Denitrification and mineralization in agricultural soi1

in Eastern Canada, as affected by

nitrogen fertilizer, tillage, and crop rotation

Melissa Abbott, Department of Nahiral Resource Sciences McGill University, Montreal

December 1996

A thesis submitted to the Faculty of Graduate Studies and Resûirch in partiai fulfilment of the requirements of the degree of Master of Science.

O Melissa Abbott, 1996

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Table of Contents

List of Tables

List of Figures

Acknowledgements

Foreword

Chapter 1 Abstract

Résumé

Chapter 2 Introduction

Cbapter 3 Literature Fteview

Corn Cropping Nitrogen and Crop Growth Denitdication Studies Mineraikation Studies Synthesis Hypotbeses and Objectives

Chapter 4 EvaIuation of closed-chamber and soil core incubation methods of mensuring denitrification.

Abstract Introduction Materiais and Methods

Experimental Design Soil Core Method Closed Chamber Method

Analyses of Results Results Discussion

Chapter 5 N mineralkation and C respiration in soils under corn in Eastern Canada.

Abstract Introduction Materiais and Methods

Expenmentai Design Sarnpling Protocol Analyses of Result s

ResuIts Discussion

Chapter 6

TabIe No.

8.0

8. la

8.lb

8.2a

8.2 b

8.3a

8.3b

8.4

Geaeral Conclusions

Literature cited

Appendices

Analysis of variance of denitrification values measured over the growing season.

Analysis of variance of temperature values over the growing season for the Ormstown soil.

Analysis of variance of temperature values over the growing season for the Ste. Rosalie (2) soil.

Analysis ofvariance of water-6lled pore space values over the growing season for the Ormstown soil.

An- of variance of mer-filled pore space values over the growing season for the Ste. Rosalie (2) soil.

Correlation of cumdative measurements on the Ste-Rosalie (1) soil.

Correlation of cumulative measurernents on the Chicot soil.

Mean values, T groupings and least significant difference of cumulative mineralized N and C on the Brandon mil.

8.5 Values for mineralization study regressions.

8.6a Repeated measures analysis of variance for N mineralized in Chicot, Ste. Rosalie, Fox and Brandon soils. Univariate test of hypotheses for within subject effects. 75

8.6b Repeated measures analysis of variance of contrat variables for N minerdized in Chicot, Ste. Rosalie, Fox and Brandon soils. 75

8.7 Pearson correlation coefficients for soils from long-tem corn fertilizer expenment S.

N fixation

List of tables

Selected properties of Ste. Rosalie, Chicot,and Omstown soils.

Fertilization treatments, procedures and tillage.

Pearson correlation coefficients between cumulative N,O values as measured by closed chamber and soi1 core incubation methods, and soi1 NO, NH,,, temperature, and wata filled pore space (WFPS). Log transformations.

Sample site characteristics.

Experimental fertilization and mage.

Total N, C, and Cm ratio for May 1995 samples in soils fiom long-tem corn feriilizer experiments.

Regression equations and coefficients of determination for linear regression of cumulative N with tirne of Brandon soil from long-term corn fertilizer expenments.

Soa poterrtjaüy mineralizable N and respired C in sob fiom long term corn fedizer experiments

Cumulative C respired and N mineraiized fkom long term corn fextilizer experiments on Brandon soi1 as percentage of total N and organic C content of soii.

Contribution of fertiliza to mineralized N in soiîs fiom long-tem corn fertilizer experiment S.

List of Figures

4.la Denitrification rates measured by the closed charnber method on the Chicot soi1 across al1 N rates as afTected by replicate. Bars indicate standard error.

4.lb Denitrification rates measured by the soi1 cure incubation method on the Chicut soii aaoss dl N rates as affected by replicate. Bars indicate standard error.

Denitrification rates measured by the closed charnber incubation rnethod on the Ste. Rosdie (1) soil across all N rates as afFected by replicate. Bars indicate standard error.

Denitrification rates measured by the soi1 core incubation method on the St. Rosalie (1) soil across ail N rates as affected by replicate. Bars indicate standard error.

Denitrification rates measured by the closed chamber method on the Ste. Rosalie (1) soi1 across aii replicates as affectecl by N rate. Bars indicate standard error.

Denitrification rates measured by the soil core incubation method on Ste. Rosalie (1) soil across di replicates as affêcted by N rate. Bars indicate standard error.

Denitnfication rates measured across al1 replicates at 400 kg N ha" on the Chicot soil using closed charnber and soil core incubation methods. Bars indicate standard error.

Denitrification rates measured under no-tiIi and conventional tillage on the Ormstown soil by the closed chamber method. Bars indicate standard error.

Denitnfication rates measured by the closed chamber method on the Ormstown soi1 across ai i N rates and tillage as affecteci by rotation. Bars indicat e standard error.

Denitrification rates measured by the soi1 core incubation method on the Ormstown soil across all N rates and tillage as afFected by rotation Bars indicate standard error.

Denitrification rates measireci by the closed charnber method on the Ste. Rosalie (2) soil across aU tillage and rotation as affected by N rate. Bars indicate standard error.

Denhification rates measured by the soil core incubation method on the Ste. Rosalie (2) soil across dl tillage and rotation as affected by N rate. Bars indicate standard error.

Denitrification rates measured by the closed chamber rnethod on the Ste. Rosalie (2) soil across ail N rates and tillage as affected by rotation. Bars indicate standard error.

Denitrification rates mearured by the soil core incubation method on the Ste. Rosalie (2) soil across al1 N rates and tillage as affected by rotation. Bars indicate standard error.

Relationship of soi1 total N to organic C in experirnentai soils.

Relationship of water-soluble organic C to potentiaily mineralizable N in soils fiom long tem corn fertilizer experiments.

Relationship of water-soluble organic matter to cumulative N mineralized in soils fiom long term corn fertilizer experiments.

Relationship of microbial biomass C to potentiaily rnineralizable N in soils from long tenn corn fedizer expenments.

Cornparison of cumulative N rnineralization fkom long term corn femiker experiments on Brandon soil. Bars indicate standard error.

Cornpanson of cumulative mineralizable N frorn long term corn fertilizer experiments on Chicot, Ste. Rosalie and Fox soifs. Bars indicate standard error.

Cumulative C respired fkom long term corn fertilizer experiments on Brandon soil. Bars indicate standard error.

Cumulative C respireci £tom long term corn fertilizer experirnents Chicot, Ste. Rosalie, and Fox soil. Bars indicate standard error.

Rdationship of initial N to potentially mineralizable N in soils fiom long term corn fertilizer experiments.

Reldonship of water-soluble organic C to microbial biomass C in mils fiom long terni corn fertilizer experiments.

Relationship of soil C to summed C respired in soils from long tem corn

fertilizer experiments.

Acknowledgements

Many people should be thanked for helping in various ways to cornplete this thesis.

Professor MacKenzie, my advisor, is thanked for his positive encouragement and gentle

direction. Dr. M.X. Fan is thanked for his enthusiastic management of the denitrification

project, and assistance with statisticd analysis. François Cadrin shared the field work and

data analysis for the denitrification expenment with me. For the mineralization study, Dr. Bao

Chang Liang was my principal instructor and helper with statistical analysis. Dr. Edward

Gregorich supplied lab space and insight, as well as being on rny thesis cornmittee. Prof

Brian Driscoii must be thanked for agreeing to be on my thesis cornmittee. Last but not lest

I would like to thank my husband David for his patience and conviction that 1 was doing a

good thing.

Foreword

This thesis consias of a number of chapters in paper format. Consequently the

following extract from Faculty of Graduate Studies and Research regulations must be

"Candidates have the option of including, as part of the thesis the text of one or more papers submitted or to be mbmitted for publication, or the clearly-duplicated text of one or more published papers. These texts must be bound as an integral part of the thesis.

If this is the option chosen, connecting texts t hat provide logical bridges between the different papers are mandatory. The thesis must be written in such a way that it is more than a mere collection of rnanuscripts; in other words, results of a senes of papers must be integrated-

The thesis must still c o d o n to dl other requirements of the "Guidelines for ïhesis Preparation". The thesis must include: A table of contents, an abstract in English and French, an introduction which clearly States the rationale and objectives of the study, a comprehensive review of the literature, a final conclusion and sumrnary, and a thorough bibliography or reference list.

Additional matenal must be provided where appropriate (eg. in appendices) and in sufficient detail to allow a clear and precise judgement to be made of the importance and originality of the research reported in the thesis.

In the case of manuscripts CO-authoreù by the candidate and others, the candidate is required to mlke an explicit statement in the thesis as to who contributed to ruch work and to what extent Supervison must attest to the accuracy of such statements at the doctoral oral defense. Since the task of the examiners is made more difficult in these cases, it is in the candidate's interest to make perfectly clear the responsibilities of ail the authors of the CO-authored papers."

The authors of Paper 1 will be Melissa Abbotî, A F. MacKenzie, M. X Fan and F.

Cadrin, and paper 2 Meiissa Abbott, A F. MacKenzie, B. C. Liang, E. Gregorich a d C .

M o d . Co-authors have been involved at a supervisory level (Mackenzie, Fan and Liang),

active in field work (Cadrin) or involved at the conceptual level (Gregorich, Monred). The

author bas been responsible for aii data collection, analyses, and presentation.

Chapter 1

A bst ract

The fate of fertilizer N is of primary concern for both agricultural productivity and

environmental quality. Concems include denitrification, leaching losses, mineralization of

organic N as plant available N. Denitrification is an important source of N,O, a greenhouse

gas but field measurements are dificult. Two methods of measuring denitrification are soi1

core (SC) incubation and closed chamber (CC) methods. These methods were assessed on

soi1 under monoculture corn, monoculture soybean, and aifalfa in a corn soybean alfdfa

rotation. Greater concentrations were found in the CC method than the SC method.

Denitrification rates ranged tiom less than 15 g N ha-lh-' to neariy 2000 g N ha%*'. The CC

method was more sensitive to treatment effects. The denitrification rates were dependent on

the soii type, being higher on soils with high clay content. The variables that had the highest

degree of relationship with denMkation were water fiiled pore space, soi1 NH,-N and NO3-

N concentrations. Higher rates of N increased denitrification. As to assessrnent of available

soil N, this was accomplished N and C mheraiization measurements. Potentially

mineralizableN (NJ ranged f?om 144 mg N kg-' to 30.3 mg N kg-'. Higher rates of organic

amendment r d e d in higher measured values on Brandon soil while hïgher rates of inorganic

N on Chicot and Ste. Rosalie soils caused no change in mineraiizable N or respired C . Total

hi, organic C, water soluble organic C (WSOC) and rnicrobial biomass C W C ) increased

with increasing amounts of organic or inorganic N amendment on Brandon soil. Higher rates

of inorganic N r d e d in lowa WSOC and MBC on Chicot and Ste. Rosalie soils. N'iogen

mineralizeà, C resplreâ, total N, organic C, WSOC and MBC were ail related to soi1 texture.

MBC and WSOC were found to have a strong positive relationship with potentially

mineralizable N.

Résumé

Le destin de l'azote d'engrais est de l'intérêt primaire pour la productivité agricole et

égaiement pour la qualité écologique. Dénitrification, les pertes par filtrage, et la

minéralisation d'azote organique comme d'azote disponible aux plantes sont des sujets

inquietants. La dénitrification produit l'émission de N,O, un gaz de serre. L'estimation des

taux de dénitrification sur champs est nécessaire pour évaluer les pertes d'azote. Deux

méthodes ont été utilisées, la chambre fermée sur place (CC) et l'incubation des échantillons

(SC). Les deux méthodes étaient évaluées sur les monocultures de maïs, de soya, et la

I m e en rotation avec le soya et le maïs. Les taux de dénitrification observés étaient plus

élevés avec la méthode CC. Les taux de dénitrification varient de 15 g N ha-'h-' jusqu'a 2000

g N ha%'. La méthode CC était plus sensible que la méthode SC aux effets des traitements.

