The potential effectiveness of eco-n nitrification inhibitor in reducing nitrification rates in a range of key New Zealand dairy pasture soils: A dissertation submitted in partial fulfilment of the requirements for the degree of Bachelor of Agricultural Science with Honours

Abstract

Increasing public concern over nitrate leaching from intensive agriculture, has led to a demand for accurate scientific research into nitrate leaching losses and the development of mitigation strategies to inhibit the detrimental effects of nitrate leaching on the environment and human health. Recent research has focussed on nitrification inhibitors as an on-farm mitigation tool to reduce nitrate leaching. This study looks at the potential effectiveness of the nitrification inhibitor eco-n at reducing nitrification rates in six different soil types from key dairying regions of New Zealand (Northland, Waikato, Bay of Plenty, Taranaki, West Coast of the South Island and Southland) when incubated at 10°C. Incubation vessels (10 cm diameter by 15 cm height) were packed with 4 mm sieved soil from the different regions and treated with plus or minus eco-n nitrification inhibitor. The experiment included five replicates of each treatment for each soil type, with the Northland soil type experiment also replicated at 15°C. Eco-n application had a highly significant (P<0.001) effect on reducing nitrification rate, with an average reduction of 47% in the total nitrate-N loss over all of the eco-n incubation vessels. Significant reductions in peak nitrate concentration in leachate and total nitrate leaching loss (63- 22%) were observed across all soil types, excluding the Bay of Plenty soil type. There were no significant differences in ammonium leachate concentrations between the control and eco-n treatments indicating that the reduction in nitrification rate in the soils did not cause increased ammonium-N loss in the leachate. The findings of this study demonstrate that eco-n has the potential to be an effective mitigation tool for reducing nitrate leaching in most of the soils studied.