An overview of changes in soil chemical and physical properties that have resulted from continuous sugar cane cultivation at Ramu Sugar plantation, Papua New Guinea, since 1979. The majority of the soils at the plantation are classified 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 changeable cations. Organic C levels had declined from about 56 g/kg in 1979 to 32 g/kg 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. Although most soil chemical properties are still favourable, a change in soil management is required. From authors' summary.