Effects Of Straw Returning Modes On Soil Nitrogen Forms,Emissions And Distribution

Northeast China is an important grain producing area and commodity grain base in our country.Crop straw resources are abundant,but the proportion of resource utilization is not high,and the phenomenon of irrational fertilization continues to highlight.In order to promote the comprehensive utilization of straw and achieve the goal of reducing fertilizer usage and increasing fertilizer utilization efficiency,it is particularly important to promote straw returning to the field according to local conditions in the utilization of agricultural resources and sustainable development.In the application of straw returning to the field,it is also of great significance to explore modes to realize the full,ecology and safety returning of straw.In this paper,the effects of different full straw returning modes on the dynamic characteristics of soil nitrogen forms,NH₃ volatilization and N₂O emission and the distribution of fertilizer nitrogen in the soil-maize system were studied by setting up field in-situ micro-area experiments and using ¹⁵N isotope tracer technology,which expected to provide scientific basis for the selection of straw returning modes and reduction of nitrogen fertilizer application in northeast China.The four straw returning modes include no straw returning?CK?,mulching returning?SM?,conventional returning?SC?and deep returning?SD?.The main results were as follows:?1?The effects of straw returning modes on soil nitrogen forms were clarified.Straw returning to the field improved the nitrogen supply capacity of soil and promoted the transformation of various nitrogen forms.Compared with CK and SM treatments,SC and SD treatments had a greater impact on the nitrogen nutrient pool of soil.Among them,straw returning to the field increased the average content of ammonium nitrogen in 0-20 cm soil layer,and SC treatment was the highest,increasing 40.82%than CK;Straw returning reduced the average content of 20-40 cm soil layer,SD treatment was the lowest,which was7.14%lower than CK.Compared with CK treatment,SD treatment increased the content of nitrate nitrogen in soil.Straw returning was helpful to the transformation of soil soluble organic nitrogen and the retention of nitrogen by soil microorganisms.Compared with CK and SM treatments,SC and SD treatments increased the size of fixed ammonium pools in0-20 cm and 20-40 cm soil layers to different degrees.?2?The characteristics of soil NH₃ volatilization and N₂O emission under different straw returning modes and their influencing factors were clarified.Compared with CK,treatments with other straw returning modes all reduced NH₃ volatilization and increased N₂O emission significantly.The accumulative amount of NH₃ volatilization in SM,SC and SD treatments decreased by 12.38%,9.87%and 5.73%and the accumulative amount of N₂O emission increased by 30.19%,82.82%and 36.53%,respectively.The order of gaseous loss rates of nitrogen in the four treatments was CK<SM<SD<SC.Two-factor fitting of air temperature and soil water content could better explain the changes of NH₃ volatilization in soil,and soil temperature had a significant exponential correlation with soil N₂O emission flux.Through correlation analysis,it can be seen that soil pH,bulk density,ammonium nitrogen and nitrate nitrogen content had extremely significant effects on gas emission.?3?The distribution characteristics of fertilizer nitrogen in the soil-maize system under various straw returning modes were clarified.The maize yield of each straw returning mode was higher than that of CK,and the yield of SD treatment was the highest and significantly higher than that of CK treatments.With the delay of the fertilization period,the utilization rate of ¹⁵N in maize aboveground increased gradually,and the utilization rate of ¹⁵N in aboveground in SD treatment was significantly improved compared with CK treatment.Under the same fertilization condition,straw returning to the field increased the retention of fertilizer nitrogen by soil microorganisms in the returning layer.Among the three returning modes,SD treatment had the greatest effect on enhancing soil microorganism to retain fertilizer nitrogen,and the promoting effect on 20-40 cm was more obvious,followed by SC treatment.Among the three fertilization periods,the nitrogen fertilizer applied in the sowing period contributed the most to the fixed ammonium pool,and each straw returning mode promoted the fixation and release of fertilizer nitrogen in soil to different degrees.Among the three fertilization periods,the nitrogen loss rate of base fertilizer was the highest,the residual rate of jointing fertilizer in soil was the highest,and the contribution of fertilization to maize grain during the silking stage was the largest.SD treatment significantly improved the ¹⁵N utilization rate of stems and leaves and ¹⁵N utilization rate of roots in each fertilization period,while its nitrogen loss rate was lower than other treatments.Therefore,comprehensive consideration of factors such as soil nitrogen supply,gaseous loss,maize yield,utilization rate of ¹⁵N in maize aboveground and the distribution of fertilizer nitrogen in the soil-maize system in different fertilization periods,deep returning is a better straw returning mode to realize full,ecology and safety of straw returning,which can more effectively improve the soil nitrogen supply capacity,increase maize yield and nitrogen fertilizer utilization rate,and reduce the loss of nitrogen fertilizer in the season.