Field studies assessing the effect of dicyandiamide (DCD) on N transformations, pasture yields, N2O emissions and N-leaching in the Manawatu region

Abstract

Nitrification inhibitors (NI) allow retention of soil nitrogen (N) in the ammonium (NH4+) form for longer periods. Therefore, they can potentially increase pasture yields by decreasing N losses via nitrous oxide (N2O) emissions and nitrate (NO3-) leaching. Multiple field experiments were conducted over 3 years at a Massey University dairy farm in the Manawatu region to determine the effect of the NI dicyandiamide (DCD) on soil N transformations, N2O emissions, pasture yields and NO3- leaching. Over the study period, DCD applied in autumn and winter had a half-life of 12-17 days and persisted in the soils between 42 and 84 days. Application of DCD inhibited the nitrification process, resulting in lower N2O emissions (54%-78% from urine patches). N2O emissions were further reduced using two applications of DCD, but more than two applications had no additional effect. Although the influence of DCD on pasture accumulation or NO3- leaching was not consistent, three applications of DCD increased pasture accumulation by 9% and reduced NO3- leaching by 22% in one of 2 years of the grazed drainage trial. However, the latter was largely influenced by lower drainage water volumes, rather than lower NO3- concentrations.