Tropical Grasslands (1993) Volume 27, 131149
Northern dairy feedbase 2001.
1. Summer pasture and crops
D.J. MINSON1, T. COWAN2 and E. HAVILAH3
1Division of Tropical Crops and Pastures, CSIRO, Brisbane, Queensland, Australia
2Queensland Department of Primary Industries, Mutdapilly Research Station, Ipswich, Queensland, Australia
3NSW Agriculture, Pasture Research Centre, Berry, New South Wales, Australia
There is a very high potential for forage growth during summer in the tropics and subtropics, but there are many problems associated with realising this potential in terms of milk production. The tropical grasses are capable of yielding 50t DM/ha/yr, though in practice yield is less than one-third of this, and the high structural fibre and low protein contents of these grasses severely restrict milk production during autumn. Twining tropical pasture legumes are unstable under commercial stocking rates and effort is now directed to species suited to heavy grazing, such as Pinto peanut (Arachis pintoi cv. Amarillo) and lotus (Lotus pedunculatus cv. Maku), and browse shrubs such as leucaena (Leucaena leucocephala). Lucerne (Medicago sativa) is recognised as an outstanding forage for grazing or conservation, but present varieties are unsuited to most soil types on dairy farms.
Water use efficiency is a high priority for research into summer forage crops. In dryland areas forage and grain sorghums (Sorghum spp.) are used to maximise dry matter production with limited moisture supply. There is a strong trend towards maize (Zea mays) for silage in irrigated areas, and areas requiring further research include delineation of areas suited to the crop, agronomy and integration into farming systems.
Legume crops promote higher intakes than grass crops, though at present there is heavy dependence on Lablab purpureus varieties developed over 20 years ago. Other crop legumes, including the soybeans, may be useful, particularly if combined with water-efficient cultural practices.
There is general concern at the cost of fertiliser inputs and their fate once they leave the pasturesoil complex. In particular, efficient methods of using nitrogen fertiliser are required. As the forage systems for the tropics and subtropics develop there will be a greater emphasis on quality of forage, emphasising characteristics such as low structural fibre content, high protein content, low degradability of protein in the rumen, a favourable amino acid composition of protein, and adequate mineral content.