Increase feedbase production and quality of subtropical grass based pastures

Summary

​Tropical grass based pastures in Northern Inland NSW are productive and persistent and provide flexibility to sustainable grazing systems. In Central West NSW, an aseasonal, low-medium rainfall environment, there is also increasing interest in tropical pastures. To maintain productivity of these pastures requires nitrogen and legumes offer the most cost effective and sustainable source.

A range of prospective tropical and temperate legumes were evaluated as companion species and component studies addressed specific aspects of their agronomy and ecology. Despite low rainfall during much of the evaluation period, the superior tropical legume was desmanthus. Leucaena was also persistent, however, will not be recommended due to its potential as an environmental weed. Lucerne was the most productive legume evaluated and studies found that to reduce its competitiveness with the grass the pasture species should be sown more closely together. Barrel medic and woolly pod vetch were superior annual temperate legumes in both regions and the dry conditions highlighted that long term persistence of annual legumes requires good establishment and first year seed set.

Component studies were conducted to increase knowledge of legume seed banks (hard seed breakdown patterns, optimum sowing time and depth), and soil water dynamics. A tropical grass pasture with 4-9 plants/m2 was optimum for herbage production and water use efficiency, and importantly provided a 2 year window for establishing a companion legume. The risk of establishment failure of tropical grasses in the Central West was evident and spring determined as the optimum time to establish these species.

Additionally, alfalfa mosaic virus was detected in desmanthus cv. Marc; this is the first report of desmanthus as a host in Australia. A number of priority areas for future research were identified and discussed in this report.