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 N 2 O 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™ : 10 kg ha ‐1 DCD). In 2005, the same treatments were applied following grazing in early and late autumn and early spring. Measurements of N 2 O emissions were made at frequent intervals following treatment application using a standardised soil cover technique. Large variability in N 2 O 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 N 2 O 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 N 2 O emissions occur during the times when nitrification inhibitor application is recommended, granular zeolite/DCD reduced annual N 2 O emission from grazed pastures by 30–45%.