Changes in Soil Properties: Introduction

The oil palm requires large amount of nutrients to sustain its growth and production so that high yield levels of 30 tons/ha/yr (Ng et al ., 1999) or more could be achieved and maintained. This is mainly due to the low soil fertility in most Malaysian soils (Law and Tan, 1973) in particular the Ultisols of Johor (Ng, 1969). High fertilizer rates are also essential to prevent negative soil nutrient balance and in many instances, to build-up the soil fertility to ensure sufficient nutrients are present in the soil solution for maximum uptake by the roots (Goh and Chew, 1995a).

Traditionally, soil samples are taken on a regular basis for nutrient analysis and are commonly used in the diagnosis of fertilizer requirements in oil palms, monitoring soil fertility and ensuring that fertilizers recommended have been applied. Thus, large long-term data set on soil nutrients are available from most big plantation houses. Despite this, changes in soil nutrients under oil palm as influenced by agro-management practices have not been reported. This is particularly important as the issues of soil nutrient changes have since gone beyond their traditional uses and are nowadays frequently regarded as one of the most important measures of sustainability and impact on the environment. Tinker (1993) pointed out that for an agriculture crop to be sustainable, one of the criteria should include preserving the resource base on which it rests upon whereas Hartemink (2003) has also argued that a drop in world food production might be attributed to the decline of soil nutrients. Soil nutrient changes with regards to the impact on the environment would normally be scrutinized from the point of land degradation and potential pollution, which should be avoided in order to be sustainable.

This paper studies 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 under oil palms. The effects of time and the different replanting practices from previously on soil nutrient changes were also investigated.