NITROGEN AND CARBON CYCLING IN RELATION TO COVER CROP RESIDUE QUALITY

The importance of cover crops as determinants of soil quality has long been recognized in agriculture, from their common use as green manure crops in the mid 1900s to the broader range of cover mop management s trategies in cropping systems of the 1990s. The two principal elements regulating soil biological activity, and hence nutrient cycling, are carbon (C) and nitrogen (N). This regulatory effect is manifested prim arily in resource quality, which is a term representing the chemical c omposition and physical characteristics of cotter crops. The primary c hemical factors determining the kinetics of residue decomposition and nutrient release are the C:N ratio and concentrations of lignin and ot her structural carbohydrates in plant tissues. With respect to N avail ability, grasses and legumes may serve different roles in cover crop-b ased production systems. Certain grass cover crops, most notably rye, have demonstrated a superior ability to scavenge for residual soil ino rganic N compared to legumes. In contrast, legume cotter mops such as crimson clover and hairy vetch have the ability to provide substantial amounts of biologically-fixed N to crops such as corn, cotton, and so rghum. However, improvements are needed in the synchrony of cover crop N release with principal mop demand for N to efficiently utilize this source of N. In this regard future avenues for research should includ e a greater emphasis on plant breeding efforts to enhance the multipur pose roles of grass and legume cover crept, innovative management stra tegies utilizing cotter crops, and the we of models to enhance our pre dictive capabilities of nutrient cycling efficiencies in cropping syst ems.