Reassessing the Value and Use of Fixed Nitrogen

Roger Lawes - CSIRO

Type: Research Paper
Knowledge level: Advanced

Farm Table says:

It is important have the tools to value N from an economic perspective, given the soil N status, climate, the suite of legumes available, the cost of N fertiliser and commodity prices. With this information, growers can then choose whether or not to reduce their reliance on N fertiliser.


What is the problem?

Australian farming systems are generally N deficient.

To address this deficiency, growers have two choices: supply N as fertilizer, or supply the N using legume crops. Both scenarios contain an element of risk. The rate of N required is dependent on season, so there is an element of risk associated with the application of nitrogenous fertilizers. Once applied, N fertilizers may be taken-up by the crop. However, there is a risk the fertilizer will be lost through volatilization or leaching if conditions are either exceedingly wet or exceedingly dry.

*The target of this research was to approximate the value of fixed N in modern farming systems and apply this valuation to cropping systems throughout Australia.*

What did the research involve?

  • An economic N budgeting model was produced following the review of N models in Australia and a rigorous assessment of Agricultural Production Systems Simulator (APSIM) N modeling capabilities
  • In the Southern Region, at Karoonda and Birchip, field peas frequently delivered a favorable return from the context of N. At Karoonda, once field pea prices reached $300/t, a field peas-wheat sequence outperformed wheat-on-wheat, regardless of soil N, fertilizer price or fertilizer rate
  • At Moree, a chickpeas-wheat sequence invariably outperformed wheat-on-wheat from the perspective of N when chickpea prices reached $400/t
  • The tools and tables delivered to the MCPN project give growers and advisers the equipment necessary to value N from the context of a legume, commodity price, fertilizer price and starting soil N

What were the key findings?

Economic Outcomes:

  • Economic simulations were conducted for six regions to identify appropriate ‘trigger points’ for when to grow the dominant legume in the region

Environmental Outcomes:

  • Incorporating high-value legume crops into the farming system generates real and economically sensible reductions in the N fertilizer needs of growers

Social Outcomes:

  • The project has delivered the outputs from the simulations to grower groups across the country. Outputs from the project were delivered to growers in the Western Region (Western Australia, WA) at the Liebe Spring Field Day and at a nutrient workshop in Kojonup
  • Alternatively, they will consider forages and green manures in an extreme situation where biotic stresses, such as weeds or disease, cannot be managed. However, their preference is to grow a crop or pasture that generates a return
  • Canola is widely grown because it adds value to the farming system and is profitable in its own right. New projects should endeavor to link agronomy, breeding, economics and grower attitudes to appropriately define local production and the real risk of growing legumes in modern farming systems

Final comment

The aim of this project was to communicate to growers the value of fixed nitrogen (N) from legume crops and pastures in modern farming systems. The research developed an economic tool to value fixed N. The key outcome was to enhance grower and adviser awareness about how to appropriately value legume crops and pastures in the context of a two-year rotation with a cereal crop

2016 - Australia - Roger Lawes - CSIRO
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