Biomass and Nitrogen Production from Diverse and High Residue Cover Crops.

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 was to document benefits of transitioning land from traditional high intensity and low biomass production (conventionally-tilled potato [Solanum tuberosum]) to systems utilizing high-residue, diverse cover crop species or alternative summer cover crops. Soils of the study area consisted of Bojac sandy loam (coarse-loamy, mixed, semiactive, thermic Typic Hapludults); at experiment establishment the soil was 0.5% organic matter, 4 mg NO3-N kg^-1, and 8 mg S kg^-1. In fall 2014, we initiated a long-term study observing 12 different treatments consisting of several combinations of cash crop sequence changes and cover crop species mixes, which will be compared to conventionally-tilled corn monoculture. Treatments ranged from no cover to cover crop mixes containing 9 different species, each containing species of at least one functional group (grass, legume, brassica, forb). At termination in year 1, above ground biomass ranged from 2054 to 9215 kg biomass ha^-1 and accumulated 57 to 244 kg N ha^-1 .The highest biomass was produced by monoculture cereal rye, a 9-species and 3-species mix and the highest N accumulation was in monoculture vetch, and the same two diverse mixes.    Corn was grown in year 1 in 8 of the 12 treatments and yield ranged from 608-1431 kg ha ha^-1,, with both the highest and lowest yields in diverse mixes. Biomass production (256 to 1466 kg ha^-1) as well as N accumulation was much lower at termination in the second year.  The highest biomass production in the second year was in the perennial cover crop established in year 1 and in a 3-species diverse mix. Cover crop mixes may provide more biomass additions to sandy loam soil production systems, which may increase overall soil organic matter concentrations and nutrient cycling than traditional one-species cover crop systems, but could have unexpected consequences on yield.