Using Diverse Cover Crop Mixtures to Increase Biomass and Nitrogen Production.

On the coastal plain of Virginia, sandy loam soils generally contain low organic matter (~0.5%) concentrations and may be conventionally tilled depending on crops in rotation. The overall goal of this project is to increase soil organic matter and nutrient cycling in soils depleted by traditional high intensity, low biomass production (conventionally-tilled potato [Solanum tuberosum]) by introducing diverse and high-residue cover crop mixtures. A long-term study was initiated in fall 2014 to observe the effects of 12 different treatments, consisting of no-till corn, wheat and soybean rotations and cover crop mixes, which was compared to conventionally-tilled corn monoculture. Treatments ranged from no cover crop and conventional tillage to no-till systems with cover crop mixes containing up to 9 different species. Cover crop biomass and N accumulation and yield were measured over 3 years. Biomass production was significantly different the three years (p<0.05) and was higher in year 1 and year 3 than in year 2 due to drought and poor cover crop establishment. Highest biomass in year 1 was produced by mixes containing cereal rye (Secale cereale L.), two diverse mixes (9212 & 8482 kg biomass ha^-1 for treatment 5 and 9) and rye monoculture ( 8453 kg ha^-1), while in year 3 most biomass was produced by diverse mixtures (1741, 3996 and 1086 kg ha^-1 for treatment 11, 9 and 5) . The highest biomass production in the second year was in the perennial cover crop (1456 kg ha^-1), which was established in year 1. Nitrogen accumulation was highly correlated with biomass production (R²= 0.94) and followed the same trend as biomass, with maximum uptakes of 310 and 84.5 kg N ha^-1 in years 1 and 2, respectively. In conclusion, cover crop mixes may provide more biomass additions to sandy loam soil systems, which may increase overall soil organic matter concentrations and nutrient cycling than traditional one-species cover crop systems.