Distribution And Transformation Mechanisms Of Maize Straw Derived Nitrogen In An Arable Soil

Crop straw mulching,as a crucial measure to maintain and improve soil organic matter?SOM?,could regulate soil nutrient cycling and reduce nitrogen chemical fertilizer loss.The decomposition of straw could provide sufficient carbon?C?and nitrogen?N?to play important role in the nutrient cycling of the soil-plant system.However,the role of N from straw mulching in agricultural system and the transformation process and regulatory mechanisms of N were still unclear.Thereby,we carried our study by using ¹⁵N isotope probing technique and multi-year field experiment to explore the distribution and transformation mechanism of N from straw mulching.a field experiment was established at the National Station of Shenyang Agro-ecosystems?N 41°31?,E 123°24??in northeastern China in 2009.Three treatments as followings:T1,the first year of application of ¹⁵N labeled straw?annual yield of 50%returning field?+non-labeled fertilizer,from the second year only the application of non-labeled nitrogen fertilizer.T2,the first year of the application of ¹⁵N labeled straw?the average annual yield of50%returning to the field?+non-labeled fertilizer,from the second year to apply non-marked straw?the upper average annual yield of 50%returning to the field?+non-labeled nitrogen fertilizer;T3,the first year of the application of ¹⁵N marked straw(the upper average annual From the second year,the application of non-labeled straw?the average annual yield of 100%field?+non-labeled nitrogen fertilizer.The distribution and residue of N in soil-plant system under different treatments were studied by quantifying the dynamics of ¹⁵N in maize plants and soil profiles.By analyzing the ¹⁵N enrichment in amino sugars,the microbial transformation and utilization of N from straw and the effect on soil C and N accumulation were studied.In addition,the relative contribution of fungi and bacteria in N transformation was also evaluated based on the heterogeneity of amino sugar.The main results are as follows:1.After 6 years mulching of ¹⁵N labeled straw,we found that the recovery rate of returned straw N in soil-plant system gradually increased with the decomposition of straw,and the residue rate of straw N in soil was significantly higher than that of plant utilization,with T2>T3 treatments due to the amount of straw returning.With the continuous decomposition of straw,compared with the single application of straw mulching,continuous straw returning increased the residues and stability of the initially applied straw N in the soil-plant system,and the N from the straw was more retained in the soil,reducing the leaching of inorganic N.In the long run,the maintenance of straw N in soil will play an important role in N absorption.2.Straw mulching could improve the content of amino sugar in soil surface,and increased with the increase of mulching amounts,indicating that the fresh organic material brought by straw mulching could promote microbial metabolism.Meanwhile,the ratio of microbial residue N to total N from straw increased gradually,indicating that straw N can be transformed into soil N reservoir through microbial transformation,and continuous straw returning increases the contribution of straw N to soil nitrogen pool.3.Bacterial residues,represented by muramic acids?Mur-N?,were mineralized rapidly in the early stages of the experiment.With the decomposition of straw,fungal residues represented by glucosamine?Glu-N?,preferred to utilizing complex substrates,succeeded bacterial residues and become dominant groups.Therefore,with the microbial transformation of the straw N,the microbial succession process shifted from bacterial dominant to fungal dominant groups,but the amount of straw returning had little effect on the succession of microbial community.The relationship between amino sugar and soil C and N accumulation was affected by the amount of straw mulching.As the experiment progresses,amino sugar C and amino sugar N accumulated in the soil and remain stable over time.Through years of research,it has been found that straw mulching has a significant impact on microbial transformation and soil nitrogen accumulation.Although the crop utilization rate of straw nitrogen is low,the straw nitrogen can effectively increase the soil nitrogen storage capacity by microbial retention.The straw nitrogen in the soil can partially meet the growth needs of the crop,thereby maintaining the sustainable development of soil fertility function.