Denitrification and N mineralization from hairy vetch (Vicia villosa Roth) and rye (Secale cereale L.) cover crop monocultures and bicultures

N mineralization, N immobilization and denitrification were determined for vetch, rye and rye-vetch cover crops using large packed soil cores. Plants were grown to maturity from seed in cores. Cores were periodically leached, allowing for quantification of NO₃ ⁻ and NH₄ ⁺ production, and denitrification incubations were conducted before and after cover crop kill. Gas permeable tubing was buried at two depths in cores allowing for quantification of N₂O in the soil profile. Cover crops assimilated most soil N prior to kill. After kill, relative rates of N mineralization were vetch > rye-vetch mixture > fallow > rye. After correcting for N mineralization from fallow cores, net N mineralization was observed in vetch and rye-vetch cores, while net N immobilization was observed in rye cores. Denitrification incubations were conducted 5, 15 and 55 days after kill, with adjustment of cores to 75% water filled pore space (WFPS). The highest denitrification was observed in vetch cores 5 days after kill, when soil NO₃ ⁻ and respiration rates were high. Substantially lower denitrification was observed on subsequent measurement dates and in other treatments probably due to either limited NO₃ ⁻ or organic carbon in the soil. On day 5, 3%, 23%, 31% and 31% of the N₂O was recovered in the headspace of fallow, vetch, rye and rye-vetch cores, respectively. The rest was stored in the soil profile. In a field study using intact soil cores, denitrification rates also peaked 1 week after cover crop kill and decreased significantly thereafter. Results suggest greater potential N losses from vetch than rye or rye-vetch cover crops due to rapid N-mineralization in conjunction with denitrification and potential leaching, prior to significant crop N-assimilation. This revised version was published online in June 2006 with corrections to the Cover Date.