Soil Suitability Evaluation for Sawah in Sumani Watershed in West Sumatra Indonesia using Surfer Tool

This study characterized the soils of the Sumani watershed, West Sumatra Indonesia, for soil-suitability evaluation for sawah using Surfer tool-based multicriteria overlay analysis techniques combine with FAO 1976 procedure. The study showed that 78 samples at four soil orders including six groups, i.e. Oxic Hapuldant(OH), Andic Humitropept(AH), Typic Kandiudult(TK), Aeric Tropaquept(AT), Typic Distropept(TD) and Typic Eutropept(TE). Soil developed from fourth geological types. Soil chemical properties were anlysed using ICP and spectrofotemetry. The analysis revealed that the sawah soils number 1-2, 5, 16, 19, 25, 27, 38, 41-42, 44-45, 53-54, 64,68 and 78 were “moderately suitable (S2)” and sawah soils number 3-4, 6-14, 17-18, 20-24, 26, 28-32, 33-37, 39-40, 43, 46-48, 49-52, 55-63, 65-66, 67-75 and 76-78 were “marginally suitable (S3)” for sawah development. In Sumani watershed, the area analysis showed that for a sawah area about 9974.43 ha (17.1%) of total sawah is moderately suitable and classified as S2. An area about 48355.57 ha (82.9%) is marginal suitable (S3). However, a 0 ha (0%) area is not suitable (N) and 0 ha (0%) area is suitable (S1) for sawah because of uncorrectable factors commonly due to low available silicate(Si) and introduce silicate fertilizer to sawah soil that change sawah soil in criteria S2 (82.9%). The study demonstrated that Surfer-based tool multicriteria overlay analysis of soil thematic parameters combine with FAO method will be of immense help in soil-suitability evaluation for present sawah condition.