Short‐Term Effects of Cover Crops on Soil Microbial Characteristics and Biogeochemical Processes across Actively Managed Farms

Abstract

Core Ideas The effect of cover crops on soil microbes and biogeochemistry was examined. Cover crops increase microbial biomass and bioavailable soil carbon. Increasing cover crop biomass amplifies belowground effects. Agricultural soils are largely degraded or under threat of degradation. Given a growing human population and the subsequent need to feed this population, agricultural practices must maintain productivity and soil quality. Cover cropping regimes are a management approach that aims to address these dual goals. Although the use of cover crops has been linked to many positive effects on soil quality and crop yields, few studies have examined their effects on soil microbial community structure and function under active farm management. We assessed soil characteristics and microbial community structure and function between agricultural field plots with and without cover crops. We expected microbes would respond in the short‐term to increasing cover crop biomass, with increases in microbial activity and a shift in C acquisition toward substrates indicative of root exudation. In the presence of cover crops, we found active microbial biomass and bioavailable‐C increased by 64 and 37%, respectively, indicating the potential for increased C sequestration. Soil NH4+ increased by 64%, whereas soil NO3‐ decreased by 30%, indicating a shift toward less mobile N forms and the potential of greater nutrient retention under cover cropping regimes. Additionally, increasing cover crop biomass was related to lower microbial biomass C/N ratios and to decreased utilization of recalcitrant C substrates. These results potentially suggest a shift toward greater microbial utilization of root‐derived compounds with increasing cover crop biomass. Together, these results indicate that, in the short‐term, the presence of cover crops may improve soil quality, as measured by indices of microbial activity, and soil C and nutrients.