Increased nutrition and disease control improve medic pasture production

William Bellotti¹, James Neal¹, Alan McKay² and Mingpei You³

1. The University of Adelaide, Roseworthy, South Australia, 5371

2. South Australian Research & Development Institute, Adelaide, SA, 5001

3. CLIMA, University of Western Australia, Perth, Western Australia, 6009

In recent years pastures based on annual medics have not met the expectations of many low rainfall farmers who rotate wheat or barley with pasture. Farmers report dissatisfaction with the low productivity of the annual medics and the poor growth of wheat following medic dominant pasture. Several contributing factors have been implicated in this scenario including; fungal root diseases, root nematodes, low soil fertility, herbicide residues, and low profitability of livestock enterprises relative to cropping enterprises.

Recent surveys have identified a number of common annual medic pathogens. In South Australia (SA) and Victoria (Vic) the most common fungal pathogens were Rhizoctonia solani, Pythium irregulare and Fusarium spp. The most common fungi in Western Australia (WA) were Pythium spp., Fusarium spp. and Phoma medicaginis. The root lesion nematode, Pratylenchus neglectus, was common in SA and Vic but in WA only 5 out of 116 sites had high nematode numbers. Soils supporting annual medic pastures in the SA and Vic study region are normally alkaline, calcareous, and often deficient in P and Zn. In the WA study region, soils supporting medics are often slightly acidic.

On-farm field experiments were conducted in 1996 and 1997 over seven locations. The design included four treatments:

1. control: untreated medic pasture regenerating from soil seed bank

2. disease control: nematicide and mixture of three fungicides

3. improved nutrition: 31 kg P/ha and 8.16 kg Zn/ha

4. combination of treatments 2 and 3

Despite different site and seasonal conditions, the response of medic dry matter at flowering to the treatments followed a typical trend (Figure), the combined improved nutrition plus disease control treatment often producing double the dry matter of the untreated control treatment.

These results demonstrate that large potential gains in productivity of annual medic pastures are possible. Practical solutions to realise this potential require ongoing research and development.