Les taux de dénitrification varient selon la texture, l'humidité du sol, et le contenu en NH, et

NO,. Les taux de dénitrification étaient en rapport avec l'azote ajouté. L'évaluation d'azote

disponible dans les sols était accomplie par une étude de minéralisation aérobie. L'azote

minéralisaide varie entre 144 mg N kg-' et 30.3 mg N kg1. L'azote rninéralisable et le C libéré

étaient plus élevés avec une plus grande quantité de tiimier ajoutée sur le sol Brandon. Les

niveaux de WSOC et MBC étaient plus bas avec les taux plus hauts d'azote inorganique

ajouté.L1azote minéralisé, le C libéré, l'azote du sol, le C organique, le WSOC et MBC varient

selon la texture du sol. MBC et WSOC étaient en rapport avec l'azote minéralisable.

Chapter 2

Introduction

Creating the b a t management systems for agriculture is a complex undertaking. The

variables and consequences to deal with are numerous. Changing agricultural management

by tillage7 rnanure application, inorganic fertilizer application and crop rotation is studied with

the sometimes cunflicting goals of increased crop production and rninimized financiai and

environmentd cost.

The pressure on agricultural land increases due to land scarcity, high yield varieties

and intensive, monoculture cropping. It becornes important to consider the resulting effects

on a soil. Intensive methods will draw nutnents fiom the soi1 and cm cause breakdown in

soil structure and a loss of fertility. Also, as fertilizers becorne more expensive, minimizing

fertilizer loss is of economic importance.

Cultivation of soi1 has been found to decrease soa organic matter (SOM) (Jenkinson

and Rayner, 1977; Campbell and S t e w a 1982; Tiessen and Stewart, 1983; Balesdent et al.,

1988). Soil organic matter is, in a sense, the basis of soi1 fertility. Its breakdown by microbial

organisns provides rnany essential nutnents to growing crops. When soi1 organic matter is

decomposed, or rnineralized, the C is released as CO2 hto the atmosphere and the N is

relead as NH, and N Q to be taken up by plants or to enter the atmosphere or water table.

This N is often transformeci by microbial populations through denitrification to N,O gas.

The release of CO, and N,O gas is of environmental significance. They both are

classified as greenhouse gases. Nitrous oxide also breaks d o m ozone, affecting the ozone

layer @CC, 1990). Sequestering soil organic matter would bind up C and N compounds.

Agricultural activities can increase N,O ernissions nom soils (Aulakh et al., 1984)

through increasing N inputs to soil and changing soi1 conditions. Agrîcultural management

systems are analyzed with the aim of deteminhg a best management system fiom a few

points of view. By studying the management effects on N,O emission, one can determjne for

a given site the activities that lead to the lowest rates of denitrification. By studying

management effects on mineralization of C and N, one can detemine which activities may

lead to a buildup of organic matter. We can also determine the effects of management on the

recaicitrance, or convenely the avaiiability, of soi1 organic matter.

The fkst aspect studied in this thesis investigated sensitivity of two different methods

of rneasuring denitrification to variables known to afKect denitrification. I t also related

denitrification to a number of management variables, narnely crop rotation, Mage and

fertilizer input. The second aspect looked at the dynamics of soil C and N cropped to

monoculture con. The effects of tillage, inorganic and organic fertilizer have been related

to the arnount, rate of availability, and lability of soil rnineralizable C and N.

Chapter 3

Literature Review

Corn C r o ~ ~ i n g

Corn for grain or todder is an important crop in Canada. In 1993,6 627 400 metric

tonnes of grain corn and 5 248 800 metric tonnes of fodder corn were grown (Statistics

Canada, 1993). Ontario and Quebec produced the majority of this crop.

The cultivation of corn also occupies a large land area, so the ecects of crop

production management on erosion, runoff, organic matter content and fertility will be

significant in d e .

Mering amounts of plant residue are left on the field, depending upon the residue

management and tillage systems. No-till has been introduced in Eastern Canada, but it is not

as widespread a s in the West (Bernard, 1993). The lower temperatures and increased moisture

under the organic matter decrease or delay the rate of germination.

Nitroeen and Crop Growth

N is an element essential for aü living things. N is almost always the rate-limiting

factor in prirnary (plant) production. N wili inaease foliar and root growth, and improve grain

quality by increasing protein levels (Brady, 1984). An insufficient quantity of N wiU reduce

transport and absorption of other essential nutrients by the plant. For this reason, agricultural

systems have developeâ ways to supply additionai N to crops. These methods range fiom

growing legurne crops, to applying N-fertilizer.

N is found in soi1 in organic and inorganic forms. It is found associateci with organic

matter pools of different degrees of availability (Paustian et al., 1 992). It is also held as NH,

by clay minerals between the lattices or by the minerai's surface charges. N is also found as

NO, in soil solution.

The rate of availability, and quantity of N available depends upon the fom in which

it is found in the soil, which can be descnied within the N cycle.

Nitrogea Cycle

The N cycle may be broken down into severai steps; kation, Vnmobilization (or

assimilation), mineralization, nitrification and denitrification (Appendix 8.8).

Greenhouse Gases

As awareness of greenhouse gases (NzO and CO3 and the ozone layer increase,

scientists have new reasons (in addition to fertilizer efficiency) to nudy N,O emission fiom

soil. N,O has been found to dter the thermal infiareci budget (Bouwman, 1990). In recent

history, atmospheric levels of greenhouse gases, such as CO2, CH, , and N,O have been

increasing. This could be due to increased emissions through biomass buniing and

agricultural practices, or due to a decrease in the size of terrestrial sinks for these gases. Soils

are also a si@cant source of CO,. In a review, Bouwman (1990) estimated the size of the

soil C pool between 700 Gt C and 3000 Gt C. For 1987, the estimated CO, emission was

5 -7 Gt C (1 Gt = 1 O1'g). The soil C loss was estimated at 0.2-0.9 Gt C y-'. CO, and N,O are

of concem because they have a high residence time in the atmosphere (1 00-200 years). Over

the past 100 yean, CO, is estimated to have contributed 50%, and N,O 4% of greenhouse

wanning.

Denitr=cation Studiq

Factors Affixting Denitrification

The occurrence of denitrification is dependent upon moisture levels (Aulakh et ai.,

199 lb; Weier a al., 1993; EstavilIo et al., 1994;). Mummey et al. (1 994) found that wet1dr-y

cycles create a pulse of N,O due to increased N availability. In dry conditions nitrification

c d 61-98% of N,O emission, while at saturation most ernission is due to denitrification.

Aulakh et al. (1991b) found that at 60% WFPS (water filleci pore space) there was little

denitrification loss of N fiom crop residue, while at 90% WFPS, the denitrification rate

iacreased 4 to 10 times in the fh 8 days of incubation Estavillo et al. (1 994) also found that

soil water content was the main factor affecting denitrification rate.

NO, is essential for denhification to take place. Aulakh et ai. (1 99 1 b) found that soils

with incorporated residues at hi& WFPS rapidly lost nitrate, while soils with no residue

appIication or residue appiied to the surface kept hi& soi1 NO, levels. Estado et al. (1994)

also observed that sol NO, levels had significant effect on differences in denitrification rates

b e e n treatments.

A C source for energy is essential for chitrification to take place. Sources of C such

as fresh plant residues and other decomposable materials rnay create "hot spots" of

dautrification due to microbial activity creating anaerobic environments (Neeteçon and Van

Veen, 1987). Aulakh and Rennie (1 987) found that in flooded soils with sufficient NO,

present, high rates of denitrification occurred only as long as there was a source of C.

McKenney et al. (1993) found that the addition of available C in organic matter would

increase denitrification. Weier et al- (1993) found a buildup of nitrate under continuously

aopped fields. The tàctor limiting the 10~s of NO, through daiitrification was a lack of energy

(C) source for the denitrifien.

Soi1 type may a h have a signjficant effect. Liang and M a c K e ~ e (1994) reported

no difference in denitdication rates with difrexnt N fertilizer rates on a Chicot sandy loam,

but a hear increase in denitrification rates with different N rates on a Ste-Rosalie clay.

Denitrification is a temperature-sensitive process, with a Q,, of about 2 (Fïrestone,

1982). ûenitdïcation wiii, however, continue through the cooler non-growing season. Liang

and MacKhe (1994) reporteci a denitrification loss of 7 to 24 kg N ha1 on a Chicot sandy

clay loarn and Ste-Rosalie clay outide of the growing season.

Study Techniqua

Researchers (Yoshinari et ai., 1 977) discovered that acetylene at a partial pressure

of 10 Pa C&I2 wiU inhi'bit the ammonium monooxygenase enzyme responsible for the

oxidation of N,O to NO.

Other tesearchers (Ryden et al., 1979; Aulakh et al., 1991 a) have also fomd that

acetylene wili, at higher Ievels, inhibit the N20 reductase of denitrification ,the enzyme that

cataiyzes the reduction of N,O to N,. This discovery has been very useful for the study of

demitrificabion, as N,O ernissions could indicate denitrification whereas studying emissions in

N, is i m p a c t i d .

Various ways of anploying the ÇH, inhibition technique have been developed. N,O

emissions oftm are below the detedon limit of open chambers of 0.06 to 0.16 g N ha-' W'

(Hutchinson and Mosier, 1979). For this reason, m o n methods invoive placing a closed

chamber over a soil study area (Ryden, 1978; Denmead, 1979).

Intact mil cores rnay be taken fiom the field and incubated in a closed chamber with

C,H2 (Aulakh et al., 1982; Parkin et al., 1985; Ryden et al., 1987). However, many

re~ea~ctiers feel that rnaintaining a closed environment around the soil core affects the water

evaporation and percolation, changing the movement of gases into and out of the soil core

(Jury et al., 1982). Many researchers dso found that there is a buildup of N,O gas in closed

chambers, which may inhibit the release of more N20 from the soi1 (RoIston et al., 1978;

Hutchinson and Mosier, 198 1 ; Jury et al., 1982).

Ryden et al. (1979) studied the use of C,H, inhibition for measurement of

denitrification. They found that the inhiiitory effèct of C2H2 on denitrification was immediate,

even in dense soils, and that the addition of C a 2 did not change the N2&0 ratios measured.

Their measurement of CO, production indicates that microbial respiration was not affected

by u2. Aithough the inhibitory effect of GHz rnay be imrnediate, Jury et al. (1 982) found

that in soils with lower diffusion coefficients it may be many days before the evolved gas

dïffûses to the soil surface, so what is measured in a short-term experiment may not provide

an accurate picture of gas evolved.

Aulakh et al. (199 la) compared four methods of m e a s u ~ g denitrification ('SN

chamber, w2 yection chamber, CaC, granule inhibition and acetylene injection soil-core).

They f o n d that soi1 core încubaîion methods, ifdd out over a period of several days, wiil

give significantly higher rates of denitrikation than other methods. On the other han4 in-

field chamber meth& can greatly underesthate N20 flux if the sampling tirnes are not at the

sarne tirne as periods of maximum flux.

Aulakh and Rennie (1987) found that the GHz-injected soi1 core method gave

denitrification readings five to seven times greater than other methods. They hypothesized

that these results could be due to a higher soi1 a r e moisture level maintained in incubated

jars, the greater buk density of the soil cores compared to the undishirbed soil, and the

changes in N,O difision rates in the incubation chamber as the concentration gradient

changed.

Mineralization Studieg

Factors Affecting Mineralization

Mineralization is closely connected with soi1 organic rnatter stability, qudity and

quantity. Soil organic matter is a highly variable mix of materials fiom living organisms to

inorganic compounds. About 15% of organic matter is comprised of polysaccharides,

polypeptides, phenols, carbohydrates, amino acids and sugars, diphatic and fatty acids. The

rest is hwnic mafier, w k h is less readiiy decomposeci (Smith et al., 1 980; Parton, 1 987). Soi1

organic rnatter stabdity is affected by temperature, moisture, soil texture, tillage, plant lignin

content and N input (Parton, 1987; Paustian et al., 1992).

Soil organic matter is a srnail fiaction of the material constituting soil, but it has an

important role providing a large fraction of t he macronutrients and binding soil aggregates.

The parent material of a soil will have an impact on it's muieralogy, which will affect

the nutrient datus of a s d . More fertile soils will produce more organic matter, thus there

d l be a greater input of organic matter to be mineralized. Soils with high clay content or

hi& CU: win retain much more organic matter. In general, finer textured soils (clay and silt)

will have higher minerahble N and C than sandy soils, for more organic matter will be

bound to or physically protected by the clays (Tiessen and Stewart, 1983 ; Angers et al.,

1993).

