Greenhouse Gases Emission From Paddy Rice Field Under Different Water And Nitrogen Interaction In Cold Region Of Northeast China

Paddy is one of the important sources of greenhouse gas in agriculture.The climatic conditions and water and fertilizer management patterns in the northeastern paddy make the greenhouse gas emissions of paddy have a great difference from those in the South.Therefore,the experimental study on the greenhouse gas?CO₂,CH₄ and N₂O?emissions from different water and fertilizer management models in the black soil rice field in the northeastern cold land can provide an important scientific basis for estimating the total greenhouse gas emissions from paddy.The experiment was carried out at the research base of Qingan National Irrigation Testing Station in Heilongjiang Province from May 2016 to October 2016 and from May 2017 to October2017.The three water management models of controlled irrigation?C?,intermittent irrigation?I?and conventional irrigation?F?were adopted in 2016,two water management methods were used in2017?C and F?,six nitrogen application levels(0,60,85,110,135,160 kg N·hm^-2)and a full test was used,using Longqingdao 3 as material.Based on the field monitoring data of greenhouse gas emissions in different water and nitrogen treatment models,the law of greenhouse gas emissions in rice fields was discussed.The main findings are as follows:?1?Different irrigation models have different patterns of GHG emissions.The peak value of CH₄ decreased by 42.8%and the peak value of N₂O increased by 26.46%in controlled irrigation compared with conventional irrigation.The peak value of CH₄ increased by 9.9%and that of N₂O decreased by 34.8%under intermittent irrigation compared with conventional irrigation.Intermission irrigation and controlled irrigation reduced CH₄ emissions but increased N₂O emissions,with variations depending on field water management.The water-saving irrigation model reduced CH₄ and N₂O combined greenhouse effects in paddy fields,controlled CH₄ and N₂O combined warming potential in irrigated and intermittent irrigated rice fields at 100a scale reduced 55.26%and 25.83%respectively from conventional irrigation,and controlled irrigation could significantly reduce CH₄ emissions from paddy.?2?CH₄ emissions from paddy fields in the cold zone were significantly affected by irrigation modes,while the application of nitrogen in the same irrigation model had no significant effect on CH₄ emissions.In terms of total growth period of rice,CH₄ emissions were mainly treated in tillering stage,spikelet stage and flowering stage,but less in foaming stage,regrowth stage and later growth stage.CH₄ emissions from paddy fields were almost detected in the foaming and regrowth stages,where no significant difference was observed.CH₄ emissions increased in the early days of the drying field and then decreased after the recharge.In the late stage of rice growth,the paddy fields were naturally dry,there was no apparent water layer on the field surface,the soil oxygen content increased,destroying the anaerobic environment needed for CH₄ generation,and CH₄ emissions decreased significantly.There was a clear positive correlation between CH₄emissions and soil temperature,and CH₄ emissions increased as soil temperature increased.?3?Irrigation methods and nitrogen application had obvious effects on N₂O emissions in paddy fields in cold regions,and the characteristics of N₂O emissions were similar at different seasons.The peak of N₂O emissions in different irrigation patterns occurred in the two stages of sun-drying-up-stage and maturation-stage,while the low emissions in the early and late tiller-tiller stages were observed.In the early stage of rice growth,the N₂O emissions from each treatment were in relatively low level.After applying a top dressing?tiller dressing?,N₂O emissions increased slightly,and a small peak occurred.After the application of secondary top dressing?spike fertilizer?,the N₂O emissions of each treatment obviously increased,and the maximum emissions appeared.With the increase of nitrogen fertilizer application,the emission flux of N₂O increased obviously,and the control of irrigation N₂O emissions increased significantly compared with that of conventional irrigation N₂O,and the peak of control N₂O emissions of irrigated paddy fields after secondary fertilization appeared earlier than that of conventional irrigated paddy fields.Temperature change is one of the important factors that affect N₂O emissions in rice paddy fields.?4?In the same irrigation model,CO₂ emissions increased with the increase of nitrogen application.The CO₂ emissions from paddy fields were closely related to the growth of rice.The dynamic changes of CO₂ emissions from paddy fields were consistent in different treatments,mainly in tillering stage and tuft stage.In the early stage of rice growth,CO₂ emissions were low.With the increasing of CO₂ emissions from rice growth,the peak emissions occurred in the peak tillering stage and the spike stage,but the emissions were small in other stages of growth.Due to the change of temperature and the influence of rice growth,the CO₂ emission flux fluctuated greatly during the whole growth period.The effect of water factor and fertilizer on CO₂ emissions in rice fields was studied.The CO₂ emissions from rice fields were positively correlated with atmospheric temperature and soil temperature,and the CO₂ from plant respiration had an important effect on CO₂ emissions from rice fields.