Effect of dicyandiamide applied in a granular form on nitrous oxide emissions from a grazed dairy pasture in Southland, New Zealand

The trial reported here investigated the effect of applying dicyandiamide (DCD) in a granular form on N2O emissions in a grazed pasture system over 2 years. In 2004, treatments of urea or urea + zeolite-DCD were applied randomly to pairs of plots following grazing in late autumn. Both treatments received urea at a rate of 50 kg N ha(-1), while the latter treatment also included an application of granular zeolite/DCD at 42 kg ha(-1) (DCn (TM): 10 kg ha(-1) DCD). In 2005, the same treatments were applied following grazing in early and late autumn and early spring. Measurements of N2O emissions were made at frequent intervals following treatment application using a standardised soil cover technique. Large variability in N2O emissions and soil mineral N levels were measured, due to the variable nature of urine N return by grazing animals. Nevertheless, the results clearly showed that the granular zeolite/DCD significantly reduced N2O emissions from grazed pasture from 1.0 to 0.3 kg N ha(-1), 3.7 to 0.7 kg N ha(-1) and 2.9 to 0.3 kg N ha(-1) for the three measurement periods. This equates to reductions of between 75 and 90% over a 2- to 3-month measurement period. Based on these results, and the assumption that 40-50% of annual N2O emissions occur during the times when nitrification inhibitor application is recommended, granular zeolite/DCD reduced annual N2O emission from grazed pastures by 30-45%.