Effect of dicyandiamide (DCD) delivery method, application rate, and season on pasture urine patch nitrous oxide emissions

Here, we report a study which was designed to examine the effect of a nitrification inhibitor dicyandiamide (DCD) on N2O emissions from pasture urine patches. The aspects of DCD use that were studied were delivery method, application rate, and timing of dairy cow urine deposition. Dairy cow urine (700 kg N ha(-1)) was applied to pasture on a free draining Otorohanga silt loam soil in New Zealand in the autumn and winter of 2013 with DCD applied at different rates (0, 10, 30, and 60 kg ha(-1)). In the autumn, DCD was delivered to the soil either by mixing DCD with the urine collected from dairy cows or by using urine from cows that had ingested DCD while being kept in a stall. In the winter, only treatments with DCD mixed in urine were used. Total N2O emissions from urine applied in the autumn or the winter were 1.66 or 1.79 kg N2O-N ha(-1) year(-1), respectively. This resulted in an annual emission factor (EF3, as a percentage of applied urine N lost as N2O-N) of 0.21 and 0.20 %, respectively. The EF3 was reduced equally with either DCD delivery method with the reductions increasing with increasing DCD rate. This indicates that DCD in urine, excreted by cows that are provided DCD-amended feed, can effectively reduce N2O emissions and that a higher DCD rate will be more effective. Further work is required to ensure that DCD applied using this innovative technique is also effective using different feed and animal types under a range of environmental conditions.