What New Soil Research Could Mean For Burdekin Cane

New research into how nitrogen moves through soil could offer useful lessons for Burdekin cane growers; but Professor Mike Bell says findings from rainfed wheat country cannot simply be transferred to the district’s irrigated sugarcane systems.

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Bell, from The University of Queensland, led a project through the Australian Government’s $20 million Soil Science Challenge Program examining nitrogen movement in clay soils used for rainfed grain production in southern Queensland. Bell said applying the findings directly to flood-irrigated cane would be “a fair stretch”, however, the research does provide insight into how soil type, water and nitrogen interact.

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Nitrogen moves through soil with water, meaning the way it behaves can vary considerably depending on the soil. In freely draining soils, nitrogen can potentially move below the active root zone, while heavier clay soils can hold water for longer and create conditions where nitrogen is lost through denitrification.

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Bell's research tested whether applying nitrogen to dry soil soon after a previous crop was harvested could improve nitrogen recovery in the following wheat crop, rather than applying it close to planting. Across two seasons, the approach produced better nitrogen recovery in a dry year without additional losses in a wetter year. However, Bell stressed that further testing is required before the approach becomes mainstream.

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In the Burdekin, local agronomist Jayson Dowie said the research reinforced principles already relevant to cane production, while highlighting the differences between farming systems.

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“There really isn't one nitrogen story for the Burdekin,” Dowie said, pointing to the district’s diverse soils and fully irrigated production system.

He said nitrogen use efficiency was influenced by more than fertiliser rates, with soil health, compaction, drainage, irrigation, weeds, crop establishment and seasonal conditions all affecting how effectively a crop could use available nitrogen. Dowie also pointed to local research into nitrogen timing.

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“In one of our larger nitrogen trials we saw better crop responses where nutrition was applied after the first irrigation, and again with later application, compared with applying it immediately behind the harvester,” he said.

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While the result raised questions around timing, Dowie cautioned against attributing the response to a single mechanism. He said later applications could also create additional labour and operational challenges, particularly where irrigation fluming needs to be moved. Irrigation itself remains an important part of the nitrogen equation.

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On heavier soils, prolonged saturation can increase the potential for nitrogen loss through denitrification, while excessive water movement through lighter soils can increase the risk of nitrogen moving below the active root zone.

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Dowie said the next challenge for local research was understanding how nitrogen and irrigation management could be better matched to individual soils and crops.

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“The bigger question is how much better we can become at matching nitrogen and irrigation management to what the crop actually needs across the Burdekin's different soils and landscapes, while improving productivity and profitability.”

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For Burdekin growers, the national research therefore provides useful evidence about the relationship between nitrogen, soil and water; but not a one-size-fits-all prescription. Further local testing will be needed to determine what strategies deliver benefits under the district’s specific soils, irrigation systems and commercial cane-growing conditions.

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