Soil Carbon and Nitrogen Dynamics Following Application of Pig Slurry for the 19th

Soil Carbon and Nitrogen Dynamics Following Application of Pig Slurry for the 19thConsecutive Year:I.Carbon Dioxide Fluxes and Microbial Biomass CarbonPhilippe Rochette,*Denis A.Angers,and Denis Coˆte ´ABSTRACTfrom storage and handling conditions (Kirchmann and Lunvall,1993).It is not clear whether information ob-Agricultural soils often receive annual applications of manure fortained from laboratory incubations can be directly ap-long periods.The objective of this study was to quantify the effects of 19consecutive years of pig (Sus scrofa )slurry (PS)application plied to field conditions where many factors simultane-on CO 2emissions and soil microbial biomass.Soil temperature,soil ously affect decomposition.We are not aware of moisture,and extractable soil C were also determined to explain the experimental data describing decomposition rates of pig variations in CO 2emissions and soil microbial biomass.Long-term slurry under field conditions.(19yr)treatments were 60(PS60)and 120Mg ha Ϫ1yr Ϫ1(PS120)of On many hog farms,the land area required to dispose pig slurry and a control receiving mineral fertilizers at a dose of 150of the volume of slurry exceeds the land available.It is kg ha Ϫ1yr Ϫ1each of N,P 2O 5,and K 2O.Very high CO 2emissions (up to therefore common that soils receive slurry every year 1.5mg CO 2m Ϫ2s Ϫ1)occurred during the first 2d after PS application.for long periods of time.The objective of this study was Following that peak,decomposition of PS was rapid,with one-half to quantify the effects of 19consecutive years of pig the total emissions occurring during the first week after slurry applica-tion.The rapid initial decomposition was exponential and was attrib-slurry application on CO 2emissions and soil microbial uted to the decomposition of the labile fraction of the slurry C.The biomass.Soil temperature,soil moisture,and extract-second phase was linear and much slower and probably involved able soil C were also determined to explain the varia-more recalcitrant C material.Cumulative annual decomposition was tions in CO 2emissions and soil microbial biomass.proportional to the application rate,with 769and 1658kg C ha Ϫ1lost from the 60and 120Mg ha Ϫ1doses,respectively.Pig slurry application MATERIALS AND METHODScaused a rapid increase in soil microbial biomass (from ≈100to up to 370mg C kg Ϫ1soil),which coincided with a peak in the concentra-The experiment was conducted from 30May 1997to 27tion of extractable C and in CO 2emissions.Field estimates of the May 1998at the St-Lambert Research Farm of the Que ´bec microbial specific respiratory activity suggested that the difference in Ministry of Fisheries,Agriculture,and Food near Que´bec soil respiration between the two slurry treatments was due to differ-City,Canada (46Њ05ЈN,71Њ02ЈW,altitude 110m).The soil ences in the size of the induced microbial biomass rather than to was a Le Bras loam (frigid Aeric Haplaquept)with 0.31g differences in specific activity.sand,0.42g silt,and 0.27g clay g Ϫ1soil.Soil C and N contents averaged across treatments were 19.9and 1.2g kg Ϫ1,respec-tively,prior to the 1997slurry application.Measurements were made on plots that were initiated in 1979to assess the impact Decomposition of soil organic matter (SOM)af-of long-term application of PS on silage maize (Zea mays L.)fects the dynamics of various nutrients such as N yields and soil properties (N’dayegamiye and Coˆte ´,1989).and P,influences soil physical and chemical properties,Tillage operations were one pass of chisel plow in the fall and and directly impacts the atmospheric concentration of two passes of field cultivator in the spring prior to planting.The CO 2,a potent greenhouse gas (Intergovernmental Panel treatments consisted of annual applications of either mineral on Climate Change,1996;Baldock and Nelson,2000).fertilizer (150kg ha Ϫ1NH 4NO 3–N,150kg ha Ϫ1P 2O 5,150kg Animal wastes are a significant source of organic C for ha Ϫ1K 2O)(control)broadcasted prior to planting (27May agricultural soils.Hog industry produces ≈8.8million1997),or pig slurry at rates of 60(PS60)or 120Mg ha Ϫ1(PS120)banded at the six-to eight-leaf stage (30June 1997)m 3of slurry annually in the province of Que´bec,Canada repeated three times in randomized blocks.In 1997,the slurry (Trudelle,1996).Most of this slurry is applied to agricul-was from a commercial hog and sow operation and containedtural soils either in spring or fall,where it is subjected to 2.1kg m Ϫ3total N,0.99kg m Ϫ3NH ϩ4–N,1.15kg m