Kerry Stott1, Bill Malcolm1 and Cameron Gourley2
1Agriculture Victoria, Parkville Centre, Department of Economic Development, Jobs, Transport and Resources, Carlton, Victoria 3053. [email protected]
2Agriculture Victoria, Ellinbank Centre, Department of Economic Development, Jobs, Transport and Resources, Ellinbank, Victoria 3821.
Decisions about using N fertiliser rely typically on rules based on expected average pasture responses to N applied. Such rules are mute on the economic limit to N use. In this paper, a new web-based application called the ‘Dairy Nitrogen Fertiliser Advisor’ (the ‘N-Advisor’) is presented. The tool uses marginal analysis and profit-maximising principles to inform dairy farmers and their advisors when they are considering how much N to apply to a particular paddock for a particular grazing rotation. The tool embodies response functions that have been derived from nearly 6,000 data sets from experiments in pasture yield response to N undertaken across Australia over the past 40 years. The response functions exhibit the diminishing returns required for marginal economic analysis. Recommendations about nitrogen fertiliser based on information from using the N-Advisor derive from (i) the expected marginal product of a response function for a particular Australian state and season calibrated to the paddock in question, (ii) the cost of the fertiliser (as spread) and (iii) the value of the extra pasture consumed. The N-Advisor enables users to perform ‘what-if’ analyses, exploring the effect on the profit maximising level of N of changing the cost of N fertiliser, or changing the value of the dry matter consumed. The N-Advisor also enables risk associated with production outcomes to be considered. The production and profit information that can be estimated using the N-Advisor has sufficient rigour and relevance to add value to decisions dairy farmers make about applying N.