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Nitrification and urease inhibitors: A review of the national and international literature on their effects on nitrate leaching, greenhouse gas emissions and ammonia volatilisation from temperate legume-based pastoral systems

TR 2004/22


Report: TR 2004/22
Author: DC Edmeades, agKnowledge Ltd.


One of the most pressing environmental issues confronting pastoral agriculture in New Zealand is the loss of soil N, derived from either fertiliser N or symbiotic N fixation by legumes, to the atmosphere as gases (ammonia (NH3), nitrogen (N2) and nitrous oxide (N2O), the latter being a potent greenhouse gas) or to groundwater via leaching as nitrate (NO3-). These losses of N not only decrease N-use efficiency, and hence have economic implications, but just as importantly, impact on groundwater quality and contribute to greenhouse gas emissions.

To safeguard public health, New Zealand has adopted the WHO standard for drinking water, limiting the nitrate N concentration to 11.3 ppm and various industry-driven voluntary codes have been developed (eg the Market Focused Accord developed by Fonterra and the Fertiliser Code of Practice initiated by the Fertiliser Industry) to encourage land users to adopted appropriate management practices to limit nitrate leaching. Additionally, the New Zealand government has signed and ratified the Kyoto Protocol which will limit greenhouse gas emissions to 1990 levels.

Losses of N via leaching and gaseous emissions generally increase with farming intensity (Ledgard 2001) and so unless effective controls can be found to minimise these losses, they could put a limit on the productivity of New Zealand pastoral soils.

This report examines the potential role of nitrification and urease inhibitors as tools to manage these losses. First, the potential size of the problem is assessed and some theory explaining the function of nitrification and urease inhibitors is discussed. The international and national literature is then reviewed and finally some unresolved issues and problems are discussed.

Nitrification and Urease Inhibitors: a Review of the National and International Literature of their Effects on Nitrate Leaching, Greenhouse Gas Emissions and Ammonia Volatilisation from Temperate Legume-Based Pastoral Systems
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Table of Contents

Executive Summary vii
1 Introduction 1
The Size of the Problem 1
Some Theory 2
2 Products 3
2.1 Nitrification Inhibitors 3
2.2 Urease Inhibitors 4
3 International Research 4
3.1 Nitrification Inhibitors 4
3.2 Urease Inhibitors 5
4 New Zealand Research 5
5 New Zealand Research in Progress 6
6 Questions and Issues 7
6.1 Soil and Water Quality 7
6.2 Plant toxicity 7
6.3 Size and duration of benefits 7
6.4 Nitrification and Urease Inhibitors: Magic Bullets? 8
7 Conclusions 9
Acknowledgments iii
References 11
Appendix Current New Zealand Research On Nitrification Inhibitors 17
Summit-Quinphos Ltd 17
Ravensdown Fertiliser Cooperative Ltd. 17
Ballance AgriNutrients Ltd 17