Impacts Of Soil Tillage And Nitrogen Fertilization With Straw Incorporation On Rice Yield And Greenhouse Gas Emission In Northeast China

Proper management under straw incorporation in paddy fields for lower greenhouse gas emission（GHG）and high crop yield is of importance in the single rice cropping system of Northeast China.The comprehensive effect and mechanism of different tillage and N fertilization management with straw incorporation on rice yield and yield components,GHG emissions in paddy field,straw decomposition and soil properties were assessed in both pot and field experiments in Minzhu experimental site of Heilongjiang Academy of Agricultural Sciences.Different tillage methods namely reduced tillage with straw（RedT+S）,rotary tillage with straw（RoT+S）,plough tillage with straw（PT+S）and conventional tillage of plough tillage（PT）as the control were investigated.The N fertilization experiment was conducted by taking with（S）or without straw incorporation（NS）,as the main factor and nitrogen fertilizer applications with 0（N0）,150（N1）,180 kg N ha^-1（N2）,as the secondary factor,making 6 treatments in total.The main results were as follows:（1）In the tillage experiment,plough tillage with straw was effective in reducing CH₄ emissions while maintaining high yield.Compared to plough tillage（PT）,the other treatments stimulated rice yield by-6.8%-3.2%,while increasing both the area-scaled and yield-scaled emissions by 19.0%–56.3%and 14.2%–59.4%respectively.Compared to RedT+S and PT+S,RoT+S reduced cumulative N₂O by 26.6%–31.2%in 2019 and by 18.1%-66.6%in 2020.Compared to Red+S and RoT+S,PT+S decreased the yield-scaled emissions by 9.7%-51.6%in 2019,and by 8.3%-21.4%in2020.Results of the pot experiment were similar,with the highest and lowest significant rice yield recorded in 14-21 cm and 0-7 cm straw depth respectively.（2）Nitrogen application rates of 150,180 kg N ha^-1 both produced significant increases in rice yield,and CH₄ emission,total GHG emission and GHGI tended to reduce with the increasing of nitrogen application.Whether straw incorporated or not,the N1 and N2 treatments both increased rice yield compared to N0.A 5.6%and 9.4%decrease in cumulative CH₄ emission was noted when N fertilization was increased from 0 to 150 kg N ha^-1 respectively in straw incorporated plots of 2019 and2020.Increasing N rate from 150 to 180 kg N ha^-1 decreased cumulative CH₄ emission by 55.8%and57.2%,respectively.Area-scaled emissions of SN1 and SN2 decreased by 15.3%and 60.8%respectively in 2019 while in 2020 it decreased by 14.4%and 58.5%respectively compared to SN0.Straw addition in 2019 triggered a 37.3%decrease in yield-scaled emission between SN0 and SN1while decreasing yield-scaled emission by 55.7%between SN1 and SN2.In 2020 straw incorporation decreased yield-scaled emission between SN0 and SNI by 50.2%while a 54.1%yield-scaled emission decrease was noted between SN1 and SN2.（3）The soil nutrient content,straw decomposition rates as well as microbial abundance related to CH₄ emission（methanogenic and methanotroph）were all decreased with increasing soil depth.Total N content of the tillage with straw decreased with increasing soil depth while the total N among the straw incorporated tillage varied significantly at 0–10 cm and 20–30 cm soil depths.The straw decomposition rate of Red+T at tillering stage was significantly higher than that of PT+S,RoT+S in both 2019 and 2020.The pot experiment noted similar trends in both years.PT+S recorded 15.5%and36.5%lower methanogenic abundance compared to RedT+S and RoT+S respectively.The methanotroph abundance of PT+S was 22.2%and 33.3%lower than RedT+S and RoT+S respectively.（4）Nitrogen fertilization hastened straw decomposition rates and reduced the methanogenic abundance related to CH₄ emission.Compared to SN0,SN2 significantly increased soil total N and available K.Straw decomposition rate was in the order SN0（65.6%）<SN1（83.3%）and SN2（86.4%）at harvest in 2019 while in 2020 straw decomposition rate was in the order SN0（76.2%）<SN2（81.2%）and SN1（85.0%）.In the straw incorporated N fertilization treatments,increasing N rates from SN0 to SN1 and SN1 to SN2 reduced the methanogenic abundance by 20.7%and 22.9%respectively while increasing methanotrophic abundance by 47.5%and 31.0%respectively.The results of this study suggest that optimized tillage and N fertilization under straw incorporation improves rice yield while mitigating CH₄ emissions by regulating methanogenic activities.In the single rice cropping system under straw incorporation in Northeast China,nitrogen application of 150～180 kg N ha^-1 significantly increased rice yield,and reduced the total GHG emission and GHG intensity.Plough tillage with straw incorporation,is also recommended to reduce CH₄ emission from the paddy field,while maintaining high yield,due to its important role in regulating the straw decomposition and microbial activities related to methane emissions.