Effects Of Returning Methods And Nitrogen Application Levels On Straw Decomposition And Straw Nitrogen Availability

Straw returning is an important agricultural production measure to maintain soil quality and return nutrients.It is of great significance for efficient utilization of resources and green agricultural production to analyze the law of straw decomposition and nitrogen release and quantify the distribution and utilization of straw nitrogen.In this study,a field experiment was set up in Siping City,Jilin Province for two consecutive years（2021-2022）.The nylon mesh bag method and isotope labeling method were used to determine the straw decomposition and nitrogen release rate of straw mulch（SM）and straw bury（SB）under three nitrogen application levels:no nitrogen fertilizer（N0）,180 kg·hm^-2（N180）and 270 kg·hm^-2（N270）,and the distribution and destination of straw nitrogen in soil crop system were quantified.The purpose of this study was to clarify the response of maize straw decomposition and nitrogen release to returning methods and nitrogen management and its effect on straw nitrogen availability in black soil area.The results show that:（1）The straw decomposition characteristics were significantly affected by the two factors of straw returning method and nitrogen application rate,and the two-year cumulative decomposition rate of deep plowing（83.0%）was significantly higher than that of mulching（65.3%）.Compared with N0 treatment,the straw decomposition rate of N180 and N270treatments increased by 9.8%.The cumulative release rate of straw nitrogen（62.5%）was significantly higher than that of mulching treatment（46.0%）,equivalent to 51 kg·hm^-2and 38kg·hm^-2nitrogen.Compared with N0 treatment,the nitrogen release rate of straw increased by12.5%.（2）Straw returning method and nitrogen application rate significantly affected maize yield and plant nitrogen uptake,and had an interactive effect.The maize yield and plant nitrogen uptake of SBN270 treatment were the highest,with an average of 11017 kg·hm^-2and 184.9kg·hm^-2.Path analysis showed that the nitrogen release of straw was significantly positively correlated with the 100-grain weight of maize and affected the grain yield.There was a significant positive correlation between straw nitrogen release and grain number per ear and harvest index in deep plowing treatment,and grain yield was affected by grain number per ear and harvest index.（3）The distribution and four fates of straw nitrogen in soil-crop system were explored by¹⁵N-labeled straw nitrogen.The distribution of straw nitrogen in various organs of the plant under the coupling of returning method and nitrogen application was grain>leaf>stem,and the distribution of cob and bract was similar.In the first year,the average utilization rate of straw nitrogen was 10.6%.The residual rate of straw nitrogen in soil after deep tillage and mulching was 59.9%and 51.9%,respectively.The increase of nitrogen application rate increased the residual of straw nitrogen in soil.The nitrogen loss rate of straw ranged from 4.1%to 11.6%,and the loss was SMN180>SMN270>SBN180>SBN270.Unreleased nitrogen accounted for 20.0%-28.2%of total straw nitrogen.In the second year,the proportion of straw nitrogen in grain decreased,and the utilization rate of residual straw nitrogen by plants was5.8%-7.1%.The utilization rate of maize plants in deep tillage was higher than that in mulching,and the utilization rate of plants was similar among nitrogen input levels.The residual rate of straw nitrogen in soil decreased to 36.2%after crop harvest,and the residual rate of straw nitrogen in SBN270 treatment was the highest,which was 41.2%.In the two years,the total loss of straw nitrogen was 24.9%-33.2%,and 14.1%-21.4%of straw nitrogen was not released.In summary,in the first two years of continuous straw returning,straw deep tillage and higher nitrogen input are relatively more conducive to straw decomposition and nutrient release,and increase the plant utilization of straw nitrogen and soil residue,reducing losses.At the same time,it also has the effect of stabilizing the yield of corn.