Nitrous Oxide Emissions from Dairy Farmlets, as Affected by Use of a Nitrification Inhibitor and a Winter Restricted Grazing Strategy

Experimental farmlets at DairyNZ’s Prototype Farm near Hamilton were used to determine potential reductions in nitrous oxide (N2O) emissions from use of a nitrification inhibitor and a restricted grazing regime. A control farmlet was managed under a conventional rotational grazing regime, while a “tight nitrogen” farmlet was managed under a similar grazing regime to that on the control farmlet, except during winter and early spring when cows grazed for about 6 hours per day on pasture with the remaining 18 hours spent in an animal shelter (e.g., a stand-off or restricted grazing regime). A nitrification inhibitor (dicyandiamide, DCD) was applied onto the “tight nitrogen” farmlet on 2-3 occasions immediately after grazing through winter and early spring. A soil chamber technique was used to measure N2O emissions from each farmlet during three contrasting periods of each year for three years. In addition, the New Zealand IPCC inventory methodology was used to calculate total greenhouse gas emissions. During winter/early spring in 2007, 2008 and 2009, N2O emission rates were lower (P<0.05) in the “tight nitrogen” farmlet than in the control farmlet. The use of a restricted grazing regime and a nitrification inhibitor reduced N2O emissions from the farmlet by 43-55%, 6479% and 45-60% during the winter/early spring seasons, respectively. During late spring/summer and autumn periods, N2O emission rates were generally similar between the two farmlets. The difference in the annual N2O emission rates between the control and the “tight nitrogen” farmlets was not significant in the first year. However, in the second and third years the annual N2O emission rate from the “tight nitrogen” farmlet was found to be between 39% and 50% lower than from the control. For the three study years, the average annual N2O emission rate from the “tight nitrogen” farmlet was 20% lower than from the control. Total annual emissions for the sum of the three major greenhouse gases, N2O, CH4 and CO2, were 11,524 and 10,871 kg CO2-equivalent per hectare from the control and “tight N” farms, respectively. The total greenhouse gas emissions from the tight nitrogen dairy system were 6% lower than those from the control.