Effects Of Straw Returning And Nitrogen Reduction On Soil Nitrogen Pool And Nitrogen Gas Loss In Wheat Rice And Oil Rice Models

Straw returning can change soil physical and chemical properties and microbial activities,and then affect the migration and transformation of nitrogen and nitrogen loss in soil.However,due to the complex decomposition and turnover process of straw in soil and vulnerable to environmental impact,the impact of straw returning on the loss,transformation and utilization of nitrogen in farml and ecosystem is still unclear.Therefore,this experiment selects the common wheat rice（W）and oil rice（R）paddy dry rotation modes in the middle reaches of the Yangtze River to explore the effects of nitrogen fertilizer application and straw returning on soil nitrogen pool and nitrogen gas loss under different modes,in order to provide theoretical and technical support for collaborative crop yield,efficient nitrogen fertilizer utilization and environmental pollution prevention and control in this area.Six treatments were designed:straw returning and conventional nitrogen application（R2S and W2S;nitrogen application rate of 210 kg N/hm²）,straw returning and nitrogen reduction by 30%（R2SN and W2SN;nitrogen application rate of 147 kg N/hm²）,straw not returning and conventional nitrogen application（R0S and W0S;nitrogen application rate of 210 kg N/hm²）.Through continuous monitoring of N₂O and NH₃gas emissions in different modes and determination and analysis of soil nitrogen pool indicators,the following research results were obtained:（1）The biomass and yield of wheat in the first season were significantly higher than that of rape;In the second season,the biomass of rice after wheat rice was significantly lower than that after oil rice by 11.3%,but there was no significant difference in rice yield among treatments.The straw returning amount of oil rice model was significantly higher than that of wheat rice model by 18.9%.（2）Under the condition of conventional nitrogen application,the average contents of soluble organic nitrogen（DON）,microbial biomass nitrogen（MBN）,inorganic nitrogen（IN）and total nitrogen（TN）in 0-30 cm soil layer of two modes of straw returning treatment were significantly higher than those of straw not returning treatment.Among them,MBN was the most sensitive to straw returning,and the content of MBN in W2S was significantly higher than R2S in two seasons.Under the condition of straw returning,the don,in and TN contents of R2SN and W2SN were significantly lower than those of R2S and W2S;The MBN content of R2SN in two seasons was significantly higher than that of R2S by 48.2%,especially in dry season;The soil MBN content of W2SN was significantly higher than that of W2S in dry season and significantly lower than that of W2S in rice season.（3）The loss of nitrogen gas in dry season was significantly higher than that in rice season.Under the condition of conventional nitrogen application,the annual nitrogen loss of oil rice model was significantly higher than that of wheat rice model.Compared with straw not returning,straw returning significantly reduced the annual nitrogen loss of oil rice model and significantly increased the annual nitrogen loss of wheat rice model.After nitrogen reduction treatment,there was no significant difference in annual nitrogen loss between R2SN and W2SN,and they significantly reduced the nitrogen loss of rotation mode compared with other treatments.（4）The accumulation of soil nitrogen net nitrogen mineralization in the rice season was significantly higher than that in the dry season.Under the condition of conventional nitrogen application,compared with the annual accumulation of soil nitrogen net nitrogen mineralization under three treatments,R2S was significantly higher than W2S,and R0S was significantly lower than W0S.R2S was significantly higher than R0S by 38.8%,especially in rice season;The annual difference between W2S and W0S is not significant,but the single season difference is significant.（5）Under the condition of conventional nitrogen application,the annual apparent loss of nitrogen under each treatment was estimated.It was found that R2S was significantly higher than W2S and R0S was significantly lower than W0S.The effects of straw returning on the annual nitrogen loss of different models were inconsistent.R2S was significantly higher than R0S by 28.9%,and W2S was significantly lower than W0S by 24.6%.To sum up,straw returning and nitrogen reduction treatment have a significant impact on soil nitrogen supply capacity,crop nitrogen absorption capacity and nitrogen loss,but the response of soil nitrogen pool indicators under different models is inconsistent,resulting in the complexity of the interaction between straw returning and nitrogen fertilizer on nitrogen transformation and utilization in paddy field.Under the experimental conditions,straw returning treatment was beneficial to increase crop yield,increase soil nitrogen pool activity and reduce nitrogen loss.On the premise of straw returning to the field,when the nitrogen application rate of oil rice model is 147 kg N/hm²and that of wheat rice model is 210 kg N/hm²,it can ensure stable crop yield and reduce environmental pressure.