Influence of dicyandiamide on nitrogen transformation and losses in cow-urine-amended soil cores from grazed pasture

Abstract

In New Zealand, urine deposited by grazing animals represents the largest source of nitrogen (N) losses, as gaseous emissions of ammonia (NH3) and nitrous oxide (N2O), and leaching of nitrate (NO3−).We determined the effect of dicyandiamide (DCD) on gaseous emissions from pasture with increasing rates of urine-N application, mineral N transformations and potential leaching of N using undisturbed soil cores of Manawatu sandy loam at field capacity. The treatments included four levels of urine-N applied at 0 (control), 14.4, 29.0 and 57.0 g N/m2 with and without DCD at 2.5 g/m2. Results showed a significant (P < 0.05) increase in NH3 and N2O-N emissions as urine application was increased. The addition of DCD to corresponding urine treatments reduced N2O emissions by 33, 56 and 80%, respectively. The addition of DCD with urine to the intact soil cores at field capacity moisture content resulted in a significant increase in the soil ammonium-N (NH4+-N) concentration but little change in NH3 emissions. Addition of DCD to urine reduced potential NO3−-N leaching by 60–65% but potential NH4+-N leaching increased by 2–3.5 times. There was no difference in pasture dry matter production with and without DCD treatments.