Changes in soil properties at Ramu Sugar Plantation 1979-1996.

Abstract

This paper presents an overview of changes in soil chemical and physical properties that have resulted from continuous sugar cane cultivation at Ramu Sugar plantation since 1979 The majority of the soils at the plantation have developed in alluvial deposits and classify as Fluvisols and Vertisols. Between 1979 and 1996, the soil pH at Ramu Sugar plantation had decreased from about 6.5 to 5.8 and this was accompanied by a decrease in CEC and exchangeable cations. Organic C levels had declined from about 56 g kg1 in 1979 to 32 g kg-1 in 1996. The inter-row of the sugar cane was compacted and had significantly higher bulk densities and a very slow water intake. Semi-quantitative nutrient budgets showed a shortfall in N, P and K, and levels of these nutrients in the sugar cane leaves had significantly decreased between the mid 1980s and 1990s. Yields at the plantation are largely determined by the insect pests, diseases and weeds. It is concluded that significant soil changes occurred at Ramu Sugar plantation and despite the fact that most soil chemical properties are still favourable for sugar cane cultivation, a change in soil management is required.