Exploring legume establishment on Mitchell grass downs: simple establishment options for the north

The challenge of seasonal nutritional deficits

North Queensland typically has summer dominant rainfall from November to April, which is then followed by a consistent and extended dry period from May to October.  Beef cattle producers in northwest Queensland face a familiar challenge every dry season – the decline in nutritional quality of native Mitchell grass and Flinders grass pastures. This causes a decline in cattle live weight gain, and eventually, weight loss by the end of the dry season. Successful establishment of legumes such as desmanthus and stylos into existing pastures, can provide a high quality, readily digestible feed source containing higher levels of crude protein (14–18%) and metabolizable energy (8–10 MJ ME/kg DM), thereby alleviating the nutritional shortfall in the dry season.

A small trial led by the North Queensland Pastures Resilience Program (NQ PRP) team, is testing the establishment of productive legumes on cracking clay soils 80km northeast of Julia Creek, northwest Queensland.

This site poses unique challenges:

• Rainfall variability: Annual averages of 550 mm, with significant variability (300 mm to 700 mm).
• High temperatures: Summer average maximum temperatures reach upwards of 38°C.
• Soil limitations: Phosphorus levels (Colwell 12 mg/kg) are adequate; however, sulphur levels (MCP 4.6 mg/kg) are low or marginal for good legume growth. Additionally, cracking clay soils dry out quickly with rainfall, meaning soil surface crusting can stifle seedling emergence.

Method and initial outcomes

In January 2024, following 350 mm of rainfall, a 10 ha unfenced site within a larger paddock was directly sown into 6 m x 1000 m strips. Caatinga stylo (Primar) and desmanthus (a mixture of Ray and Progardes) were germination tested and based on the results treated for hard seed dormancy by mechanical scarification prior to planting. Sowing rates were adjusted to account for low germination percentage (hardseed content) as shown in the table below.

The site was previously dense Flinders grass that had been baled to reduce existing dry matter. No fertiliser or herbicide was applied to best represent typical extensive beef production systems in the region and to determine viable options for legume establishment in existing conditions. The seed was broadcast directly into the strips using a fertiliser spreader. Rainfall on the site (30mm) shortly after planting meant planned rolling could not take place.

A further 130 mm of rainfall was recorded on the site from planting until the first growth assessment in March 2024, where seedling populations were measured based on frequencies per m². Desmanthus populations averaged ~20 plants/m², which is a good starting population for legumes in dryland pastures. Caatinga stylo showed lower establishment, however, with around 5 plants/m². Observations in May 2024 confirmed seedling survival under heavy competition from Flinders grass.  Further population counts and pasture yields will be taken at the end of the 2024/2025 wet season.

Addressing challenges in establishment

The trial demonstrates the potential for legume establishment in the region but also highlights the challenges posed by the dominating Flinders grass , which needs to be addressed before or after sowing. Possible strategies to improve establishment include:

• Staggered cultivation: staggered cultivations to kill Flinders grass seedlings before sowing, either by repeated cultivation or application of a suitable herbicide before or immediately after sowing
• Herbicide application: using selective herbicides to reduce competition post emergence.

Despite the competition from the Flinders grass, this small strip trial indicates potential for simple approaches to desmanthus and Caatinga stylo planting and establishment into Mitchell Grass Downs pastures. If further yield measurements confirm successful establishment, it will indicate successful introduction of legumes into these environments is possible, with a range of associated benefits for pasture quality, soil improvement and animal performance.

This work is made possible through the Queensland Pasture Resilience Program, a partnership between the Department of Primary Industries, Meat & Livestock Australia, and the Australian Government through the MLA Donor Company. If you would like to know more or get involved in the program, please contact one of the following team members: