Investment

Difficulties in matching N supply to crop N demand and understanding the potential to utilise a 'Nitrogen banking' strategy to simplify decision making was raised as a priority issue and opportunity by the Medium Rainfall Zone members of the National Grower Network, and by FarmLink members as a priority area for investigation. There are a number of studies that indicate low Nitrogen (N) supply is still the single largest contributor to the water limited yield gap in wheat (Armstrong et al., 2019 and 2021; Hochman and Horan, 2018; Sadras and Angus, 2006). Alongside this research, the relatively high proportion (~30%) of Australian wheat with low grain protein, provides further evidence that yield is being limited by N supply (Sandral et al., 2018; GrainCorp report, 2015/16).

As part of the NGN process, growers identified that current approaches utilised to determine tactical N applications utilise N crop demand (i.e yield potential) to estimate N supply. This has a high level of uncertainty associated with it due to error associated with prediction of August to October rainfall. The N bank approach is a target soil N reserve that is set in perpetuity and therefore is known.

The proposed solution is to test a range of 'N banking targets' and 'N demand scenarios' on-farm to establish the profits and risks associated with both strategies. Within the strategy testing different N bank targets and different N demand scenarios will refine and optimise the equalisation of N supply and N demand using profits and profit-risk ratios to identify the best refinements within each of the two broader strategies. Learnings based around this investment are likely to simplify the approach to N management in cereals and canola for growers and assist in closing the yield gap for non-leguminous crops. Specifically, the investment will need to pull together yield results to compare yield variability, yield gap compared with water use efficiency, protein against industry benchmark on yield and protein associations, input costs, returns, profits and profit variability.