Study On The Fate Of Fertilizer Nitrogen Under Different Straw Returning Methods Of Maize In Black Soil

Northeast black land is an important commodity grain production base in China,which provides an important guarantee for national food security.Straw returning is an effective measure for the protection of black land and an inevitable trend of agricultural production at present and in the future.Straw returning significantly improved soil structure and hydrothermal conditions,thus affecting the migration and transformation of nitrogen in farmland soil.Clarifying the fate of fertilizer nitrogen in soil-crop system under different straw returning methods can provide scientific basis for comprehensive utilization of straw and nitrogen fertilizer management under black soil protection.In this study,the black soil maize in Northeast China was taken as the research object,and the field positioning test was carried out in the black soil area of Lishu County,Jilin Province for three consecutive years from 2020 to 2022.Through the combination of field test and micro-area test,¹⁵N tracer technique and ventilation method were used to monitor the absorption and utilization of fertilizer nitrogen in the continuous three-season crop system,soil residue and NH₃ volatilization loss characteristics of farmland.In this experiment,three straw returning methods were set up:straw leaving field（CK）,straw deep tillage（DTS）and no-tillage with straw mulching（NTS）.Three nitrogen application levels were set up under each method:no nitrogen fertilizer（N0）,180 kg·hm^-2（N1）and 270 kg·hm^-2（N2）.The main conclusions are as follows:（1）38.0%～46.8%of the nitrogen absorbed by crops in the current season comes from fertilizer,and this proportion increases significantly with the increase of nitrogen fertilizer application rate.The distribution of ¹⁵N-labeled nitrogen fertilizer in various organs of the plant was:grain>leaf>stem>cob>bract.The seasonal utilization rate,soil residual rate and loss rate of fertilizer nitrogen in each treatment were 32.4%～43.9%,32.8%～51.4%and 13.2%～32.7%,respectively.Compared with CK,NTS treatment significantly increased the seasonal utilization rate of fertilizer nitrogen by 29.5%under N1,and the loss rate was significantly reduced by 45.0%.Compared with CK,DTS treatment significantly increased the soil residual rate of fertilizer nitrogen by 18.8%（CK,DTS average,the same below）,and significantly reduced its loss rate by 38.2%.（2）The utilization rates of residual fertilizer nitrogen in the second and third seasons were8.5%～14.9%and 1.2%～1.8%,respectively.The soil residual rates of labeled nitrogen fertilizer after harvest in the second and third seasons were 10.4%～26.4%（second season）and 7.3%～17.5%（third season）,respectively.After three consecutive crops,the total crop uptake,soil residue and potential loss of fertilizer nitrogen applied in the season were 86.2～139.1 kg·hm^-2,14.8～47.2kg·hm^-2 and 56.2～131.8 kg·hm^-2,respectively,accounting for 42.0%～60.6%,7.3%～17.5%and31.0%～48.8%of the total application of ¹⁵N,respectively.DTS treatment could significantly increase the total retention of fertilizer nitrogen in soil,especially at higher nitrogen application rates.NTS treatment significantly increased the cumulative utilization rate of fertilizer nitrogen,and both significantly reduced the total loss rate of fertilizer nitrogen.（3）Straw returning method and nitrogen application rate had significant effects on soil ammonia volatilization rate.The results of two years showed that the average NH₃ volatilization accumulation in the whole growth period of each treatment was 20.0～38.0 kg·hm^-2.At the N1level,DTS and NTS significantly reduced NH₃ volatilization accumulation compared with CK treatment,with a decrease of 9.5%and 6.9%,respectively（CK,NTS,DTS two-year average）.Compared with N0,N1 and N2 significantly increased the accumulation of ammonia volatilization.Correlation analysis showed that NH₃ volatilization rate was significantly positively correlated with soil water content,NH₄⁺-N and NO₃^--N content.In summary,straw returning combined with reasonable nitrogen application can effectively reduce the ammonia volatilization loss of farmland soil and reduce environmental risks.In summary,straw mulching combined with appropriate amount of nitrogen fertilizer can significantly improve the current season and cumulative utilization efficiency of fertilizer nitrogen,while straw deep tillage can significantly increase the residue of fertilizer nitrogen in soil,especially under higher nitrogen application rate,it enhances the soil’s ability to retain fertilizer nitrogen and improves the cumulative utilization efficiency of fertilizer nitrogen.Both treatments significantly reduced NH₃ volatilization and other potential losses.