Effective farm management promotes native AMF and benefit organic farming systems

Abstract

Using soil inoculants containing naturally occurring beneficial microorganisms has become a popular practice in sustainable agriculture. However, an understanding of the environmental variables that affect plant-microbe interactions and the benefit of using commercial inoculum is relatively sparse. To address this, we examined the efficiency of three different methods to inoculate AMF (Arbuscular Mycorrhizal Fungi) in organic vegetable farms in south Texas: cover cropping, application of farm-produced (indigenous) AMF inoculum, and use of commercially available AMF inoculum. We examined these different application methods on growth of jalapeno pepper (Capsicum annuum), and bunching onions (Allium fistulosum). We found that abundance of AMF could be significantly augmented using cover crops such as sunn hemp (Crotalaria juncea), sorghum (Sorghum drummondii), and cowpea (Vigna unguiculata) during the summer fallow periods. These cover crops were associated with a 2.5–3-fold increase in spore abundance in the rhizosphere. In addition, on-farm produced inoculum had a higher root colonization rate in cash crops compared to the commercial inoculum. Pepper plants treated with indigenous AMF flowered and produced fruits 5 days earlier on average compared to the commercial inoculum and control, but there was no significant difference in the total yield across the different treatments. However, for bunching onions, plants treated with on-farm produced indigenous AMF resulted in bigger plants, with about 5 g more total biomass, resulting in higher yield, and with no significant difference between commercial AMF treatment and control. Taken together, our study shows that the on-farm produced inoculum has the potential to provide greater agronomic benefits than commercial AMF inoculum in organic agriculture systems.