Abstract
Sugarcane-legume intercrops have gained attention because of their ability to improve crop productivity in an ecofriendly manner. We investigated the roles of rhizospheric and endospheric diazotrophs in soil nutrient transformation. We conducted two field experiments with three treatments: sugarcane monoculture, sugarcane + peanut intercrop, and sugarcane + soybean intercrop. Soil and plant samples were collected and the nutrient content, enzymatic activity, and diazotroph population were assessed. The nitrogenase (nifH) gene and 16S rRNA gene were used for molecular characterization. Correlation analysis was performed to discover the relations among the soil variables, plant variables, and microbial communities. The multiple variance analysis results indicated that the intercropping systems had a significant (p < 0.05) effect on soil total P, available K, and soil enzyme dehydrogenase. Higher diazotrophic populations in the rhizosphere and plant endosphere were recovered by sugarcane intercropping. The soybean intercrop had the maximum unique operational taxonomic units (OTUs). A total of 64 nifH gene-positive bacteria were identified by 16S rRNA gene sequencing. The BLAST search results classified all diazotrophs into five taxonomic groups: γ-Proteobacteria (28%), Actinobacteria (28%), Firmicutes (25%), β-Proteobacteria (11%), and α-Proteobacteria (8%). All identified bacteria had multiple plant growth-promoting abilities, and only 58% of the bacteria utilized aminocyclopropane-1-carboxylic acid (ACC) as their sole carbon source. Furthermore, the higher yield and γ-Proteobacteria positively correlated with soil organic matter, and urease activity revealed that intercropping improved soil fertility. Our study concluded that the intercropping system enriched the beneficial diazotrophs in the plant rhizosphere and endosphere and that these microbes could enhance plant growth and serve as effective bioinoculants to sustain sugarcane production. Moreover, higher soil nutrients (NKP) and biological activity showed the significance of our intercropping practice of a short-duration leguminous crop and a long-duration grass crop, and this practice would be a good solution to reduce the overuse of chemical fertilizers.
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