.37
111.90
37.53
34.12
38.51
81.42
63.21
157.01
108.97
127.82
160.40
100.55
91.98
87.95
85.26
89.08
156.37
100.17
49.35
42.18
100.95
85.71
124.10
89.07
105.08
116.52
88.03
72.52
69.99
112.18
38.68
72.48
124.01
60.66
49.48
88.01
58.21
101.78
68.39
92.28

Sample t
III1H133663
III2H133663
1II0Hr33663
III1Hr33663
III2Hr33663
1V0C33663
IV1C33663
IV2C33663
IV0Hr33663
IV1Hr33663
IV2Hr33663
1V0H133663
IV1H133663
IV2H133663
I0C33693
I1C33693
I2C33693
I0Hr33693
11Hr33693
I2Hr33693
I0H133693
I1H133693
I2H133693
II0C33693
II1C33693
IV2H133635
I0C33663
I1C33663
I2C33663
I0Hr33663
I1Hr33663
I2Hr33663
I0H133663
I1H133663
12H133663
II0C33663
II1C33663
II2C33663
II0H133663
II1H133663
II2H133663
II0Hr33663
II1Hr33663
II2Hr33663
III0C33663
III1C33663
III2C33663
1110H133663
PR §
0.516
0.383
0.178
0.399
0.051
0.227
0.316
0.818
0.492
0.822
0.319
0.452
0.210
0.279
0.000
0.196
0.791
0.339
0.240
0.494
0.325
0.288
0.110
0.000
0.530
0.392
0.528
0.427
0.166
0.215
0.214
0.287
0.163
0.491
0.307
0.694
0.830
0.645
0.444
0.400
0.510
0.372
0.518
0.256
0.200
0.573
0.107
0.345
P-G t
81.75
108.29
92.01
98.89
96.69
67.21
72.44
76.03
54.71
64.72
55.97
55.28
53.56
59.80
76.30
46.32
65.80
64.47
50.27
63.62
66.44
63.98
76.13
70.75
80.84
48.34
53.53
73.15
57.43
67.68
71.25
52.62
75.98
64.71
68.04
67.95
71.52
80.53
77.22
79.16
65.29
87.57
114.19
77.40
91.88
92.87
56.84
65.32
MBc 1
57.12
50.94
80.60
35.70
48.40
51.08
58.86
58.52
50.08
59.36
52.45
150.38
51.29
196.37
226.92
271.12
46.01
43.19
41.97
43.67
40.97
82.84
36.50
43.88
47.96
175.42
187.52
205.20
203.70
157.10
162.89
54.50
51.76
72.70
50.33
46.71
44.10
52.60
57.12
62.27
189.64
55.90
54.26
56.09
69.57
73.18
49.76
57.36
1 1
0
MBN tt
14.81
5.56
14.95
8.30
17.60
4.65
13.76
6.16
19.41
14.32
20.28
6.10
12.71
20.08
28.74
7.27
34.56
12.69
23.03
16.69
28.09
21.40
19.89
10.49
13.79
11.11
7.71
28.89
23.71
18.61
30.13
14.75
25.34
14.36
20.31
35.52
23.64
17.68
8.65
14.91
32.70
28.64
17.19
16.81
18.64
18.16
13.61
18.42
Resp #
100.22
79.84
77.29
59.06
95.83
115.31
86.34
75.71
94.01
110.50
24.50
27.41
18.62
7.35
33.99
26.87
26.60
31.94
38.63
24.48
30.90
34.04
13.32
34.03
28.03
26.66
24.25
25.35
27.39
22.13
19.45
13.04
21.65
27.45
25.62
28.64
16.80
23.58
50.29
64.09
16.25
30.01
23.05
17.36
23.32
16.17
22.48
24.26

Sample t
II2C33693
II0H133693
II1H133693
II2H133693
II0Hr33693
II1Hr33693
II2Hr33693
III0C33693
III1C33693
III2C33693
1110H133693
III1H133693
III2H133693
III0Hr33693
III1Hr33693
III2Hr33693
1V0C33693
1V1C33693
IV2C33693
IV0Hr33693
IV1Hr33693
IV2Hr33693
1V0H133693
IV1H133693
IV2H133693
10C33740
I1C33740
I2C33740
I0Hr33740
I1Hr33740
I2Hr33740
10H133740
I1H133740
12H133740
110C33740
II1C33740
II2C33740
110H133740
II1H133740
II2H133740
II0Hr33740
II1Hr33740
II2Hr33740
III0C33740
III1C33740
III2C33740
1110H133740
III1H133740
P-G $
72.88
88.46
56.87
74.82
83.05
55.51
82.64
62.70
89.02
100.38
99.22
85.58
90.32
110.43
74.33
76.64
70.75
111.40
109.25
99.83
93.00
103.91
80.82
62.41
74.73
84.58
77.16
79.68
72.55
100.93
84.35
81.13
69.13
69.38
71.99
60.43
63.07
66.94
62.28
76.13
90.45
48.54
69.70
53.12
56.50
71.38
70.18
59.39
PR §
0.506
0.571
0.574
0.241
0.161
0.434
0.409
0.081
0.680
0.414
0.316
0.073
0.305
0.529
0.379
0.555
0.614
0.778
0.441
0.239
0.371
0.127
1.009
0.428
0.271
0.173
0.241
0.382
0.186
0.349
0.215
0.285
0.150
0.561
0.175
0.252
0.276
0.488
0.536
0.597
0.189
0.426
0.316
0.406
0.323
0.195
0.387
0.198
MBc 11
197.50
116.81
180.04
205.27
206.55
183.79
183.21
184.72
169.54
165.30
152.28
160.82
190.76
177.87
173.80
259.91
178.26
218.21
162.26
59.40
129.87
204.56
269.88
191.26
179.51
159.85
136.82
130.68
159.03
181.97
174.14
166.51
210.82
229.87
190.20
221.92
208.88
177.53
167.18
190.87
199.49
243.56
176.56
225.18
209.03
202.63
173.94
159.01
1 1
1
MB, tt
19.09
25.11
23.85
4.70
19.21
13.71
13.51
12.15
22.34
17.29
21.59
24.23
18.69
14.57
28.16
0.00
17.83
23.39
20.85
13.75
27.65
17.13
25.74
13.52
17.04
19.01
17.41
17.67
17.85
20.32
17.64
11.89
13.63
24.49
23.99
16.36
9.43
16.69
14.08
23.02
17.73
24.24
29.85
25.07
19.08
32.89
18.24
18.52
Resp #
34.08
81.09
88.46
75.08
53.51
61.84
49.75
73.67
76.17
97.88
89.83
46.45
47.30
38.12
55.65
107.77
75.79
71.67
121.90
101.25
84.45
111.36
84.54
80.76
67.40
81.07
97.95
85.90
90.30
95.78
110.46
85.25
97.82
96.23
95.83
95.72
85.89
83.06
57.18
87.95
49.94
67.42
72.05
43.41
36.95
44.38
66.98
69.73

Sample t
II1H133814
112H133814
II0Hr33814
II1Hr33814
II2Hr33814
III0C33814
III1C33814
1112C33814
1110H133814
III1H133814
1112H133814
III0Hr33814
III1Hr33814
III2Hr33814
1V0C33814
IV1C33814
IV2C33814
IV0Hr33814
IV1Hr33814
IV2Hr33814
1V0H133814
1V1 H133814
III2H133740
III0Hr33740
III1Hr33740
III2Hr33740
1V0C33740
IV1C33740
IV2C33740
IV0Hr33740
IV1Hr33740
IV2Hr33740
1V0H133740
1V1H133740
IV2H133740
10C33814
I1C33814
12C33814
I0Hr33814
11Hr33814
I2Hr33814
10H133814
I1H133814
I2H133814
II0C33814
II1C33814
112C33814
110H133814
PR §
0.571
0.241
0.263
0.264
0.469
0.454
0.535
0.569
0.358
0.302
0.466
0.306
0.554
0.349
0.414
0.628
0.461
0.254
0.690
0.496
0.603
0.507
0.444
0.224
0.369
0.414
0.280
0.456
0.508
0.408
0.393
1.053
0.849
0.343
0.935
0.247
0.271
0.313
0.471
1.000
0.464
0.351
1.188
0.534
0.180
0.388
0.386
0.559
13-G f
88.48
94.69
97.19
102.67
77.73
95.42
108.15
55.47
58.08
85.48
94.75
89.27
89.10
79.73
92.27
67.58
70.52
72.33
54.13
85.08
75.84
70.67
77.19
83.81
82.07
93.15
86.81
74.29
64.47
107.96
66.41
89.64
97.39
72.20
62.21
72.20
73.30
81.33
100.35
72.28
109.45
94.86
64.35
120.58
100.80
63.39
82.33
93.24
M13c (11
165.38
170.23
87.76
179.80
212.27
217.60
208.90
202.92
132.33
147.09
110.93
96.62
198.36
202.11
141.29
209.41
159.65
176.36
187.02
112.42
150.67
135.42
187.67
304.47
200.78
153.17
172.61
154.27
222.21
151.82
224.73
175.44
150.15
171.32
177.52
232.13
292.97
235.03
235.04
210.32
173.64
147.95
149.83
164.57
150.21
137.97
171.25
134.91
112
MB, tt
25.31
21.56
16.00
19.97
20.27
19.04
18.06
26.78
11.99
13.13
2.23
14.90
17.47
21.68
15.29
16.81
55.02
21.81
0.00
0.00
17.69
44.96
17.68
19.95
20.31
19.34
18.17
12.25
3.70
17.81
15.08
11.17
15.55
15.13
16.58
16.87
11.22
23.17
17.17
1.05
11.24
11.71
9.51
14.40
15.10
16.47
12.07
8.99
Resp #
66.31
72.30
90.17
44.69
51.39
52.85
44.68
58.46
96.78
138.14
56.24
72.95
70.40
55.16
62.04
63.09
65.43
56.15
77.39
46.81
46.63
58.46
99.14
112.15
68.52
75.46
58.74
59.22
64.32
41.10
65.77
37.53
56.42
53.59
76.92
77.05
60.77
63.65
57.25
57.75
77.77
68.14
89.17
98.23
55.77
61.09
63.09
76.26

