Quantitative assessment of nitrogen utilization rates by the combined return of 15N-labeled maize straw and its relation to microorganisms under an intercropping system

Intercropping leguminous and gramineous crops represents a sustainable strategy to optimize nutrient cycling and enhance soil fertility in agricultural production. While most studies on straw returning to field focus on mono4cropping systems, research on mixed decomposition has predominantly been conducted in forest ecosystems, leaving its potential in diverse farmland systems largely unexplored. This study investigated nitrogen utilization rates of maize straw by subsequent crops through 15 N-labeled maize straw incorporated into soil and integrated high-throughput sequencing to identify key driving microorganisms. Four kinds of straw incorporated into soil treatments were designed: maize straw alone returning (M), soybean and maize straw mixed 1:1 returning (MS), soybean straw alone returning (S), and control without straw (CN). Following combined straw returning, the average utilization rate of maize straw 15 N by maize and soybean increased by 9.40 % and 51.14 %, respectively, compared with maize straw returning to field alone. Under the M and MS treatments, the utilization rate of maize straw 15 N by maize increased by 51.23 % and 38.74 %, respectively, under intercropping compared with monocropping. Intercropping significantly enhanced soil microbial diversity, network complexity, and straw degradation potential compared with monocropping. Soil nitrogen content was markedly enhanced and key bacterial genera such as Sphingomonas was enriched, which accelerated straw decomposition in soil, thereby boosting nitrogen utilization efficiency of maize straw in MS treatment. Functional prediction analyses revealed that microbial activities associated with cellulose degradation, aromatic compound metabolism, and nutrient cycling were strengthened. In this study, 15 N isotopically labeled maize straw were used to quantitatively analyze the nitrogen utilization of maize straw by subsequent crops. The advantages of soybean/maize straw combined returning and intercropping were quantitatively evaluated. The findings of this study offer new ideas into enhancing the nutrient utilization efficiency of maize straw through mixing decomposition effects in diversity cropping system.