Communications in Soil Science and Plant Analysis, 42:2751–2766, 2011 Copyright © Taylor & Francis Group, LLC ISSN: 0010-3624 print / 1532-2416 online DOI: 10.1080/00103624.2011.622822 Growth of Cocoa Planted on Highly Weathered Soil as Affected by Application of Basalt and/or Compost J. SHAMSHUDDIN, 1 M. ANDA, 2 C. I. FAUZIAH, 1 AND S. R. SYED OMAR 1 1 Department of Land Management, Faculty of Agriculture, Universiti Putra Malaysia, Serdang, Selangor, Malaysia 2 Center for Agricultural Land Resource Research and Development, Bogor, Indonesia Oxisols, which are highly weathered, occupy a large area of Malaysia. These soils are infertile because of low pH, calcium (Ca), magnesium (Mg), and potassium (K) lev- els but high aluminum (Al) content. The infertility can be ameliorated by applying soil amendments. A study was conducted to determine the effects of basalt and/or rice husk compost application on cocoa growth planted on an Oxisol. The results showed that either basalt or rice husk compost and their combinations were effective ameliorants. Basalt application increased soil pH and exchangeable Ca and Mg while decreasing exchangeable Al. Accordingly, soil solution Ca, Mg, and K increased and Al and man- ganese (Mn) concentrations decreased. Silicate released from basalt was able to lower the pHo (the pH at which the net charge of the variable charge minerals is zero), indicat- ing a negative charge was being generated, which led to increase in the cation exchange capacity (CEC) of the Oxisol. The improvement in soil fertility because of application of the amendments had improved cocoa growth. Leaf K and P of the cocoa planted on the basalt-treated soils were within the sufficient range for cocoa growth. Rice husk compost applied at a rate of less than 20 t ha -1 in this trial was not able to supply suf- ficient N to the cocoa. Basalt application at an appropriate rate effectively ameliorates acidic soil infertility, but it takes time to realize the positive effects of application as it slowly dissolves under field conditions. Keywords Aluminum, basalt, cocoa, Oxisol, soil acidity, variable charge mineral Introduction Highly weathered soils, classified as Oxisols, are very widespread in Malaysia (Tessens and Shamshuddin 1983; Paramananthan 2000). The area occupied by Oxisols together with the Ultisols (another group of highly weathered soils) is about 72% of the country’s land surface. The clay fraction of these soils is dominated by kaolinite and sesquioxides (Tessens and Shamshuddin 1983), which are termed variable charge minerals (Uehara and Gillman 1981). In Malaysia, most of the Oxisols are cropped to rubber, oil palm, and various types of fruit trees, while selected areas are cropped to cocoa with mixed Received 1 July 2009; accepted 15 May 2011. Address correspondence to J. Shamshuddin, Department of Land Management, Faculty of Agriculture, Universiti Putra Malaysia, 43400 Serdang, Selangor, Malaysia. E-mail: samsudin@agri.upm.edu.my 2751