Nitrous oxide emission from soils amended with crop residues

Crop residues incorporated in soil are a potentially important source of nitrous oxide (N2O), though poorly quantified. Here, we report on the N2O emission from 10 crop residues added to a sandy and a clay soil, both with and without additional nitrate (NO3-). In the sandy soil, total nitrous oxide emission from wheat, maize, and barley residues was not significantly different from the control. The total nitrous oxide emission from white cabbage, Brussels sprouts, mustard, sugar beet residues and broccoli ranged from 0.13 to 14.6% of the amount of N added as residue and were higher with additional nitrate than without additional nitrate. In the clay soil, similar effects of crop residues were found, but the magnitude of the nitrous oxide emission was much smaller than that in the sandy soil: less than 1% of the residue N evolved as nitrous oxide. The C-to-N ratio of the residue accounted for only 22-34% and the mineralizable N content of the residue for 18-74% of the variance in nitrous oxide emission. We suggest that the current IPCC methodology for estimating nitrous oxide emission from crop residues may be considerably improved by defining crop specific emission factors instead of one emission factor for all crop residues.