Preliminary findings from a GRDC investment suggest wheat yields can be boosted by up to 26 per cent following a balansa clover compared to wheat-on-wheat rotations.

The research, conducted as part of the 'Integrated farming systems in the medium-rainfall zone' project, is focusing on the upper south-east of South Australia and looking to provide information on the whole-farming system impact of diverse crop rotations, including the incorporation of a pasture phase.

Trials were established at Sherwood and Bordertown, both in South Australia's upper south-east, in 2017 to evaluate 18 different crop sequences over a four-year rotation, among them:

• continuous pasture;
• continuous wheat;
• single and double break rotations; and
• a traditional grower rotation of wheat, canola, oats and faba beans.

Pasture phases in the trials are being mowed to mimic livestock grazing.

A regional research agronomist with Primary Industries and Regionas South Australia's research division at the South Australian Research and Development Institute (SARDI), Amanda Pearce, says that the project is intended ultimately to provide growers with more profitable crop sequencing decision-making.

"We are looking to increase farm sustainability, diversity and ultimately profitability through the adoption of improved rotations and break crop management options," she says.

"We are collecting an array of data, including yield, soil nitrogen, annual ryegrass populations, water-use efficency of crops, soil-borne disease numbers, grazing and hay value of crops, pasture biomass production, grain quality and the economics of break crops and rotations."

Prior to the project's commencement, a literature review and research gap analysis report into the use of break crops and pastures in integrated farming systems in the MRZ was completed.

This identified key issues that limit their adoption and potential opportunities to expand their use.

As such, the trials are examining the questions as follows:

• What is the magnitude of impact of an annual pasture legume in the integrated farming system rotation in the MRZ?
• Is the break effect of an annual pasture legume phase (environmental, agronomic, economic and risk) comparable to that of pulse and canola break crops?
• Do double breaks incease subsequent wheat yields compared to single breaks?
• Does the break effect impact on the second wheat crop and beyond?

Wheat yields

Ms Pearce says wheat yields at Sherwood in 2018 - the lower-yielding of the two sites - were responsive to legume break crops.

"At Sherwood, wheat yields were greater following balansa clover and subterranean clover, compared to the break crop canola and cereal options," she says.

"There was up to a 26 per cent increase in wheat yields following balansa clover, compared to a wheat-on-wheat rotation. When reviewing wheat grain yields in 2018, it was observed that at Bordertown - the higher-yielding site - the value of a legume break crop to increase subsequent wheat crop yields was not realised in 2018.

"We have also found that at Bordertown following the 2018 crops, balansa clover, lentils and faba beans, post-harvest soil nitrogen levels were significantly higher compared to after cereals and canola, while at Sherwood, subclover had greater residual soil nitrogen than all other crop types.

This indicates that pasture legume phases can provide residual soil nitrogen level comparable to that of puse crops."

Ms Pearce says research will continue for the next two seasons, including a sentivity analysis accounting for variation in crop commodity proces, grain quality and grade classification, to prevent any bias towards a particular crop and/or rotation.

More information: Amanda Pearce, SARDI, 0407 400 939, amanda.pearce@sa.gov.au