Temperature is ofien found to be important in the rate of mineralLation (Fisk and

Schmidt, 1995). Alvarez et aL (1 995) found the qCO, increased with increasing temperature.

The quality of the substrate addition has a very significant effect on mineralition

rates. Bosatta and Agen (1994) found that microbiai growth rate was detemiined by the

quality and availability of the substrate. A larger microbiai biomass pool should mineralize

a larger quantity of organic matter.

Models

There are numerous studies descnbing N-mineralization. Muieralization has been

obsaved to have a curvllinear relationship with time (Deans et al., 1986). Other researchen

found N mineralized to increase linearly with t h e (Tabatabai and Al-Khafaji, 1980;

Addiscott, 1983). This mheralization-tirne relationship is ofien described by a hyperbolic

(Nt=&[t/(p+t)]) or more &equentIy a single exponentid first-order equation N=&(l -e")),

where N,=N mineralized at time t; N,=potential minerdizable N; k=initial rate of N

mineralization; t-time (Stanford and Smith, 1972; Maq and Remy, 1979; Smith et a]., 1980).

Other researchers (Lindeman and Cardenas, 1984; Deans et al., 1986) found that a

double exponential equation, (N,=&s(~ -eT+N,-, ( 1 -S)( 1 - e 3 ) with variables representing the

labile N (S) and recalcitrant N (I-S) fractions, provided a better fit for the N-mineralization

time curve.

Non-linear least squares analysis is used to compute No (potentially mineralizable N),

and k (the rate of mineralization).

Incubation Studies

Aerobic incubation studies (Stanford and Smith, 1972; Campbell et al., 1993) have

been conducted under controlled conditions to determine potential mineralization rates of a

soil. The study may be set up as repeated measures over time, or a single measurement at the

end of a given period. The common way to measure CO, evolved is with a NaOH trap

(Campbell et al., 1993), while the N mineralization is generally measured by leaching soluble

N out of the soil samples with 0.0 1 M CaCl, (Groot and Houba, 1 99 5). The rationale for this

type of study is that a measurement of N released over time wiIl give an estimation of the N

available to a crop over the growing season. Measurement of total N or C M ratios will not

give an accurate idea of the labile fraction of N, or the rate of soil organic matter

decomposition (Gregorich et al., 1994).

Microbial Biomass Studies

Microbial biomass (MB) is a significant pool in the cycling of nutrients in soil. MB

is a sink for nutrients during immobilization, or growth MB releases N fiom net

mineralization from organic materials or by microbial N turnover.

Many studies find a high correlation between potential N minera l ion and initial

biomass N (Carter and Rennie, 1982). Some scientists see MB as the rate-limiting step in

nutrient cycling (Voroney and Paul, 1984; Fisk and Schmidt, 1995). Other scientists see a

value in studying MB, for unlike soil organic matter, it will respond quickly to changes in soil

managemeat (Bosatta and &m, 1994). Research (Groot and Houba., 1995) has found that

biomass N and C are not significantly correlated with N mineralization.

Svnthesis

N is important for the growth of crops. It will continue to be applied to agricultural

soils for this reason. As understand'ig of the environmental cost of N losses grows, so does

the interest in understanding how different agricultural practices affect the cycling of N.

There are various points in the N cycle where N may be lost. N may be volatilized

into the atmosphere through denitrification, and it may be leached as NO,. If N is available

in excess of crop requirments or at a time where crops will not take up the NO,, it will aiso

be Iost.

Conversely, N is ais0 sequestered and immobilized in organic matter and microbial

biomass. This N store is of vital importance for crop growth and long-term productivity of

a =il. This loss and storage of N is affecteci by cropping procedures, such as tillage, rotation,

and rate and type of fertilizer applied.

HJJothtscs

1, Organic fertilizer applications will result in soil changes which will have different N

mineralization rates due to the difEering quantity and availability of minerabable N;

2, Tillage will affect the rate of mineration and reduce the labile N fiaction by

increasing the rate of breakdown of organic matter;

3 , Denitrification will be increased by higher N availability, temperature, moisture;

4, Closed chamber methods of measuring denitrincation will be more sensitive to

variables that affkt denhification than the soü core incubation method, shce the

closed charnber method has less impact on the soil conditions.

ObieetivcJ 1, To measure effects of N fertilizer rate, type of fertiiizer, and tillage on N and C

mineralization, and ratios of labile N;

2, To meaaire effeds of N rate, rotatioq temperature, water-fled pore space and tillage

on denitrification rates;

3, To correlate denitrification measured by closed chamber and soil core incubation

rnethods with variables that wodd affect the rate of denitrincation. The preferred

method should be more sensitive to changes in signifiant variables.

Chapter 4

Evaluation of closed-chamber and soil core incubation methods of rneasuring

denitrification

Abstract

Denitrification in agricultural soils is an important source of N,O, a greenhouse gas. Field

measurements of denitrification are used to evaluate N loss. Two common methods of

measuring denitrifidon are the soi1 core incubation and the closed chamber method. These

two methods were assessed on soi1 planted to monoculture corn, monoculture soybean, and

alfalfa in a corn soybean alfalfa rotation. Denitrification rates measured by the closed

chamber method were higher than those measured by the soil core incubation rnethod.

Denitrification rates ranged fkorn less than 15 g N hdh-' to nearly 2000 g N ha-'h-'. The

closed chamber method was more sensitive to treatment effects. The denitrification rates

were dependent on the soi1 type, being higher on soils with high clay content. The variables

that had the greatest reiationship with N,O emission were water filled pore space, soil NH,-N

and NO,-N concentrations. The rate of N-fertilizer had a si@cant effect on the rate of

denitrification. Temperature, a variable expected to have a sigsufïcant relationship with the

rate of denitrification, was not found to be statistically significant in some cases.

Introduction

Incrases in greenhouse gas emissions have been documented ([PCC, 1992). One of

the gases of interest is N20, producd through nitrification and denitrification in soil. N 2 0 has

a global waming potential 200 times greater than COz on a molecular basis (PCC, 1992).

Denitrification processes can be measured using the addition of C2H, which functions by

inhibiting the reductases that reduce N,O to NO (Ryden et al., 1987). Thus denitrification

canbeestimated by measuringN20 emission in a &Hz-modified soil. N,O exists in very low

concentrations in the atmosphere, so changes may be easily detected.

There are several sources of error when measunng denitrification, due to the nature

of denitrification itself Denitrification tends to occur on an "event" basis, triggered by

rainfàii, N or C arnendments (Auiakh et al., 199 1 b). Wetting of a dry soi1 results in a flush of

N,O (Murnmey et ai., 1994). It has been established that moisture, temperature, NO,', and

C availability afFect the rate of denitrification (Aulakh and Rennie, 1987; Aulakh et al.,

1991b). Denitrifcation dso depends on nitrEcation as a source of NO,. Nitrification depends

upon a source of NH, to be oxidized (Brady, 1984).

Therefore, management sy stems will affect the rate of denitrification through tillage,

fertilizer and crop effects (Rice and Smith, 1982). Cultivation wiii affect the structure of a

soil, and the structure of the soil will affect the rate of denitrification, by afEêcting oxygen

dfision (Jury, 1982; Knowles, 1982). Added N, as soil organic matter or inorganic fertilizer,

may incrase denitrification losses (Ryden, 1986). Denitrification losses have been shown to

increase with decreasing C/N ratios (Aulakh et al., 1991 b). Crops species may affect the rate

of denitrification through residue retum to the soil. There wiiS be difFerent levels of organic

C and N remaining in or rehimed to the soil, with different Cm ratios.

There are a variety of ways to measure N,O emission fkom soil. Two rnethods hold

promise, the soi1 core incubation and in-field closed cylinder methods. The soil core

incubation method (SC), where soil cores are removed and incubated in closed containers,

wiU alter soi1 temperature, moisture level and the N,O gradient around the soil core fiom that

of the soi1 in situ (Jury, 1982; Aulakh and Rennie, 1987; Aulakh et al., 1991a). The SC

method is usefiil in measuring total denitrification over a long penod of tirne. The closed

cyiinder (CC) method measures N,O emission by placing the cylinder on the soil, trapping

emitted gases without changing soil variables (Aulakh et al., 199 1 a). The closed cylinder is

in place for a limited time, and may miss denitrification events. The N20 gradient may also

decrease in the cylinder, inhibiting N20 difision from the soil. When these methods are

employed on C,H,-amended soil, the N20 emission measured is due to denitrification.

Methods of quantifjing N,O emission as denitrification must be evaluated in studying

N-loss and the variables that affect it.

The research objectives were;

1. To compare methods of measuring denitrification as to sensitivity to variables that would

affect the rate of denitrification.

2. To relate tillage, fertilker N rates, and crop rotation, to the rate of denitrification.

Materials and Methods

Denitrification was studied on an Ormstown silty clay loarn (Humic Gleysol), a Ste-

Rosalie clay (Humic Gleysol) and a Chicot sandy clay loarn (Gray Brown Luvisol) in 1994.

The Ste-Rode (1) and Chicot plots were at the Ernile A Lods Agricultural Research Centre

at MacDonald Campus, McGili University (Table 4.1).

At two sites (Ste. Rosalie (1) and Chicot), monoculture corn was compared at four

N rates, arranged as a randomized complete block with four replicates. The plots were

planted to corn (Zea rncrys L.) the ûrst week in May and harvested the second week of

October.

At two sites (Ste. Rosahe (2) and ûnnstown), treatments included tillage, N rate and

species. At the Ormstown site, near Omstown, Q u h , and the Ste-Rosalie(2) site at Iie

Perrôt, Québec, treatments were anangeci in a split-split plot design. Tiage was the main

plot (tilVno-a), rotation was the sub-plot, and fertilizer N-rates were the sub-sub-plot.

Samples were taken fiom continuous corn y contuiuous soybean (Gfycine m m L. Merill), and

aifàiià in a corn-soybean-alfalfaarn rotation There were three levels of fertilizer, 0,90, and

180 K g h for corrtinuous corn, 0,20, and 40 Kgha for continuous soybean , and O kg N ha-'

for alfafa (Table 4.2).

Soii Core Method

Intact soil cores were taken from the surface soi1 of the experimental plots using

aiumuium cores 6 cm diameter by 15 cm long. The sarnples were collected weekiy in May,

lune, and July, every other week in August and once a month in September and October. The

samples were placed in 2 L plastic jars with a septum seal in the lid to allow sarnples of gas

to be taken. One hundred mL C2H2 was added to the jars, afier 100 mL of air was removed,

to inhibit denitrification. Sarnples were incubated for 24 hours in a partially shaded area.

Airtight syringes were used to mix and then sample the gas in the jars. The samples were

analyzed for N,O content using a 5 8 70 series-lI Hewlett-Packard gas chromatography using

a Tractor electron capture detector (%)(Hewlett-Packard Company, Avondale, PA) in the

constant current pulsed mode (Mosier and Mack, 1980). Soil cores were then used to

determine bulk density, water Uled pore space, and moisture. Soil NO, and NH, were

measured by extraction in M KCI and analysis on Lachat Quickchem Automatic Row

Injection Ion Andyzer (Lachat Instruments, Milwaukee, WI) using the salicylate (for NH,)

and the Cd reduction sulphanilamide (for NO,) methods (Sechtig, 1990, 1992).

CIosed Chamber Method

N,O sarnples were taken in the field using 25 cm high x 10.2 cm i.d. PVC cylinders,

closed at one end. Cylinders bad a septum seal at the top with a 5 cm long Tygon tube

attached for samphg. To obtain samples, 100 ml GHz was injected into the soil at four

points to a depth of about 3 cm The charnber was placed over these four points and pushed

into the soil to a depth of about 3 cm. Mer one hour gas samples were taken using airtight

10 ml syringes. At the same sites, cyiinders were set up without C&I, injection and gas

samples were taken to measure N,O emission. The N,O concentration of sarnples was

measured using the same method as the soil core incubation method.