Sample t
111H133922
II2H133922
II0Hr33922
II1Hr33922
II2Hr33922
III0C33922
III1C33922
III2C33922
1110H133922
III1H133922
1112H133922
III0Hr33922
III1Hr33922
III2Hr33922
1V0C33922
IV1C33922
1V2C33922
IV0Hr33922
IV1Hr33922
IV2Hr33922
1V0H133922
IV1H133922
IV2H133922
10C34013
I1C34013
I2C34013
10Hr34013
I1Hr34013
I2Hr34013
10H134013
I1H134013
I2H134013
110C34013
II1C34013
IV2H133814
I0C33922
I1C33922
12C33922
I0Hr33922
I1Hr33922
I2Hr33922
10H133922
11H133922
12H133922
II0C33922
II1C33922
II2C33922
II0H133922
I3-G
89.17
PR §
0.644
MB, 91
90.00
103.18
133.16
197.33
188.55
75.96
124.98
130.38
108.04
155.53
146.49
137.76
222.92
130.24
225.83
214.65
182.98
276.61
253.80
218.55
183.47
152.29
121.42
208.65
228.25
161.74
184.78
184.20
155.93
69.39
94.31
221.70
179.75
198.86
184.77
191.62
246.51
233.18
222.26
179.33
220.46
255.10
217.20
194.55
215.68
187.46
173.66
209.42
113
MB, fit
19.73
21.42
12.63
24.45
20.89
21.39
20.13
17.09
19.65
16.72
15.79
20.90
21.57
25.50
23.72
24.61
19.50
30.95
29.42
29.31
17.08
27.61
34.68
28.34
21.47
19.36
19.12
22.69
24.68
22.00
30.85
19.40
23.48
33.89
32.27
25.42
18.21
16.86
13.97
24.78
19.90
25.84
27.18
23.39
13.28
24.02
21.33
27.48
Resp #
80.98
56.10
25.42
54.76
56.53
92.09
76.23
64.85
73.65
164.37
104.67
103.37
85.72
99.04
84.41
111.74
100.65
123.90
90.49
68.32
129.95
66.95
91.44
94.39
76.81
85.44
73.56
112.66
94.41
56.27
79.87
63.83
88.45
82.83
126.28
107.23
50.63
115.71
74.38
82.45
92.81
65.74
84.77
77.60
79.03
95.72
99.92
89.15

Sample t
112C34013
II0H134013
II1H134013
II2H134013
II0Hr34013
II1Hr34013
II2Hr34013
III0C34013
III1C34013
III2C34013
1110H134013
III1H134013
III2H134013
III0Hr34013
III1Hr34013
III2Hr34013
1V0C34013
1V1C34013
IV2C34013
IV0Hr34013
IV1 Hr34013
IV2Hr34013
1V0H134013
1V1H134013
IV2H134013
I0C34111
I1C34111
I2C34111
I0Hr34111
I1Hr34111
I2Hr34111
I0H134111
I1H134111
I2H134111
II0C34111
II1C34111
II2C34111
II0H134111
II1H134111
II2H134111
II0Hr34111
II1Hr34111
II2Hr34111
III0C34111
III1C34111
III2C34111
1110H134111
III1H134111
13-G $
PR § MB, 9[
165.49
159.83
267.14
214.65
209.39
209.35
210.73
240.45
254.26
225.05
192.29
237.78
213.92
212.01
204.10
254.45
210.88
139.92
171.80
212.68
235.88
238.30
219.40
208.03
217.11
212.70
167.84
163.54
171.83
295.87
220.92
197.49
261.14
211.98
181.68
247.92
239.69
225.37
166.06
176.76
178.67
77.98
225.42
187.00
164.82
181.97
173.30
149.45
114
MBN if
25.25
23.49
35.77
15.43
18.53
23.69
22.00
29.71
25.62
24.06
21.55
24.42
27.67
16.28
26.38
27.16
21.11
7.68
36.94
33.44
11.95
15.43
21.31
27.36
26.00
24.06
25.06
16.36
27.12
25.46
20.99
22.00
19.23
18.99
24.34
27.05
20.07
20.98
28.61
26.37
18.74
19.32
21.97
18.29
18.07
14.89
24.87
10.21
Resp #
79.47
113.67
190.17
109.72
58.64
87.16
119.03
112.67
124.02
149.37
111.38
142.72
125.89
66.81
66.98
85.67
133.33
109.11
97.94
99.76
85.50
140.69
97.56
90.42
68.46
105.71
80.36
191.49
159.76
122.95
117.51
136.64
145.19
100.57
84.53
82.08
76.99
82.59
63.28
22.53
73.29
75.22
93.86
55.67
87.96
84.56
114.83
96.82

Sample t
110H134185
II1H134185
II2H134185
II0Hr34185
II1Hr34185
II2Hr34185
1110C34185
III1C34185
III2C34185
1110H134185
III1H134185
III2H134185
III0Hr34185
III1Hr34185
III2Hr34185
1V0C34185
1V1C34185
IV2C34185
IV0Hr34185
IV1Hr34185
IV2Hr34185
1V0H134185
IV1H134185
III2H134111
III0Hr34111
III1Hr34111
III2Hr34111
1V0C34111
IV1C34111
IV2C34111
IVOHr34111
IV1Hr34111
IV2Hr34111
1V0H134111
IVIH134111
IV2H134111
10C34185
I1C34185
I2C34185
I0Hr34185
11Hr34185
I2Hr34185
I0H134185
11H134185
12H134185
110C34185
II1C34185
II2C34185
I3-G $ PR §
115
MBN if
41.56
0.00
13.09
34.54
50.80
15.83
12.34
26.48
3.07
33.34
20.03
22.87
28.73
0.00
15.10
23.18
17.05
0.00
77.68
23.58
39.31
28.14
16.41
22.08
32.51
36.37
20.08
24.76
19.56
23.99
20.16
28.88
25.93
8.12
16.81
18.76
55.43
22.53
0.91
19.65
16.92
22.69
19.39
17.16
20.35
19.22
30.59
29.62
Resp #
73.88
78.53
72.17
62.66
77.01
79.17
84.59
63.34
74.64
67.69
58.81
49.86
28.15
54.24
71.76
85.23
61.97
73.18
39.82
40.46
75.38
52.82
32.29
63.21
80.73
71.18
80.68
75.06
52.12
86.36
82.24
122.44
81.69
115.05
104.87
52.93
71.75
86.62
181.16
152.26
151.02
120.32
96.60
156.91
65.83
55.76
49.80
62.36
MB, 91
217.02
195.96
250.41
160.64
135.13
124.37
126.10
191.27
132.69
191.05
207.25
181.82
290.34
189.35
215.28
155.07
138.57
200.74
121.27
219.91
229.87
218.91
157.56
173.56
161.73
166.18
135.60
160.57
155.13
186.97
177.24
184.39
167.11
210.14
168.41
155.59
178.31
152.92
285.39
147.90
164.38
183.22
106.65
187.12
122.43
72.50
155.33
132.61

Sample t
IV2HI34185
I3-G t PR § MBc 1
154.93
Resp #
83.07
116
MBN tt
27.29
t Sample identification: I = Replication 1
II = Replication 2
III = Replication 3
IV = Replication 4
0 = No Urea Rate
1 = N, Urea Rate
2 = N2 Urea Rate
C = Conventional Wheat/FallowNegetable Rotation
Hr = Alternative Vegetable/Cover Crop Rotation; Rye/Pea Mix
HI = Alternative Vegetable/Cover Crop Rotation; Rye Alone
33497 = 16 Sept. 1991
33542 = 31 Oct. 1991
33575 = 3 Dec. 1991
33606 = 3 Jan. 1992
33635 = 1 Feb. 1992
33663 = 29 Feb. 1992
33693 = 30 Mar. 1992
33740 = 16 May 1992
33814 = 29 Jul. 1992
33851 = 4 Sept. 1992
33922 = 14 Nov. 1992
34013 = 13 Feb. 1993
34111 = 22 May 1993
34185 = 4 Aug. 1993
34215 = 3 Sept. 1993
§
(II p-Glucosidase units: mg p-nitrophenol kg' soil hr'.
Protease units: mmol tyrosine kg' soil hr-1.
Biomass C units: mg CO2 C kg' soil.
# Respiration units: mg CO2 C kg-1 soil 10 d"'.
ti- Biomass N units: mg Inorganic N kg-1 soil.

Appendix B: Data files for inorganic N.
Sample t NH4 20 NH4 40
I0C33542
I1C33542
12C33542
I0Hr33542
I1Hr33542
I2Hr33542
I0H133542
I1H133542
I2H133542
110033542
II1C33542
II2C33542
110H133542
II1H133542
112H133542
II0Hr33542
II1Hr33542
112Hr33542
1110C33542
III1C33542
1112C33542
1110H133542
1111H133542
1112H133542
III0Hr33542
III1Hr33542
III2Hr33542
1V0C33542
1V1C33542
IV2C33542
IV0Hr33542
IV1Hr33542
IV2Hr33542
1V0H133542
1V1H133542
IV2H133542
I0C33575
11C33575
I2C33575
I0Hr33575
I1Hr33575
I2Hr33575
I0H133575
I1H133575
12H133575
2.23
1.11
0.00
1.39
2.23
1.67
4.17
4.17
4.17
3.34
2.23
1.39
1.67
4.45
2.78
6.68
2.23
3.76
2.23
1.95
4.45
13.63
3.06
3.06
2.23
0.28
1.39
0.56
1.67
2.23
0.56
0.00
3.06
2.23
2.23
2.78
2.68
1.69
3.95
3.95
2.82
5.64
3.95
3.38
3.95
6.79
2.62
4.56
2.62
0.00
0.00
0.00
0.00
0.00
6.12
0.00
0.28
1.11
0.00
0.00
0.00
0.28
0.83
2.06
4.01
2.89
2.89
1.78
1.95
0.28
0.56
0.83
1.67
0.28
0.00
0.11
0.00
0.11
0.11
0.11
0.00
5.68
6.79
2.34
3.45
3.45
4.56
2.62
4.84
1.22
1.13
0.00
1.13
0.00
1.69
3.38
2.26
3.10
2.82
NH4 80
1.39
2.78
0.00
0.56
2.23
1.39
0.00
0.56
0.00
NO3 20
12.24
22.26
28.38
9.46
27.82
44.24
9.74
33.39
45.35
12.52
31.72
46.74
16.14
21.70
37.84
7.51
18.08
32.97
4.73
13.63
36.45
24.20
33.11
40.06
10.99
18.64
31.44
6.40
18.64
32.55
23.09
30.33
26.43
20.31
21.42
24.20
13.63
26.99
13.35
10.02
21.70
51.75
15.02
31.72
37.84
NO3 40
13.91
21.70
6.68
13.08
25.60
10.57
18.92
23.37
12.80
16.69
25.60
7.79
8.90
15.30
5.56
10.29
18.36
24.20
8.07
29.21
39.23
10.85
24.76
26.43
13.35
29.21
35.89
13.91
14.47
26.71
10.57
17.25
28.66
7.23
18.92
18.92
0.85
0.56
2.82
2.26
3.38
4.51
2.82
2.26
6.20
4.51
0.00
10.43
3.38
6.20
10.71
5.64
8.46
27.06
NO3 80
0.83
5.56
0.00
0.00
10.57
5.56
1.95
5.56
1.67
117

