Growth potential of twelve Acacia species on acid soils in Hawaii.

Abstract

Reforestation of degraded tropical sites is often hampered by soils of high acidity, high aluminum saturation, and low fertility. To evaluate the possibility of cultivating Acacia species on such soils, a study was conducted at Waiawa, to test growth under conditions of (1) high acidity (primarily aluminum) and nutrient stress, and (2) no acidity stress and high nutrient availability. Twelve Acacia species, including the important native Hawaiian species Acacia koa as well as provenances from Papua New Guinea, Queensland and Northern Territory (Australia), were established on a Ustic Kanhaplohumult soil. The experimental design was a split plot with two fertility treatments as the main plots and the 12 Acacia species as subplots. The treatments were: low fertility (143 kg ha^-1, 14-14-14 plus micronutrients) and high fertility (8 t ha^-1 lime, 143 kg ha^-1 14-14-14 plus micronutrients, 200 kg P ha^-1, and 77 kg K ha^-1). Acacia angustissima, Acacia aulacocarpa, Acacia auriculiformis, Acacia cincinnata, Acacia crassicarpa, Acacia implexa, Acacia koa, and Acacia mangium grew significantly faster under the high fertility treatment. Three species, A. cincinnata, A. crassicarpa, and A. mangium, are recommended for planting on infertile acid soils. The volume of A. koa was increased ten-fold by the high fertility treatment. Additional study on the nutritional requirements of A. koa is suggested in order to identify the nutrients contributing to this increased growth. (Other species tested in the study were A. leiocalyx, A. leptocarpa, A. orites and A. polystachya.).