​​Improving farmers’ knowledge and capacity to increase nitrogen use efficiency and reduce grain crop carbon emissions through optimised rotations and in-seasonnitrogen strategies in the highly inefficient high rainfall zone of Western Australia.​

PROJECT SUMMARY:

Western Australian baseline emissions output data from broadacre grainbelt properties shows the high rainfall zone is approximately 30% and 50% less efficient than the medium and low rainfall zones, respectively (Aglytica, 2022). This is largely driven by much higher and often inefficient fertiliser inputs. This project aims to build farmers’ knowledge and capacity to manipulate rotations and nitrogen management strategies to increase nitrogen use efficiency and reduce emissions from grain crop production on commonly occurring soil types in this highly productive and important grain region. Capacity building within the project is twofold. The project builds the capacity of local farmer group staff and First Nations Rangers in conducting and analysing soil/plant assessments and emissions accounting and also builds the capacity of farmers and advisers to make better, data-driven and, locally validated decisions to improve sustainability without compromising on financial sustainability.

TRIAL OBJECTIVES:

To build farmers’ knowledge and capacity so they can manipulate rotations and nitrogen management strategies to increase nitrogen use efficiency and reduce emissions from grain crop production on commonly occurring soil types in this highly productive region, while not compromising (or at least better understanding the compromise) on profitability.

METHOD:

Four, fully phased, triple replicated, small plot trials will be implemented across the high rainfall parts of the West Australian South Coastal & Great Southern Regions. Each trial will contain three nitrogen fertiliser treatments (mimicking different appetites for risk amongst local farmers and including a nil treatment) by two crop rotation strategies (with and without legume).

Examples of nitrogen application treatments include:

• Setting N strategy to rainfall deciles: Decile 4 (low N) and Decile 8 (High N) + 0N

• Replacement N strategy: Whereby the amount of grain N removed from the prior season is replaced.

• N banking strategy: Where a N bank target is set at the start of the trial and N is applied to meet this maintenance levels. EG N300 and N200 where the soil N is measured at the start of the trial and additional units are applied to maintain the N levels at the target rate.

• N timing strategy: Small and often vs all upfront or upfront and one in season application. Here the same number of units would be applied across treatment plots, however how they N is applied would change.

• Playing the season vs set and forget: Here a set N rate would be measured against playing the season.

Rotation treatments aim to separate the influence of rotation history on nitrogen demand, and whether diverse sequences reduce reliance on applied fertiliser.

Year one results (2025):

The first season of data was collected across all four sites during a decile 8 to 9 year for much of the trial area. While rotation treatments are not yet fully expressed as plots require several seasons to build the intended rotation history. The year one data provides an early look at how nitrogen rate interacts with yield and gross margin under current regional conditions.

Key observations from year one:

• For most cereals, reducing from a high to a moderate nitrogen rate had a limited impact on gross margin. Under high fertiliser price scenarios, moderate rates often returned more than high rates.

• Nil nitrogen was difficult to justify economically in most crops. Applying a low rate consistently outperformed nil, even under elevated input costs.

• Canola gross margins were variable and in some cases negative across sites, reflecting a combination of site conditions and seasonal factors rather than a consistent pattern. This will be monitored as the trial continues.

• The rotation effect on nitrogen response is expected to strengthen considerably in years three and four as paddock history accumulates.

The full year one analysis, including site-level results and gross margin modelling, is available to download below.

Year two (2026):

Seeding for the 2026 season has commenced across all four trial sites. Year two will begin to establish the rotation sequences central to the trial design, and the combined dataset from 2025 and 2026 will support modelling to identify how previous land use, soil type, and seasonal timing influence nitrogen response across the region. Results will be shared with growers and advisers as the season progresses.