Ϫ3P,and decomposition by the soil biota.Application of animal 1.29kg m Ϫ3Ca.Maize was planted on 28May 1997at 76000slurry usually increases the size of the soil microflora seeds ha Ϫ1and 0.75-m interrows.Slurry was applied in 0.6-both in the short (Opperman et al.,1989)and long termm-wide bands and shallow-incorporated (0.075m)in each (N’dayegamiye and Coˆte ´,1989;Rochette and Gre-interrow using a liquid manure spreader equipped with drop gorich,1998).tubes and tines mounted on a boom at the rear of the spreaderDecomposition of pig slurry in soils has been studied (Jokela and Coˆte ´,1994).Average maize aboveground dry in laboratory rge variations in decompo-matter yields between 1990and 1995were 7.1Mg ha Ϫ1for sition rates have been observed between slurries (Den-the control,7.9Mg ha Ϫ1for PS60,and 9.3Mg ha Ϫ1for PS120.dooven et al.,1998a,1998b;Morvan and Leterme,1999)(Table 1).These differences have been related to varia-Soil Surface Carbon Dioxide Fluxestions in slurry composition resulting,among other fac-In situ CO 2fluxes were measured by the dynamic closed tors,from animal type (Morvan and Leterme,1999)andchamber method detailed by Rochette et al.(1997)and briefly described as follows.Three acrylic frames (0.60by 0.60m;Philippe Rochette and Denis A.Angers,Soils and Crops Research 0.14-m height;6.35-mm wall thickness)were inserted to a and Development Centre,Agriculture and Agri-Food Canada,2560depth of 0.10m in each plot on 29May 1997.The framesHochelaga Blvd.,Sainte-Foy,QC,Canada,G1V 2J3;Denis Coˆte ´,Institut de recherche et de de ´veloppement en agroenvironnement,Complexe Scientifique,2700Einstein St.,Sainte-Foy,QC,Canada,Abbreviations:MBC,microbial biomass C;PS,pig slurry;PS60,appli-G1P 3W8.Received 1July 1999.*Corresponding author (rochettep@cation of pig slurry at 60Mg ha Ϫ1yr Ϫ1;PS120,application of pig em.agr.ca).slurry at 120Mg ha Ϫ1yr Ϫ1;SOM,soil organic matter;SRA,specific respiratory activity.Published in Soil Sci.Soc.Am.J.64:1389–1395(2000).13891390SOIL SCI.SOC.AM.J.,VOL.64,JULY–AUGUST 2000Table 1.Summary of the dynamics of liquid hog manure decomposition in laboratory incubations.Temperature Duration C loss Remarks Reference؇C d %of added C162417–4313pig slurries Morvan and Leterme (1999)252860Dendooven et al.(1998a)257075Fresh Bernal and Kirchmann (1992)257023Aerobic Bernal and Kirchmann (1992)2570105Anaerobic Bernal and Kirchmann (1992)257065FreshKirchmann and Lundvall (1993)257048AnaerobicKirchmann and Lundvall (1993)25155Dendooven et al.(1998b)2223044Saviozzi et al.(1997)232847Castellanos and Pratt (1981)completely covered the width of the slurry application band late the MBC (Wu et al.,1990).Specific respiratory activity of soil microbial biomass was calculated as the quotient of between maize rows and were left at the same locations for the duration of the experiment.When slurry was applied,the respired CO 2to MBC.For that purpose,MBC was expressed in grams of C per square meter using bulk densities measured tines were lifted to clear the frame and the slurry was deposited at the surface and immediately mixed into the top 7.5cm of soil in 1994(1.24g cm Ϫ3in the control,1.24g cm Ϫ3in the PS60,and 1.30g cm Ϫ3in the PS120plots [M.A.Bolinder,1995,with hand tools.The frames height was measured at regular intervals during the experiment (48measuring points per personal communication]).A fraction of the soil samples was air dried and sieved at frame)to account for variations in headspace due to soil settling.2mm for the determination of soil pH (CaCl 2,0.01M ).Total C and N contents were determined on a Leco CNS 1000The CO 2flux measuring system was equipped with an LI-6200CO 2analyzer (LI-COR,Lincoln,NE)and a 0.15-m-(LECO,St.Joseph,MI)on finely ground (0.05mm)soil samples.high square plexiglass chamber covering the same area as the frames.During each CO 2flux measurement,the chamber was fixed to a frame and the CO 2concentration inside the chamber RESULTS AND DISCUSSIONwas measured once every second during four 20-s successive periods.The mean CO 2flux (F CO2)on each frame was calcu-Soil temperature at 10cm was not affected by the lated as follows:treatments (Fig.1a).In 1997,temperature increased in June,peaked in July,was slightly lower in August (probably as a result of the shading by the maize can-F CO2ϭ͚31΄΂C i ϩ1ϪC i t i ϩ1Ϫt i ΃m m m v VA΅3[1]opy),and gradually decreased in September and Octo-ber.In 1998,soil temperature increased rapidly in May where C i is the mean CO 2concentration during period i (L due to a warm and dry spring.Soil moisture was similar L Ϫ1);t i is the mean time of period i (s);m m and m v are the between treatments and was averaged across treatments molecular mass and volume of CO 2,respectively;V is the total for each depth (Fig.1b).Soil moisture below 5cm re-system volume including chamber,frame,and gas analyzer mained between 0.20and 0.35m 3m Ϫ3during most of tubings (≈68L depending on frame height);and A is the area the study.Water contents above 0.35m 3m Ϫ3were mea-covered by the chamber (0.36m 2).sured in early July 1997following slurry application and Soil temperature at a depth of 10cm inside each frame and abundant rainfalls in the fall of 1997and in the spring volumetric water content at depths of 5,10,20,and 40cm of 1998(Fig.1b).