G. Ecological compatibility

Environmental compatibility is an important characteristic of a sustainable system. Deforestation of the TRF ecosystem supposedly contributes 1.1 to 3.6 pg-C/yr as a principal greenhouse gas into the atmosphere (Houghton, 1991). The TRF ecosystem should be managed to sequester carbon into the soil and biomass rather than release carbon and nitrogen into the atmosphere, improve water quality rather than accentuate sediment load and eutrophication of surface and ground waters, and increase soil biodiversity within a simplified and managed ecosystem. Next to production, environmental concerns are very important for the sustainable management of the humid tropics.

Fig. 22 An ecological approach to sustainable land use in the humid tropics

The sustainability of a land-use system depends on a set of science based agronomic practices. These practices involve appropriate methods of forest conversion, erosion preventive and control measures, nutrient management techniques involving nutrient cycling through returning biomass and organic wastes to the soil, and production systems that optimize the use of the most limiting resources. A flow chart depicting the interaction among these technological options is depicted in Fig. 22. These practices interact with soil properties in determining productivity and impact on the environment, and are very specific to soil types and ecoregions.

The adoption of improved technologies on existing land can reduce pressure and the need for deforestation and clearing new land. Sanchez (1993) estimated that the adoption of science-based improved technologies on I hectare of land can save between 5 and 11 hectares of TRF from deforestation (Table 49). However, these technologies have to be adapted for soil and environmental conditions specific to each ecoregion. Developing locale-specific packages for alleviating specific soil and environmental constraints to sustainable land use requires fine-tuning and adaptive research for specific regions. In fact, it is difficult to provide blueprints for soil- or site-specific cropping/farming systems. Some systems have proven successful on research farms and under farmers, conditions and can be applied to similar soils and ecological conditions elsewhere in the humid tropics. Examples of such systems are outlined in Table 50.

Table 49 Estimates of TRF saved from deforestation by adoption of improved technology

Sustainable (1 ha)	TRF saved (ha)
Flooded rice	11.0
Low-input cropping	4.6
High-input cropping	8.8
Legume-based pastures	10.5

(Sanchez. 1993)

Improved germplasm plays an important role in the development of sustainable land-use systems. It is important to select new crops and develop improved varieties that can tolerate acid soil conditions and high concentrations of Al and Mn in the sub-soil, and grow under continuously warm and humid environments with high pressure from diseases and pests. The positive role that genetic resources and improved germplasm can play in developing sustainable systems cannot be overemphasized.

Table 50 Examples of potentially sustainable land-use systems in the humid tropics

Ecoregion	Sail type	Rainfall (mm/yr)	Potentially sustainable system
Lowland moist forest	Alfisols, Ultisols	1500 2000	Root crops, plantain, banana with mulch farming and chemical fertilizers
Lowland wet forest	Oxisols, Ultisols	2000 6000	Tree crops (e.g., rubber, oil palm, Gmelina, teak with cover crops and fertilizer use) and agro-forestry systems
Pre-montane rainforest	Oxisols, Ultisols	1500 2500	Coffee, pineapples, pastures with low stocking rate and live fences