The RiskWi$e initiative is indicating that ‘good’ nitrogen application decisions based on sound analysis will result in the ‘right’ yield and profit outcomes in the long run

Despite – or perhaps because of – the abundance of options concerning nitrogen fertiliser, decisions around its application can be tricky. In a 2024 CSIRO survey conducted as part of the GRDC RiskWi$e project, growers rated the difficulty of specific farming decisions.

More than half of respondents found nitrogen management decisions somewhat difficult –harder than decisions around herbicide choice, enterprise mix and varieties.

‘Good’ and ‘right’

At the 2025 GRDC Grains Research Updates, University of Melbourne and CSIRO agronomist Professor James Hunt shared a useful tip for improving the decision-making process.

Drawing on a past GRDC Update paper by agronomist Cam Nicholson, Professor Hunt said growers should focus on making ‘good’ decisions, rather than the ‘right’ ones.

This is because ‘good’ (and bad) decisions refer to the decision-making process. The ‘right’ (and wrong) decisions, however, relate to the outcome, influenced by seasonal conditions such as rainfall, he said.

A ‘good’ nitrogen application decision based on evidence and with an understanding of possible outcomes may not be the ‘right’ one in terms of optimal yields and profits in a given year. But this decision-making process increases the chance of achieving the ‘right’ outcome in the longer term, he said.

Evening out

Professor Hunt said a network of RiskWi$e experiments across the country was comparing different nitrogen decision-making systems, providing a unique insight into which approach was “more right more often”.

As the trials were comparing different systems at the same sites over multiple years, the effect of applied nitrogen was carried over year-on-year, he said.

The trials were already finding that yield and profit were largely dependent on the mean
long-term nitrogen fertiliser rate.

This is important because systems might differ in how much nitrogen is applied in a given year. In that single season they might be ‘right’ or ’wrong’, depending on the seasonal conditions. But the key is that those differences even out over time.

The experiments showed that any ‘good’ decision-making process that led to the optimum mean nitrogen rate would end up being ‘right’, he said.

“It doesn’t matter actually how you make the decision, as long as it gets close to that long-term optimal average over time,” he said. “So, inaccuracy in a single season doesn’t matter that much.”

Most ‘right’ over time

Professor Hunt said yearly differences evened out over time. This was because there was compensation in the cropping system, as RiskWi$e experiments showed at Bute on South Australia’s Yorke Peninsula and Curyo in the Victorian Mallee.

“If you have over-fertilised in a single year, the unused nitrogen carries over to the next season and is used by subsequent crops,” he said. “And we have seen that if you under-fertilise, water can carry over from one season to the next and can also be used by subsequent crops.”

At Bute, in 2023 for example, an under-fertilised nitrogen-deficient barley crop used less available water than treatments with sufficient nitrogen, he said. This caused the subsequent lentil crop to yield more, making a significant profit. This compensated for lower profit due to nitrogen deficiency in the previous season.

Trials since 2018 at Curyo comparing a range of strategies showed Yield Prophet Lite assuming a decile five finish was most consistently ‘right’ over individual years. It also returned the highest relative gross margin over the long term. The nitrogen bank system, while not far behind in the longer term, was more variable year-on-year.

These findings were consistent with all nine south-eastern Australian sites across three states in the RiskWi$e trials.

“The least variable outcome, or the most ‘right’, is the most analytical. This is Yield Prophet Lite using the Bureau of Meteorology forecast, with decile five not far behind,” Professor Hunt said. “The nitrogen bank isn’t that far behind that in terms of the mean (relative gross margin) over time. But you get a bigger scatter of outcomes. It’s less ‘right’ in some seasons and that’s the difference.”

Better decision-making

RiskWi$e aims to achieve the GRDC goal of enduring profitability for the grains industry by empowering growers and advisers to make better decisions and, in particular, risky decisions, Professor Hunt said.

The initiative defines risky decisions as those that have a range of outcomes – both positive and negative. The key to making these decisions – and how much risk to take – is knowing the range and probability of the possible outcomes associated with these choices.

The RiskWi$e initiative partners with dozens of growers, advisory and extension groups across Australia’s growing regions. In the nitrogen decision project, it has teamed with six Action Research Group leads: Charles Sturt University (NSW), Queensland Department of Agriculture and Fisheries, Hart Field-Site Group Inc (SA central), Agricultural Innovation and Research Eyre Peninsula Inc (SA western), Birchip Cropping Group (Victoria and SA south-east), and Grower Group Alliance (WA).

While many growers were already making analytical decisions for nitrogen application based on soil tests and climate probability, Professor Hunt encouraged those who wanted to embark on that path to contact a local research group or the RiskWi$e team. “RiskWi$e is here for you and that’s what it wants to do – help growers make better decisions by considering risk,” he said.

More information: RiskWi$e - the National Risk Management Initiative.

Resources:

• GRDC – RiskWi$e
• GRDC Update paper – Nitrogen fertiliser decisions - the good, the right and the risky.