(one profile per plot)were measured at the time of the CO 2flux measurements.Soil temperature and soil moisture were measured using copper-constantan thermocouples and time Carbon Dioxide Emissions in the Control Plotsdomain reflectometry probes,respectively.The effects of Soil surface CO 2fluxes in the control plots receiving treatments were analyzed at each date using a two-way analysis of variance (SAS Institute,1989).mineral fertilizer were exceptionally low throughout the experiment (Fig.2).Values above 0.05mg m Ϫ2s Ϫ1were measured only between 15July and 15September when Soil Analysesthey reached a maximum of 0.09mg m Ϫ2s Ϫ1.In compari-Soil samples were collected from the 15-cm surface soil son,Gregorich et al.(1998)and Rochette and Gregorich layer 19times during the experiment.Samples were sieved in (1998)reported values up to 0.21mg m Ϫ2s Ϫ1for miner-the field at 6mm and stored immediately at 3ЊC.Soil microbial ally fertilized grain maize fields in Ottawa,Canada.Low biomass C (MBC)measurements were carried out within 24h F CO2in the control plots has to result from the low of sampling using the chloroform fumigation–extraction tech-nique (Wu et al.,1990).Two 50-g subsamples of field-moist activity of one or both main CO 2sources:the oxidation soils were placed in 100-mL beakers.One subsample was of soil C by heterotrophs and the root–rhizosphere res-fumigated for 24h at room temperature in a vacuum desiccator piration.The activity of heterotrophs is driven by the containing 25mL of CHCl 3.The other subsample was kept availability of substrates and is modulated by the envi-in the dark at 3ЊC for 24h.Both fumigated and nonfumigated ronmental conditions.Under conditions of abundant soils were extracted with 100mL of 0.25M K 2SO 4.After substrates and sufficient moisture,respiration is strongly shaking for 1h on an oscillating shaker,the suspensions were correlated with soil temperature (Rochette and Gre-centrifuged at 1000g and filtered.The organic C content of gorich,1998).In the control plots,respiration values the extracts was determined by UV-persulfate oxidation on were weakly correlated with soil temperature (r ϭ0.35,a DC-180Carbon Analyzer (Dorhman Co.,Santa Clara,CA).An extraction efficiency (K ec factor)of 0.45was used to calcu-P Ͼ0.1),thereby suggesting that respiration was limitedROCHETTE ET AL:CARBON DYNAMICS AFTER19YEARS OF PIG SLURRY APPLICATION1391Fig.1.Temporal variations of(a)soil temperature at a depth of10cm for maize soils amended with mineral fertilizer(control)and pig slurry at60(PS60)and120Mg haϪ1(PS120)and(b)soil moisture at depths of5,10,20,and40cm averaged across treatments.by the availability of organic substrates and was domi-tend to converge,so that the amount of stored C is nated by root–rhizosphere respiration.relatively static(Janzen et al.,1997).After19yr of The amount of organic C that is oxidized in the soil uniform tillage and cropping practices,one can assume annually by heterotrophic respiration can be estimated.that the soil C is near equilibrium and that the amount With time,the rates of input and loss of C from soil of C that is oxidized annually is approximately equal toFig.2.Temporal variations of CO2flux from maize soils amended with mineral fertilizer(control)and pig slurry at60(PS60)and120Mg haϪ1 (PS120).Mineral fertilizer was applied on29May and pig slurry on30June1997.1392SOIL SCI.SOC.AM.J.,VOL.64,JULY–AUGUST2000Fig.3.Slurry-induced CO2–C losses from maize soils amended with pig slurry at60(PS60)and120Mg haϪ1(PS120).Pig slurry was applied on30June1997.the amount of C that is returned to the soil.The average during these first2d.Carbon dioxide is produced in aboveground yield of the fertilized silage maize(con-slurry during storage by the hydrolysis of urea and the trol)between1990and1995was7.1Mg dry matter anaerobic decomposition of volatile fatty acids(Som-mer and Husted,1995).The CO2in