Sample t
1112H133575
III0Hr33575
III1Hr33575
III2Hr33575
1V0C33575
1V1C33575
IV2C33575
IV0Hr33575
IV1Hr33575
IV2Hr33575
1V0H133575
1V1H133575
IV2H133575
10C33606
11C33606
I2C33606
I0Hr33606
I1Hr33606
I2Hr33606
I0H133606
I1H133606
12H133606
110C33575
111C33575
112C33575
II0H133575
II1H133575
II2H133575
II0Hr33575
II1Hr33575
II2Hr33575
III0C33575
III1C33575
III2C33575
1110H133575
III1H133575
110C33606
II1C33606
II2C33606
II0H133606
II1H133606
II2H133606
II0Hr33606
II1Hr33606
II2Hr33606
III0C33606
III1C33606
1112C33606
NH4 20
0.56
5.56
1.95
5.29
4.17
1.95
6.40
5.56
2.50
5.56
4.45
2.23
3.90
8.90
6.68
3.90
3.90
1.95
1.95
0.00
1.95
1.95
2.50
0.83
0.00
3.62
2.50
3.62
2.50
3.62
0.56
0.28
2.78
2.50
4.17
1.39
1.39
0.28
1.11
0.83
0.00
1.53
4.73
1.39
0.28
0.00
1.95
0.28
NO3 20
22.54
22.26
28.93
15.02
21.42
26.71
27.82
26.99
26.71
31.72
27.27
24.48
20.03
26.15
22.26
24.76
23.79
22.54
27.82
24.48
23.37
27.82
24.48
17.25
18.36
19.48
19.48
20.87
26.43
21.42
26.43
26.15
26.99
26.43
28.66
19.20
21.98
21.98
20.87
21.98
23.65
22.26
25.60
22.67
18.36
20.03
22.54
20.59
NH4 80
1.69
2.26
0.85
1.69
2.26
2.26
2.26
1.13
0.56
1.13
2.26
2.26
0.85
2.26
1.69
0.56
0.56
0.56
1.69
1.13
1.13
1.97
3.38
0.00
3.95
2.26
2.26
0.00
1.97
1.69
1.69
2.26
2.82
3.95
0.00
2.26
2.82
8.46
1.13
0.56
3.38
3.38
3.38
1.69
3.95
0.56
0.00
1.69
NO3 40
13.25
10.71
4.79
4.51
21.42
19.17
15.22
2.26
5.07
6.77
6.77
9.58
1.97
3.95
3.95
1.69
6.20
4.23
1.69
2.26
7.33
2.26
2.26
1.69
0.00
3.10
4.51
1.69
0.00
2.26
0.56
4.51
2.82
9.58
5.07
13.53
11.84
4.79
0.56
4.51
9.02
2.26
4.79
1.41
4.51
0.56
7.61
10.71
NH, 40
1.97
1.13
4.51
5.64
3.95
2.26
3.95
3.38
2.54
5.07
7.05
3.10
1.69
0.00
2.82
3.95
1.41
1.13
1.97
1.69
3.95
1.69
0.56
1.69
5.36
3.66
4.23
5.36
4.23
3.95
2.54
2.26
3.38
4.51
2.82
0.28
1.69
2.26
1.69
3.95
4.51
5.36
5.36
4.79
5.36
5.36
6.20
3.10
NO3 80
8.46
14.94
4.51
10.15
10.71
3.95
3.95
10.71
23.12
4.23
12.97
15.79
4.51
6.20
6.20
2.26
3.95
12.97
0.00
5.64
10.15
2.54
8.17
15.22
2.26
4.79
8.46
1.97
3.38
7.89
2.26
2.82
1.97
10.15
3.95
18.04
5.64
6.77
7.89
5.64
6.20
19.73
4.79
6.20
10.15
2.26
6.77
9.02
1 1
8

Sample t
1V1H133606
IV2H133606
I0C33635
I1C33635
12C33635
I0Hr33635
I1Hr33635
I2Hr33635
10H133635
I1H133635
I2H133635
II0C33635
111C33635
II2C33635
II0H133635
II1H133635
II2H133635
II0Hr33635
II1Hr33635
II2Hr33635
III0C33635
III1C33635
1112C33635
1110H133635
1111H133635
III2H133635
1110Hr33635
III1Hr33635
III2Hr33635
1V0C33635
IV1C33635
IV2C33635
IV0Hr33635
IV1Hr33635
IV2Hr33635
1110H133606
III1H133606
III2H133606
III0Hr33606
III1Hr33606
III2Hr33606
1V0C33606
1V1C33606
IV2C33606
IV0Hr33606
IV1Hr33606
IV2Hr33606
1V0H133606
NH4 20
4.73
1.39
2.50
1.53
0.83
0.28
3.06
0.00
0.00
0.00
2.62
3.17
4.98
1.25
2.23
0.28
1.95
4.73
3.06
2.92
4.17
1.39
3.06
1.95
3.06
1.95
9.74
4.17
5.01
4.73
9.18
4.17
1.95
3.62
1.11
5.84
9.18
14.19
2.36
0.83
0.83
1.95
2.50
0.00
0.00
0.00
1.39
1.67
NH4 40
2.82
1.69
2.26
1.13
1.13
0.56
0.00
1.41
1.69
1.69
3.95
2.82
2.26
2.82
3.95
4.79
2.82
2.82
2.82
0.56
0.00
0.00
0.00
1.97
0.56
6.20
2.82
5.07
4.51
5.07
2.82
6.77
2.82
0.56
2.82
2.82
0.00
1.13
2.82
1.13
2.26
3.66
2.82
2.82
2.82
4.51
6.20
2.26
NH4 80
2.26
2.26
2.26
0.28
2.26
1.13
1.69
1.69
1.69
1.69
1.13
1.69
6.20
0.00
0.00
2.26
0.00
10.15
2.26
2.26
0.00
0.00
0.00
0.00
0.00
0.00
2.26
0.00
1.69
0.56
0.00
1.13
1.69
1.69
2.26
2.26
6.20
6.20
4.51
4.51
4.51
1.69
7.33
2.26
1.69
4.51
3.95
0.85
NO3 20
22.81
26.71
25.32
21.14
25.87
26.71
16.69
30.05
23.65
25.04
23.93
25.87
24.48
21.70
22.81
26.71
27.27
28.38
23.37
26.15
21.14
15.02
16.69
18.36
16.69
39.51
36.45
18.36
21.70
18.64
18.92
18.92
16.69
14.47
39.51
23.65
17.81
16.69
16.69
14.47
13.91
16.69
20.31
51.19
46.18
16.41
21.42
14.19
NO3 40
1.13
2.82
2.82
3.95
7.33
2.82
3.38
2.26
1.69
3.38
2.82
5.07
2.82
1.97
0.56
2.82
2.82
2.82
5.07
0.00
2.82
2.54
0.56
0.85
0.00
1.69
2.26
5.64
4.79
2.26
4.51
2.26
1.41
0.00
1.69
0.00
2.26
0.00
0.00
2.26
1.69
1.97
4.51
2.82
0.56
2.26
0.00
1.69
NO3 80
2.26
3.95
4.51
5.07
3.38
5.07
3.38
4.51
2.82
3.66
3.38
1.69
3.66
9.02
3.38
5.07
3.38
0.85
2.82
0.56
2.26
9.02
0.56
0.56
2.26
4.79
2.26
1.13
1.13
3.38
1.69
1.13
3.38
2.82
1.13
10.15
7.33
12.69
7.33
4.51
11.84
11.28
5.07
5.07
7.33
2.82
7.33
7.33
119

Sample t
1110H133663
III1H133663
III2H133663
III0Hr33663
III1Hr33663
III2Hr33663
1V0C33663
IV1C33663
IV2C33663
IV0Hr33663
IV1 Hr33663
IV2Hr33663
1V0H133663
1V1H133663
IV2H133663
I0C33693
I1C33693
I2C33693
I0Hr33693
11Hr33693
I2Hr33693
I0H133693
I1H133693
I2H133693
1V0H133635
IVIH133635
IV2H133635
10C33663
I1C33663
I2C33663
I0Hr33663
I1Hr33663
I2Hr33663
10H133663
I1H133663
12H133663
II0C33663
II1C33663
II2C33663
II0H133663
II1H133663
II2H133663
II0Hr33663
III Hr33663
II2Hr33663
III0C33663
III1C33663
III2C33663
NH4 20 1
3.06
2.50
4.73
1.39
0.28
0.83
4.17
4.73
4.17
4.45
2.50
3.62
2.50
2.50
1.39
2.50
4.73
4.73
5.01
6.96
0.56
0.00
0.00
4.45
5.84
4.73
4.73
4.73
3.90
4.17
1.39
0.00
0.56
0.28
0.83
3.62
3.62
3.62
2.50
2.50
0.83
2.50
1.11
3.06
1.95
1.95
2.50
3.06
NH4 40
1.41
0.99
2.26
2.26
1.97
1.41
1.41
1.69
0.85
2.26
1.41
2.40
2.54
0.85
1.69
2.26
2.26
0.00
1.27
2.26
1.69
2.54
2.26
3.38
2.54
1.69
2.54
2.26
1.97
0.56
1.69
1.97
2.82
4.51
1.69
1.69
1.69
2.54
1.55
2.82
7.47
4.65
5.78
5.78
3.38
4.09
3.24
4.37
NH4 80
2.54
2.26
2.26
2.26
1.97
2.26
2.82
3.10
2.26
2.54
1.97
3.10
2.26
1.41
1.97
1.69
4.51
1.97
2.26
2.68
2.26
2.54
2.26
2.26
4.51
5.64
3.95
3.38
3.66
3.95
1.83
1.97
1.41
1.97
1.13
0.99
1.69
3.10
1.97
1.69
0.00
0.00
0.00
2.26
2.26
2.26
2.26
2.26
NO3 20
13.63
9.18
14.19
18.08
10.85
14.19
12.52
18.08
20.31
15.86
15.30
16.97
16.41
18.08
18.08
15.02
18.08
14.75
11.41
20.31
20.03
18.08
13.63
8.62
12.24
13.35
8.35
8.35
7.51
10.02
10.02
10.02
13.63
10.85
14.19
15.86
15.86
25.32
16.41
16.41
13.63
18.64
24.48
19.20
30.88
24.76
16.41
14.19
NO3 40
2.11
4.65
4.65
1.27
3.24
4.51
2.68
3.81
4.93
0.99
1.69
1.55
0.00
5.78
6.91
4.23
2.68
2.68
3.24
0.70
2.11
5.22
6.48
4.23
4.23
4.23
1.13
2.82
0.85
1.97
6.62
5.50
8.32
5.64
3.52
3.24
3.52
3.24
8.74
11.13
2.11
0.56
1.41
1.69
5.36
6.06
2.40
3.24
NO3 80
2.82
0.00
1.69
3.38
0.28
3.66
5.92
0.85
1.69
2.54
1.97
2.82
3.38
1.69
1.69
2.26
2.26
2.54
3.38
0.42
1.69
1.41
1.69
3.66
1.69
0.56
0.56
0.56
3.66
1.13
0.56
0.28
3.95
3.38
3.38
5.64
2.68
5.92
3.66
1.69
1.69
3.52
6.77
2.82
1.69
1.41
1.41
1.41
120

