Utilization and Improvement of Marginal Soils for Agricultural Development in Indonesia

Indonesia is a humid tropical country that has very intensive weathering of soils resulting acidic soils such as Oxisols and Ultisols. In swampy ecosystems, organic matters accumulated become peat soils or Histosols. Reclamation of shallow peat for agricultural land will induce the forming of acid sulfate soils (Sulfaquept and Sulfaquent). Due to low fertility soils, the three of above soils are classified as marginal soils and now they are used for agricultural activities and some of them are still in forests. The use of marginal soils should refer to land suitability whether it is retained as a forest or used as agricultural land. The development of agricultural commodities on marginal soils must consider soil characteristics and agro-climate conditions. Oxisols and Ultisols have characteristics of low pH, low organic C, low macro and micro nutrients. In areas where rainfall is higher than 2,000 mm/year and evenly distributed throughout the year, oil palm plantations can be well developed. Meanwhile in the rainfall between 1,750-2,000 mm/year, rubber, cacao, coffee plants can be cultivated. Agricultural development in acidic soils need to be followed by the addition of soil amendments such as organic materials, humic substances, lime, fly ash, steel slag as well as fertilizers. Acid sulfate soils have a pH value of around 3 due to pyrite oxidation and usually low macro and micro nutrient content. Acacia mangium plants as raw material for pulp and oil palm plantation can grow quite well if followed by application of fertilizers and appropriate soil amendments. Peat soils are very fragile ecosystem so that in the upstream area and peat dome, they must be retained as forests. Peat can be developed for Acacia crassicarpa , oil palm, and rubber plants with good water and fertilizer management. Thin peat underneath mineral soil from river sediments can be developed rice field.