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 denitrificati on incubations were conducted before and after cover crop kill. Gas permeab le 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 mixt ure > 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 we re 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 h igh. Substantially lower denitrification was observed on subsequent measure ment dates and in other treatments probably due to either limited NO3- or o rganic carbon in the soil. On day 5, 3%, 23%, 31% and 31% of the N2O was re covered in the headspace of fallow, vetch, rye and rye-vetch cores, respect ively. The rest was stored in the soil profile. In a field study using inta ct soil cores, denitrification rates also peaked 1 week after cover crop ki ll and decreased significantly thereafter. Results suggest greater potentia l N losses from vetch than rye or rye-vetch cover crops due to rapid N-mine ralization in conjunction with denitrification and potential leaching, prio r to significant crop N-assimilation.