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

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.