Effects Of Flooding-wetting Events,N Fertilizer,DCD And Rice Straw On Soil N₂O,CH₄ And CO₂ Emissions From Paddy Soils

Nitrous oxide(N2O),methane(CH4)and carbon dioxide(CO2)are main greenhouse gases(GHGs)releasing from arable lands.Anthropogenic and natural processes mainly influence the production and release of GHGs from soils to the atmosphere.Arable lands undergo temporal fluctuations in moisture regimes during crop cultivations that can cause changes in soil properties.Soil moisture/water content is an important soil parameter for microbial activity and processes.Nitrifying bacteria require oxygen residing in soil pores.It can be expected that changes in soil moisture regime can also affect the turnover of carbon(C)and N in soils and thus GHG's.To understand the effect of different water regimes(flooding and wet(60%WFPS))on GHGs emissions from soils,we conducted several laboratory studies.It is hoped that the results could provide scientific basis for exploring the important fundamental scientific and technological issues relevant to GHG emissions from soils.Rapeseed-rice soil and rice-fallow/flooded soil were collected from Xianning city of Hubei province,China.Air-dried soils were treated with different treatments(with and without combination of DCD,fertilizer and organic matter(rice straw))and comparison between continuously flooding,continuously wet and flooding-wet stage which were incubated at constant temperature of 25? in the chamber.Conversion of flooded to wet soil was achieved by using silica gel to absorb water,hanging in the headspace of bottles/jars used in the experiment.Soil sub-samples were taken during all the experiment at regular intervals to analyze soil properties and gas concentrations.Soil pH was determined using pH-meter and ammonium(NH4+-N)and nitrate(NO3--N)concentrations were determined colorimetrically using auto analyzer(Seal,Germany),microbial biomass carbon(MBC)and dissolved organic carbon(DOC)were analyzed using TOC analyzer,concentrations of gases nitrous oxide(N2O),methane(CH4)and carbon dioxide(CO2)were analyzed using gas chromatography.The main results and conclusions are as following.With the change of water regimes flooding to 60%WFPS N2O emissions were markedly increased when compared to continuously flooding or continuously wet level.When soil treated with DCD,the N2O peak produced during conversion of flooding to wet soil was suppressed.Fertilizer addition largely increased the N2O emissions in both water regimes.Nitrous oxide emissions were highly increased in rice straw addition at wet stage when flooding soil was converted into wet condition.Generally,CH4 was absorbed when soil was at low moisture level(wet conditions).However CH4 emission was observed but when soil was under flooding condition.The maximum concentration of CH4 emission was found in rice straw and rice straw plus fertilizer(OM+N)addition i.e.380.241 ?g kg-1h-1 and 298.940 ?g kg-1h-1,respectively.High emission of CO2 was found at the start of flooding stage.After 4 days of experiment CO2 emission declined but it was high when soil moisture changed from flooding to 60%WFPS.Comparing cumulative CO2 emissions from different treatments of rice straw and rice straw+ N fertilizer,higher emissions of CO2 were occurred in in rice straw(OM)treatment which was 65.307 mg d-1.Application of rice straw(OM),rice straw+ N fertilizer(OM+N),N fertilizer(N),and DCD plus fertilizer(D+N)increased DOC and MBC in flooding and wet soil(60%WFPS)conditions.DOC and MBC contents were decreased by addition of DCD.Ammonium and nitrate concentrations were high in N addition(N),D+N and OM+N.Overall,results showed that change in water regime(flooding soil to wet 60%WFPS)increased N2O and CO2 emissions,but decreased CH4 emissions.The change in soil moisture triggered soil organic C and mineral N which subsequently influenced GHG's emissions.Application of DCD mitigated N2O emissions.Application of N fertilizer and rice straw increased N2O,CH4 and CO2 emissions.Results suggest that change in water regime is an important phenomenon for altering greenhouse gas emissions from soils.