L.'t MANNETJE

Agricultural University, Department of Agronomy, Wageningen, The Netherlands

Abstract

This paper consists of two parts. First the N fixation, C storage and animal production of legume-based pastures are reviewed; then the adoption of pasture legume technology is discussed in terms of technical,biological and socio-economic constraints. Different forage production systems and their place in livestock production systems are described. The prospects for legume use in Australia, south-east Asia, Africa south of the Sahara and Latin America are discussed in relation to forage and animal production systems.
Tropical legumes fix as much N as temperate ones. Measured amounts of N added to pasture systems range from 30–290 kg/ha/yr for herbaceous legumes in mixtures with grasses to 575 kg/ha/yr for a pure stand of Leucaena leucocephala. Soil N increments under tropical legumes were up to 140 kg/ha/yr in Australia and 128 kg/ha/yr in Costa Rica.
Legume-based tropical pastures store more C than pure grass or native pastures. In Colombia,an improved grass-legume mixture had accumulated 237 t/ha C to a depth of 1 m over 6 years compared with 186 t by a grass only pasture.
The highest cattle liveweight gain recorded from an irrigated pure stand of L. leucocephala was 2000 kg/ha/yr in the Kimberleys, Western Australia. On herbaceous legume-grass pastures the highest liveweight gain measured was 937 kg/ha/yr on Brachiaria brizantha — Arachis pintoi in the humid tropics of Costa Rica. Maximum milk production on tropical grass legume pastures without concentrates is around 10–12 kg/cow/d. However, due to high carrying capacities, milk yields per ha of about 8000 kg/ha/yr have been recorded in north Queensland and in Malaysia.
There is reasonable adoption of legume-based technology in tropical Australia and parts of south-east Asia and Latin America. However, many countries, particularly in Africa, have such a low development status that problems related to land tenure, infrastructure and social justice need to be solved first.