REVIEW REPORT FOR NEW ZEALAND
5. Indirect emissions – N2O
72. Indirect N2O emissions are a key category for New Zealand. For ammonia emissions from mineral fertilizer New Zealand uses the default IPCC methodology. In New Zealand 75 per cent of the fertilizer consumption is urea, which is known to have a high ammonia (NH3) EF, consistent with results from the model OVERSEER, showing that the average NH3 volatilization from mineral fertilizer consumed in the country is approximately at the same level as the IPCC default value (10 per cent). New Zealand is recommended to use a higher tier for this category in its next submission.
73. For the estimation of NH3 emissions from animal excreta, New Zealand uses the default value of 20 per cent for FracGASM although it is a key category. This default value includes emissions from stables, storages, manure application, and grazing animals. In this review no recommendation on appropriate NH3 EFs is made; however, the review showed that NH3 emission from grazing animals could be substantially lower than the default value. New Zealand is recommended to implement a higher tier approach for NH3 emissions from animal excreta, especially on pastures, in order to improve the transparency and the accuracy of the estimated N2O emissions from indirect sources. The ERT encourages New Zealand to investigate a country specific FracGASM or document why the IPCC default value is considered appropriate for New Zealand conditions.
74. In the 2006 submission the fraction of N leached (FracLEACH) has been changed from 0.15 to 0.07 based on calculations using the OVERSEER model. A recalculation has been performed for the whole time series. The rationale for this change is documented in a peer-reviewed article by Thomas et al. (2005). A FracLEACH of 0.07 in all-year pastoral systems as in New Zealand may be a proper value of the N leaching although there are very few references to similar systems in the international literature; therefore its use could be seen as the best available value and the indirect N2O emissions from leaching in combination with the default EF5 of 0.025 is justified.
C. Non-key Categories
Field burning of agricultural residues – N2O and CH4
75. Nitrogen and carbon are closely linked in agriculture, which means that both N2O emissions from crop residues returned to soil and CH4 and N2O emissions from burned crop residues have the same origin. New Zealand in its calculations used different N contents for agricultural residue regardless that it is returned to soil or burned. Furthermore, the fraction burned has been reduced from 2003 to 2004 without a similar increase in the fraction returned to soil. Such changes also affect the carbon stock in soil. New Zealand is recommended to develop a simple methodology for all crop residues accounting for both N and C which takes into account gathered crop residues, burned residues, and residues returned to soil using national data on N content in crop residues.
END OF REPORT
|
