Nitrogen decisions for cereal crops: a risky and personal business
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Proceedings of the 2016 International Nitrogen Initiative Conference
Abstract
Cereal crops principally require Nitrogen (N) and water for growth. Fertiliser economics are important
because of the cost at sowing with expectation of a financial return after harvest. The production economics
framework can be used to develop information for ‘best’ fertiliser decisions. But the variability of yield
responses for rainfed production systems means that fertiliser decisions are a risky business. How do farmers
make such decisions, and can economics give any guidance? Simulated wheat yield responses to N fertiliser
applications show tremendous variation between years or seasons. There are strong agronomic arguments for
a Mitscherlich equation to represent yield responses. Plots of the 10th, 50th and 90th percentiles of yield
response distributions show likely outcomes in ‘Poor’, ‘Medium’ and ‘Good’ seasons at four Australian
locations. By adding the prices for Urea and wheat we predict that the ‘best’ decisions vary with location,
soil, and (sometimes) season. We compare these predictions with typical grower fertiliser decisions.
Australian wheat growers understand the yield responses in their own paddocks and the relative prices, so
they are making relevant short-term fertiliser decisions. These are subjective or personal decisions. Myanmar
smallholders grow rice and maize in the Central Dry Zone, with relatively low levels of fertiliser and low
crop yields. They have pre-existing poverty, high borrowing costs and are averse to risky outcomes. A
Marginal Rate of Return (MRR) analysis with a hurdle rate of 100% is illustrated for the Australian
locations, and this approach will be tested in Myanmar.
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Proceedings of the 2016 International Nitrogen Initiative Conference, "Solutions to improve nitrogen use efficiency for the world", 4, pp. 1 - 4