Reducing nitrous oxide emissions from grazed winter forage crops

Abstract

Wintering cows on forage crops leads to urine being excreted onto wet, compacted soils. This is likely to result in significant gaseous emissions of nitrous oxide (N2O), which may be reduced through strategic applications of nitrification inhibitors. A study was established on a winter swede crop to (i) determine N2O emissions from compacted soil treated with cattle urine, and (ii) quantify the effectiveness of a nitrification inhibitor, dicyandiamide (DCD), in reducing these emissions. Nitrous oxide emissions from the urine + compacted soil were significantly greater (P < 0.001) than from compacted soil without urine, with 3.2% of the urine-N being lost as N2O. DCD application significantly reduced this loss (P < 0.05) to 0.8% of the applied urine-N. Expressed at a paddock scale, total N2O emissions from the winter-grazed swede crop were 7.9 kg N ha-1, which was reduced to 3.4 kg N ha-1 when DCD was applied. Keywords: urine, dicyandiamide, nitrification inhibitor, soil compaction, nitrous oxide.