Inoculation is more effective for main crops than for preceding cover crops and does not affect the arbuscular mycorrhizal community in no-till vegetable systems

Arbuscular mycorrhizal fungi (AMF) establish symbioses with most terrestrial plants, enhancing nutrient uptake, stress tolerance, and soil quality. We evaluated the use of Rhizophagus irregularis-based inoculants in cover crops and subsequent commercial crops in a no-till system and assessed their effects on soil biological attributes and crop yield. Three on-farm field experiments in different locations were conducted with common bean, okra, and corn cultivated after the winter cover crops. The assays were arranged in a randomized complete block design with a split-plot scheme and four replicates, with cover crop inoculation (black oats) as the main factor and crop inoculation in the subplot. The treatments included (i) inoculation in the cover crop and no inoculation in the main crop; (ii) no inoculation in the cover crop and inoculation in the main crop; (iii) inoculation in both crops; and (iv) no inoculation in either crop. Soil acid phosphatase activity, fluorescein diacetate hydrolysis, AMF spore density, and crop yield were measured at the end of each cycle, and the AMF community composition was characterized. The AMF inoculant increased the soil quality indicators (acid phosphatase activity and fluorescein diacetate hydrolysis). Inoculation of the cover crops did not replace the beneficial effects of direct inoculation on the yields of beans, okra, or corn. The results of the experiments in locations with different soils revealed that, overall, direct crop inoculation increased the yields of bean, okra, and corn by 30%, 33%, and 19%, respectively, and intensified soil enzyme activity, with no detectable effects on soil AMF community diversity or structure.