Soil chemical properties under primary forest and coffee in the Kutubu area of Papua New Guinea.

Abstract

This paper presents some preliminary investigations in the topsoil (0-0.2 m) chemical properties under primary forest and arabica coffee in the Kutubu area (Southern Highlands). The coffee gardens were established from primary forest about 3 years prior to the soil sampling in 1996. Most of the arabica coffee in the Kutubu area is not fertilized and overall the coffee is growing poorly. Both soils under forest and coffee had moderate to low fertility levels with strongly to moderately acid soil reactions (pH H20: 4.7 to 5.4). There was little difference in the chemical fertility between the topsoils under forest and coffee although exchangeable calcium and base saturation were significantly higher under coffee possibly as a result of the ash addition after the forest was slashed and burned. All soils had extremely low levels of available phosphorus but high total P-levels. Nutrient deficiencies, in particular P and micronutrients, may be factors explaining the poor coffee performance in the Kutubu area but additional research is required.