NH, 20 $
1.39
3.06
1.39
0.56
0.83
0.00
1.39
2.23
0.83
1.67
2.23
1.95
2.78
3.06
5.29
3.06
1.39
1.95
6.40
5.84
6.40
3.62
4.17
2.36
6.96
6.96
8.62
1.95
1.39
0.28
1.95
1.39
2.50
1.39
3.06
4.17
2.23
3.62
1.95
0.00
1.39
2.23
2.50
2.50
0.28
0.00
1.39
1.95
Sample 1
II0C33693
II1C33693
II2C33693
II0H133693
II1H133693
II2H133693
II0Hr33693
II1Hr33693
II2Hr33693
III0C33693
1111C33693
III2C33693
1110H133693
III1H133693
III2H133693
III0Hr33693
III1Hr33693
III2Hr33693
1V0C33693
IV1C33693
IV2C33693
IV0Hr33693
IV1Hr33693
IV2Hr33693
IV0H133693
1V1H133693
IV2H133693
I0C33740
I1C33740
12C33740
I0Hr33740
11Hr33740
I2Hr33740
I0H133740
I1H133740
I2H133740
110C33740
II1C33740
112C33740
II0H133740
II1H133740
II2H133740
II0Hr33740
II1Hr33740
II2Hr33740
III0C33740
III1C33740
III2C33740
NO3 20
7.51
11.96
11.41
9.74
4.17
5.84
10.29
11.96
8.07
10.29
10.02
9.18
8.35
10.29
10.57
18.08
11.96
12.52
11.96
11.96
11.69
7.51
7.51
5.29
7.51
11.96
10.29
1.67
2.78
8.35
10.02
12.24
10.57
12.80
15.02
10.57
3.90
3.90
11.13
25.04
21.70
20.59
11.69
15.86
13.91
3.90
5.01
20.03
NO3 40
1.13
1.55
3.38
3.38
1.41
1.97
2.40
1.41
2.26
1.13
2.26
2.11
1.13
2.26
2.26
1.13
3.38
9.30
10.43
2.26
9.58
2.54
1.13
2.26
3.24
1.41
2.26
1.13
0.00
1.97
4.23
8.46
8.46
8.46
4.51
5.36
2.54
0.85
2.40
13.81
1.13
1.13
1.41
1.13
2.26
3.95
7.61
1.69
NH4 80
2.54
4.23
5.07
1.41
2.26
1.97
2.40
2.82
1.13
3.24
4.93
3.52
2.96
2.11
3.66
2.26
2.54
2.26
5.78
2.96
4.37
5.78
3.81
2.68
3.81
4.93
4.93
5.78
6.06
11.70
8.60
9.73
13.11
1.13
1.69
1.27
2.26
2.54
2.26
2.26
2.40
2.82
2.26
4.79
3.95
1.97
4.51
1.13
NH4 40
3.81
3.24
3.52
3.81
3.52
3.52
4.09
4.79
2.96
4.65
4.93
3.52
3.52
3.81
3.52
3.81
3.81
4.93
4.93
5.78
6.06
5.78
2.96
4.37
5.78
3.81
2.68
11.70
8.60
6.62
5.78
4.65
3.81
3.52
3.52
3.52
4.65
4.37
6.06
4.65
9.73
13.11
3.24
4.93
3.52
2.96
2.11
3.66
121
NO3 80
0.56
0.42
2.54
0.00
0.28
0.00
0.00
0.56
0.00
0.56
0.56
0.56
0.56
0.56
0.85
0.56
1.13
0.56
0.56
1.69
3.38
4.51
7.61
6.62
4.51
3.10
5.07
2.26
2.82
5.92
9.87
7.61
4.79
4.09
1.41
0.70
0.85
0.28
0.00
0.56
0.14
1.83
3.38
3.10
4.51
1.13
0.00
5.50

Sample t
1110C33814
1111C33814
1112C33814
1110H133814
III1H133814
III2H133814
III0Hr33814
III1Hr33814
1112Hr33814
IV0C33814
IV1C33814
IV2C33814
IV0Hr33814
IV1Hr33814
IV2Hr33814
1110H133740
III1H133740
1112H133740
III0Hr33740
III1Hr33740
III2Hr33740
1V0C33740
IV1C33740
IV2C33740
IV0Hr33740
IV1Hr33740
IV2Hr33740
1V0H133740
IV1H133740
IV2H133740
10C33814
I1C33814
I2C33814
I0Hr33814
I1Hr33814
I2Hr33814
I0H133814
I1H133814
I2H133814
II0C33814
111C33814
112C33814
II0H133814
II1H133814
II2H133814
II0Hr33814
II1Hr33814
II2Hr33814
NH4 20 $
0.56
6.68
5.01
0.56
0.56
1.67
2.23
0.00
0.56
5.01
11.69
2.23
3.06
4.45
2.78
6.12
8.90
5.01
6.12
4.45
0.00
2.23
2.23
3.90
4.45
7.23
1.95
1.67
1.95
3.90
0.56
2.78
2.23
5.01
3.90
14.75
5.01
4.73
5.84
6.40
5.84
3.62
2.50
3.06
4.17
4.73
3.62
3.62
NH4 40
2.68
2.40
3.81
2.68
2.54
7.75
2.40
6.91
3.81
6.48
2.68
2.68
3.52
2.68
2.68
NH4 80
6.91
3.81
6.48
2.68
2.68
3.52
2.68
2.68
2.68
2.40
3.81
2.68
2.54
7.75
2.40
NO3 20
72.89
19.20
20.03
41.18
0.00
2.23
2.50
24.48
24.48
60.65
16.97
28.66
33.66
0.28
8.35
37.84
49.52
22.81
17.25
57.31
1.11
0.00
9.46
12.24
42.85
11.69
10.57
15.02
17.81
17.67
0.00
0.00
5.56
17.25
19.48
21.98
10.57
11.69
15.02
2.50
2.78
13.35
8.35
1.95
15.30
26.43
31.99
59.82
NO3 40
3.38
3.81
4.23
4.51
3.38
3.95
6.91
8.17
6.77
6.48
4.51
3.81
4.23
0.28
1.13
NO3 80
3.38
2.26
3.10
2.26
1.97
2.26
2.26
3.95
3.38
3.10
2.26
2.26
2.26
2.26
3.24
122

NH, 20 $
1.83
1.83
1.83
1.83
2.96
1.97
1.55
1.83
1.83
1.13
0.56
0.00
0.28
0.85
0.56
0.56
0.56
0.99
0.56
0.56
0.28
0.00
0.42
1.69
1.13
1.13
1.13
2.54
0.28
1.13
0.28
1.13
0.42
1.13
0.85
0.56
0.85
0.28
1.13
1.13
1.41
2.54
1.69
1.41
1.13
0.56
0.85
1.41
Sample t
IV0HI33814
IV1H133814
IV2H133814
10C33922
I1C33922
I2C33922
I0Hr33922
I1Hr33922
I2Hr33922
I0H133922
II H133922
I2H133922
II0C33922
II1C33922
II2C33922
II0H133922
II1H133922
II2H133922
II0Hr33922
II1Hr33922
II2Hr33922
III0C33922
III1C33922
III2C33922
1110H133922
III1H133922
1112H133922
III0Hr33922
III1Hr33922
III2Hr33922
1V0C33922
IV1C33922
IV2C33922
IV0Hr33922
IV1Hr33922
IV2Hr33922
1V0H133922
1V1H133922
IV2H133922
10C34013
11C34013
I2C34013
I0Hr34013
I1 Hr34013
I2Hr34013
I0H134013
I1H134013
I2H134013
NH, 40
1.69
1.13
2.82
1.41
1.55
1.69
2.26
1.69
2.54
1.97
1.41
1.97
1.69
2.26
1.55
1.69
1.41
1.69
1.69
1.69
0.70
1.97
0.85
0.56
1.69
1.13
0.85
0.85
0.85
1.41
2.54
1.69
1.41
2.54
1.69
3.95
4.79
2.68
2.54
1.69
2.54
1.41
1.69
1.69
1.41
NH, 80
NO3 20
4.93
4.65
6.06
6.06
4.09
4.93
4.93
9.16
2.96
4.93
4.93
5.22
3.95
6.20
5.78
4.93
6.06
3.81
9.16
4.09
15.93
6.34
3.95
4.09
7.47
2.96
4.93
9.30
17.53
53.70
46.46
5.78
4.09
4.09
4.09
4.93
6.77
4.93
4.09
4.93
3.38
4.51
3.38
4.51
4.37
1.41
1.97
1.97
1.69
1.41
0.99
1.41
1.13
1.69
0.00
1.69
2.26
1.13
2.26
1.41
0.70
1.13
1.13
0.85
1.13
1.13
0.56
0.85
0.85
1.41
1.13
1.41
2.26
1.83
1.69
0.85
2.26
1.41
1.27
2.26
1.41
1.41
1.41
1.41
0.56
0.56
0.00
0.56
0.28
0.00
0.56
0.56
0.00
NO3 40
18.75
7.19
9.44
9.16
10.71
6.62
17.62
5.22
10.85
14.80
4.93
8.60
6.77
6.34
7.47
19.87
8.32
7.33
12.83
19.87
8.60
12.54
21.00
5.50
1.97
1.13
1.13
1.13
8.46
4.37
4.37
4.09
8.60
5.50
8.03
10.85
19.59
8.32
4.93
8.32
13.11
1.13
1.41
0.00
0.85
NO3 80
123
4.93
3.38
3.38
4.23
6.77
6.48
3.38
4.51
8.46
4.51
4.09
4.51
7.05
4.51
9.58
2.11
5.36
8.74
2.26
8.46
5.64
2.82
4.51
6.77
2.54
2.26
18.61
2.54
3.38
8.46
2.26
2.54
8.46
1.97
6.48
4.51
2.11
2.54
2.82
2.54
4.79
2.11
2.82
2.54
7.05

