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Biophysical characterization of rainfedsystems in Java and South Sulawesiand implications for researchI. Amien and I. LasLimited suitable land for rice production in the past has forced the developmentof terraced and bunded rice fields at a higher elevation. Because therice-cropping system lacks terrestrial water resources, it totally depends onavailable rainfall. Java, North Sumatra, and South Sulawesi have the largestareas of rainfed lowland rice fields, 796,900, 210,300, and 259,100 ha,respectively. Because of high competition for space, rainfed rice area is steadilydeclining on Java but is relatively stable outside Java. A high proportion ofthe rainfed rice area is in the northern part of Java and eastern part of SouthSulawesi. The soils of rainfed areas in West Java were formed from acid tuft.In the other provinces of Java and South Sulawesi, the soils were formedfrom limestone or marine sediments. Less fertile soil that is low in P and Kand the low adoption of modern technology in rainfed areas resulted in lowerrice yields. Yields in rainfed areas were 10% to 25% less than the averageyield in Java and 15% to 20% less than the average yield in South Sulawesi.Yield levels of lowland rice on Java are inversely related to the proportion ofrainfed lowland rice areas. With monsoonal rainfall patterns, the rainy seasonbegins in October in West and Central Java, in November in East Java,and in March in South Sulawesi. West Java and South Sulawesi have nodistinct dry period, while in Central and East Java the dry period varies from4 to 5 mo. During El Niño years, the rainy season comes about a month later,with rainfall less than 70% of that of normal years. Dependence on rainfallalso makes rainfed rice more susceptible to drought, particularly during ElNiño years. This rainfed rice system helps reduce water runoff during therainy season, but differs with deep-rooted vegetation, because the waterretained is mostly lost through evapotranspiration. In the increasingly globalizedeconomy, labor shortages and more competitive markets threaten thesustainability of the rainfed rice system.Biophysical characterization of rainfed systems . . . 145