Guideline Index

Chapter 12: Nitrogen and Nitrogen Fertilisers

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Productive pastures require nitrogen in large amounts. Find out how nitrogen cycles in a grazed pasture system; the sources of plant nitrogen; and how to optimise fertiliser use while minimising losses to the environment.

12.1 Introduction

Pastures require N in large amounts, therefore N is generally the major limiting nutrient in terms of plant growth. Find out how N cycles in a grazed pasture system; and how to optimise fertiliser use while minimising losses to the environment.

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12.2 Sources of nitrogen in pasture systems

The sources of nitrogen in a dairy pasture system include: fixation by legumes; brought in feed; nitrogen recycling; dairy effluent and other organic sources; and synthetic fertilisers. Find out the importance of each nitrogen source; the nutrient analysis of some common nitrogen fertilisers and blends; and how to choose N fertilisers for an optimum response.

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12.3 Losses of N to the environment

Significant amounts of N may be lost to the environment under certain climatic, soil and management conditions. There are four main processes that can cause N loss from pasture systems including: denitrification, ammonia volatilisation, surface runoff losses, and leaching losses. Find out more about these N loss processes and the relative importance of each; and the recommended management options to reduce N losses.

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12.4 Responsible management of N fertiliser on farms

Responsible management of N fertiliser begins with the question – why should it be applied? Then it comes down to the 4Rs: use the Right Source of fertiliser, at the Right Rate, in the Right Place and at the Right Time. Find out how to work through each of these steps, and how to work out the economics of N fertiliser use.

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12.5 Expected pasture growth response to N application

Pasture growth responses to N are greatest when conditions for pasture growth are optimal – in other words, when soils are not dry or waterlogged, when there is adequate sunlight, and temperatures are not too hot or cold. Find out when to apply fertiliser to get the highest responses in pasture growth.

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12.6 Other issues to be managed when applying N fertiliser

When applying N fertiliser there are several issues that need to be considered including: potential poisoning effects of nitrates/nitrites; soil acidification; and maintenance of clover in mixed pastures. Find out when these issues are likely to occur; how to recognise the symptoms; and how to avoid or manage these issues.

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12.7 Summary

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12.8 References

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