NH, 20
1.83
1.83
2.40
2.11
2.11
3.81
4.37
2.40
1.27
2.68
4.37
3.52
3.52
3.24
2.68
2.96
2.68
2.40
2.54
1.55
1.83
2.40
4.37
2.68
1.83
3.52
2.40
1.83
0.70
3.52
1.55
2.96
1.83
0.70
1.83
1.83
0.70
1.83
1.55
1.83
1.83
0.70
1.55
1.97
1.83
1.55
1.55
0.99
Sample t
II0C34013
II1C34013
II2C34013
II0H134013
II1H134013
112H134013
II0Hr34013
II1Hr34013
II2Hr34013
III0C34013
III1C34013
III2C34013
1110H134013
III1H134013
III2H134013
I110Hr34013
III1Hr34013
III2Hr34013
1V0C34013
IV1C34013
IV2C34013
IV0Hr34013
IV1Hr34013
IV2Hr34013
1V0H134013
1V1H134013
IV2H134013
10C34111
I1C34111
I2C34111
I0Hr34111
11Hr34111
I2Hr34111
I0H134111
I1H134111
I2H134111
II0C34111
111C34111
II2C34111
110H134111
II1H134111
II2H134111
II0Hr34111
II1Hr34111
II2Hr34111
III0C34111
III1C34111
III2C34111
NH, 40
1.27
0.42
1.55
1.55
0.85
3.24
2.96
2.40
0.99
1.97
1.97
1.13
0.70
0.85
1.69
0.85
0.00
0.85
1.13
1.97
0.85
0.00
0.56
0.56
0.70
0.85
0.85
0.56
0.85
0.85
0.56
0.56
0.85
0.85
0.56
0.85
1.69
0.00
14.24
1.83
1.27
1.83
0.99
2.11
0.99
1.27
0.99
0.70
NO3 20
1.97
3.95
4.23
4.65
4.23
5.36
3.10
2.54
3.24
3.10
6.48
3.95
4.23
1.97
2.26
2.82
3.10
3.10
1.97
0.85
1.13
2.26
1.97
3.10
3.38
2.40
2.54
4.23
1.41
3.10
3.81
4.09
3.95
1.41
2.54
2.26
2.26
2.26
3.10
3.52
1.41
3.10
1.69
4.51
4.37
5.36
2.26
2.26
NH4 80
0.00
0.56
0.56
1.13
0.99
3.66
1.69
0.85
0.56
1.27
1.69
0.85
0.56
0.56
1.27
0.56
0.56
0.56
0.56
0.56
1.69
0.42
0.85
0.28
1.69
0.85
0.28
0.56
0.28
0.56
0.00
0.56
0.00
1.41
0.56
0.85
0.28
0.85
0.56
0.56
0.85
0.56
0.85
1.69
0.85
0.85
0.56
1.13
NO3 40
3.10
0.85
0.00
0.00
0.00
1.97
1.97
0.28
0.85
0.00
0.28
1.97
1.97
1.69
1.97
1.41
0.85
0.99
0.00
0.85
1.13
3.10
3.10
3.10
0.00
1.13
1.97
0.85
0.85
0.85
0.85
1.69
3.38
1.97
1.13
0.28
0.00
0.00
0.00
0.00
0.00
1.97
1.41
1.13
3.66
0.00
1.97
4.23
NO3 80
1.41
3.66
3.66
4.09
0.56
1.69
1.69
1.41
0.70
1.69
0.56
0.28
0.00
0.70
0.56
0.56
1.69
2.54
3.66
1.69
1.41
2.82
1.41
5.07
3.95
1.97
2.26
1.69
1.69
1.13
1.69
2.82
3.66
1.69
2.82
2.82
2.82
5.92
4.51
2.26
2.68
3.95
3.95
2.82
2.82
1.69
2.54
5.07
124

Sample t
IV1H134111
IV2H134111
I0C34185
I1C34185
I2C34185
I0Hr34185
11Hr34185
12Hr34185
I0H134185
I1H134185
I2H134185
II0C34185
111C34185
II2C34185
II0H134185
II1H134185
II2H134185
II0Hr34185
III Hr34185
II2Hr34185
III0C34185
III1C34185
III2C34185
1110H134185
III1H134185
III2H134185
III0Hr34185
III1Hr34185
III2Hr34185
1V0C34185
IV1C34185
IV2C34185
IV0Hr34185
IV1Hr34185
IV2Hr34185
1110H134111
III1H134111
III2H134111
III0Hr34111
III1Hr34111
III2Hr34111
1V0C34111
IV1C34111
IV2C34111
IVOHr34111
IV1Hr34111
IV2Hr34111
1V0H134111
NH4 20
2.11
2.40
23.96
122.34
2.82
37.21
101.62
4.23
33.55
40.03
1.27
0.99
1.27
2.40
3.24
2.11
4.37
3.52
3.95
72.59
4.79
40.31
34.67
3.38
29.74
35.80
2.82
29.32
80.62
5.22
5.07
66.81
3.10
32.14
61.74
2.54
35.80
79.49
3.66
26.50
19.73
2.26
3.52
3.24
2.40
1.55
2.40
1.55
NH, 40
1.83
8.60
19.87
2.40
24.67
22.13
1.27
39.32
16.77
2.54
5.50
6.06
1.27
3.81
110.64
3.24
11.13
23.82
2.96
15.22
17.05
2.96
24.38
28.61
4.09
30.30
63.57
0.99
0.99
0.99
0.99
1.27
0.70
3.10
24.38
85.56
7.19
25.79
42.14
2.11
1.27
0.99
0.99
0.99
0.70
0.42
1.27
1.55
NH4 80
18.75
26.64
0.00
25.23
32.00
0.70
61.88
59.90
2.40
30.59
14.80
2.68
6.91
64.13
2.68
18.75
66.67
1.83
8.03
27.48
0.70
1.97
0.85
0.85
0.99
11.98
85.27
6.91
57.65
46.79
1.55
44.68
96.27
2.40
8.03
44.12
1.13
0.56
0.00
1.13
0.70
0.00
0.00
0.56
0.85
0.85
3.95
1.13
NO3 20
17.48
31.85
6.48
39.18
51.02
1.97
27.91
45.95
1.97
15.93
22.83
9.30
24.24
35.80
1.97
20.01
33.83
1.97
3.66
4.37
4.79
22.55
39.47
9.87
30.44
40.59
9.30
25.93
51.02
3.10
2.54
2.54
1.97
4.23
2.26
4.23
4.23
7.05
5.07
2.26
1.97
0.85
1.97
17.48
31.01
2.54
24.24
34.39
NO3 40
0.56
0.56
4.51
0.00
0.56
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
10.43
4.23
12.69
18.04
1.13
10.15
16.07
1.13
5.92
40.45
2.82
14.94
23.68
0.28
9.30
19.45
2.54
16.63
14.09
2.54
31.85
19.45
0.00
3.38
9.58
24.52
5.07
14.66
23.68
12.40
18.89
27.06
0.85
10.01
NO3 80
1.13
1.13
1.97
0.85
0.14
0.28
1.13
1.97
1.13
1.55
1.13
0.85
1.69
1.13
0.99
3.24
6.91
24.10
3.52
19.87
22.41
9.73
21.28
24.67
2.40
23.54
35.10
3.52
8.88
23.82
1.55
9.58
14.24
4.65
50.88
41.86
1.41
31.43
17.90
3.24
10.85
33.97
3.24
21.00
31.43
2.40
5.50
24.67
125

Sample t
1V0H134185
IV1H134185
IV2H134185
NH4 20 $
7.33
32.42
74.00
NH4 40
2.68
21.56
57.22
NH4 80
0.99
10.29
53.28
NO3 20
5.36
22.83
61.45
NO3 40
4.51
21.99
46.09
NO3 80
1.83
13.39
28.19
126 t Sample identification: See Key, Appendix A.
t All Inorganic N expressed as mg NH4+-N or NO3--N kg' soil.

