Semiarid Soils of Eastern Indonesia: Soil Classification and Land Uses

Abstract

Despite the high annual rainfall (2,000–5,000 mm) of Indonesia, 3.3 × 10⁶ ha area of East Nusa Tenggara (NTT) province receives annual rainfall between 1,000 and 2,000 mm with 5–8 dry months (<100-mm rainfall), and about 1 × 10⁶ ha area receives <1,000 mm annual rainfall with 8–10 dry months. About 1.7 × 10⁶ ha land is mountainous (>30% slope), and 1.5 × 10⁶ ha is hilly (15–30% slope). The steep slopes and high-intensity rainfall in rainy season cause high erosion and sedimentation. This results in >1-m soil depth at the valley bottom dominated by Haplustepts and Haplustolls, and <50-cm soil depth in the upper slope dominated by Lithic Ustorthents or Lithic Haplustepts. The soil reaction is acidic to slightly alkaline (pH 4.1–7.8), low to high organic carbon (1.2–5.4%), high to very high (25%-HCl extractable) P and K, moderate to high exchangeable cations (18–41 cmol(+) kg⁻¹), and high base saturation percentage. About 2.4 × 10⁶ ha land is suitable for agriculture, of which 0.5 × 10⁶ ha occurs in the <1,000 mm; 1.7 × 10⁶ ha in the 1,000–2,000 mm; and 0.2 × 10⁶ ha in the >2,000 mm annual rainfall areas. Due to low rainfall, the recommended commodities were tailored to the availability of water. Based on soil characteristics and rainfall, recommendations are made for crop selection. Annual crops are recommended for the flat areas and valley bottoms, while perennial crops are recommended on the sloping areas. It is recommended, for example, for annual crops, adjustment of the planting time is to be made with the rainfall distribution, whereas for perennial crops, selection of those crops is to be made which require several months of dry period, such as candlenut, cashew nuts, kapok, and Jatropha.