Nitrogen Release from Grass and Legume Cover Crop Monocultures and Bicultures

Abstract

AbstractThe use of grass‐legume bicultures grown as winter annual cover crops may provide farmers with additional cover crop management options regarding the availability of cover crop residue N. A 2‐yr field experiment was conducted to determine dry matter (DM) accumulation, chemical composition, and N release from grass and legume cover crops grown in monoculture (rye, crimson clover, and hairy vetch) and biculture (rye‐crimson clover and rye‐hairy vetch). Air‐dried plant material was placed on the soil surface in 1‐mm mesh nylon bags for 1, 2, 3, 4, 6, 8, and 16 wk. Following retrieval, mesh bag contents were analyzed for total N, C, cellulose, hemicellulose, and lignin concentrations. The 2‐yr mean cover crop DM production was in the order of rye‐hairy vetch > hairy vetch > rye‐crimson clover > rye > crimson clover. The greatest cover crop N content (2‐yr mean) occurred with hairy vetch monoculture (154 kg N ha−1), compared with a low of 41 kg N ha−1 for the rye monoculture. When grown in biculture with rye, hairy vetch accumulated more DM and biomass N compared with crimson clover, both as a proportion of the biculture and as DM yield. In general, the order of N release rates (rapid to slow) was hairy vetch > crimson clover = rye‐hairy vetch > rye‐crimson clover = rye. Estimates of N (kg ha−1) released from cover crop residue after 8 wk of field decomposition, averaged over 2 yr, were 24 for rye, 60 for crimson clover, 132 for hairy vetch, 48 for rye‐crimson clover, and 108 for rye‐hairy vetch. Results of this study demonstrate only slight reductions in N release from grass‐legume bicultures compared with legume monocultures.