Priming the decomposition of cover crop residues in no-till organic cropping systems

Effective cover crop termination by roller crimping remains a challenge in organic no-till systems. Slow decomposition of surface residues can delay planting and lead to competition for soil resources. Little research has investigated the potential for application of microbial inoculants to promote residue decomposition and accelerate C and N cycling. Two field studies were conducted to evaluate the effects of microbial inoculants on cover crop residue decomposition, labile soil carbon (POXC) and inorganic N pools, and sweet potato yield under contrasting environmental conditions. In a fall termination study, vermicompost tea, a microbial inoculant (EM-1), and thermophilic compost tea were applied after roller crimping sorghum-sudangrass. In a spring termination study, vermicompost tea, EM-1, and a treatment with tillage were applied after roller crimping a multispecies cover crop mixture. Results indicate there was no effect of the microbial tea treatments on the rate of residue decomposition or soil inorganic N and POXC concentrations in either study. However, soil ammonium-N and nitrate-N concentrations were significantly higher in the tilled vs. roller crimped treatments in the spring termination study. Moreover, POXC increased significantly over time in the fall termination study but decreased in the spring termination study. There were no differences in sweet potato yield among microbial inoculants or between the roller crimped and tilled treatments. These results provide insights into the limitations of promoting cover crop decomposition following roller crimping in organic no-till systems to enhance labile C and inorganic N pools while improving yield of the succeeding cash crop. • Residue decomposition of a roller-crimped cover crop was studied under field conditions. • Application of microbial inoculants onto surface residues had no effect on decomposition rate. • Cover crop residues released greater inorganic N under tilled conditions. • Increases in labile C were only observed following roller crimping of the summer cover crop. • Surface residues had no effect on yield of the subsequent sweet potato crop.