Analvses of Results

N,O emission from the soil core was caiculated by the following formula

N,O emission Cg ha-'h-')=

(~,0~~rn*(28/44)*0.04 l6*28*volume*(2.8*2.8*3.l4)"/24* 10"

N,O ppm is the concentration of N@ in the jar,

where 28 is molecular weight of N, g;

44 is molecular weight of N,O, g,

0.0416 is nrnoi/d equd to 1 ppm at a given temperature;

volume is total volume of air in the incubation jar, in L:

(2.8*2.8*3.14) is surface area of soi1 in core, in cm2;

24 is length of time of incubation, in hours.

The fornula for calculating emission by closed chamber method in was the same as

for the soil core incubation method, with a few alterations. The air volume was 1750 mL, the

surface area of the soil was 80 cm2, and the time period of incubation was 1 hour.

Values from each method were correlated with water-filled pore space (WFPS),

temperature, rate of N fertilizer application, NO,-N, and NH,'-N contents using Pearson

Correlation Coefficients. Data were anaiyzed by regression with emission as the dependent

variable. The analysis of variance included sarnple (the date of sampling), replicate in the field,

rate of N fertilizer appiied, crop rotation, tillage, and the interactions of these factors.

Resu1t.s

Corn Monoculture Ex~erirnenQ

On the Chicot site denitrification values fiom the closed charnber method indicatixi

that sample date was significant, and there was an interaction of sarnple date by replicate

(Figure 4.h; Appendix 8.0a). Soi1 core incubation were sirnilar with the addition of a

significant replicate effect (Figure 4.1 b: Appendix 8.Ob).

On the Ste. Rosalie site, the closed chamber method showed a significant effect of

replicate, sample date, and N rate (Figures 4.2% 4.3% Appendix 8.0~). Interactions were

noted with replicate by sample date and wunple date by N rate . With the soil core method,

significant effeds were found with replicate, sarnple date, N rate and interaction of sample

date by N rate ( Figures 4.2b, 4.3b, Appendix 8.0d). Sample date effects in the Ste. Rosalie

soi1 were simikr to the Chicot soi1 with rates near zero in the spring and high rates of 250 mg

N ha'' (soil core method) to 1800 mg N ha1 If1 (closed charnber method) at the 180 to 200

day period (Figure 4.1 a).

N fertüizer rates were sigdicanîly related to deuitrification on the Ste. Rosalie soil,

but not on the Chicot soil. For the Ste. Rosalie (1) soil the highest rate of denitrification was

measured under the 170 kg N ha'' fertiliter rate, however it was not significantly different

&om the 285 and 400 kg N ha-' treatments.

The closed chamber gave higher values at 400 kg N treatments in the Chicot soi1

(Figure 4.4) and at ail N rates with the Ste. Rosalie soil. The closed chamber method tended

to give similar values across treatments by sarnple date.

Corn Rotation Ex~erimenu

At the Omistom site, using the closed chamber technique, sarnple date, tillage and

rotation were significant as were sample date by tiilage, sample date by rotation and tillage

by rotation interactions (Figures 4.5 and 4.6% Appendix 8.0e) . Using the core method,

signincant effects were sarnple date, tillage, sample date by rotation and tillage by N rate

interactions (Figure 4.6b, Appendix 8.09. For the Ste. Rosalie (2) soi1 the highest mean

denhification values were obtained on 06/07/94 under corn rotation, and under the highest

rate of fertilizer application, The maximum value of 77.4 g N ha-' h-' was obtained by closed

chamber method unda corn monocrop. Soybean was oflen signi-ficantly direrent h m corn

and alfalfa over the growing saison, k g lower values than corn, and having higher values

later in the growing season when corn and aifdfa were low (Figure 4.8a). Denitrification

under soybean generaily was pater than alfalfa. Under corn monocrop the denitrification

trend was linear with keasing N f e r t h , while for soybean there was no clear relationship.

At the Ste Rosalie (2) site, the closed chamber method resulted in significant effécts

with sarnple date, rotatioq and N rate, with sample date by rotatioq sample date by N

interactions Figures 4-74 4.8a, Appaidk 8.0g). W~ the core method, treatment effkts

wae noted with samp1e date, repliate, rotation, and sample date by rotation and sample date

by N me Eneractions 4.7b7 4.8b, Appendix 8.0h) Differences in the methods were

n& with the cure method which had sigdicast replicate differences but wt N rate effects

comparai with the closed chamber method.

Pattern of Denitrification across a4 Exgerimen&

Fdl and spring values were lo w and maximum rates were found between 1 80 to 200

days in Chicot and Ste. Rode (1) and (2) mils (Figures 4 -6% 4 -8a). Treatment effects were

only f d at peak emission periods.

The analysis of variance of temperature for the Ormstown soil shows a sigdicant

eff'i of sample period, tiaage7 and a sample by tillage interaction (Appendix 8.1 a). Over the

whle growing season there was no &kt of replicate, rotation, or N rate on temperature.

For SteRosalie (2) so3 the analysis had the sarne r a f t (Appendix 8. lb).

'Ibe analysis of variance of water-filed pore space for the Ormstown soil shows a

signifiant 8- of s a q l e period, and rotation, and an interaction of sample by rotation

(AppendO< 8 2 ) . For the Ste. Ros& (2) mil the r d of adysis were the same (Appenda

8.2b). . omehbons rnd Fhmssioq

Clrmuktive d u e s korn the two mahods of meamring denitrifidon were conetated

for ail soils sbdied (Table 4.3). Other variables were correked with denitrification rates to

varying degres (Table 4.3). NH, was pasitiveIy correhed with denitrifidon measurd by

the d d chamber method for Ste. Rosalie (1) but negatively corraated with Ste. Rosalie

(2) (Table 4.3). Correlations with the soil core method were positive for Chicot and Ste.

Rosalie (2) soils. Soi1 NO, was significantly positively correlated with denitnfication

measured by closed chamber method on three sites, and when denitrification was measured

by soil core incubation there was a positive cordation with Ste. Rosaiie ( 1 ) and (2) soils.

Temperature was significantly positively correlated with denitnfication measured by closed

chamber method on Ste. Rosalie ( l ) and (2) soils, while denitrification rneasured by soil core

incubation was positively correlated with temperature in Ste. Rosalje (2) and Chicot soils.

Water-£Zed pore space was significantly positively correlated with denitrification for Chicot

and Ste. Rosalie (1) and (2) mils with both methods of measuring de~hfication.

Cornparison of Methoda

During hi& denitdication periods, the closed chamber mefhod measured greater rates

than the soi1 core incubation methoci. At low levels of denitrification, the values were similar.

Correlations of individuai sampling day results revealed minimal correlation between

the two methods of measuring denitrification. Correlations over an entire sampling season

resulted in a correlation between the two methods.

The closed chamber method exhiiited denitrikation peaks that were several times

larger than those measured by mil core incubation method.

Discussion

This study found that at various times in diEerent soils, mil moisture (WFPS), NH,

and NO, values, and temperature had significant correlations with denitrification. NH,

correlations were both positive and negative indicating that the relationship was not

consistent and that nitrification was not widely responsible for loss of N,O. Values of NO,-N

had a signifiûuit relaiionship with denitrification with most soils, which was consistent with

the positive regression of fertilizer N rate on denitrification

The closed charnber method mea~u~ed higher peak rates of daijtrification than the soil

core incubation method. This could be due to a difference in the soil water status between

the two methods. Aulakh et al. (1991a) f d that the soi1 cores retained more moisture tbao

the dosai chamber method. However, their d d y average gaseous-N flux ranged fiom 168

to 327 g N ha-Id-' for the soil core method and 25 to 80 g N ha"bl measured with the

chamber method. The higher values rnea~u~ed with the closed chamber method could be due

to a larger area sampled than with the core method. The closed chamber method also

m m e d N,O only at the peak emission point of the day. In any event the closed chamber

method seemed superior due to a larger and more sensitive rneasured denitrification value.

One of the problems with rneasurement of denitrification is a high degree of soi1

microsite heterogeneity found in nutnent levels, mineralkation rates, and diffusion rates

(Davidson and Hackler, 1994; Goovaerts and Chiang, 1993). Goovaerts found that many soi1

properties had large variance at small (cl m) distances and independence of observations

beyond 12m.

The pattern of denitrification seems to be related to the changes in temperature,

moisture, fertilizer application, and crop effects. The most important variables were NO,-N

and WFPS (WFPS = Vaeration). The NO, level peaked middune and rapidly decreased

thou& the rest of the growing season (data not shown). The addition of N fertilizer side

dressing at the end of June did not increase either the NT& or NO, found in the soil at that

time. Ste. Rosalie (1) soi1 did not have the highest denitrification rneasured in the soiI

receiving the highest rate of N fertilizer. The fermizer on this plot was apptied in several

hmiments, and consequently at some times the fertilizer was applied when conditions were

more conducive to denitrification. When the final fertilizer application was applied for the

highest rate, soil moimire was lower, aeration higher and thus less N would be denitrifid.

Tillage and rotation m the h s t o w n soil afEècted denitrification. On the Ormstown

site the d&cation rates were greater for n-till than conventional till at peak rates. No-till

increased the moisture at the surface and decreased the temperature. Apparently the

inaeased moisture was effective in increasing denitrification rates. Decreases in temperature

with no-tiu were not of large enough magnitude to have an effect.

Rotation effects were largely a resdt of highet dues with corn, especidy eariy in the

growing season, and lower values for soybean and alfalfa plots. Later in the growing season

there was a tendency for soybean to have higher values than corn or alfalfa. However,

overd, corn cumulative values were higher than the other two crops.

Table 4.1: Selected properties of Ste-Rosalie, Chicot and Ormstown soils

Soi1 DH m,O) Clay Silt ûrganic CL Total W

Monoculture corn expriment ---------- g kg1 ------.O----

Ste-Rosalie 6.7 710 190 3 0

(1)

Chicot 5.2 180 170 15

Corn rotation expriment

Ste-Rosalie 5.3 568 2 93 2 5 1.11

( 2 )

ûrmstown 6.2 368 443 19 1,9

Walkley-Black procedure (Nelson and Sommers, 1982)

'H,SO,-CuSO, Kjeldahl digestion method (Bremner, 1965)

(1) Emile A. Loâs Agncultural Research Station

( 2 ) Qdnn's Farm, Ormstown

Table 4.2. Fertilization treatments, procedures and tillage

Soi1 Fertilizer application Fertilizer rates Tillage

kg N ha"

Ste. Rosalie (Humic Gleysol) 170 kg N ha" mil-

incorporateci urea at

planting

1 15 kg N ha-' side-dress

early June

1 15 kg N ha'' side-dress

late June

Chicot (Gray Brown Luvisoi) Same as Ste. Rosalie

Onnstown (Humic Gleysol) and N ( 3 4 4 4 ) broadcast

Ste. Rosalie (2) (Humic Gleysol) at seeding

170,400

O, 90, 180 corn

0,20,4O soybeûn

Primary- fat1 after hanlest moldboard

plough 0.20 m depth

Secondary- spring Triple-K vibrashank

cultivotor 0.10 m depth

Same as Ste. Rosalie

Conventional tillage-

Primary- fall &er hanest molciboard

plough 0,20 m depth

Secondary- spring Triple-K jlibnshank

cultivator 0.10 m &pth

No-till- direct seeding zAmmonium nitrate

-f- Replicate 1 L + Replicate 2

I -A- - Replicate 3

l -t- Replicate 4

\

120 140 160 180 200 220 240 260 280

Julian days

Figure 4.la. Denitrification rates measured by the closed chamber method on the Chicot soi1 across al1 N rates as affected by replicate. Bars indicate standard error.

-t Replicate 1 + Replicate 2 - - Replicate 3 -7-- Replicate 4

t i I I I 1 I 1

140 160 180 200 220 240 260 280

Julian days

Figure 4.1 b. Denitrification rates measured by the soi1 core incubation method on the Chicot soi1 across al1 N rates as affected by replicate. Bars indicate standard error.

+ replicate 1 + replicate 2 - - replicate 3 - r-- replicate 4

-500 1 i I I I I I I 1

120 140 160 180 200 220 240 260 280

Julian days

Figure 4.2a. Denitrification rates measured by the closed chamber incubation method on the Ste. Rosalie (1) soi1 across al1 N rates as affected by replicate. Bars indicate standard error.

