Treating grazed pasture soil with a nitrification inhibitor, eco‐n™, to decrease nitrate leaching in a deep sandy soil under spray irrigation—a lysimeter study

Abstract

In grazed dairy pasture systems, a major source of nitrate (NO₃ ⁻) leached is the nitrogen (N) returned in the urine from the grazing animal. The objective of this study was to use undisturbed soil monolith lysimeters to quantify the effectiveness of treating a grazed pasture soil with a nitrification inhibitor, trade name eco‐n™ (active ingredient— dicyandiamide, DCD), in decreasing NO₃ ⁻ leaching losses from a deep sandy Templeton soil (Udic Haplustept) with a mixture of perennial ryegrass (Lolium perenne) and white clover (Trifolium repens) pasture. Simulated rainfall was applied in the winter to supplement the natural rainfall to the 75th percentile of local rainfall records, and spray irrigation was applied in the summer. The treatment of the soil with eco‐n decreased NO₃ ⁻‐N leaching from 85 to 20–22 kg N ha⁻¹ yr⁻¹ (equivalent to 74–76% reduction) for the dairy cow urine N applied in the autumn at the rate of 1000 kg N ha⁻¹. This reduced annual average NO₃ ⁻‐N concentration under the urine patch from 25 to 7 mg N litre⁻¹. The eco‐n treatment also reduced Ca²⁺ leaching by 38–56% and Mg leaching by 21—42%. Ammonia volatilisation was not affected by the eco‐n treatment. In addition, the eco‐n treatment increased herbage dry matter yield in the urine patch areas by 33%, from 15.9 t ha⁻¹ yr⁻¹ without eco‐n to 18.2t ha⁻¹ yr⁻¹ in the single eco‐n application in May and to 21.1 t ha⁻¹ yr⁻¹in the May plus August eco‐n treatment. Treating grazed pasture soil with eco‐n is thus not only beneficial to the environment by reducing NO₃ ⁻ leaching but also has economic benefits by increasing nutrient use efficiency and pasture production.