solution forms pH-haϪ1(Coˆte´et al.,1996).Neglecting the contribution ofstubble and assuming a root/shoot ratio of0.2and a dependent chemical equilibriums(carbonates)with plant residue C content of40%,570kg C haϪ1wereother species such as NH3(Sommer and Husted,1995). returned as crop residues annually.The oxidation of The pH of the slurry was≈8,while that of the surface this amount of C in the growing season(150d)corre-soil was5.69Ϯ0.13in PS60and5.79Ϯ0.15in the sponds with an average flux of0.016mg CO2mϪ2sϪ1.PS120plots following PS application(1July).These Therefore,the low return of residue C to soil in thisvalues are lower than the threshold(7.2)below which continuous silage maize system can alone explain the ammonium carbonates are dissociated and CO2is re-leased.Ge´nermont(1996)also reported very large car-low F CO2measured in the control plots.Also,consideringthat root–rhizosphere respiration of a maize crop in bonate-induced CO2emissions(1.4mg CO2mϪ2sϪ1) eastern Canada is insignificant prior to1July(Rochettefollowing application of132m3haϪ1of cattle(Bos tau-and Flanagan,1997;Rochette et al.,1999b),most of the rus)slurry under field conditions.respired CO2–C that occurred in June arose from soilFollowing this initial burst,an adjustment phase of C oxidation.Cumulative CO2–C emitted during that≈20d was observed during which the differences be-tween manured and control plots decreased gradually. period corresponded with234kg C haϪ1or41%of theannual return of crop residue C.This indicates that the We postulate that this period reflected the time during contribution of soil C oxidation during the remainingwhich the soil heterotrophs were using up the amount part of the growing season was even less than0.016mg of readily decomposable organic substrates of the PS. CO2mϪ2sϪ1and that F CO2measured from July to the endFinally,the adjustment phase was followed by a period of the season probably reflected the root–rhizosphere of small but fairly constant differences between the ma-nured plots and the control plots.During this period, respiration of the maize crop.This is supported by theobservation that the temporal pattern of F CO2was similar more recalcitrant organic substrates were probably de-composed.The temporal pattern of F CO2from late July to that of the maize crop growth after1July.to the end of1997was the same on manured and control Carbon Dioxide Emissions in the Manured Plots plots,indicating that the temporal variations of the fluxwere governed by factors other than the addition of Values of F CO2on the manured and control plots wereslurry,probably the root–rhizosphere respiration of the similar early in the season when significant differencesmaize crop.(PϽ0.05)were measured only on the last day prior toapplication of PS(Fig.2).Thus,addition of PS in the Slurry-Induced Carbon Dioxide-Carbon Losses 18previous years had little impact on the oxidation ofsoil C early in1997.In contrast,significant differences Slurry-induced CO2–C emissions were estimated bysubtracting F CO2on the control plots from F CO2on the (PϽ0.05)were observed on14of the18sampling datesfollowing the application of PS in1997.The increase in manured plots.For this purpose,only the CO2emissions F CO2resulting from the addition of PS could be split intofrom within the slurry application band were considered. three periods.First,the fluxes were increased by a factor Cumulative slurry-induced CO2–C losses were then cal-culated by linearly interpolating CO2emissions between of10to30compared with background values duringthe first2d following application.These values are very sampling dates,assuming that measurements made be-tween0900and1200h were a good estimator of average high,and CO2release from displacement of physico-chemical equilibrium probably dominated the emissions daily F CO2.The early PS-induced CO2kinetics were simi-ROCHETTE ET AL:CARBON DYNAMICS AFTER19YEARS OF PIG SLURRY APPLICATION1393Fig.4.Temporal variations of soil microbial biomass C for maize soils amended with mineral fertilizer(control)and pig slurry at60(PS60)and 120Mg haϪ1(PS120).Mineral fertilizer was applied on29May and pig slurry on30June1997.lar for both slurry doses,with50,60,and70%of the Microbial Biomass and Activitytotal emissions lost after11,21,and40d,respectively.Despite an apparently higher(50%)MBC content After70d,87%of the total PS-induced CO2was lost in the two PS-amended soils than in the control,the in the PS60plots and82%in the PS120plots.Approxi-differences in MBC prior to the annual PS application mately one-half of the losses occurred during the