-. -C replicate 1 -+- replicate 2 - - replicate 3 - - replicate 4

140 160 180 200 220 240 260 280

Julian days

Figure 4.2b. Denitrification rates measured by the soi1 core incubation method on the Ste. Rosalie (1) soi1 across al1 N rates as affected by replicate. Bars indicate standard error.

120 140 160 180 200 220 240 260 280

Julian days

Figure 4.3a. Denitrification rates measured by the closed chamber method on the Ste. Rosalie (1) soi1 across al1 replicates as affected by N rate. Bars indicate standard error.

--

-C O kg N ha'' + 170 kg N ha-'

- 285 kg N ha-' -r-- 400 kg N ha-'

Julian days

Figure 4.3b. Denitrification rates measured by the soi1 core incubation method on the Ste-Rosalie (1) soi1 across ali replicates as affected by N rate. Bars indicate standard error.

i -C closed chamber method I -ic soi1 core incubation method

120 140 160 180 200 220 240 260 280

Julian days

Figure 4.4. Denitrification rates measured across al1 replicates at 400 kg N haœ1 on the Chicot soi1 using closed chamber and soi1 core incubation methods. Bars indicate standard error.

+ closed chamber conventional tillage 1 + closed chamber no-till l

I I I I I I I 1

140 160 180 200 220 240 260 280 300

Julian days, 1994

Figure 4.5. Denitrification rates measured under no-till and conventional till on the Ormstown soi1 by the closed chamber method. Bars indicate standard error.

-

-0- corn + corn soybeân alfalfa corn -&- soybean

Julian days

Figure 4.6a. Denitrification rates measured by the closed chamber method on the Ormstown soi1 across al1 N rates and tillage as affected by rotation. Bars indicate standard error.

Julian days

Figure 4.6b. Denitrification rates measured by the soi1 core incubation method on the Ormstown soi1 across al1 N rates and tillage as affected by rotation. Bars indicate standard error.

-+- O kg N ha-' + N rate = 1 (90 kg N ha-' for corn,

20 kg N ha-' for soybean) - - N rate = 2 (1 80 kg N ha-' for corn,

40 kg N ha-' for soybean)

Julian days

Figure 4.7a. Denitrification rates measured by the closed cham ber method on the Ste-Rosalie (2) sail across al1 tillage and rotation as affected by N rate. Bars indicate standard error.

+ O kg N ha-' + N rate = 1 (90 kg N ha-' for corn,

20 kg N ha-' for soybean) - - N rate = 2 (1 80 kg N ha-' for corn,

40 kg N ha-' for soybean)

---

Julian days

Figure 4.7b. Denitrification rates measured by the soi1 core incubation method on the Ste. Rosalie (2) soi1 across al1 tillage and rotation as affected by N rate. Bars indicate standard error.

- - 7

-0- Corn -+- Corn-soybean-alfalfa-corn -A--- Soybean

Julian davs

Figure 4.8a. Denitrification rates measured by the closed chamber method on the Ste. Rosalie (2) soi1 across al1 N rates and tillage as affected by rotation. Bars indicate standard error.

Julian days

Figure 4.8b. Denitrification rates measured by the soi1 core incubation method on the Ste. Rosalie (2) soi1 across al1 N rates and tillage as affected by rotation. Bars indicate standard error.

Connceting Text

The previous study looked at N properties in soil as related to denitrificaton. It

showed application of minimum inorganic N fertilizer and use of conventional Mage resulted

in the lowest loss of N through denitrification.

Mineralization of N wül show how much N was available in the soil. Larger pools of

mineralizab1e N indicate greater quantities of N have been immobilized in the soil. The next

study investigates the effect of different fertilizer N treatments and soi1 type on the arnount

of mineralizabIe N.

Chapter 5

N and C mineraliurtion in soils under corn in Eastern Canada

A bstract

The assessrnent of available soil N under continuous corn on Ste. Rosalie, Chicot,

Brandon and Fox soils with different treatments was accomplished through a laboratory N

and C aerobic mineralization shidy. Resuhs of soil chernika1 and biological analyses (total N,

organic C microbial biornass C (ME3C) and water soluble organic C (WSOC)) were correlated

with results of the longer-term mineralization studies to see if any variables could act as an

indicator of potential mineralization. N rnineralized, C respired, total N, organic C, W SOC

and MBC were all related to soi1 texture. Potentially mineralizable N (No) ranged fiorn 144

mg N kg-' under 100 kg N as aockpiied m a u r e on Brandon soil to 30.3 mg N kg-' on Fox

soil. Total N, organic C, WSOC and MBC were also related to the amount of organic or

inorganic N amendment on Brandon soil. Higher rates of organic amendment resulted in

higher measured values on Brandon soi1 wtùle higher rates of inorganic N on Chicot and Ste.

Rosalie soils caused no change in mineraiizable N or respired C . Higher rates of inorganic

N resulted in lower measured WSOC and MBC on Chicot and Ste. Rosalie soils. N S .

mimalmûon 6t linear relaîionships on the Brandon mil, however rnineralization on the other

soils was weU explaineci by the first order equation. MBC, WSOC, were found to have a

strong relationship with potentidy mineralizable N. PotentiaiIy mineralizable N was strongly

correlated with potentially respired C.

In traduction

M h e n h b I e soi1 N is imponant for it is the N that can be made available to a plant

during the growing season. This N is fd as o r p i c N, and is made available by conversion

to inorganic N through microbial activity Pools of organic matter of differing N availability

include k h crop and animal residues, microbial biornass microbiai metabolites, organic

matter adsorbed to colloids, and very stable material. N rnineralization is affécted by soi1

charaderistics such as clay type, pH and drainage, as well as organic matter characteristics

such as minenilizable dstrate, total C and total N and f o m of C and N Soil management

including f* and organic matter inputs can affect N availability (Parton et al., 1987).

Changes m soJ management cm alter input and removal rates of organic matter, and the rate

of decornposition of soi1 N

.Meawing available N is corhcted in a varkty of ways. Soil N supply in agriailtural

soils has b e n estimated by analysis of nitrate (Keeney, 1982). A laboratory incubation

mahod was developed (Stanford and Smith, 1972; Chae and Tabatabai, 1986; Campbel et

al., 1993) to cietennine the potentidly minerdiable N (NJ, and the mineralization rate, k.

.Mineralization midies (Campbell and EUext, 1993) may be wnducted both in the field and

in the Iab to measure the rate and amount of ptemially minaalizable N and C.

Stanford and Smith (1972) hypohsizd that the rate of mineralizaticn varies with the

amount of potentially mineraiizable N present initidy in the mil. This is expressed by the

fkt-order rate equation:

dN/dT = -kN

and the integrated equation was:

Iog(NO-NJ = log N0-(kQ.303)(t)

ïhey used this equatïon to determine the No value (soi1 N minefalization potemial)

that w d d fit best on the rektionship of (No-NJ vs. t, d e r e N, = cumulative amounts

o M rnhahd. ïhey f o d that the refationship b-ea the No and N mineralized was low

ai the dart of the incubation but as tbe t h e of incubation inaeased, the relationship became

betîer. Jwna and Paul (1 984) found thaî Iinear regression resulted in a poorer fit thao f h t

orda equations. Since Stadord and Smith's method of calculating No and k involves a lot of

approximations and is cornplex (Smith et al , 1980) non-linear regression programs such as

SAS proc NLiN (SAS, Inc., 1985) both sirnpIi@ and render more acairate the caicuiations.

Campben and Eiiert (1993) based their caidations of No and k on the same first-order

rate equation as Stanford and Smith (1972). Howwer, they modified the equation to the

following:

r n d T = kN

and the integated equation was

I d , - InNo = -kt

taking the antilog resulted in

N, = Yoe ii

so at tirne = O

N, = N,e -M

Since N, is the difference between the initiaily mineralitable N (NJ and the amount

inineralized at time t pJ

N, = No - NI

Since NI = ~ , e "

N, = No- N0ea

N,=N,(II*)

This equation was used to detemiine No and k in this paper. Sarnplw are taken

periodically rather than once at the end of a certain length of time, following the a h d o n

of Ellat and Bettany (1988). Thqr niggested that an iocremental model wodd fit better, it

would show differences in rates of m i n e r w o n over the incubation t h e thai wiii not be

evident with a single sample.

The objectives of this midy were to measure the effeçts of monocube corn

maDagenrent such as binage, f e inputs, organic matter (mure) inputs on the amount

and rates o f mùieralizable N and C .

Materials and Methods

Exnerimental Desiva

The soil samples used in this study were from southem Quebec and Ontario under

continuous corn. Four soils were used, a Ste-Rosalie clay (Humic Gleysol), a Chicot sandy

clay loam (Gray Brown Luvisol), a Brandon silty loam (Humic Gleysol) and a Fox loarny sand

(Gray Bmwn Luvisol) (Table 5.1). The Chicot and Ste-Rosaiie soil sites were located at the

E d e A Lods Agronomy Research Centre on the Macdonaid Campus, McGill University,

Ste. Anne de Bellevue, Québec. FertiIker studies had continued since 1984 on the Chicot

site, since 1987 on the Ste-Rosalie site. At the Chicot site, samples were collected from the

plots receiving fertilizer rates of 4OO-3OO-4OO and 1 70- 100- 1 70 for spring of 1995. On the

Ste-Rosalie site, samples were collected at the control (0-04) low (1 70-300400) medium

(285-300-400) and high (400-300-400) rates (Table 5.2). Samples were collected in the

spring of 1995. The plots were arranged in a randornized complete block design with four

replications.

Fox soil samples were coilected in the spring of 1995 at the Research Station of

Agriculture and Agri-Food Canada, Dehi, Ontario. Samples were coiiected from

conventional tillage and no-tiliage treatments using 200 kg N ha-'.

The Brandon soil site was Iocated at the Central Experimentai Farm, Agriculture and

Agri-Food Canada, Ottawa, Ontario. Sarnples were taken fiom the rotation experirnent with

five N treatments (morganic N alone, composted or stockpiled dairy manure at two rates).

The treatments were arranged as a split-split plot with three repiications; the main plot being

the N treatment, split-plot corn cultivars, and split-split plot rotation crop.

Sam~tinn Protocol

Soils were sampled at a depth of 0-20 u n @low layer) (Table 5.2). Four aibsamples

wae taken f?om randorn points in eacb treatment plot and combineci. Moist soi1 was passed

through a 2 mm screen and stored at 2OC until incubation. Samples for 0 t h analyses were

aUdried after collection and crushed to pass a 0.25 mm sc~een (60 mesh).

Nmineraluati . .

on and C respiration were rneasued simuhaneously using the same soi1

sample.

N Mineralkation

The mineralization study used the method of Campbell et al. (1993) and was

conducted for 1 19 to 147 days.

Fifky g soil was combined with 50g acid-washed Ottawa sand except Delhi samples which

were incubated as is. Seventy mm büchner fumels were prepared as filtration chambers. A

glass microfibre filter (Whatman 934-AH glass rnicrofibre filter) was placed in the bottom of

the firnnei, foilowed by a 5 mm pad of glass wool to prevent clogging the filter with repeated

leachg. The soiYsand mixture was then placed on top of the glas wool, and topped with

another pad of glass wool to disperse the leaching solution. The büchner fùmels were

incubated at 25°C in sealed 2L polyethylene jars. The soil samples were penodically removed

from the jars and leached to measure NH,+-N and NO,-N. Leachates were analyzed for

w ' - N and NO3'-N on Lachat Quickchern Automatic Row Injection Ion Analyzer (Lachat

Instruments, Milwaukee, WI) using the salicylate (MI4), and the Cd reduction sulp hanilamide

(NO3 methods (Sechtig, 1990, 1992). Values of No and k were obtained from the cumulative

curve of N03+NH, release (Campbell et al., 1993).

C Respiration

Respired CO2 was trapped in 20 mL of 1 M NaOH placed in a 1 00 mL plastic via1 in

the incubation chamber. The NaOH was titrated with 1 M HCI and carbonic anhydrase using

a Mettler DL 12 auto-titrator (MettIer-Toledo AG CH-8606 Greifensee, Switzerland). The

rneasurement of CO, began at Tl, after the soil samples had incubated for a week.

