Study On Greenhouse Gas Emissions From Cold-region Black Soil Paddy Fields Under Different Irrigation Systems And Straw Return Year

A large amount of straw is produced and a large amount of water is consumed during rice production.Straw return and water-saving irrigation regime are two commonly used field management methods in Heilongjiang Province.They can make full use of straw and reduce the waste of water resources,which is in line with the goal of sustainable development of green agriculture.In addition,paddy field is an important source of greenhouse gas emissions,which is affected by environmental factors in different regions.How to make rational use of straw and irrigation regime is of great significance to reduce greenhouse gas emissions,improve water use efficiency and ensure crop yield.This experiment was conducted in a field experiment at the Qing’an County Irrigation Experiment Station in Heilongjiang Province.Four treatments were used:controlled irrigation combined with one year of straw return（C1）,controlled irrigation combined with five consecutive years of straw return（C5）,conventional flooded irrigation combined with one year of straw return（F1）and conventional flooded irrigation combined with five consecutive years of straw return（F5）.In this study,fluxes of N₂O,CO₂ and CH₄ were measured using a static chamber-gas chromatography,their global warming potential（GWP）and greenhouse gas intensity（GHGI）in terms of CO₂equivalent on a 100-year scale were calculated,and soil physicochemical properties such as soil temperature,inorganic nitrogen,microbial carbon and nitrogen and dissolved organic carbon were measured during rice growth.In addition,this experiment measured the abundance of microbial communities in the soil and analyzed the effects of methanogens and methanotrophs on CH₄ emissions from black soil paddy fields in cold region.The main findings of the study were as follows:（1）Returning straw to the field for five consecutive years reduced N₂O emissions,but increased CH₄ emissions.Compared with C1 and F1,C5 and F5 reduced N₂O emissions by 73.1%and 44.9%,respectively,and increased CH₄ emissions by 101.7 and195.8%.Under different irrigation regimes,controlled irrigation reduced CH₄ emissions by 50.4-79.7%and increased CO₂ emissions by 8.2-44.9%compared to conventional flooded irrigation.The contribution of N₂O and CO₂ emissions was higher in the milk stage and mature stage,with 41-52%and 16-54%respectively.While CH₄ emissions were mainly in the tillering stage,with 36-58%contribution to CH₄ emissions from each treatment.Due to the high CH₄ emission of conventional flooding irrigation,the GWP of controlled irrigation treatment was 1.4-47.6%lower than that of conventional flooded irrigation treatment.In addition,the yield of controlled irrigation was 10.0-11.5%higher than that of conventional flooded irrigation,and its GHGI was 11.5-52.4%lower than that of conventional flooded irrigation,among which C5 treatment was the lowest.（2）Under the same irrigation regime,the soil temperature of the 5 cm soil layer treated for five consecutive years was 2-4%lower than that of one year straw return treatment.Soil temperature in the 10 cm soil layer under conventional flooded irrigation was 1.8-4.6%lower than under controlled irrigation.Nitrate-N content was reduced by3.6%in the five consecutive years of straw return under controlled irrigation.In the conventional flood irrigation treatment,DOC content was 3.5-24.8%higher than in the controlled irrigation treatment and straw return for five consecutive years increased nitrate-N content by 2%.In addition,straw return for five consecutive years increased soil MBC and MBN contents by 22.3-40.6%and 18.0-20.6%,respectively.Correlation analysis showed that CH₄ and CO₂ emissions were significantly correlated with DOC and MBC contents.（3）Both the irrigation system and the number of years of straw return significantly increased the relative abundance of methanotroph.After five consecutive years of straw return,the relative abundance of methanogens increased by 367.7%and that of methanotrophs increased by 52.2%under controlled irrigation,whereas the relative abundance of methanogens increased by 95.2%and that of methanotrophs increased by22.6%under conventional flooded irrigation.The dominant methanotrophs genus in each treatment were Methylibium and Methylosinus,and the dominant methanogens genus were Methanosaeta and Methanosarcina.Methanotroph communities were reduced in C5 and F5 after five consecutive years of straw return.