Effects of straw return on soil carbon and nitrogen pools and on the diversity of microbial structures and functions

Scientific and rational straw return can release certain nutrient resources and improve soil structure, thus affecting soil microbiological environments. Here, the effects of replacing some fertilizers with different amounts of straw return on soil carbon and nitrogen changes and on microbial metabolism were conducted from 2018 to 2023 in the winter wheat Triticum aestivum cultivation area of the Loess Plateau drylands in Jinnan. Four treatments were used: S0 (0% returned), S1/2 (50% returned), S1 (100% returned), and S2 (200% returned), based on the range of straw yields for winter wheat production in the region (straw was returned to the soil at a depth of 0-20 cm in all treatments). The results showed that straw return increased the total organic carbon and nitrogen content and their fractions in the tillage soil of wheat fields, and the enhancement increased with the rise in straw return. The soil total organic carbon/nitrogen, dissolved organic carbon/nitrogen, microbial biomass carbon/nitrogen and light fraction organic carbon/nitrogen of S2 for five consecutive years were elevated by 39.82/15.14, 37.93/33.08, 129.30/62.59 and 155.86/166.69%, respectively, compared with S0. The straw returned to the field greatly increased the content of active carbon and nitrogen fractions. Additionally, straw return elevated microbial community abundance and significantly increased soil carbon metabolism. Based on the results of redundancy and correlation analyses, Proteobacteria (p = 0.002), Acidobacteriota (p = 0.004), Mortierellomycota (p < 0.05), and amino acid-based carbon sources (p < 0.01) were closely associated with changes in soil carbon and nitrogen fractions. Under the conditions of this experiment, S2 (10 682.4 kg ha(-1)) significantly enhanced the soil nutrient supply capacity and microbial metabolism of dryland wheat fields. Hence, scientific straw return is an effective way of comprehensively solving the problem of dryland soil fertility enhancement and utilizing agricultural by-products.