Soil Analysis

Total N and organic C was measured by dry combustion of 1 0 mg of dry soi1 ground

to pass 60 mesh on a Carlo Erba NA 1500 N/C/S analyzer (Miian, Italy).

Microbial biomass C was rneasured using the chloroforrn fumigation direct

measurement rnethod (Voroney et al., 1993). Dissolved organic C was measured on a

Shirnadzu TOC andyzer (Shirnadni TOC-5050, Shimadni Co., Tokyo, Japan) . Microbial

biornass C was measured by subtracting soluble soi1 organic C in the non-fùmigated soil £iom

soluble soi1 organic C in the furnigated soil, and dividing this value by 0.35.

Water-soluble Organic C was determinecl using 10 g of fiesh s d agitateâ in 25 mL

of ultra-pure water for 30 minutes then centrifùged for 10 minutes. The solution was

suctioned through a glass fibre filter at -7 kPa. A Shimadzu Total Organic Carbon Analyzer

(Shimadni TOC-5050) was used to measure soluble organic C in the filtrate.

Anatvsis of Resultg

Vahies of C and N evolution were analyzed by SAS nonlùiear least squares regression

to give values for No (potentidy mineralitable N) and k (initial rate) (Campbell et al., 1993).

Variables were correlated using PROC CORR. Significance of soil type, treatment,

and tirne was measured using SAS procedure GLM repeated measures anaiysis. Cornparison

of treatment effects was determined using least significant difference.

Resu t ts

Total N and Organic C

Total N had a significant relationship with organic C (Figure 5.1 ).

Total N measurements varied with site, (Table 5.3). Treatrnent effects were noted for

Brandon and Ste. Rosalie sites. Values ranged fiom 0.500 g N k g soil on Fox no-till to 2.98

on Ste. Rosalie soil amended with 285 kg Nha. Added manure at 28 Mg ha-' resuited in

higher N values than plots receiving no N. On Ste. Rosdie site there was a higher N level on

plots reoeivmg 285 kg N ha-'. On the Chicot soil and Fox soils there were no dierences in

totai N due to treatment.

ûrganic C measurements ranged f?om 34.4 gkg on Brandon arnended with 100 kg

N fiom composted manure, to a Iow of 7.4 gkg on Fox no-till. Organic C measurements

showed treatment e f f i for Brandon and Chicot sites. C was higher on the higher fertilizer

rate in the Chicot mil, and was higher with 28 M g m u r e than O Mg manure on the Brandon

soil. For the Ste. Rosalie soii, there was no significant ciifference in organic C due to

inorganic fertilizer additions. Fox had no difference in organic C due to treatment.

CM ratios varied with d, ranging ffom 8.1 to 15.6 (Table 5.3). On the Ste. R o d e

site the CM ratio d e c r d with inmeasing rates of inorganic N fertilizer application. W a ter

Soluble O q p i c C: Water soluble organic C (WSOC) varied with soil and treatment on Brandon and

Chicot soils (Table 5.3). On Brandon soc higher rates of manure addition increased WSOC,

with composteci manure producing higher values than stockpiled manure. lnorganic fertilizer

addition reduced WSOC in the Chicot soil.

Microbial Biomass C

The MBC levels ranged from 0.84 1 g Ckg on Brandon with 100 kg N composted

amendment, to 0.200 g C/kg on the Fox soi1 (Table 5.3). Microbial biomass C (MBC) varied

with treatment on al1 soils except Fox. On Brandon soil under 28 Mg of manure there was

increased MBC but there was no effect of inorganic fertilizer or low rate of stockpiled rnanure

on MBC. On Ste. Rosaiie soil the highest rate of inorganic fertilizer reduced MBC. On the

Chicot site there was a decrease in MBC at the high rate of inorganic fertilizer.

Minerrlized N and Res~ired C

Mineralizable N varied among mils but was affected by treatment only in the Brandon

soil. Values ranged fiom 30.3 mg N kg-' in the Fox soi1 to 1 44 mg N kg-' in the Brandon soi1

amended with 100 kg N as stockpiled manure (Table 5.4, Figures 5.5, 5.6). in the Brandon

soil, inorganic N had no &ect but stockpiled and composted manure increased mineralization

rates. Composted manure had a higher muieralizable N rate than stockpiled manure at the 50

kg N rate, but ihe reverse occurred at the 100 kg N rate (Table 5.4, Figure 5.5).

T-tests of the linear regression coefficients (Table 5 -4) indicate that fiom day 2 1 to

1 12, the slopes of the composted manure and the higher rate of stockpileci rnanure are

significantly different from the inorganic treatment, and the highest rates of manure addition

are significantly dflerent from the control.

Rate of minexahfion as measured by k vaiues ranged fiom 0.0 1 8 &yy1 t O 0.066 day" .

Treatment effects were found only with the Brandon SOC where k values were increased with

added inorganic N and rnanure. Values of k with m u r e were similar to those with inorganic

N, except for the 100 kg N composted manure which had a higher value.

Values of k were inversely related to No values, (Table 5.5) indicating that Iow

potentidy mineraLiZable N was inversely related to rate of mineralkation.

Cumulative rnineralized N varied arnong soils but was affected by treatment only in

the Brandon soil (Table 5.6). Values ranged from 65.4 mg N kg" in the control soi1 to 160

mg N kg-' in the Brandon soi1 amendai with 100 kg N as stockpilexi manure. Inorganic N and

the lowest rate of stockpiled manure had no effect on the cumulative N mineralized, but the

highest rates of manure resulted in significant effects.

The cumulative N mineralized as a percentage of soil total N ranged from 3.22% in

the control soil to 5.58% in the soil amended with 100 kg N as composted manure (Table

5.6).

Potentially respired C (Co) varied among soils but was affected by treatment oniy in

the Bmndon soi1 (Table 5.5, Figures 5.7, 5.8). Vaiues ranged from 467 mg C kg*' in the Fox

soil to 4330 mg C kg-' in Brandon soil amended with 100 kg N as composted manure. In

Brandon soi& inorganic N and manure Vicreased the potentially respired C. The higher rates

of both composted and stockpiled manure resulted in higher Co values, with composted

manure giving the higher values at both N rates.

The rate of C respiration as measured by k values ranged from 0.004 day" in Brandon

soil with inorganic N amendment, to 0.016 day" in Brandon soil control. Treatment effects

were found only with Brandon mil. In the Brandon suil, the k values with manure amendment

were between the values obtained in the control and inorganic N amended soi].

The C M ratio of potentially respired C and mineralbble N ranged from 32.2 in

Brandon soii amended with 100 kg N as composted manure, to 1 1.9 in the Brandon wntrol

soil.

Cumulative respired C foliowed a pattern similar to rnineralized N. Vaiues in Brandon

soil ranged fi-om 533 mg U k g in inorganic N amended soi1 to 2580 mg C k g in soi1 amended

with 100 kg N as composted manure. These high and low values were significantly different

fkm the cumulative C measured in the other treatments.

The cumulative C respired as a percentage of the total C measured in the soil varied

from 2.79% in soi1 with inorganic N amendment to 7.50% in soi1 with 100 kg N as composted

manure.

The T groupings and least significant difference values of cuniulative N and C for

Brandon soil (Appendk 8.5) indicate that the different treatments maintain consistent rank

through the length of the experiment.

Wression~

Regressions of rnean treatment values indicated significant effects of percent N on

percent C, WSOC on No, WSOC on MBC, initial N on No, and MBC on No. For regressions

run on individual plot values, significant effects of %C on summed rnineralized C and %Y on

%C were noted (Appendix 8.6, Figures 5.1, 5.2, 5.3, 5.4, 5.9, S. 10, 5.1 1 ). Mineralizable N

rates were related to clay content, but not to N or C content arnong the soils (Table 5.1).

WSOC had a significant effect on potential and cumulative mineraiized N (Figures 5.2,s .3).

MBC had a significant relationship with N, (Figure 5.4). Values of k were related to clay

content (Table 5. l), but not total C or N.

MANOVA for within subject eEects showed that time and N rate by time interaction

were significant for N mineralization measured on Brandon, Chicot, and Ste. Rosalie soils.

The univariate tests of hypothesis show that N mineralization rates changed with different N

rates ( Appendix 8.7).

There were significant between subject effects on N rnineralized for soi1 type and N

rate, indicating effects of added N on mineralization rates were different among soil types.

Correlationg

Correlation showed differences among soils, except for organic C and total N, total

N and initial NO,-N, initial NOrN and cumulative N mineralled, and initiai C respired and

cumulative C respired relationships (Appendix 8.8).

Discussion

The net N minemlized increased with increasing WSOC, MBC, and organic C in the

soil. Total net N mineralized, at 3 1 -8 to 160 mg kg-', was simüar to published values. Liang

et al. (1995) obtained values of 71-89 mg kg" for N rnineralization on Brandon soil.

Beauchamp et al. (1986) obtained values of 55*5 mg kg'' for air-dried Conestogo Ioam

planted to mm. EUert (unpublished data) obtained values of 52 mg kg-' in the plow layer of

a cultivated Gray Luvisol (Gregorich et al., 1994).

The net N mineralization of finer textured soils was greater than more coarse soils,

which is in contrast to other studies (Catroux and Schnitzer, 1987). Muieraiization of organic

matter has been reported to occur more rapidly in sandy soils than clay soils (Campbell et ai.,

1982; riessen et al., 1983; Hassink et ai., 1990; Ladd et al., 1 990). Sandy soils have greater

aeration. They are ais0 poorly protected fiom aggregate dismption upon cultivation (Van

Veen et al., 1981; Campbell et al., 1987). Clay soils may have been reported to have slower

rates of mineralization, possibly due to greater physical protection of SOM and MB by clays

(Balesdent et al., 1988).

ln this study, the soils with the high manure input had the highest rate of N

mineralization across al1 the soils and heatrnents. Based on the C to N correlation, this could

be due to the effêct of C that was added to the soil dong with the N in the manure (Hébert

et al., 1991; Johnston et al., 1991).

On Brandon soil, the net N rninerdized was related to total N as welî as to type of N

amendrnent, similar to studies by Motavalli et al. (1 9%), and Hébert et al. (1 99 1 ). There was

also a positive relationship noted between the net N rnineralized and organic C.

Reports show addition of inorganic fertilizer N promotes minerakation of soil N

(Azam et al., 1991). Treatments with inorganic fertilizer generally had lower measured values

of total N, organic C, WSOC, MBC, N,, C, than did treatments with high organic

additions. This agrees with a study by Johnston et al. (1991), which found that the application

of manure to agridtural soi1 wilî increase C content, but aiso increase the amount of N lost

through mineraiization. Fauci and Dick (1994) found that recent organic inputs greatly

increased MB levels.

The contribution of fertilizer to mineraiized N shows that N, following organic

amendment is greater than the arnount of N applied. For inorganic amendrnent on Ste.

Rosalie soil the impact on rnineralïzation was zero. This would indicate that for the soils

under organic amendment there was a buildup of mineraiizable N.

Azarn et al. (1993) hypothesized that a buildup of soil N could ocair if the applied

organic materiai had a high ligno-ceiiulose content, because this would lead to the

incorporation of indigenous soil N into forms that were less susceptible to rernineralîzation.

The addition of ligno-cellulose in the manure applied to the soii on the Brandon site could

explah the greater quantity of rnineraIizab1e N found, as compared with the sites receiving

only inorganic N. Tiiiage at the Fox site had no effect on mineralizable N or respired C.

This corresponded with studies showing no difference in TOC at any depth with tillage

treatrnents (Angers et al., 1993). However, researchers have found that reducing Mage

intensity can result in maintenance or increase of more labile fractions of SOM. Doran ( 1980)

found that soi1 organic, mineralizable, and microbial biomass N are usually greater in surface

soil receiving no tillage than when residues are incorporated by tillage. Carter and Rennie

(1 982) aiso found that minerahable C and N were significantly greater in sunace soil under

no mage than conventional tillage, although there was no difference in organic C and N. The

findings in this study do not agree with Doran or Carter's results, possibly due to the sandy

texture of these soils which would be minimally afTected by tillage.

