Improvement of Livestock Production in Crop-Animal Systems in ...

declining soil fertility reduce yields. The soil is left fallow for four to ten years, which allows for the regrowthof forest species and the restoration of soil fertility. However, the fallow periods that once lasted 10–40 yearsare being reduced in most countries due to increasing population pressure. This development significantlyaffects the restoration of soil fertility.Land degradation has occurred often in the humid tropics when shifting cultivation is practised bymigrants, with little experience of the system or soil conservation, and the land is left devoid of vegetationfor a considerable time. Under these conditions, there has been major erosion in hilly areas and siltation ofrivers. In the Philippines, soil erosion is a serious problem in areas with rolling to steep slopes and is enhancedwhere upland rice is grown. Shifting cultivation in these hilly areas causes average annual soil losses of 100t/ha. However, trials by Labios et al (1995) on sloping land showed that, over two years, average soil lossesfrom the use of alley-cropping with Flemingia macrophylla was only 42.4 m 3 /ha compared to 139.6 m 3 /haunder farmer practice without contour hedgerows. Rice yields were highest in the alley-cropping system. Therisk of erosion is much greater in the humid zone than in the sub-humid zone as a result of higher intensityrainfall.Animal production systemsAnimal production systems involve both ruminants and non-ruminants, and systems integrating crops andanimals occur throughout South-East Asia. These have considerable potential for further improvement andthe benefits are associated with complementary interactions between sub-systems (e.g. crops, animals or fish)in which the products are additive (Edwards et al 1988). Two examples of such integrated systems, theireconomic benefits and contribution to sustainability are given by Devendra (1993). These arepig–duck–fish–vegetable systems in Vietnam, Indonesia and the Philippines, and small ruminant–perennialtree crop systems throughout South-East Asia and the Pacific.Ruminant production systemsThere are three major categories of ruminant production systems.Extensive grazing systemsThese tend to be low-input–low-output systems, with less opportunities for development through improvedtechnology use.• Grazing of native grasslands.• Grazing of upland forests and forest margins.Systems combining arable cropping with pasturesCrop–animal interactions are particularly important in these systems, and the opportunities for interventionsare significant.• Roadside and communal grazing combined with stubble grazing.• Animals tethered or allowed free access.• Stall-feeding of grasses, crop residues and AIBP.Systems integrated with perennial tree crops• Grazing under coconut, rubber, oil palm and fruit trees.An estimated area of about 210 million ha are found under perennial tree crops in South-East Asia(Alexandratos 1995).These systems will be expected to respond increasingly to changing demand and consumer preferencesat varying levels through diversification, intensification, specialisation and commercialisation, depending onresource endowments, supporting infrastructure, market potential and policy.