Optimizing organic cover crop-based rotational tillage systems for early soybean growth

Abstract

Cover crop-based rotational tillage (CCBRT) practices continue to be adopted on organic farms across the globe. In these systems, fall-planted cover crops are mechanically terminated in the spring and used to suppress weeds and eliminate the need for tillage and cultivation in the soybean (Glycine max L.) phase of the rotation. However, challenges remain as to maximization of soybean yields due to later planting dates of soybean and delayed early soybean growth. In this study, soybeans were planted into cereal rye (Secale cereale L.) using two strategies (planting at Zadoks’ stage 45 and 69), with termination with the roller-crimper occurring at Zadoks’ stage 69 for each rye variety which differed in their time to maturity. The impacts of cover crop variety and planting strategies were compared through measurements of (1) cover crop biomass; (2) the regrowth of cover crops; (3) soybean plant populations; (4) weed densities and biomass; and (5) soybean nodulation. Biomass production of each cover crop differed significantly by year, ranging from 7907 kg DM ha−1 to 11,466 kg DM ha−1. Significant differences in weed densities and weed biomass were found between rye varieties and control treatments across the different planting strategies. Soybean nodulation was suppressed by CCBRT management, potentially impacting early soybean growth. Soybean yields were equivalent from both the earlier vs. late maturing varieties of rye. Soybean yields varied across planting strategies of soybeans when cereal rye reached Zadoks’ stage 45 versus stage 69, with greater or equivalent yields of the early planting strategy beans in 2016 and lower or equivalent yields in 2017. Further work must be conducted to understand the benefits and risks of earlier planting of soybeans in the CCBRT system and to develop best management practices to promote early soybean growth.