The yield, quality and irrigation response of summer forage crops suitable for a dairy pasture renovation program in north-western Tasmania

Abstract

The yield and quality of perennial ryegrass, short-rotation ryegrass–perennial ryegrass mix, oats, millet, maize, rape, kale, pasja and turnips were determined over a 13-week summer period in 1995–96 and 1996–97. The experiment was conducted on the Elliott Research Station in north-western Tasmania (145˚E, 41˚S) and consisted of 2 irrigated and 2 dryland main plots. Within each main plot was a randomised complete block design with 9 forage crop subplots. Where forage is required through the summer, there is little advantage in establishing millet or oats over a spring-sown ryegrass pasture, mainly as the former still require replacement with permanent pasture in the autumn. However, if additional forage is required from late January then turnips are clearly superior to the other forages evaluated in all respects, apart from a low bulb crude protein (CP) content. Turnips responded significantly to irrigation, producing between 15 and 22 kg DM/ha.mm irrigation applied, with yields ranging between 7.9 and 10.6 t DM/ha dryland and between 13.5 and 14.4 t DM/ha under irrigation. The metabolisable energy (ME) and CP contents of turnips were 12.5 MJ/kg DM and 12.4% in the shoots and 13.4 MJ/kg DM and 7.0% in the bulbs, respectively. In comparison, the other fodder crops tested yielded between 4 and 6 t DM/ha under dryland conditions and between 5 and 7 t DM/ha under irrigated conditions. Turnips were most economic, costing on average A$120/t DM irrigated and $160/t DM dryland, while spring renovation to perennial ryegrass cost $385/t DM irrigated and $344/t DM dryland; clearly more expensive than purchased feeds for this period. These findings confirm the choice of many farmers that, of the species examined, turnips are the most suitable as a summer fodder crop, both irrigated or dryland, and integrate well with a pasture renovation rotation.