The use of a nitrification inhibitor, dicyandiamide (DCD), to decrease nitrate leaching and nitrous oxide emissions in a simulated grazed and irrigated grassland

TLDR

Urine from grazing animals is a major source of nitrate leaching and nitrous oxide emissions in dairy pastures. The study aimed to quantify how the nitrification inhibitor dicyandiamide (DCD) reduces nitrate leaching and nitrous oxide emissions from urine patches in irrigated grazed dairy pastures using lysimeters. Lysimeters were installed in a free‑draining Lismore stony silt loam pasture of perennial ryegrass and white clover to monitor nitrate leaching and N₂O emissions. DCD lowered nitrate leaching by up to 76% (average 59%), cut N₂O emissions by 82%, and boosted herbage yield by over 30%, demonstrating substantial environmental and productivity benefits. Abstract.

Abstract

Abstract. In grazed dairy pasture systems, a major source of NO 3 – leached and N 2 O emitted is the N returned in the urine from the grazing animal. The objective of this study was to use lysimeters to measure directly the effectiveness of a nitrification inhibitor, dicyandiamide (DCD), in decreasing NO 3 – leaching and N 2 O emissions from urine patches in a grazed dairy pasture under irrigation. The soil was a free‐draining Lismore stony silt loam (Udic Haplustept loamy skeletal) and the pasture was a mixture of perennial ryegrass ( Lolium perenne ) and white clover ( Trifolium repens ). The use of DCD decreased NO 3 – ‐N leaching by 76% for the urine N applied in the autumn, and by 42% for urine N applied in the spring, giving an annual average reduction of 59%. This would reduce the NO 3 – ‐N leaching loss in a grazed paddock from 118 to 46 kg N ha –1 yr –1 . The NO 3 – ‐N concentration in the drainage water would be reduced accordingly from 19.7 to 7.7 mg N L –1 , with the latter being below the drinking water guideline of 11.3 mg N L –1 . Total N 2 O emissions following two urine applications were reduced from 46 kg N 2 O‐N ha –1 without DCD to 8.5 kg N 2 O‐N with DCD, representing an 82% reduction. In addition to the environmental benefits, the use of DCD also increased herbage production by more than 30%, from 11 to 15 t ha –1 yr –1 . The use of DCD therefore has the potential to make dairy farming more environmentally sustainable by reducing NO 3 – leaching and N 2 O emissions.