Optimising Crop Yields: 2024 Season So Far…

Due to the delayed start to the season, crops across the Eyre Peninsula have mostly started emerging in early to mid-June. Generally, crops that establish in June don’t have enough time to build up biomass before they enter the reproductive stage. This increases the likelihood of flowering during hotter conditions, which usually results in lower yield potential compared to crops that establish in early May.

However, tools like Yield Prophet® are forecasting that a wide range of potential yields are still possible across all Eyre Peninsula environments given the range of climatic conditions that may still eventuate. Examining the six focus paddocks being followed by the GRDC RiskWi$e project, in some cases, sees shortfalls in the amount of nitrogen available in the soil, if potential yields are to be realised.

Table 1. Eyre Peninsula focus paddock summary information: paddock history, yield potential and nitrogen shortfall, June 2024.

This poses questions like how much N should be applied, where and when? The following article aims to provide a framework that might be a useful guide to work through the decision.

What is Yield Prophet?

Yield Prophet® is a crop modelling tool that simulates crop yields based on local climate data and soil conditions. It predicts potential yield outcomes across various seasonal conditions, ranging from the wettest to the driest years. These outcomes are often expressed in deciles: Decile 1 represents the lowest 10% of years, and Decile 10 represents the highest 10%.

The platform generates graphs that illustrate potential grain yield outcomes. A solid blue line shows yield based on rainfall alone, while a dotted blue line accounts for the negative effects of frost and heat. The green line indicates current yield potential, considering initial nitrogen levels and modelled nitrogen availability through mineralization. These graphs help farmers understand crop yield potential and make informed decisions about inputs and economics.

Decision-Making with Yield Prophet

Making economic decisions about nitrogen application is most effective when considering multiple seasonal outcomes. Farmers aim to either profit from the yield response or minimize losses when there’s no response. However, oversimplifying these decisions can lead to unexpected results.

The RiskWi$e Project

Funded by GRDC, the RiskWi$e project aims to help farmers with decision-making in complex or complicated situations. Using focus paddocks across different environments on Eyre Peninsula, we examine yield potential, yield gaps, and decision-making processes to reduce risk and uncertainty.

Example Scenario: Eyre Peninsula Wheat Crop

Consider a wheat crop with a 2.5-tonne yield potential in an average year. If a grower has enough nitrogen for a 2-tonne crop, what should they consider when deciding on additional nitrogen application? Here’s a breakdown:

• Urea cost: $730/tonne (including freight)
• Spreading 40 kg/ha of Urea: $37/ha
• Total cost for 1,500ha: $55,500
• Profit from a 0.5 t/ha yield increase: $285,000 (1,500ha at $380/tonne)
• Yield increase needed to cover input costs: 0.1 t/ha

Based on this information, the potential outcomes could be:

• In 3 out of 10 years, no yield response (loss of $55,500)
• In 4 out of 10 years, full yield response (profit of $285,000)
• In 3 out of 10 years, partial yield response (breakeven)

On average, spreading Urea could yield a profit of $103,000 per year. Conversely, not spreading could cost the grower $103,000 annually.

Key Questions for Decision-Making

To make a well-informed decision, consider the following:

• Can my business handle a $55,500 outlay if it’s not recouped? How many years can I sustain this without financial risk?
• Will unused nitrogen remain in the system for future use?
• Is my paddock responsive to nitrogen? Do I understand soil nitrogen levels well enough?
• Can I expect a response across all soil types? If not, how can I address this?
• Do I need more information, and where can I find it?

Conclusion

Having a structured decision-making process can be really valuable when making decisions that are complex or have high levels of uncertainty. While no single method is perfect, a thoughtful approach helps manage the complexities of farming decisions. Below are the yield potentials and nitrogen-limited yields for six focus paddocks, providing valuable insights. More detailed Yield Prophet reports are available on the project webpage.

Note that sowing dates are relative to establishment, many sites were sown earlier but the dry start to the season has resulted in delayed establishment dates. For individual focus site summaries, see the RiskWi$e June 2024 newsletter.