A monitoring study on nutrient cycles in soils used for shifting cultivation under various climatic conditions in tropical asia. I. The influence of simulated burning on form and availability of plant nutrients

Abstract

Laboratory burning of selected surface soil samples (0–2 cm) from a site in Sarawak (Malaysia), through a temperature range of 20–350°C, decreased the cation exchange capacity and values for most exchangeable cations, whereas values for pH, electric conductivity, base saturation and available phosphorus increased. Most significant was the disappearance of organic matter and the subsequent release of nutrients stored therein. As a consequence of burning the organic materials at temperatures between 150 and 250°C, calcium and magnesium may exist as salts, whereafter resorption may occur at higher temperatures. There was a marked decrease in exchangeable aluminium at temperatures above 150°C. Because temperatures of over 150°C are seldom reached below a depth of 2 cm from burning under field conditions, it is suggested that the microbiological changes from heating are probably of greater importance than the chemical ones, taking into account the normal rooting depth of annual crops of about 25 cm.