Growth Response of Crop Legumes to Soil Microbiota Is Linked With Soil Nutrients and Planting History.

Soil microbiota provide essential services to plants, but predicting or manipulating these benefits is difficult. Here, we investigated microbial benefits to legume crops at a landscape level to uncover factors that predict those services and can be modified by growers. We sampled cultivated soils across a 1000 km transect of production farms and experiment stations with cowpea cultivation. Bioinoculant practices and crop histories were evaluated. Soils were characterized using bacterial metabarcoding and physicochemical analysis, and soil microbial extracts were created to test the capacity of the microbiota to induce root nodulation and growth effects in six legume cultivars, including cowpea, soybean, and lima bean. Resident soil microbiota enhanced cowpea growth, whereas soybean and lima bean experienced negligible benefits. Grower application of bioinoculants was associated with altered microbial communities and enhanced root nodulation but did not affect crop growth. Soil nutrient makeup was correlated with changes in the resident microbial communities and growth benefits to plants, growth effects that were eliminated in sterile soil inoculation treatments, suggesting that they are microbially mediated. Our findings that both planting practices and abiotic soil factors can indirectly affect plant performance, mediated by restructuring of the soil microbial community, suggest how soils could be inexpensively modified to enhance microbial services.