Reducing environmental impacts of agriculture by using a fine particle suspension nitrification inhibitor to decrease nitrate leaching from grazed pastures

Nitrate (NO3−) leaching from intensively grazed pasture systems, e.g. dairy farming, is of increasing environmental concern worldwide. The major source of the NO3− leached in grazed pastures 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 fine particle suspension (FPS) nitrification inhibitor, dicyandiamide (DCD), in decreasing NO3− leaching losses from a deep sandy soil with a mixture of perennial ryegrass (Lolium perenne L.) and white clover (Trifolium repens L.) pasture. The application of DCD as a FPS at 10 kg ha−1 in autumn (May) and late winter (August) decreased NO3−-N leaching from 134 kg N ha−1 year−1 to 43 kg N ha−1 year−1 (equivalent to a 68% reduction) from the dairy cow urine N applied in the autumn (May) at the rate of 1000 kg N ha−1. This reduced the annual average NO3−-N concentration under the urine patch from 43 mg NO3−-N L−1 to 18 mg NO3−-N L−1. The DCD FPS also reduced Ca2+ leaching by 51% and Mg2+ leaching by 31%. In addition, herbage dry matter yield in the urine patch areas was increased by 33%, from 15.3 t ha−1 year−1 without DCD to 20.3 t ha−1 year−1 when DCD was applied at 10 kg ha−1. However, DCD applied at 5 kg ha−1 (May and August) did not provide significant environmental and agronomic benefits under the experimental conditions. Results from this study when compared with those reported previously show that DCD, when applied as a FPS at 10 kg active ingredient ha−1, is just as effective in reducing NO3− leaching in grazed pasture soils, as when it is applied as a solution.