Effects Of Straw Returning On Soil Organic Nitrogen Stability And Active Organic Nitrogen Components In Long-term Continuous Cropping Cotton Fields

Xinjiang is the largest commercial cotton planting area.In 2020,the cotton planting area is 2501.9×10~3hm~2,account for 79.00%of the country’s cotton planting area.The proportion of cotton planting is very large in Xinjiang cotton area which also makes cotton face the big problem of continuous cropping obstacles caused by cotton continuous cropping.Straw returning to the field can effectively alleviate this continuous cropping self-poisoning problem,in order to explore the changes in soil organic nitrogen after continuous cropping of cotton fields and straw returning,in this paper we basis on the long-term continuous cropping cotton fields to find the changing situation of“long-term continuous cropping+full straw recovery”in Xinjiang cotton field.The changes in soil organic nitrogen storage and stability and organic nitrogen active components in oasis cotton fields under the"field+chemical fertilizer"farming system.The balance state,stability degree and nitrogen supply capacity changes of organic nitrogen in Xinjiang oasis cotton fields were discussed,and the changes in cotton are further revealed.The effect of continuous cropping and returning straw to soil on cotton field soil quality and fertility.The experiment mainly got the following conclusions:1.The reserves of organic nitrogen in the soil are mainly concentrated in the 20-60 cm soil layer.The return of straw to the field plays an important role in increasing the reserves of organic nitrogen in the soil.The return of straw to the field for 28 years of continuous cropping has increased by 22.34%compared with 8 years,While the continuous cropping without straw returning to the field for 18 years was 4.17%lower than that of 8 years.With the condition of returning straw to the field,the reserves of soil recombined organic nitrogen and light form organic nitrogen in continuous cropping cotton fields are much higher than those without straw returning to the field.The reserves of light form organic nitrogen and recombined organic nitrogen are gradually increased with the length of straw returning to the field.Increase,the 8 years and 18 years of straw returning to the field have increased by-7.49%,12.95%,94.13%,159.63%,respectively,compared with the same continuous cropping years without straw returning to the field.2.Returning straw to the field in continuous cropping cotton fields changed the stability of organic nitrogen in the soil.Returning straw to the field increased soil aggregates of<0.053 mm and>2 mm,and increased the content of organic nitrogen in soil aggregates of 0-60 cm.Compared with the 8 years and 18years of continuous cropping without straw returning,the soil layers of 0-20cm,20-40cm,and 40-60cm increased by 4.12%,48.23%,9.93%,49.93%,20.75%,80.57%.Returning straw to the field increased the contribution rate of organic nitrogen to total nitrogen in aggregates with particle sizes of<0.053 mm and2-0.25 mm,and increased by 31.17%and 61.12%,32.47%,128.27%,20.76%.in the 0-20cm,20-40cm,and40-60cm soil layers,Compared with straw not returning to the field,with the increase of continuous cropping years,straw returning to the field increased the organic nitrogen activity index in the soil,while reducing the organic nitrogen inertia index.3.Returning straw to the field can significantly increase the content of total nitrogen and active organic nitrogen in the soil of continuous cropping in Xinjiang oasis cotton fields,and increase with the increase of continuous cropping years.Among the active organic nitrogen components,the distribution ratios of POM-N and LFOM-N in total nitrogen are 40.93%,40.89%,16.65%and 46.89%,50.89%,78.76%,which are the main organic nitrogen components added in the soil.And the distribution ratio of DON and SMBN in total nitrogen is relatively small.Active organic nitrogen components are concentrated in the 0-40 cm soil layer of the soil surface.With the increase of soil depth,the proportion of LFOM-N in total nitrogen increases,increasing by 15.50%,13.76%and 18.55%.POM-N and DON the proportion is gradually decreasing.The distribution trend of active organic nitrogen components in cultivated soil is:LFOM-N>POM-N>SMBN>DON.In summary:In the process of continuous cotton cropping,returning straw to the field increased the soil organic nitrogen storage,increased the total nitrogen content in soil aggregates of<0.053 mm and>2 mm,enhanced the organic nitrogen activity index,and increased the content of active organic nitrogen components.Therefore,in the Xinjiang oasis cotton field,with the long-term continuous cropping of cotton and the return of straw to the field,the soil organic nitrogen content and nitrogen supply potential have been increased,and the availability and long-term storage of organic nitrogen have been improved.