Sustainable agriculture can provide opportunities to address productivity and environmental goals simultaneously. By adopting alternative land use practices that can reduce the need to abandon established farmland and that can restore degraded land to economic and biological productivity, farmers can meet their food needs and make an adequate living without contributing to the further depletion of forests and other natural resources.

The development of sustainable production systems suitable for areas with low-quality soil and water resources rests on an appreciation of the constraints on agricultural productivity in the humid tropics (National Research Council, 1982; Savage, 1987). Agriculture is fundamentally a process of converting solar energy, through photosynthesis, into useful biomass. Biological productivity requires solar energy, water, and nutrients. These are abundantly available in the humid tropics, but this productive potential is not reflected in the performance of agricultural systems, which is typically poor. Intensive farming in temperate zones converts 2 percent of photosynthetically active incident solar energy to dry matter; in the humid tropics, the conversion rate is no more than 0.2 percent (Holliday, 1976). This relative inefficiency is a reflection of both socioeconomic and environmental constraints. This discussion focuses on the latter.

Water can be a limiting factor in the humid tropics, despite periods of abundant rainfall (Juo, 1989; MacArthur, 1980). Many high-rainfall areas have dry periods of sufficient length to adversely affect plant growth. Water shortages often occur where the soils have low water-holding capacities, but they can also affect areas with more favorable soil environments. A few days without rain can seriously impinge on biological productivity. For example, Omerod (1978) compared rainfall distribution and water retention in London, England, with those in Lagos, Nigeria. Although the total rainfall (1,820 mm) in Lagos was 220 percent higher than that in London, the probability of drought was much higher in Lagos because of the erratic distribution of rainfall in Lagos in contrast to the relatively uniform distribution in London. Also important were the relative rates of evaporation, leaching, and runoff (higher in Lagos) and the water-holding capacity of the soils (much lower in Lagos).

The combination of high temperatures and humidity in the hu-

Front Matter (R1-R16)

Executive Summary (1-18)

Part One (19-20)

1 Agriculture and the Environment in the Humid Tropics (21-65)

2 Sustainable Land Use Options (66-137)

3 Technological Imperatives for Change (138-158)

4 Policy-Related Imperatives for Change (159-191)

References (192-214)

Appendix: Emissions of Greenhouse Gases from Tropical Deforestation and Subsequent Uses of the Land (215-260)

Part Two: Country Profiles (261-264)

Brazil (265-351)

C te d (352-392)

Indonesia (393-439)

Malaysia (440-482)

Mexico (483-548)

The Philippines (549-624)

Zaire (625-658)

Glossary (659-674)

Authors (675-678)

Index (679-704)