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Beyond the Bale : September 2016
Native grasses provide native pastures with stability and ground cover, and respond to summer rainfall – while volunteer annual legumes and grasses in native pastures provide much of the winter and spring feed. Both components are essential for the long-term sustainability of the pasture. Research undertaken by Drs Malcolm McCaskill and Meredith Mitchell has demonstrated that substantial increases in carrying capacity can be achieved by addressing P and sulphur (S) deficiencies in native pastures, and that in many cases economic responses can be achieved without a need for pasture sowing. Dr McCaskill from Agriculture Victoria says applications of P stimulate the annual legume component of native pastures, increasing the nutritive value of the feed and animal growth rates. Nitrogen (N) fixed by the legume stimulates the native perennial grass, but also the volunteer annual grasses and weeds. “When fertiliser is applied to native pastures often an explosion in production of both annual grasses and legumes is seen, particularly in the spring,” Dr Mitchell said. “For species such as wallaby grass and redgrass this can be quite detrimental if there is insufficient grazing pressure, especially in the spring, because this allows annuals to shade and smother the native perennials. “In many native pastures, the productivity of the system is driven by the annual components. These annual species are generally more responsive to fertiliser applications than are the native perennial grasses, but not always. Responsiveness to fertiliser applications depends upon the dominant native grass species that is present.” Knowing the species in your paddock provides an indicative guide to how responsive they would be to the increased P, and the additional grazing pressure (see section below) required to utilise the additional feed. Onion grass rather than native grasses dominate many pastures of low fertility in Victoria. The onion grass first needs to be controlled by herbicide before a worthwhile response to fertiliser can be expected. GRAZING MANAGEMENT If fertiliser is applied, which in turn grows more grass, the stocking rate should also be increased – there should be sufficient livestock to utilise the extra feed. “The volunteer annual grasses and weeds tend to be more competitive as P and N fertility increases, leading to a decline in the native perennial grass component. This leads to an uneven feed supply, with an excess in the spring and then poor growth over summer leading to bare ground and erosion risks.” To avoid this, it is recommended that legumes should be at most 20 per cent of pasture on offer in spring. Grazing and lower fertiliser rates (<10 kg P/ha/year) can be used to hold the legume content to this level. At higher legume contents, a sown grass is required to provide stability. “Deferral of grazing over summer favours the native grass, because this is the time of year that they produce seed and build up root reserves. Paddocks can then be grazed in late summer or early autumn. “Hard grazing in summer and autumn favours annual legumes by providing bare spaces for them to colonise at the autumn break, but there are erosion risks of bare ground particularly on steep areas. Therefore, it is critical to maintain ground cover targets on slopes and shallower soils.” DEEP SOILS ARE NEEDED Soils that are deeper and therefore have a greater water holding capacity show a stronger economic responsive to fertiliser application, Dr Malcolm McCaskill adds. “Some areas of native pasture should not be fertilised, such as rocky soils, steep hills, and westerly aspects. On these areas, responses to increased fertility are poor, and it is more important to preserve the native perennial grass cover to control erosion.” MORE INFORMATION A new ‘Managing phosphorus in native pastures’ fact sheet that includes a guide to the differing levels of responsiveness to P of native pasture and common introduced species is available on the AWI website at www.wool.com/publications MANAGING PHOSPHORUS IN NATIVE PASTURES Research undertaken by Agriculture Victoria and supported by AWI has demonstrated that where there is a sufficient density of high-quality native grasses in native pastures, fertility can be increased to moderate levels by the application of phosphorus (P), without the expense of pasture sowing. Native pasture species dominate the wooded hills in the background, while sown species dominate paddocks in the foreground. KEY POINTS • Applied P boosts the legume component of native pastures, but too much leads to annual grasses and weeds. • Grazing management is essential if fertilisers are applied to native pastures. Rotational grazing is critical to ensure maintenance of the perennial native grass component of the pasture. • Native pasture species have differing responses to P. Find out what species are on your farm. • The more productive areas of the farm such as valleys with deep soils should be the first priority in applying fertilisers. 44 ON FARM
In the Shops - September 2016