Estimating crop nitrogen (N) requirements can be used to develop an accurate fertiliser strategy to support financial and agronomic efficiencies in production. Important components include estimating yield potential, estimating crop N requirements and matching the two.
Over the years, a range of tools have been developed to estimate yield potential including the French and Schultz equation (1984), the 2006 Sadras and Angus formula (which is the formula used in Yield Prophet Lite®), the Harries et al. estimate (2022), the crop modelling product, Yield Prophet® and the N Banks approach.
Determining which N budgeting tool is best for you is dependent on many factors including your appetite for risk (your risk profile) and experience. A long term, N systems trial conducted at Curyo, Victoria, shows N Banks and Yield Prophet® were both effective at closing crop yield gaps equations, formulas and estimates have been widely adopted for a long time, with success.
Harries et al. (and other formulas as outlined above)
This method can be calculated each year on a piece of paper, relatively quickly, and is based on input that is relatively easy to access.
Helps match N input to potential yield via Agricultural Production Systems sIMulator (APSIM) modelling. It is a predictive management tool requiring a relatively high level of input, particularly in relation to soil characterisation, often requiring detailed soil testing. It is best suited to growers who like to take ‘active’ approaches to N management.
This is considered a more ‘passive’ approach. It aims to maintain a base level of soil mineral N that is topped up each season to a target N bank level that is most appropriate for a given location to achieve the water-limited potential in most seasons. Like Harries et al., the initial calculation is simple and establishes a target rate of N fertiliser requirement. This method is yet to be validated for regions with high summer rainfall such as northern NSW so growers may consider other tools.
