Nutritional limitations to the early growth of rainforest timber trees in north Queensland

Abstract

Most of the soils in the humid tropics of north Queensland available for growing rainforest trees are low in available nutrients. The major nutritional deficiencies have been classified according to soil parent material in order to develop a deficiency ‘risk’ table. From glasshouse trials using soils from across the region, most macronutrients (nitrogen (N), phosphorous (P), potassium (K), calcium (Ca), and sulphur (S)), apart from magnesium (Mg), has been found to be deficient in at least one soil, and every soil studied was deficient in at least one nutrient. Rainforest tree species responded to nutritional deficiencies in different ways and there may be an unrecognised loss in growth potential. Tree growth can be depressed under limiting nutrient supply but remain undiagnosed, as visual deficiency symptoms may not develop. We present a number of techniques to manage nutrients in timely and cost effective ways. These include techniques to ensure a continuous supply of nutrients to the roots during transplanting, rapid tests for deficiencies of N and P, and recognition of visual diagnostic symptoms of deficiency.