Appendix C: Enzyme activities after harvest (1991, 1992).
13-G 10 t Sample 1
I0C33497
11C33497
I2C33497
I0Hr33497
11Hr33497
I2Hr33497
I0H133497
I1H133497
I2H133497
II0C33497
II1C33497
II2C33497
II0H133497
II1H133497
II2H133497
II0Hr33497
III Hr33497
II2Hr33497
III0C33497
III1C33497
III2C33497
1110H133497
III1H133497
III2H133497
III0Hr33497
III1Hr33497
III2Hr33497
1V0C33497
1V 1C33497
IV2C33497
IV0Hr33497
IV I Hr33497
IV2Hr33497
1V0H133497
1V1H133497
IV2H133497
10C33851
I1C33851
I2C33851
I0Hr33851
11Hr33851
I2Hr33851
I0H133851
I1H133851
12H133851
G 20
90.04
88.55
110.97
101.30
77.04
94.17
88.85
53.57
50.04
69.25
62.96
46.56
59.14
53.44
48.73
48.61
56.99
78.03
116.76
55.23
0.00
35.44
49.46
52.07
41.80
51.79
43.12
23.99
47.65
65.36
101.02
88.30
71.00
143.51
108.66
72.90
58.20
61.60
50.00
73.28
67.09
73.54
69.67
0.00
55.42
53.48
42.88
65.67
44.69
60.81
58.67
76.96
123.15
91.22
65.58
101.82
107.88
98.12
95.13
67.79
99.73
59.30
0.00
76.66
77.71
108.50
45.96
67.07
110.09
74.32
82.80
96.27
82.98
86.56
97.12
72.78
79.00
74.35
68.13
123.45
124.81
93.44
0.00
117.16
69.07
140.33
110.85
50.85
99.16
97.59
PR 10 §
0.61
0.14
0.11
0.17
0.00
0.40
0.40
0.32
0.68
0.92
0.60
0.51
1.01
0.47
0.64
2.50
0.61
0.38
0.29
1.01
0.38
0.57
1.20
0.58
0.46
0.68
0.00
0.32
0.21
0.89
0.44
0.52
0.29
0.42
0.73
0.57
0.92
0.00
0.52
0.12
0.20
0.61
0.16
0.39
0.23
127
PR 20
0.08
0.00
0.17
0.12
0.38
0.50
0.33
0.00
0.00
0.30
0.10
0.45
0.30
0.62
0.19
0.09
0.51
0.25
0.00
0.21
0.00
0.48
0.50
1.01
0.43
0.23
0.46
0.34
0.81
0.22
0.31
0.00
0.18
0.58
1.00
0.40
1.09
0.57
0.46
0.21
0.19
0.32
0.33
0.53
0.66

Sample t
III1H133851
III2H133851
III0Hr33851
III1Hr33851
III2Hr33851
1V0C33851
1V1 C33851
IV2C33851
IV0Hr33851
1V1Hr33851
IV2Hr33851
1V0H133851
1V1H133851
IV2H133851
II0C33851
II1C33851
II2C33851
II0H133851
II1H133851
112H133851
II0Hr33851
II1Hr33851
II2Hr33851
III0C33851
III1C33851
III2C33851
1110H133851 t Sample identification: See Key, Appendix A.
$ I3-Glucosidase units: mg p-nitrophenol kg' soil hr'.
§ Protease units: mmol tyrosine kg' soil hr"'.
13 -G 10 $
58.57
71.71
78.21
87.05
111.01
108.48
69.07
87.21
92.69
68.70
79.47
96.30
77.39
96.48
117.86
69.74
93.63
82.81
69.58
73.85
90.82
90.52
94.40
95.71
78.57
72.80
87.50
13- G 20
66.48
79.50
64.74
82.21
88.99
73.35
52.92
74.49
71.69
78.51
77.97
75.30
70.71
65.31
96.38
123.05
87.37
117.08
107.83
92.28
95.35
111.31
76.43
70.79
63.21
69.91
80.48
PR 10 §
0.23
0.26
0.39
0.22
0.27
0.22
0.64
0.75
0.51
0.44
0.16
0.23
0.40
0.66
0.64
0.44
0.27
0.54
0.50
0.47
0.64
0.67
0.20
0.40
0.35
0.51
0.46
128
PR 20
0.43
0.24
0.84
0.64
0.28
0.32
0.16
0.46
0.33
0.90
0.73
0.40
0.33
0.63
0.60
0.25
0.53
0.45
0.34
0.51
0.35
0.70
0.53
0.81
0.07
0.21
0.30

129
377.47
446.38
251.70
329.68
261.76
492.87
295.08
208.80
317.23
377.98
245.96
267.91
244.40
328.42
381.60
404.66
357.47
210.37
307.27
140.69
0.00
300.00
369.66
296.66
143.11
220.47
228.01
257.79
307.85
247.49
278.20
213.88
346.12
254.66
258.22
166.64
238.71
174.20
332.92
492.40
375.75
425.02
726.54
419.34
413.92
Appendix D: Microbial biomass after harvest (1991, 1992, 1993).
Sample t Ml 3c 10 t M13c 20 Resp 10 § Resp 20
298.01
194.22
416.43
364.40
293.20
250.78
349.44
316.50
418.96
320.44
239.17
247.10
228.73
252.23
264.30
298.57
316.76
267.52
284.16
276.95
305.68
250.48
202.03
210.31
147.53
688.55
333.86
238.15
189.36
240.88
232.40
365.01
456.53
424.89
417.39
528.77
357.08
389.72
348.60
244.36
200.87
412.52
326.36
446.27
389.06
III0C33497
III1C33497
III2C33497
1110H133497
III1H133497
1112H133497
III0Hr33497
III1Hr33497
III2Hr33497
1V0C33497
IV1C33497
IV2C33497
IV0Hr33497
IV1Hr33497
IV2Hr33497
1V0H133497
IV1H133497
IV2H133497
I0C33851
I1C33851
12C33851
I0Hr33851
I1Hr33851
I2Hr33851
I0C33497
I1C33497
12C33497
I0Hr33497
I1Hr33497
I2Hr33497
I0H133497
I1H133497
I2H133497
110C33497
II1C33497
112033497
II0H133497
II1H133497
II2H133497
II0Hr33497
II1Hr33497
II2Hr33497
10H133851
I1H133851
I2H133851
267.97
285.31
287.45
276.67
442.90
328.31
108.02
268.51
225.03
282.27
218.50
231.80
260.65
350.58
283.09
105.97
286.18
220.21
MBN 10 I MBN 20
28.23
21.85
23.18
26.06
35.06
28.31
10.60
28.62
22.02
2.82
2.19
2.32
2.61
3.51
2.83
1.06
2.86
2.20

Sample t
1111H133851
III2H133851
III0Hr33851
III1Hr33851
III2Hr33851
1V0C33851
1V1C33851
IV2C33851
IV0Hr33851
IV1Hr33851
IV2Hr33851
1V0H133851
1V1H133851
II0C33851
II1C33851
II2C33851
110H133851
II1H133851
II2H133851
II0Hr33851
II1Hr33851
II2Hr33851
III0C33851
III1C33851
III2C33851
1110H133851
IV2H133851
10C34215
I1C34215
I2C34215
I0Hr34215
I1Hr34215
I2Hr34215
10H134215
I1H134215
I2H134215
II0C34215
II1C34215
II2C34215
II0H134215
111H134215
II2H134215
II0Hr34215
II1Hr34215
II2Hr34215
1110C34215
III1C34215
1112C34215
MB, 10
206.53
252.55
274.47
196.29
196.51
199.27
211.71
207.25
208.26
215.80
189.93
183.14
204.23
193.27
227.52
177.57
185.91
187.99
241.62
249.31
252.40
271.98
248.53
216.20
193.24
188.06
195.63
192.98
216.35
204.16
195.27
331.22
216.80
234.27
243.99
211.62
166.24
173.02
202.08
304.88
250.53
193.10
247.15
196.64
193.30
119.31
278.53
170.13
130
MB, 20
323.51
205.52
181.51
178.32
196.49
92.33
259.46
215.81
219.18
230.92
213.87
209.98
260.02
241.22
173.83
173.65
216.20
315.94
264.41
233.30
179.54
186.31
201.75
177.97
252.23
213.93
158.64
200.90
305.63
202.19
270.65
205.87
262.60
220.06
251.78
145.89
186.98
133.80
195.88
170.57
159.79
162.07
228.42
192.31
158.36
191.64
166.00
228.40
Resp 10 § Resp 20 MBN 10
134.52
150.61
198.44
132.54
249.77
66.37
160.10
139.57
214.31
256.82
230.25
186.24
153.79
136.40
184.68
219.15
148.59
128.28
161.10
202.91
233.33
98.09
109.28
158.68
146.34
137.53
189.53
249.74
235.67
421.94
132.21
146.34
199.78
255.86
196.74
227.30
169.88
270.09
257.54
131.93
268.80
242.29
202.95
211.26
188.59
289.44
372.63
485.60
116.31
158.85
120.47
144.14
133.89
44.01
136.39
192.73
206.43
110.81
140.97
160.27
200.84
202.36
257.35
260.03
181.67
226.20
136.55
238.29
228.99
242.79
131.26
132.23
204.15
190.80
193.51
97.72
198.47
140.63
358.67
186.44
191.56
215.98
177.49
185.53
142.80
114.77
201.63
168.91
139.34
255.64
463.83
119.57
297.84
172.66
290.33
218.89
13.39
4.40
13.64
19.27
20.64
11.08
14.10
16.03
20.08
13.65
23.83
22.90
24.28
11.63
15.88
12.05
14.41
13.13
13.22
20.41
19.08
19.35
9.77
19.85
14.06
13.93
25.56
46.38
11.96
29.78
17.27
29.03
21.89
35.87
18.64
19.16
21.60
17.75
18.55
14.28
11.48
20.16
16.89
20.24
25.73
26.00
18.17
22.62
MBN 20
1.31
1.32
2.04
1.91
1.94
0.98
1.98
1.41
2.38
2.29
2.43
1.16
1.59
1.20
1.44
1.34
0.44
2.57
2.60
1.82
2.26
1.37
1.77
1.86
1.43
1.15
2.02
1.69
2.02
1.36
1.93
2.06
1.11
1.41
1.60
2.01
1.39
2.56
4.64
1.20
2.98
1.73
2.90
2.19
3.59
1.86
1.92
2.16

Sample 1-
1110H134215
III1H134215
III2H134215
III0Hr34215
III1Hr34215
III2Hr34215
1V0C34215
1V1C34215
IV2C34215
IV0Hr34215
IV1Hr34215
IV2Hr34215
1V0H134215
IV1H134215
1V2H134215
131
MBc 10 $
191.08
199.86
198.02
164.45
197.27
177.09
172.14
181.22
234.32
162.84
226.73
194.29
150.30
142.75
178.28
237.97
234.57
290.77
179.91
210.29
178.25
149.42
231.06
202.20
203.80
189.12
180.05
184.81
170.32
201.47
MBc 20 Resp 10 § Resp 20 MBN 10 91 MBN 20
108.96
67.89
153.37
108.51
68.79
63.45
113.67
123.04
152.49
157.99
121.92
131.23
127.97
91.37
120.02
135.03
115.41
105.71
112.27
144.04
79.54
122.24
192.27
118.90
180.60
131.33
168.63
117.27
86.22
125.52
19.23
11.89
18.06
13.13
16.86
11.73
8.62
12.55
13.50
11.54
10.57
11.23
14.40
7.95
12.22
1.92
1.19
1.81
1.31
1.69
1.17
0.86
1.26
1.35
1.15
1.06
1.12
1.44
0.80
1.22
t Sample identification: See Key, Appendix A.
f Biomass C units: mg CO3-C kg"' soil.
§ Respiration units: mg CO3-C kg' soil 10 d"'.
1 Biomass N units: mg Inorganic N kg' soil.