first(25June)were not statistically significant at PϽ0.05. week after slurry addition(Fig.3).Total losses in1997This indicates that there were no significant long-term from the PS60plots(769kg C haϪ1)were46%of those(18yr)residual effects of PS on MBC.The long-term measured from the PS120plots(1658kg C haϪ1),indi-effect of PS on total C content was not significant either cating a linear response of C oxidation to the amount(17.9,20.6,and20.8g C kgϪ1soil for the control,PS60, of substrate added and suggesting that there were no and PS120,respectively).The field variation in total C physical or chemical limitations to increased microbial content(coefficient of variation of24%,nϭ9on25 activity with increased amount of PS added.Gregorich June)is often high to the point that management-in-et al.(1998)reported a decreasing response of CO2duced differences in soil C content may be difficult to emissions with increasing dose of solid cattle manure detect(Paustian et al.,1997).under field conditions.Differences between the CO2–C The1997annual PS application caused a rapid in-emissions induced by solid and liquid manures can be crease in MBC in early July,which was linear with the explained at least partly by the easier access to the highly rate of application(Fig.4).Laboratory studies have diluted substrates in PS than in solid manure,which shown this rapid increase in MBC immediately follow-usually forms clods in which the inner portions are physi-ing PS application(Saviozzi et al.,1997).The peak in cally protected from the attack by decomposers.MBC lasted only for a few days but the difference be-Fig.5.Temporal variations of extractable C for maize soils amended with mineral fertilizer(control),and pig slurry at60(PS60)and120Mg haϪ1(PS120).Mineral fertilizer was applied on29May and pig slurry on30June1997.1394SOIL SCI.SOC.AM.J.,VOL.64,JULY–AUGUST 2000Fig.6.Temporal variations of specific activity of soil microbial biomass for maize soils amended with mineral fertilizer (control)and pig slurry at 60(PS60)and 120Mg ha Ϫ1(PS120).Mineral fertilizer was applied on 29May and pig slurry on 30June 1997.MBC is microbial biomass C.(Rochette et al.,1999a).In our study,CO 2fluxes and tween the two amended treatments lasted for ≈2mo.MBC were influenced by three C sources:native soil The peak in early July,right after PS application,coin-C,plant activity,and PS.In order to isolate the effect cided with the peak of respiration activity (Fig.2).Jen-of PS from the contribution of plant roots and native sen et al.(1997)studied the dynamic response of MBC soil C to respiration and microbial biomass,we sub-and field respiration to rape (Brassica napus L.var.tracted the values of the control from the slurry treat-napus )straw application and found that MBC did not ments.The values of SRA induced by PS ranged from contribute significantly in explaining the variability of zero or slightly negative to 0.37g CO 2–C g MBC d Ϫ1soil surface CO 2flux.A similar conclusion was reached (Fig.6),which is in the range of values found under by Rochette and Gregorich (1998)using solid cattle laboratory conditions (Santruckova and Straskraba,manure.Our results are in agreement with those obser-1991).vations,except for the period immediately following PS Specific respiratory activity has been used to charac-application when both CO 2flux and MBC increased for terize the effect of disturbance on microbial biomass a short time.The difference between our study and the and its activity.In general,SRA increases following two others may be that PS contains high levels of soluble disturbances such as rewetting of dry soil,herbicide C and this was reflected in an increase in extractable C application,acidification or substrate addition,and de-in the soil following PS application as well (Fig.5).clines following recovery from disturbance (Wardle and Differences in extractable C between treatments were Ghani,1995).The decline would be due to approaching only significant for a few days after PS application (P equilibrium conditions,which would cause the mi-Ͻ0.01on 2and 8July).It is also possible that part of croflora to become more efficient at conserving C.The the increase in MBC measured a few days following PS ratio rapidly increased and declined after PS applica-application be attributable to the presence of microbes tions (Fig.6),which is characteristic of an easily decom-in the applied manure as proposed for compost by Per-posable substrate (Wardle and Ghani,1995).As men-ucci (1990).tioned above,the increase in CO 2flux in the first 2d After a low in mid July,MBC as