Sustainability of upland agriculture in the Philippines : evaluating the potential of a tree fallow system

Abstract

Smallholder farmers in the uplands of Southeast Asia practice a form of short fallow shifting cultivation that has been shown to be unsustainable in the long term. This study examines the potential of an improved fallow system that can improve soil fertility, crop yield and the farmer ' s economic situation. The improved fallow system involves the establishment of a nitrogen fixing multipurpose tree plantation during a short fallow period. The tree foliage is used as green manure, maintaining soil fertility and providing improved crop yields. A bioeconomic model is used to compare the improved fallow system with a traditional short fallow shifting cultivation system. The model is a combination of cost benefit analysis and the SCUAF model (Soil Changes Under Agriculture, Agroforestry and Forestry). Cost benefit analysis is used to identify the most economically efficient system. The SCUAF model is integrated within the cost benefit analysis framework, and is used to observe changes in crop productivity over time. It is a relatively simple deterministic model designed to predict the effect of various tree and crop combinations on soils and commodity outputs. From a biophysical perspective, soil nutrient levels (Carbon, Nitrogen and Phosphorus) improved by up to 80 per cent, soil erosion decreased and crop yield was found to be sustainable, under the Gliricidia fallow system. In comparison, soil nutrients fell to approximately 30 per cent their initial levels, soil erosion increased and crop yield declined, under an Imperata fallow system. Economically, from both social and private perspectives, the Gliricidia fallow system was shown to be quite profitable when a market for firewood is available, but showed a small loss based on revenue from maize only. The Imperata fallow system, in comparison, was only marginally profitable from a private perspective, and quite unprofitable from a social perspective. In the transition between an Imperata fallow and a Gliricidia fallow system, it takes four years for crop yields to rise from the low levels obtained from an Imperata fallow system to the higher levels obtained from a Gliricidia fallow system. Economically, the system incurs a loss in the first two years of the transition period, and it is not until after the sixth year that these initial losses are recovered. Thus, unless farmers are able to absorb these initial losses, they- will be unlikely to adopt the Gliricidia fallow system, even though it is more profitable over the long term. Introducing cattle in the Gliricidia fallow system, while involving a trade-off between the use of Gliricidia for cattle fodder and for green manure, can significantly improve the profitability of the system. A system with two cows, two Imperata fallow plots, three Gliricidia fallow plots and one maize crop plot, will maximise both economic and environmental benefits. This provides a sustainable maize crop and a high return to farmers from cattle, maize and firewood. Show more