1110H133497
III1H133497
1112H133497
III0Hr33497
III1Hr33497
III2Hr33497
1V0C33497
IV1C33497
IV2C33497
IV0Hr33497
IV1 Hr33497
IV2Hr33497
1V0H133497
1V1H133497
IV2H133497
10C33851
I1C33851
I2C33851
I0Hr33851
I1Hr33851
I2Hr33851
I0H133851
I1H133851
I2H133851
I0C33497
Il C33497
I2C33497
I0Hr33497
I1Hr33497
I2Hr33497
I0H133497
I1H133497
I2H133497
II0C33497
111C33497
II2C33497
110H133497
II1H133497
II2H133497
II0Hr33497
II1Hr33497
II2Hr33497
III0C33497
III1C33497
1112C33497
Appendix E: Ammonium after harvest (1991, 1992, 1993).
Sample t NH4 10 t NH4 20 NH4 40
6.50
0.00
3.90
0.00
0.56
0.00
1.67
42.85
0.00
3.90
8.90
2.97
5.01
7.23
0.00
4.08
9.28
0.00
2.97
13.54
0.00
3.90
13.36
2.60
0.00
6.86
0.00
0.56
2.97
11.13
5.75
1.67
5.94
9.09
6.31
7.14
6.68
4.54
14.47
18.18
0.00
7.05
2.60
5.01
0.00
1.48
3.24
3.24
3.52
3.24
3.52
23.68
4.37
3.52
8.60
3.71
1.48
3.34
4.82
3.71
3.71
3.71
0.00
3.34
0.00
0.00
4.64
4.82
3.71
2.60
3.52
0.74
2.23
11.13
0.00
2.97
1.30
6.68
5.94
1.86
0.00
4.08
5.19
11.50
3.71
5.19
6.68
2.23
5.19
3.71
1.97
3.66
1.97
1.41
3.38
1.13
1.41
3.95
0.00
4.08
2.23
4.45
7.98
3.34
3.34
3.34
0.00
2.23
5.94
0.00
4.27
3.15
3.15
2.97
2.97
5.94
3.15
2.60
4.45
0.74
1.48
4.45
2.23
3.15
5.38
2.78
1.11
0.00
1.86
0.37
4.08
3.71
5.01
3.34
1.69
132
NH4 80
1.48
5.19
0.00
0.56
2.97
3.34
1.48
1.67
1.30
2.97
3.90
3.15
3.52
0.00
8.35
1.13
1.13
2.40
1.41
1.69
2.54
2.04
1.67
1.86
5.19
1.86
0.00
1.86
2.23
2.97
1.69
1.69
3.66
1.11
1.48
1.48
0.56
0.00
0.00
2.23
1.11
1.48
5.38
3.34
7.42
NH4 120
1.86
1.11
0.00
0.00
0.00
0.00
0.00
0.00
1.69
0.85
0.00
0.00
0.00
0.00
0.00
0.00
0.00
1.69
1.13
0.56
1.69
1.69
1.97
0.74
1.67
0.56
0.00
0.00
0.00
0.00
0.00
0.00
0.93
1.86
0.56
0.00
0.00
0.00
0.00
0.00
0.00
2.23
2.41
0.56
1.69

Sample t
II0C33851
II1C33851
II2C33851
II0H133851
II1H133851
II2H133851
II0Hr33851
II1Hr33851
II2Hr33851
1110C33851
III1C33851
1112C33851
1110H133851
III1H133851
III2H133851
1110Hr33851
III1Hr33851
III2Hr33851
1V0C33851
IV1C33851
IV2C33851
IV0Hr33851
IV1Hr33851
IV2Hr33851
1V0H133851
IV1H133851
IV2H133851
10C34215
I1C34215
I2C34215
I0Hr34215
11Hr34215
I2Hr34215
I0H134215
I1H134215
12H134215
II0C34215
II1C34215
II2C34215
II0H134215
II1H134215
II2H134215
II0Hr34215
II1Hr34215
II2Hr34215
III0C34215
1111C34215
III2C34215
NH, 20
14.94
1.97
29.88
134.46
3.10
6.77
43.13
4.93
2.82
30.73
3.38
8.74
67.37
2.11
26.78
296.84
3.38
3.10
5.07
3.38
19.73
2.11
2.26
2.40
7.47
4.37
2.68
3.38
4.37
4.37
4.37
3.95
3.52
2.40
4.37
3.52
3.38
2.40
4.09
2.40
4.65
4.65
4.09
4.09
5.50
3.24
2.96
4.51
NH, 10
2.50
0.56
2.78
2.23
0.99
64.84
133.02
2.68
2.26
45.67
1.41
14.66
61.45
1.13
31.43
134.18
1.13
2.78
4.45
11.69
3.62
2.78
2.23
1.11
0.56
8.17
25.65
2.82
1.97
14.09
1.97
8.46
125.73
0.56
0.00
1.11
3.90
1.11
1.11
1.11
0.56
2.78
0.00
1.11
0.00
0.56
34.78
6.68
133
NH, 120
1.69
0.56
2.82
1.69
1.69
2.54
2.54
2.26
1.69
1.69
2.82
1.41
1.69
2.82
1.69
2.54
1.69
2.54
1.55
1.97
1.41
1.41
1.97
2.54
1.41
1.69
2.82
1.69
1.97
1.97
0.56
0.56
1.69
0.85
0.56
1.97
0.56
2.82
0.00
0.85
1.97
0.56
0.00
3.10
1.41
0.85
1.69
2.11
NH, 80
1.13
1.97
2.54
1.69
3.66
2.11
2.40
2.11
1.55
2.54
2.54
2.26
2.11
2.26
1.97
3.66
3.66
2.54
2.68
1.97
2.11
2.11
3.24
1.27
10.01
3.24
2.11
0.99
2.11
2.40
7.47
3.38
1.55
2.54
1.41
3.38
2.82
2.54
2.54
2.54
4.37
1.69
2.54
1.97
1.69
2.40
2.11
3.24
NH, 40
1.41
1.41
0.70
1.69
1.69
2.82
0.85
2.40
0.85
1.41
1.69
2.82
2.82
1.69
2.82
8.17
2.54
18.18
2.26
1.97
3.38
3.10
2.26
2.26
1.97
1.41
0.85
2.11
2.68
2.54
3.10
2.26
1.97
2.11
22.27
3.38
2.54
0.85
1.55
1.69
2.82
1.41
1.97
1.69
1.69
0.85
2.82
1.69

Sample 1"
1110H134215
III1H134215
III2H134215
III0Hr34215
III1Hr34215
III2Hr34215
1V0C34215
IV1C34215
IV2C34215
IV0Hr34215
IV 1 Hr34215
IV2Hr34215
1V0H134215
1V1H134215
IV2H134215
NH4 10
5.07
4.79
88.23
4.51
16.07
38.62
4.23
12.97
24.81
1.83
12.97
81.75
2.26
1.13
88.94
NH, 20
4.65
5.36
33.26
4.79
4.23
19.31
4.79
4.23
24.81
3.66
11.98
5.64
5.36
17.48
13.25
NH, 40
1.13
0.42
3.38
16.35
2.26
1.41
2.11
2.26
7.33
3.38
1.41
0.99
2.26
0.85
3.10
NH, 80
2.11
2.26
3.24
4.37
2.40
1.27
2.11
2.54
3.24
4.65
3.24
1.97
0.99
1.27
1.27
134
NH4 120
1.69
1.13
4.23
0.56
0.70
0.85
0.28
0.85
1.41
1.83
1.97
0.56
1.69
1.13
1.69
t Sample identification: See Key, Appendix A.
mg NH4` -N kg` soil.

10C33497
I1C33497
I2C33497
I0Hr33497
11Hr33497
12Hr33497
I0H133497
I1H133497
I2H133497
II0C33497
II1C33497
II2C33497
II0H133497
II1H133497
II2H133497
II0Hr33497
III Hr33497
II2Hr33497
III0C33497
III1C33497
III2C33497
1110H133497
III1H133497
1112H133497
III0Hr33497
III1Hr33497
III2Hr33497
1V0C33497
IV1C33497
IV2C33497
IV0Hr33497
IV I Hr33497
IV2Hr33497
1V0H133497
IV1H133497
IV2H133497
I0C33851
I1C33851
I2C33851
I0Hr33851
11Hr33851
I2Hr33851
10H133851
I1H133851
I2H133851
Appendix F: Nitrate after harvest (1991, 1992, 1993).
Sample t NO3 10 1 NO3 20 NO3 40
5.52
12.23
7.11
45.99
7.50
6.61
23.32
3.14
13.95
40.64
19.72
27.24
37.17
7.95
5.50
57.23
6.98
16.45
50.06
22.92
25.26
31.95
2.78
4.45
6.12
0.00
11.96
52.86
1.67
4.45
58.43
3.59
28.49
37.38
5.64
19.24
17.22
6.22
24.61
3.70
15.89
36.51
42.35
30.89
15.33
4.39
7.08
10.63
2.74
9.41
6.84
4.16
7.65
15.64
3.39
3.02
4.91
8.32
5.50
13.95
3.24
13.95
46.65
2.11
3.81
24.10
5.91
2.45
4.34
3.89
3.64
4.10
18.84
21.48
10.40
5.81
2.73
18.08
29.16
3.68
6.68
5.51
3.89
13.64
19.02
3.14
3.46
6.22
2.74
5.42
13.59
4.20
10.65
18.14
7.67
11.14
25.94
3.64
11.13
15.51
4.53
3.46
7.43
15.21
4.34
9.04
38.09
3.62
11.33
15.86
9.93
9.36
2.49
3.27
12.39
3.58
7.63
5.39
2.74
8.19
3.04
5.28
7.42
25.46
7.79
10.66
9.16
9.87
7.05
3.66
7.05
8.03
1.41
3.66
5.64
135
NO3 80
3.25
4.80
10.99
1.65
4.64
4.68
0.70
2.47
2.42
6.19
4.03
3.66
2.11
2.44
2.15
1.33
1.34
12.38
2.44
4.37
5.24
2.79
6.17
7.76
11.27
1.12
2.40
4.92
1.91
2.89
1.43
2.84
2.53
1.16
1.81
5.32
3.51
1.69
1.13
0.85
1.69
2.82
0.85
0.28
3.10
NO3 120
0.96
1.37
2.18
4.03
3.85
3.53
1.55
8.81
3.93
5.65
9.97
0.00
5.83
6.34
2.26
2.26
0.56
0.00
2.68
0.00
0.00
4.51
8.42
0.90
2.04
5.24
1.87
2.11
7.25
4.28
3.85
7.30
2.05
2.72
2.56
4.07
3.04
0.90
1.42
6.32
3.34
1.58
0.82
3.10
5.29