well as extractable after PS application was probably not of biological ori-C started to increase until early September in all treat-gin and therefore should not be considered in the discus-ments.The high value at that date also corresponded sion on specific activity.However,the high values on with the highest gravimetric soil water content (data not 8July suggest that the higher soil respiration in both shown).Overall,a weak but significant correlation was manured plots (Fig.2)was not only due to the increased found between MBC and gravimetric soil water content size of the microflora (Fig.4)but also its activity.It is (r ϭ0.45;P Ͻ0.01).In October 1997and in the spring noteworthy that both slurry treatments showed the same of 1998,MBC was similar in both slurry treatments as SRA,which indicates a similar efficiency at decompos-it had been similar in the spring of 1997before slurry ap-ing PS and an adaptation of the microflora to the amount plication.of substrate.This observation also suggests that the dif-Higher respiration following addition of PS can be ference in total respiration between the two PS treat-the result of an increase in microbial biomass or its ments (Fig.2)was due to a difference in the size of the activity.Specific respiratory activity (SRA)of the soil microbial biomass and not to a difference in its specific microbial biomass,which is the ratio of the respiratory activity.The SRA quickly decreased after the peak to reach a temporary equilibrium level at 0.02to 0.04g activity to microbial biomass,was calculated to de-termine the relative contribution of these two factors.CO 2–C g MBC d Ϫ1.After 50to 60d following PS applica-tion,the quotient was close to zero,which suggests that Specific respiratory activity has been determined under laboratory incubation conditions (Santruckova and the microflora induced by the addition of PS was not active anymore.Straskraba,1991)but rarely under field conditionsROCHETTE ET AL:CARBON DYNAMICS AFTER 19YEARS OF PIG SLURRY APPLICATION1395Soil carbon dynamics in Canadian agroecosystems.p.57–80.In R.CONCLUSIONSLal et al.(ed.)Soil processes and the carbon cycle.CRC Press,Boca Raton,FL.Our approach allowed the characterization of the Jensen,L.S.,T.Mueller,J.Magid,and N.E.Nielsen.1997.Temporal mineralization of PS under field conditions.The decom-variation of C and N mineralization,microbial biomass and extract-position of PS was rapid,with one-half the total emis-able organic pools in soil after oilseed rape straw incorporation in sions occurring during the first week after slurry applica-the field.Soil Biol.Biochem.29:1043–1055.Jokela,W.,and D.Coˆte ´.1994.Options for direct incorporation of tion.The early decomposition was proportional to the liquid manure.p.201–215.In Proceedings of the liquid manure application rate.The rapid initial decomposition was application systems:Design,management and environmental as-exponential and was attributed to the decomposition of sessment.Rochester,NY.1–2Dec.1994.Northeast Regional Agric.the labile fraction of the slurry C.The second phase was Eng.Serv.,Ithaca,NY.linear and much slower,and probably involved more Kirchmann,H.,and A.Lunvall.1993.Relationship between N immo-bilization and volatile fatty acids in soil after application of pig recalcitrant C material.Pig slurry application caused a and cattle slurry.Biol.Fertil.Soils 15:161–164.rapid increase in soil microbial biomass that coincided Morvan,T.,and P.Leterme.1999.Short-term C and N transformations with an increase in the concentration of extractable C following pig and cattle slurry incorporation in soils.p.113–127In and in CO 2emissions.Field estimates of the microbial J.Martinez and M.N.Maudet (ed.)Ramiran 988th Int.Conf.on Management Strategies for Organic Waste Use in Agriculture.specific respiratory activity suggested that the difference Rennes,France.26–29May 1998.Cemagref Editions,Antony,in soil respiration between the two slurry treatments was France.due to differences in the size of the induced microbial N’dayegamiye,A.,and D.Coˆte ´.1989.Effect of long-term pig slurry biomass and not to its specific activity.and solid cattle manure application on soil chemical and biological properties.Can.J.Soil Sci.69:39–47.Opperman,M.H.,M.Wood,and P.J.Harris.1989.Changes in micro-ACKNOWLEDGMENTSbial populations following the application of cattle slurry to soil at two temperatures.Soil Biol.Biochem.21:263–268.This work was supported by the PERD-Climate Change Paustian,K.,H.P.Collins,and E.A.Paul.1997.Management controls 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