Legumes Combat Sown Pasture Rundown

AUSTRALIA - Adding legumes to sown grass pastures is the most viable option for Queensland producers to combat pasture rundown, a phenomenon that reduces pasture production and animal performance by up to 50 per cent over 5–20 years.
calendar icon 26 September 2012
clock icon 2 minute read
Meat & Livestock Australia

Incorporating legumes into grass-only pastures was the best long-term option for increasing pasture production, animal performance and economic returns on ageing sown grass pastures in central and southern Queensland, an MLA-funded project has revealed.

The research completed by Queensland Department of Agriculture, Fisheries and Forestry (DAFF) found the mitigation of pasture rundown effects by introducing pasture legumes returned a net value of $400–1,400/ha, far exceeding other options such as mechanical renovation, protein supplements, herbicides and fertilisers.

DAFF conservatively estimated the cost to industry of pasture rundown would exceed $17 billion in the next 30 years. This is based on productivity decline across 12 million hectares of established improved pastures in northern Australia, around 75% of which is buffel grass.

DAFF Senior Pasture Agronomist (Sown Pastures) in Toowoomba, Gavin Peck, said symptoms of pasture rundown are widely recognised, but often wrongly attributed to water or seasons.

He said pasture rundown is not due to a loss of nitrogen from the system. The initial high production of sown pastures results from increased available nitrogen and water that accumulates in the soil during a fallow.

After sowing, available soil nitrogen is progressively incorporated into soil organic matter which breaks down slowly, nitrogen is effectively tied up in the soil and unavailable for plant growth.

Previous trials have shown that incorporating stylos into grass-only pastures can increase animal performance by 40–60kg/head/year and well-managed leucaena by 70–110kg/head/year.

DAFF also estimated stylos could increase nitrogen fixation and cycling by 20–50kg N/ha/year, leucaena by 60–75kg N/ha/year and medic by 20–50kg N/ha/year, leading to improved grass growth and pasture quality. The review identified persistent and productive legumes for permanent grass pastures on clay soils.

However, Gavin said options for the Brigalow Belt were commercially released relatively recently, and commercial plantings have had mixed results.

MLA is funding a five-year project with DAFF to increase the adoption of legumes and other options for improving productivity of sown-grass pastures in central and southern Queensland.

Another project is looking at how alternative rhizobia inoculation practices could increase pasture productivity three-fold across the northern beef industry.

The effectiveness of ‘native’ rhizobia in soils collected from across the region will be assessed in glasshouse trials. New inoculation approaches in the hot, dry environments in which perennial tropical legumes are typically grown will be assessed through field trials.

Trial results will be discussed with producers participating in the ‘Pasture Rundown’ project to determine the most practical methods for commercial properties and develop recommendations for their use across the region.

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