Soil Management: Changes in Soil Properties

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The soil nutrient changes under oil palm need to be examined to ensure agro-management practices go along the lines of sustainability and not harm the resource base on which the oil palm rests upon. As most large plantation houses carry out regular soil sampling of their fields for the diagnosis of fertilizer requirements and monitoring soil fertility, long-term data are available to study the soil nutrient changes of pH, organic carbon, total nitrogen, total and Bray-2 phosphate and exchangeable potassium and magnesium in different micro-sites (palm circles and interrows) and depths. The effects of time and different replanting practices on soil nutrient changes were also investigated. This study was restricted to the Ultisols in Johor.

Results indicated that soil pH, organic C and total N tended to decrease with time in the oil palm agro-ecosystem. However, the decline in soil pH was slight whereas those related to organic C and total N corresponded to the period where the oil palm biomass was burnt or partially burnt at replanting. The large increases in soil organic C with the current norm of zero burn replanting technique were favourable with regard to sustainability and land degradation. There were large positive changes in soil P and exchangeable K, which might be attributed to the applications of higher rates of phosphate rocks and K fertilizer especially from the 1990s following the results of fertilizer response trials. Exchangeable Mg tended to decrease with burn or partial burn replanting techniques but showed large increases in both micro-sites and soil depths with zero burn techniques. Excessive build-up of soil nutrients on the highly weathered tropical soils of Ultisols should be avoided due to their generally low nutrient holding capacity, which may increase the risk of pollution. On the other hand, nutrient depletion should also be prevented as they commonly lead to lower production in the long-term.

This study shows explicitly that the soil fertility status of the Ultisols under oil palm in Johor has been enhanced through current fertilizer management practices and zero burn replanting technique.

Ng PHC, Gan HH and Goh KJ (2004) Soil nutrient changes in Utisols under oil palm in Johor, Malaysia. In: Oils and Fats International Congress (OFIC) 2004 in module on Agriculture, Biotechnology and Sustainability (AB), 29-9 to 2/10 2004, PWTC, Kuala Lumpur: Preprint.

Note: The full list of references quoted in this article is available from the above paper.