Summary
In this report, a number of methods to reduce nitrate leaching from grazed grassland were examined. The body of detail given in this report originates from research at Lincoln University in New Zealand, by Dr Keith Cameron and his team. New Zealand is a country with similar climatic and agricultural production systems to that of Northern Ireland. With the incoming Nitrates Directive and Water Framework Directive in Northern Ireland, the potential application of the New Zealand approach in dealing with nitrate leaching, to Northern Ireland may offer potential.
The effectiveness of a number of products in reducing nitrate leaching from grazed grassland was examined. The products examined were icyandiamide (Marketed in liquid form as Eco-N), Dicyandiamide (Marketed in granular form as N-care), Taurine (device to distribute the nitrification inhibitor) and Dimethylpyrazole– phosphate (DMPP) (Marketed as Entec).
The conclusions drawn from this report were:
- Nitrification inhibitors can be effective in reducing levels of nitrate leaching, but this varies with time (decreasing after application to soil), soil conditions, temperature, moisture content and pH.
- A problem associated with the majority of research to date in New Zealand which examines the usefulness of nitrification inhibitors, is that studies have largely been conducted on a small-scale experimental basis with field lysimeters. Researchers have subsequently extrapolated such data to yield field results. Further research in this area is currently underway through PhD studies at several universities, in collaboration with Summit-Quinphos, Ravensdown and Balance AgriNutrients. Further long-term full-scale farm research is required to examine the effect of DCD on plant toxicity, soil type and climatic variation.
- Good management practice may be as effective as nitrification inhibitors in reducing nitrate leaching.
- Nitrification inhibitors alone will probably not provide a complete solution to the problem of nitrate leaching, but they could be incorporated as a useful tool in conjunction with the adoption of good management practices.
- A concern regarding toxicity to plants is a potential drawback to the use of nitrification inhibitors such as DCD. No research evidence indicating toxicity of DCD or nitrification inhibitors per se to other flora, fauna or animals was reported.
- Factors limiting the use of nitrification inhibitors include cost and the period of time (3 weeks) for which their application remains viable. Dicyandiamide retails at approximately $78/ha (New Zealand) per application, being equivalent to £29/ha (sterling).
- Natural sources of nitrification inhibitors are being sought to reduce cost.
- Smaller scale laboratory studies have indicated that the effectiveness of DCD is temperature dependant and its half-life was reduced from 114 days to approximately 20 days, with an increase in temperature from 8oC to 20oC.
- It is estimated that several applications of Eco-N (Ravensdown Co-operative) would be required during a grazing season, as it may only remain effective for a period of 3-4 weeks. Consequently, cost could be a limiting factor with its application.
- N-care (Balance Agrinutrients Ltd), when applied as a fertiliser, can also prove costly.
- Taurine is currently being patented and is hoped to be commercially trialled in 2005 (Summit–Quinphos Ltd).
- Nitrification inhibitors could offer potential for use in Northern Ireland agriculture, however, they will not provide the complete answer to the problem of nitrate leaching. An adoption of good management practices and the use of nitrification inhibitors to reduce the level of nitrate leaching may offer potential in addressing the local nitrate problem.
- Dimethylpryazole-phosphate (DMPP) is a much superior nitrification inhibitor to DCD and is effective at lower concentrations.
- It has not been possible to obtain information on the current scale of usage of DMPP in Europe.
- Further work in Northern Ireland should be based on DMPP rather than DCD.
