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ABSTRACT
Traditional shifting cultivation is only sustainable with long fallow periods. In many upland areas of Southeast Asia, fallow lengths have shortened to a point where the objective of the fallow, to restore soil fertility, is not being met, and shifting cultivation is no longer sustainable, either economically or environmentally. On steeply sloping land, soil erosion is substantial, especially as soil fertility declines.
‘Improved’ fallows can hasten the process of soil fertility recovery, and provide alternative products for market. A bioeconomic analysis of one such improved fallow—namely a fallow involving a Gliricidia plantation on Imperata grassland—is reported here. A Gliricidia fallow system is not commonly practiced by smallholders. It is modelled here to assess its potential as an alternative to traditional shifting cultivation systems on steeply sloping land. The analysis is undertaken using a computer model, which is an amalgamation of an existing biophysical, agroforestry model (SCUAF version 4), and an associated economic spreadsheet model.
The model predicted that a Gliricidia fallow can increase soil nutrient concentrations (carbon, nitrogen, and phosphorus) and reduce soil erosion. This contrasts with the negative effects of an Imperata fallow. As well as enhancing maize production by maintaining higher soil fertility, Gliricidia fallows offer revenue from other products, such as firewood. Although the Gliricidia fallow system does require significantly more labour to operate than the Imperata system, this is compensated by the higher level of productivity and revenue from other products. Overall, the Gliricidia fallow system is potentially more profitable and more productive than the Imperata fallow system, especially where there is a reasonable market for firewood.
The time taken to establish the Gliricidia fallow system in the first instance is an important factor in adoption by smallholders. During the conversion period, smallholders will incur a loss in the first year, and it will take approximately four years for smallholders to begin making a profit above that which is achievable with the Imperata fallow system.
The approach to evaluation reported in this paper has merit in being relatively inexpensive, yet powerful. However, the time frame and cost of this analysis are minute in comparison to what would be involved in field experiments.