ABSTRACT

Upland rice is grown on about 19 million ha globally and takes up about 13% of the world’s rice-growing area. In some regions it covers more than half of the total rice-growing area (Gupta and O’Toole 1986). It is an important staple crop for shifting cultivators in many parts of the humid tropics. Nevertheless, it is generally grown only as a subsistence crop planted by resource-poor farmers who apply little or no fertilizer, generally resulting in grain yields of less than one metric ton/ha. There are an estimated 250 million shifting cultivators worldwide and about 100 million of them live in Southeast Asia (Christanty 1986). As demand for land increases because of an increasing human population, the area available to shifting cultivators for fallowing becomes smaller and smaller, so to maintain their cropping area, farmers fallow their land for shorter periods. One result of this is lower crop yields (Warner 1991). One strategy for slowing the decline in crop yields is the use of fast-growing, nitrogen-fixing tree species as fallow crops to improve nutrient availability for subsequent crops in the shifting cultivation cycle (Ahn 1979; Unruh 1990).