Promotion of Maize Straw Degradation Rate by Altering Microbial Community Structure through the Addition of Soybean Straw

The carbon-nitrogen ratio (C/N ratio) of straw significantly influences its mineralization and nutrient release when returned to the soil. This study utilized indoor culture and outdoor pot experiments to investigate the impact of varying straw ratios on straw mineralization, soil property dynamics, soil microbial communities, soil enzyme activities, and maize growth. Design of treatments included: (1) maize straw return (M), (2) soybean straw return (S), (3) 1:1 ratio of maize straw and soybean straw return (MS), (4) 2:1 ratio of maize straw to soybean straw return (2MS), (5) maize straw return combined with nitrogen fertilizer (MF) and (6) no straw return (NS). Compared with M treatment, MS and MF treatment enhanced the straw mineralization rate and nutrient release, thus increasing the biomass of succeeding maize. The MS treatment increased the relative abundance of Chloroflexi, Acidobacteriota, and Proteobacteria by 15.54%, 5.36%, and 14.29%, respectively, compared to the M treatment. Straw return treatments significantly decreased the prevalence of the pathogenic fungus Fusarium compared to the NS approach. Correlation analyses indicated a positive association between soil chemical properties and the presence of Proteobacteria, Firmicutes, Bdellovibrionota, and Nitrospirota. Conversely, these factors showed a negative correlation with Actinobacteriota, Gemmatimonadota, Funneliformis, Trichoderma, and Fusarium. These changes in microbial communities are beneficial for straw degradation and nutrient release. In summary, the combined addition of soybean straw and maize straw in a 1:1 ratio optimizes the microbial community, enhances soil nutrient cycling, improves soil fertility, and positively affects corn biomass and nutrient uptake.