The tirst order equation explained cumulative C respired on ail soils, and the

cumulative N mineralized on Chicot, Ste. Rosalie, and Fox soils. The net N mineralization

of Brandon soil was more clearly explained by two zero order equations for each treatment

for the periods of 0-2 1 days and 2 1- 1 12 days (Figure 5 -5 ) . The rapid initial minerd~ation

could be caused by the flush of decomposition after storage (Beauchamp n al., l986), in that

they found about 10% of the soi1 microbial population to be killed by air-dxying, with a

resulting increase in mineralizable material.

Rate constants of N mineralization were found to be related to soil texture. The rate

constants in this experiment were similar to those obtained on Brandon loam by Liang et al.

(1995). Values in that study for Brandon loam ranged fiom 0.033 to 0.050 mg N kg-Id-'.

Stanford and Smith (1972) obtained a mean N mineralization rate constant of O.O%I0.OW,

somewhat higher than this study.

Soi1 type, s pecificdy clay content, will, under cultivation, hprove rnineraiizable N.

TiI1age and inorganic N additions had no effect on mineralizable N. The application of N as

manure lead to a more mineraiiible N than a similar amount of inorganic N. To have high

levels of mineralizable N, conditions that support microbial activity should be promoted, such

as irnproved source of C. Therefore, to maintain high levels of minerahable N, the

application of composted or stockpiied manure should be considered.

Table 5.1 ; Sample site characteristics

Site Brandon n= 18 Ste-Rosalie Chicot Fox n=8 n= 16 n=8

PW 6.5 (0.34)' 6.2 (0.37) 6.0 (0.42) 5.9 (O. 11)

Silt (%) 30 19 22 6

Sand (%) 42 1 O 50 88

Total Cw 27.5 (8.40) 29.6 (2.33) 15.8 (1.38) 7.70 (1 .13) (&3 kg-'1

Total N"' ( f i kg") 2.28 (0.694) 2.6 (0.489) 1.44(0.160) O. 5 13 (0.0835) ()' standard deviation YpH in watcr "total C and N measured by dry combustion

Table 5.1; Sample site ch~racteristics

Site Brandon n= 18 Ste-Rosalic Chicot Fox ii=8 n=16 n=8

-- - - -

PW 6.5 (0.34)' 6.2 (0.37) 6.0 (0.42) 5.9 (O. i 1 )

Clay (%) 28 7 1 28 h

Silt (%) 30 19 22 6

Sand (%) 42 1 O 50 88

Total Cw 27.5 (8.40) 29.6 (2.33) 15.8 (1.38) 7.70 (1 .13 ) (8 kg') TotalNW(gkg") 2.28(0.694) 2.6 (0.489) 1.44(0.160) 0.5 13 (0.0835)

()' standard deviation 'pH in water "total C and N measured by dry combustion

Tabie 3.2. Eyrûmntai fertîiizaiion and tillage

Soi1 Fcrtilizcr application Fcrtilizer rates Ckhcr mtmcnts TiUagc

Brandon I m CHumïc Gl-1)

Ste-Rode clay (EiUIZUc G l e p L )

Chicot sana clay Iœm (Gray Broun h i s o l )

Fox Ioamy sand (Gray Brown hisQ1)

AW banded at 6-leaf stage (raid-J une) Manun: appIied and incorporatexi in spring

170 kg N ha-' =il- incorporated urea at planting 1 15 kg N ha" side- dress early Iune I l 5 kg N hà' si&- dress late Jurie

Same as Ste. Rosalie

Solid mer (5-10-30) at seeding 150 kg N ba" U N injeded at bleaf stage

P n v - faH afler han- moIdboard plough 0.20 m de@ Scconàaty- spring disc harrow 0.10 m depth spring tooth hanow

Rimry- fa11 after hanest molciboard plough 0.20 rn depth W n d a r y - spring Triple- K dmsbank cultiwor 0.10 rn depth

Samc as Ste. Rosalie

0.9 kg ha" Comentional tiilage- &phosate in sprhg moldboard plough May 0.15 m Qptb, c k

barrow0.10 mde@h Netiüage- fluted coulter. double-disc planter

'Ammonium nitrate Wrea ammonium nitrate

% - C O -

$ $ -.OV NS

Table 5.3 continueci

Chicot

285 O 2.980 a 30.6 a (2.26) 10.2 b 0.075a 0.60% (0.263) (O. 1137)

400 O 2.750 ab 29.3 it (2.95) 8.09 ab 0.109a 0.521b (O. 173) (4.6 1)

170 4' 1.350 a 15.3 bc 11.3 û 0.064a 0.3 76a (O. 173) (1.59) (2.53)

Fox no-till 200

Fox conventional till 200 0.525 a 7.93 a 147 a O.01Ja 0.200a (0.0957) (1.02) (0.3 11)

'water soluble organic C; Ymicrobial biornass C '"Means followed by the same letter at any one site are not significanily different ai the 0.05 probability levcl using the leasi significant diffcrcncc tesi; " standard deviation; 'stockpiled manure; 'composted manure < manure added from 1984 to 1988

Table 5.4; Regression equations and coefficients of determination for linear regression of cumulalive N wiih tirne of Brandon soi1 from long-term corn fertilizer experiments.

N addeà Linear regression equation R2 Linear rcgression equation R~

kg N ha" Day 0-2 1 Day 21-1 12

lOOC N,2.72t+43.4 0.574 Nw=0.657't+82. 4 0.618 XN ,, N mineralized, t time in chys. Ystockpiled rnanure. "composted manwe. 'significantly dinerent fiom other regression coenicients ai P<O.O5.

Table 5.5; Soil potentially mincralizablc N and rcspircd C in soils froni long-tcrm corn fcrlili~cr çspcriiircnts.

Soi1 W d N Added N: No1 hid kY Co'" Co ha1 k' C:N rnanure

kg N ha" Mg ha" mgN kg" kg N ha" &y" mg C kg" kg C ha.' &y"

Brandon O O 66,7 160 0.024 795 1910 0.0 16 11.9

Ste-Rosalie al1 treatrnents 87.3 209 0.018 1990 4780 0.007 22.8

Chicot al1 treatments 4" 58,6 152 0.02 1 1450 3 770 0.000 24.5

Fox al1 treatments 30.3 84.8 0.048 467 13 10 0.008 15.4

wtentially mineralizablc N; N,-N.(l+~lb); Ypotcntial N mineralization raie wpotentialiy respired C; C,=C.(lr"); 'potential C respiration rate; 'manure added from 1984 to 1988; 'approsimate values for 1 hectare roi1 of 20 cm W h 0% ha")

Table 5.6; Cumulative C respired and N mineralized from long-term corn fcrtilizer eqxriments on Brandon Ioam as percentage of total N and organic C content of soil.

N added Manure added NpX C,,J % of total N % of total C C/N

kg N ha" Mg N ha" -..----mg kg"--.--

LSD 34.3 000.3 1

(19,9) a (603) a Lnimulative N rnineralized; Ycumulative C respired; " standard dariaiion "means followed by the same letter are not significantly àifferent at the O 05 probability level using the least signifiant diffennce test. SU stockpiled manure Ct compostcd manun

Table 5.7; Contribution of fenilizer to mineralized N in soils from long-term corn fcnilizcr esperiments.

Soi1 N added Manure added Change in mineralized N as a percentage of applied nutricntz

Brandon

1 O0 2 8 213 'measured as ([minemlized N(trea tmen t ) -mineralized N(cont rol)]/N applied) x 1 00

Soil organic C g kg-' Figure 5.1. Relationship of soi1 total N to organic C in experimental soils.

Water soluble organic C g kg-'

Figure 5.2. Relationship of water-soluble organic C to potentially mineralizable N on soils from long-term corn fertilizer experiments.

WSOC

Figure 5.3. Relationship of water-soluble organic C to cumulative N mineralized in soils from long-tenn corn fertilization experiments.

Microbial biomass C g kg"

Figure 5.4. Relationship of microbial biomass C to potentially mineralizable N in soils from long-term corn fertilizer ex~eriments.

l

i 0 O kg N ha-' 1 ! i W 200 kg N ha-' 8

1 I A 50 kg N haS' stockpiled manure

!

' r 100 kg N ha" stockpiled manure 1 i 50 kg N ha-' composted manure 1 100 kg N ha1 cornposted rnanure 1

O 20 40 60 80 1 O0

tirne (days)

Figure 5.5. Comparison of cumulative N m ineralization from long term corn fertilizer experiments on Brandon soil. Bars indicate standard error. Bars at bottom of graph indicate least significant difference.

O kg N ha-' Ste. Rosalie 170 kg N ha*' Ste. Rosalie 285 kg N ha-' Ste. Rosalie 400 kg N ha-' Ste. Rosalie 170 kg N ha*' Chicot 400 kg N ha-' Chicot Delhi 200 kg N ha-' no-till Delhi 200 kg N ha-' conservation till

O 14 28 42 56 70 84 98 1 1 2 1 2 6 1 4 0 1 5 4

Time (days)

Ste-Rosalie

Chicot

Delhi

Figure 5.6. Cornparison of cumulative mineralizable N from long-term corn fertilizer experiments on Chicot, Ste. Rosalie, and Fox soils. Bars indicate standard error.

O treatment 1 (O kg N ha-') W treatrnent 3 (200 kg N ha-') A treatment 4 ( 50kg N ha-' stockpiled manure) v treatment 5 ( 100 kg N ha-' stockpiled manure)

treatment 6 ( 50 kg N ha-' composted manure) treatment 7 (100 kg N ha-' composted manure)

U i 1 1 1 I I 1

O 20 40 60 80 1 O0 120

Time (days)

Figure 5.7. Cumulative C respired from long term corn fertilization experiments on Brandon soil. Bars indicate standard error.

O 14 28 42 56 70 84 98 112 126 140 154

Time (days)

Figure 5.8. Cumulative C respired from long-term corn fertilizer experiments on Chicot, Ste. Rosalie,

C and Fox soils. Bars indicate standard error.

O 5 10 15 20 25 30 35 40 Initial N mg kg-'

Figure 5.9. Relationship of initial N to potentially mineralizable N on soils from long-term corn fertilizer experiments.

Water-soluble organic C g kg" Figure 5.1 0. Relationship of water-soluble organic C to microbial biomass C in soils from long-term corn fertilization experiments.

Soil organic C g kg-'

Figure 5.1 1. Relationship of soi1 organic C to cumulative C respired in soils from long-term corn fertilization experiments.

Chapter 6

General Conclusions

The CC rnethod recorded higher denitrification values than the SC method.

Consequently, the CC method seemed to be more sensitive to treatment effects than the SC

rnethod. Soi1 moisture and soil NO,-N had signifiant relationships with denitrification

measured by both methods.

Results indiateci that increased denitdication was a result of fertilizer N applications,

precipitation events, and no-till management. The addition of N fertilizer will triple or

quadruple the rate of denitrification detected as cornpared to the control. On the Omstown

soil no-tillage doubled the rate of denitrification, fkom 200 to 400 g N ha-' h-' at it's highest

point. However, variation between soils was considerable, and generalizations would have

to be made with caution. Management with conventional soi1 tiilage and N fertilization as low

as possible would seem to be beneficial for reduction of greenhouse gases.

N mùieraiization is higher under high rates of organic fertilizer addition. Tiilage and

inorganic f m addition seems to have no effect on N mineralkation. Therefore, to build

up the rnineralizable N in a soil, organic, rather than inorganic, sources of N must be added.

Both denitrification and heraiization Vary with soil type. Clay content, which would

affect the aeration and ability of a soi! to hold N, had significant relationships with

daiitrification and rnineraliition. Chicot soil, a sandy clay loam, had lower mineralizable N

and rates of denitnfication than Ste. Rosalie, a clay soil. Soils wiîh high rates of N loss

through denitrification appear to have higher rates of mineralkition as well. Therefore, a soil

losing N through denitnfication will possibly have a high mineraiization potential.