Sample t
III0Hr33851
III1Hr33851
III2Hr33851
1V0C33851
IV1C33851
IV2C33851
IV0Hr33851
IV1Hr33851
IV2Hr33851
1V0H133851
IV1H133851
IV2H133851
I0C34215
I1C34215
I2C34215
I0Hr34215
11Hr34215
I2Hr34215
I0H134215
I1H134215
I2H134215
II0C34215
II1C34215
II2C34215
II0H134215
II1H134215
II2H134215
II0Hr34215
II1Hr34215
II2Hr34215
III0C34215
III1C34215
III2C34215
II0C33851
II1C33851
112C33851
II0H133851
II1H133851
II2H133851
II0Hr33851
II1Hr33851
II2Hr33851
III0C33851
III1C33851
III2C33851
1110H133851
III1H133851
1112H133851
NO3 10
7.33
36.93
11.28
7.33
17.76
0.00
9.58
53.28
1.67
8.62
0.00
7.23
1.67
0.14
29.60
26.78
2.26
0.85
40.45
0.00
28.75
36.93
1.13
23.26
36.93
1.41
1.11
32.83
22.26
0.56
8.35
18.92
7.51
4.45
6.68
0.00
4.73
8.35
22.26
2.23
3.34
18.36
1.67
4.45
5.84
0.00
2.23
1.67
NO, 40
1.41
2.54
16.35
0.56
0.85
1.41
3.66
4.79
4.79
1.55
4.51
5.92
7.89
1.69
2.54
4.79
0.00
2.54
2.54
3.66
8.17
2.40
1.41
2.54
3.66
3.10
1.41
4.09
2.54
2.26
2.54
3.38
1.41
24.81
1.41
3.66
1.55
3.10
12.12
19.17
2.54
2.54
3.52
3.66
3.66
1.97
2.54
3.95
NO3 20
0.14
2.40
6.62
2.40
10.57
11.84
4.23
24.24
104.02
3.95
2.54
18.04
3.10
43.69
22.83
1.69
25.65
37.77
3.66
11.28
43.98
27.91
3.66
34.39
2.54
17.20
51.59
4.37
5.78
6.20
3.24
40.17
22.41
2.40
6.62
10.85
8.60
6.34
12.83
8.60
6.62
17.34
2.40
10.57
10.85
4.51
2.96
13.95
136
NO3 120
1.13
2.26
0.00
5.36
0.85
0.28
3.10
10.43
0.00
0.00
2.26
1.13
0.00
2.11
5.36
1.13
2.26
3.66
0.14
1.13
1.97
0.00
0.00
0.00
2.54
0.85
0.56
0.85
2.26
0.56
2.26
0.56
1.69
2.26
0.56
1.55
0.28
0.00
0.00
4.23
1.41
1.97
2.26
2.26
3.81
0.28
1.41
0.00
NO3 80
1.41
0.85
0.85
6.20
7.61
9.87
2.54
2.54
2.26
3.38
2.26
2.26
1.13
1.83
2.26
4.23
1.69
1.69
1.41
8.46
2.82
2.26
2.26
4.09
1.97
1.69
2.82
1.69
1.97
2.82
5.92
1.83
1.69
1.97
8.17
1.69
1.69
1.41
1.97
2.82
0.85
1.97
1.69
0.85
2.82
0.85
0.00
1.69

Sample t
1110H134215
III1H134215
1112H134215
1110Hr34215
III1Hr34215
III2Hr34215
1V0C34215
IV1C34215
1V2C34215
IV0Hr34215
IV1 Hr34215
IV2Hr34215
1V0H134215
1V1H134215
IV2H134215
NO3 10 t
4.23
10.15
92.74
2.26
12.83
67.09
2.26
24.24
17.48
0.00
13.53
45.95
0.00
11.84
57.51
NO3 20
19.45
0.99
14.09
25.93
1.69
5.92
29.88
4.79
10.15
61.74
6.20
12.97
11.28
2.82
25.09
NO3 40
5.92
6.77
10.43
1.41
4.65
14.38
3.38
5.36
4.79
1.69
10.99
24.81
7.05
15.79
7.05
NO3 80
1.41
2.26
2.54
1.83
4.51
2.54
2.26
5.64
2.54
2.96
3.38
9.87
3.38
4.51
4.51
137
NO3 120
0.00
0.00
5.07
0.00
1.41
0.14
0.28
0.56
5.07
0.85
0.42
1.69
1.69
0.00
1.41
t Sample indentification: See Key, Appendix A.
t mg NO3 -N kg"' soil.

Appendix G: Analysis of variance for nitrate-N in year one.
Source
Crop
Rep X Crop
N rate
Crop X N rate
Error b
Time
Time X Crop
Time X Rep X Crop
Time X N-rate
Time X Crop X N-rate
Error (time) df
2
4
2
6
18
8
10
48
16
32
144
0 to 20
341***
22
2316***
35
22
1210***
599
38
343***
80***
25
*, **, and *** P level = 0.05, 0.01, and 0.001, respectively.
14
28
126
7
14
42
Soil depth (cm) df 20 to 40 mean square
14
14
383***
9
14
1063***
16
18
93**
21**
10
40 to 80
50***
2
260***
2
8
199***
14***
6
52***
4
4
138

Appendix H: Analysis of variance for nitrate-N in year two.
Source df 0 to 20
Crop
Rep X Crop
N rate
Crop X N rate
Error
Time
Time X Crop
Time X Rep * Crop
Time X N rate
Time X Crop X N rate
Error (time)
2
6
2
4
18
5
10
30
10
20
90
*, **, and *** P level = 0.05, 0.01, and 0.001, respectively.
140
61
4331**
38
49
2880***
118
57
1037***
58***
61
Soil depth (cm)
20 to 40
Mean square
31
14
614***
14
12
939***
46*
20
174***
16
17
40 to 80
37
23
508***
5
14
1119***
35**
25
254***
13
11
139

Appendix I: Analysis of variance for nitrate-N with time as a factor for September 1991, 1992, and 1993.
140
Source
Crop
Rep X Crop
N rate
Crop X N rate
Error b
Time
Time X Crop
Time X Rep X Crop
Time X N rate
Time X Crop * N rate
Error (time) df
18
2
4
12
4
2
0
2
4
8
36
Soil depth (cm)
0 to 10
Mean square
10 to 20
261
202
7136***
119
94
1547***
34
65
547*
245
185
134
104
2711***
79
98
1505***
207
153
632**
217
122
*, **, and *** P level = 0.05, 0.01, and 0.001, respectively.

Appendix J: Analysis of variance for MBc, CO, respiration and N flush at 0 to 20 cm depth.
MBc
Source
Crop
Rep X Crop
N rate
Crop X N rate
Error b
Time
Time X Crop
Tim X Rep X Crop
Time X N rate
Time X Crop X N rate
Error (time) df
18
5
2
6
2
4
10
30
10
20
90
Yr 1
13910
4601
257
12492
5804
32188***
8006*
526
3691
5709
4169
*, **, and *** P level = 0.05, 0.01, and 0.001, respectively.
Yr 2
15506*
3459
3532
1777
2208
19276***
3530***
2456
835
1002
999
Respiration
Yr 1 Yr 2
116
Mean square
206
126
131
125
106
1163***
133
101
51
66
40
85
1516***
200***
66
51 30
123
82
27
36
Yr 1
N flush
Yr 2
9
131
126
69
100
199**
70
77
57
67
59
97
110
81
79
131
269*
34
64
34
119
93

Appendix K: Analysis of variance for M13c, CO2 respiration and MBN with time as a factor for September at 0 to 20 cm depth.
1991, 1992, and 1993.
Source
Crop
Rep X Crop
N rate
Crop X N rate
Error b
Time
Time X Crop
Time X Rep X Crop
Time X N rate
Time X Crop X N rate
Error (time) df
4
18
2
4
12
4
2
6
2
8
36
0 to 101-
MB,
10 to 20t
1552
8801
8456
9167
3938
145453***
6128
2661
2340
4404
3599 tSoil depth in cm
*, **, and *** P level = 0.05, 0.01, and 0.001, respectively.
9167
11401
8104
6738
3427
148478***
13763*
3184
3448
3788
3730 df
1
2
6
2
4
18
Respiration
0 to 10 10 to 20
Mean square
2653** 115
1089 505
957 2354**
222
312
425
565
38420***
2997***
21371***
1017
581
780
600
800
591
282
817
321 df
6
2
1
2
4
18
0 to 10
MBN
10 to 20
188
192
121
25
142
1039***
47
154
5
145
104
292
49
646
528
779
451
527
369
614
214
735

Appendix L: Analysis of variance for enzyme activity in year one at 0 to 20 cm depth.
Source DF
Crop
Rep X Crop (error a)
N rate
Crop X N rate
Error b
Time
Time X Crop
Time X Rep X Crop (error c)
Time X NTR
Time X Crop X NTR
Error (time)
18
36
162
9
18
54
3
6
2
4
18
*, **, and *** P level = 0.05, 0.01, and 0.001, respectively.
0.091
0.055
0.039
0.024
0.043
0.139
0.314***
0.100
0.100
0.048
0.271***
Protease 13-glucosidase
Mean square
70
1517
7430***
383
232
2765***
358***
170
73
61
102
143

Appendix M: Analysis of variance for enzyme activities with time as a factor for September
1991 and 1992.
144
Source
Crop
Rep X Crop
N rate
Crop X N rate
Error b
Time
Time X Crop
Time X Rep X Crop
Time X N rate
Time X Crop X N rate
Error (Time)
DF
2
4
18
2
6
1
2
6
2
4
18
0.233*
0.109
0.086
0.108
0.151*
0.049
0.031
0.220
0.250
0.145
0.113
0 to 20t
Protease
10 to 20t
0.048
0.074
0.015
0.018
0.044
0.236*
0.306
0.039
0.0004
0.039
0.061
tSoil depth in cm
*, **, and *** P level = 0.05, 0.01, and 0.001, respectively.
P-glucosidase
0 to 10 10 to 20
797
193
3243***
449
500
323
421
525
283
346
345
12533*
235
190
486
207
222
193
460
1495**
385
234***