The effectiveness of dicyandiamide in reducing nitrous oxide emissions from a cattle-grazed, winter forage crop in Southland, New Zealand

A study was conducted in Southland, New Zealand to: (i) measure nitrous oxide ( N2O) emissions and nitrate (NO3--N) leaching losses from a cattle-grazed, winter forage crop; and (ii) quantify the effect of dicyandiamide (DCD) in reducing these losses. Drainage losses were measured for 12 months ( December 2005-November 2006) from a December-sown kale crop using 12 hydrologically isolated drainage plots at the Woodlands Research Station. N2O emissions were measured for 6 months (June-November) following simulated grazing of the crop in mid-June. N2O emissions from the bare ground following grazing of the crop amounted to 3.6 kg nitrogen (N)/ha for the winter-spring period. This figure is higher than that measured for pasture on the same soil type over a similar period. DCD application significantly reduced N2O emissions for the whole crop area by 25% over this period and reduced the N2O emission factor for urine by 54%. DCD application increased the length of time mineral N (0-10 cm soil depth) was maintained in the ammonium form and significantly reduced soil NO3--N levels for 6 weeks following the simulated grazing. Annual NO3--N losses in drainage under this winter forage crop were relatively high at 79 kg N/ha. year, with the majority of this (67%) being lost over the wet summer months (December-January rainfall 434mm or 200% of normal) during crop growth. The application of DCD following the grazing resulted in a 47% decrease in NO3--N leached over the winter-spring period (26 kg N/ha nu. 14 kg N/ha) with this equating to a 29% decrease over the full 12-month measurement period. This study suggested that winter forage crops are major contributors to N losses from livestock farming systems in Southland and that DCD application following the grazing of such crops by cattle can significantly reduce N2O emissions and leaching N losses.