Non-target impacts of the nitrification inhibitor dicyandiamide on soil biota

Intensively grazed dairy pastures in New Zealand routinely receive concentrated inputs of nitrogen (N) both through application of fertiliser and deposition of urine by grazing animals. Leaching of nitrate from soil into aquifers, rivers and lakes is a source of increasing environmental and public health concern. Nitrification inhibitors have been shown to decrease leaching and denitrification from urea- and ammonium-based fertilisers and from urine patches in pastures. To date there have been few studies on effects of nitrification inhibitors on non-target soil biota. Three laboratory experiments were carried out to measure the short term effects of a nitrification inhibitor, dicyandiamide (DCD), on diversity of soil bacterial populations, earthworms and Collembola. Molecular analysis of the soil bacterial community indicated that application of DCD to soil did not affect the composition of the predominant bacterial phyla present in soil, unlike the addition of bovine urine which caused rapid changes in bacterial diversity. Survival and growth of the earthworm Aporrectodea caliginosa was unaffected by application of urine or DCD to soil. Collembola populations were not inhibited by DCD, while the addition of urine appeared to increase numbers. Results confirm the view that DCD can be considered one of the more environmentally benign nitrification inhibitors, making it an important tool in countering the environmental impacts resulting from ongoing land use intensification.