Pulse crops a standout feature of southern NSW rotation trials

These are finding based on five years of data, from an extensive GRDC-funded southern NSW research project. Ongoing crop rotation research is located at Wagga Wagga, Greenethorpe, Urana and Condobolin. The research will continue so that final conclusions from the extensive study will be based on six years of data.

CSIRO farming systems agronomist Dr John Kirkegaard leads the study supported by other CSIRO scientists, a team of researchers from NSW DPI led by Mat Dunn, and a number of agricultural advisers from across the southern NSW cropping belt. More than 300 farmers were involved in consultation when devising the research in 2017. FarmLink, a major southern NSW grower organisation, which leases the Temora Research Centre, is also involved in extending the outcomes through its grower networks.

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Grain legumes, as part of the rotation, provided profits and return on investment that matched or exceeded the baseline canola-wheat-wheat/barley sequences at all sites during 2018 to 2022. This has included extremes of very dry (2018/19) and very wet seasons (2020 to 2022). Added profitability and return on investment of rotations that include pulse crops (chickpeas), despite their low area in southern NSW, has been a standout feature of the rotation trials.

The driver of profitability in the systems with legumes has been the significant legacy of soil nitrogen (50 to 100 kilograms per hectare) on subsequent crops, which reduced nitrogen input costs in subsequent seasons. Canola following legumes has also yielded up to 0.7 tonnes per hectare more. These legacy effects across the sequence more than compensate for lower profit from the legumes in specific years.

In some cases Dr Kirkegaard said the legacies of extra water left by legumes at harvest had diminished at sowing time of subsequent crops due to reduced soil cover after the legumes. But this was dependent upon the pattern of summer fallow rainfall he said.

Of the non-grazed rotations, the most consistently profitable involved pulses (faba bean, chickpeas, lupin) with following canola and wheat crops, which required less nitrogen fertiliser (up to 50kg N/ha) than the baseline canola-wheat-barley systems. Nitrogen benefits of legumes have proven especially valuable as fertiliser prices have risen dramatically.

Early sowing of slower-maturing wheat and canola varieties, both for grazing and grain, compared to more traditional May onwards sowing can be more profitable due to higher yields in better years. The exception is sowing wheat and canola at the same time as dual-purpose crops (March), but where they were not grazed. They tend to use more soil water (excessive growth), suffer yield penalties in dry spring years and have no grazing income.

Early-sown, dual-purpose grazed crops (wheat and canola) as part of the rotation have been highly profitable and the most profitable phase of the rotation in all seasons. Dual-purpose grazed wheat and canola were especially responsive to higher nitrogen (both fertiliser and legumes) due to increased forage and grain yield. In all cases, early-sown un-grazed systems were less profitable than the baseline, partly due to limited varietal choice for this practice.

Higher nitrogen rate strategies (targeting Decile 7 finish to the season) provided increased biomass for grazing crops or hay cuts, but had either no effect or negative effects on grain yield and profit in the dry 2018/19 years. However, the unused nitrogen in dry seasons carried over to improve biomass and yield in subsequent years, especially in the wet 2020 to 2022 years. Residual nitrogen from legumes and fertiliser significantly increased yield.

This research aims to find strategies for improved efficiency and profitability, but also highlight possible problems and limitations. For example, early sown high nitrogen high, yielding cereals and canola may leave soil water at lower levels post-harvest than lower yielding later planted crops. This may have negative impacts on following crops in dry seasons. In contrast, rotations with pulses boost canola yield, reduce cereal disease, and provide more weed control options and sometimes more soil water for following crops.

For more details of the research, contact FarmLink Research Limited PO Box 521, Temora, NSW, 2666. Call (02) 6980 1333 or email admin@farmlink.com.au

Next week: More fertiliser myths exposed.