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Appendices

Appendir 8.0a. Analysis of variance of denitrification values measurcd owr the growing season by ihe closed chamber method on the Chicot soi1

Source DF Sum of squares M a n F value Pr) F C.V. square

Model 90 8488 154 943 12 2.67 0.000 1 230.0

Error 9 1 32 14302 35322

Comted total 18 1 11702457

Source DF ?Spc III SS mean F wluc Pr) F square

Replicatc 3 98 188 32729 O. 93 0.43 13

Sample 12 &te

Sample x rep 36 2060490 57235 1,62 0.0343

N rate 3 222565 74 188 2.10 0.1057

sample x N rate 35 1 2 99909 37140 1 ,O5 0.4129

Appendix 8.0b Analysis of variance of denitrification values measured over the growing season by the soi1 core incubation method on the Chicot soi1

Source DF Sum of squares Mean F value Pr) F C.V.

Correctecl total 123 982822

Source DF Type III SS mean F value Pr> F squrc

Replicate 3 3625 1 12083 5.6 1 0.00 18

Sample date 8 540854 676606 31.41 0.000 1

Sample x rep 24 88586 369 1 1.71 0,0462

N rate 3 1 1896 3965 1.84 0.1487

Sample x N rate 22 3 72 85 1694 0.79 0.7282

Appendix 8.0d Analysis of vnriancc of dcniirificution values mciisurcd ovcr thc growing scmon by iIic soil corc incubation mcthod on thc Sic-Rosulic ( 1) soil.

Source DF Suni of Mcaii sqwurc F wiuc Pr) F C.V. S(IUi1TCS

Modcl 62 65 1752 IO5 12 3 .OH O . 000 1 83.7

Error 8 1 214016 2042

Corrcctcd total 14 3 HbS700

Sourcc DF Typc I l l SS nicün sqiiurc F vliliic Pr? F

RepIicatc 3 30998 10332 3.91 0,O l 1

Samplc &tc 8 330755 4 1344 15.65 0.000 1

Samplc x rcp 24 99832 4159 1,57 O. OOU

N ratc 3 25280 8429 3 . 1 9 0.02tS

Samplc x N rntc 24 l(i4H70 6809 2.60 0,000 1

Appleadix 8.W Analpis of variance of&nilrification values rneasurcd mer the g M n g smson by thc closcd chambcr method on the Orrnstown soi1

Moclel

E m r

C o m c d total

Source

Sample &te

Replicate

Till

Rep x ?dl

Sarnple x till

Rotation

Sample x rot

Tdlxrot

N rate

Sarnple x N rate

Ti x N rate

Rot x N rate

3 36û59 1

782642

4 143233

T)pc III SS

2539335

9484

89730

1181

365205

37736

166378

35535

12885

54180

30015

161%

65893

3932

mean square

523222

9484

89730

1181

6087

i 8868

13683

17717

6442

45 15

15007

16.75

F value

107.61

2.4 1

22.82

0.30

15.48

4-80

3.53

4.5 1

1 . 6 4

1.15

3.82

Appcndix 8-Of Analysis of variance of denitrification valucs measured ovcr the growing season by soi1 core incubation mcihd on thc Ormstown soi1

S o m DF Sum of squarcs Mcan F value Pr) F C. V.

Modcl

E m r

Corralcd total

Source

Sample date

Rcpticate

Till

Rep x till

Sample x tili

Rotation

Sample x rot

Till x rot

N rate

Sample x N rate

Till x N rate

333442

267506

600948

Type III SS

233255

3732

5728

156 1

9 165

748 1

33232

2329

6228

11697

1 1329

7282 Rot x N rate

Mode1

Error

Corrected total

Source

Sample date

Replicate

Till

Sample x tiil

Rotation

Sample x rot

N rate

~ppendi s 8.0s Anslysis df variance of denitrifiwtion values mearured b) the clowd ehambcr mîihod oreçr ~ h e growing season on the SieLRosalie (2) soi].

1

Source lx 1 Sum of Mean Fvalue PdF C.V. l squares square

2994 13.65 0.000 1 78.6

219

mean Square

16062

2

349

101

71 9

944

1593

885

F value

73.20

0.0 1

1.59

0.46

3.28

4-30

7.26

4 .O3 raie

1

l

Appendis 8.lb Analysis of variance of temperature values over the growing season for the Ste. Rosalie (2) soi1

Source DF sum of squares mean square F value Pr) F C.V.

Mode1 36 1519 42.19 68.96 0.0001 5,050

E rror 92 56.29 0.61 19

Corrected total 128 1575

Source DF Spe III SS mean square F value Pr) F

sample pericxi 5 1470 294.0 480.6 O ,000 1

*eP 1 0.2534 0.2531 0.4 1 0.5215

till 1 3.097 3.097 5.06 0.0268

sample X till 5 14.23 2.847 4.65 0.0008

rot 2 0.06483 0.03242 0.05 0.9484

sample X rot 1 O 4.548 O. 45.18 0.74 0.682 1

N 2 0.4643 0.2322 0.38 0.6853

sample X N 1 O 1.959 O. 1959 0.32 O. 9740

Appendix 8.2a Analysis of variance of water-fiiled pore space values over the growing season for ihe Ormstown soi1

Source DF Sum of squares Mean F value Pr) F C.V.

Mode1

Error

Corrected total

Source

Sample pend

R ~ P

Till

Sample x till

Rot

Sample x rot

N

6 1727

855.39

62582

Type III SS

6 1475

2,7168

6.6624

40.366

25.236

167.07

0.997 15

1285.98

3.579

m a n square

8782.2

2.7168

6.6624

5.7667

12.618

11.934

0.4985

359.3 1

F value

2453.8

0.76

1.86

1.61

3.53

3.33

O, l-l

Pr) F

sample x N 14 8.4 147 0.6010 O. 17 0.9998

Y2DE S2IXi

0.355 a*.

0.41 1 8..

0.752 ***

0.373 8..

SS

NS

YS

3s

YS

0.439 W..

0.527 8..

0.392 0.516 NS NS !CS 35 0.364 0.494 o.ng s s *** *** m.. I.. B.*

O . ï93 O 921 S S SS SS 0.763 O. *II 8.. 8.. 0 8

SS SS SS 0.723 O. m.. m.

Appeadu 8.4. Mean valus. T groupings and least significant M k m œ ofcumulatht m i d w z d N and C on the Brandon soi1 (data for figura 6.1.6.2. and 6.3)

T r e a m i (kg N ha-"

LSD 93.0 117 180 319 514 639 7% 801 900

Treatment (kg S ha-1)

Appendix 83. Regression values for mineralizi~tion study

relationship bo bl b2 r2

Regression on treatmcnt mean values

Ntotal vs. No 64.4 61.3 O. 148

Corg vs. Niotal 4.03

WSOC va. No 36.8

WSOC vs. MBC 171

INITIALNvs.No 49.1

50,7

MBC vs. No 16.3

25.2 0.09 13 4.6 1 O. 770

Rcgrcssion on individual plot values

O/oN vs. SUM N 26.8 24 1.4 0,338

SUM N vs. SUM C 155 11.8 0,484

22.7 15.2 -0.0 172 0.486

%C vs. SUM C -254 555 0.737

iNiTIAL N vs. 50.3 SUM N

O/d3 vs. SUM N 12.0 26.9 0.497

Appeadir 8.6% Rcpcatcd rntxmms anaiysis of variancc for N rnincrdizcd in Chico~ Stc. Rosalie. Fox ruid Brandon soils. Univariate test of hypothcscs for wiihin subjcct cffccts

Souce D.F. F-Value Pr) F Adj. Pr, F

G-G H-F

Time 9 34 0.000 1 0.0001 0.0001 Greenhouse-Gei sscr Epsilon = 0.3 139

Time x soi1 18 1.6 0.0718 O. 1743 O, 1427 Hm-Feldt Epsilon = 0.4600

Time x N rate 72 4.8 0.000 1 0.0001 0.0001

Appendix 8.6b Repeated measUres analysis of variance of contrast variables for N minecalizd in Chicot, Ste. Rosalie. Fox and Brandon soils.

&der Source D.F. F-Value Pr) F

Time x 1 Mcan 1 61 0.000 1

Soi1 2 0.3 1 0.7378

Time x 2

N rate 8 9.5 0.000 1

Soi1 2

N rate 8

Timex3 Mean 1

N rate 8 3.80 0.0032

~ ~ ~ e n d i i 8.7a Pearson correl~tion coenicien~s for soils from long-tem corn fertilizer t?xperiments.

l

I Nuiiai Clnul WSOC MBC N,

WSOC I .869** .814**

TOTMM NS .830** .924*+ .905** .Y38+* C I

*, T * represent significant at PC 45, .01, NSI not significant N,h tom1 N percent of dry soi1 weight Cm/,, total C percent of dry soi1 weight WSOC water soluble otganic C MBC microbial biomass C No tential mineralimble N PO kN N mincraliwtion ratc Co ptential rninenlizable C kC C mineralization rate T O ~ MIN N rurnrned N rnineralized by &y 1 19 of incubaion T V MIN C summed C mineralized by day 1 19 of incubation

Appendir 8.7b Pearson correlation mficients of measuremcnts from long-term corn fertilizer cxpcrimcnts on the Brandon soil.

~~ PH initial initial C summed surnmed C NO,-N rcspircd N03-N min.

min.

Initial C respired O.S16* 0.915***

CumuIative N 0.536* mineralkaF

'ovcr initial 7 days Yover 1 12 days

Appendix 8.7~. CornlaLion of mcasurerncnts from long-term corn fertilizer e.uppcriments on the Stc- RosaIie soil.

Gota, PH initial N initial C summed summed C (leached) (=Pi&) NQ-N min

min.

Nt, 0.617* -0.5 t3* 0.0526 4. 114 0.019 4.0050 NS NS NS NS

initial N (leacheci)

summed N 0.346 min. NS

Appendix 8.7d. CorrcIation of masurcmcnts from long-km corn fertilizcr e'cperiments on the Chicot mil.

initial N (Icac hed)

surnmed N 0.274 min. NS

Appendu 8 . 7 ~ Comlation of mmsutcments h m long-krm corn fertïhcr eqxriments on the Fox mil.

LI PH initia1 N initiai C s~nmed summed (lcached) (respire4 NQ-N min. C min.

initiai N Oeachcd)

\

Appendix 8.8

N Fixation

N fixation is the reduction of dinitrogen gas (N3 to amrnonia (NH,). N fixation is not

accomplished by plants, but micro-organisms which may or may not be associated with plants.

N - h g organisms are found in a variety of associations. They rnay be in symbiosis,

ie. Rhizobium-legume, Fmikia-woody non-legume; they rnay be in an associative

morphological involvement, such as iichen (fiingus, bhe-green bacteria and green aigae); they

may be found in the rhizosphere or phyllosphere of plants, or they rnay be in the soil but not

in association with a plant. N is aiso fixed uidustnally by the Haber-bosch process to provide

N for fertilizer. Pratt (1977) estimated the quantity of N fixed each year to be 237 MT. N

fixation in agiailturai systems and industrial production are responsible for almost 40% and

25% of ali N fixed respectively.

Nitrification

Nitrification is the oxidation of ammonium to nitrate.

NH4'+2O2-N0,'+2H'+H,O

This readon takes ammonium, which rnay be volatile but not leached as amrnonia, and forms

nitrate, which is kachable. Also, this reaction wili decrease pH. This is important in

agricultural systems, for applied fertilizer in the forrn of NH,-N rnay be lost through

nitrification and subsequent leaching (Angle et ai., 1993).

Denitrification

Denitrification is the reduction of nitrate (NO;) or nitrite (NO;) to NO, Ntrous oxide

(Nfl), or dinitrogen gas (NJ. This reaction will increase pH. This reaction involves the inner

membrane and periplasm of denitri@ing bacteria.

4N0,'+4H++5CH20 - SCO2+2N2+7H,O

This is a multistep reaction.

Immobilization and Mineralization

Organic residue such as sewage sludge, manure, and plant and animal material rnay

be taken up and immobilized by rnicrobial organisms, becoming part of their tissues. Organic

nitrogen can be mineralized t o fonn inorganic soü nitrogen. The diverse matenal is broken

down by enzymatic digestion and hydrolyzed. The end product is arnmonia. For instance;

R-M12(îmino uxnhimtion)+HOH- R-OH+Ml,+energy

2 N H 3 + ~ 2 C ~ , - ~ , ) ~ ~ , ~ 2 ~ , ' + C 0 , L '

(from Brady, 1 984)

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