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Developing revised emission factors for nitrous oxide emissions from agricultural pasture treated with nitrification inhibitors

Recommendations

• Because the rate of DCD degradation in soils depends strongly on temperature (i.e., slower degradation rate in cooler soils), for October – April when soil temperature beneath pasture generally exceeds 12 °C, DCD should not to be used because it is unlikely to be optimally effective. A suitable DCD application rate is 10 kg/ha and two applications each year, one following grazing in autumn and another following grazing in late winter.

• Based on the New Zealand peer-reviewed literature in conjunction with dairy cattle urine application to soils located at Lincoln, Hamilton, Taupo and a confidential trial in Southland that included dairy cattle grazing, DCD application is expected to correspond with a 67 ± 6% reduction in the direct N₂O emissions factor called EF_3(PRP).

• Based on the New Zealand peer-reviewed literature in conjunction with dairy cattle urine application to soils located at Lincoln, DCD application is expected to correspond with a 74 ± 4% reduction in nitrate leaching (Frac_LEACH). We acknowledge that confidential trials yielded smaller and more variable percentages, but due to the relatively small absolute value of Frac_LEACH, the N₂O emissions inventory was not sensitive to its response of Frac_LEACH to DCD application.

• The quantity of nitrogen applied to pastoral soils as excreta from grazing animals and fertiliser should be disaggregated into May – September and October – April periods. Monthly values are already available for the excreta. For nitrogen fertiliser, FertResearch should be consulted each year for advice about the required disaggregation. This involves estimation of the land area grazed by different types of animal and the fractions of fertiliser applied to this land during each of the two periods. The revised values of Frac_LEACH and EF_3(PRP) should apply to May – September. The revised value of EF_3(PRP) should be applied to EF₁.

• Because method 2 is most strongly supported by research that has been conducted in New Zealand, recognising only sparse data are available for emissions from excreta disaggregated into urine and dung components, method 2 is recommended to describe how anthropogenic N₂O emissions from pastoral agriculture soils can be reduced using nitrification inhibitors.

Contact for Enquiries

Sustainable Land Management and Climate Change
MAF
Pastoral House
25 The Terrace
PO Box 2526, Wellington
Tel: 0800 CLIMATE (254 628)
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