Restoring Properties of Artificially Degraded Ultisols and Oxisols and the Effect on Crop Yields under Tropical Conditions

Upland agriculture in Indonesia mainly relies on Ultisols and Oxisols, which have serious problems resulting from severe erosion and low organic-matter content. The objectives of the study were (i) to assess the effect of long-term rehabilitation techniques on soil organic carbon (SOC) and maize yields of a desurfaced Ultisol and (ii) to assess the effect of short-term rehabilitation techniques on desurfaced Oxisol properties and soybean yields. A 7-year field experiment was conducted on artificially desurfaced Ultisol grown with maize (Zea mays L.). The results showed that rehabilitation techniques using cattle manure, rice straw mulch or Mucuna sp. mulch were successful in restoring SOC content of degraded Ultisol to its initial natural state. All sources of organic-matter rehabilitations significantly increased maize yields on an Ultisol. Rehabilitations of degraded Oxisol under glasshouse conditions using phosphorus (P) fertilizer, organic matter, basic slag, and lime could increase cation exchange capacity (CEC) and nutrient availability and suppress Al toxicity. At the same time, soybean yields increased 11-14, 2-10, 1-5, and 1-3 times, respectively.