Effects of Heating on Some Changes in Soil Properties in Relation to an Ethiopian Land Management Practice

Abstract

AbstractThe physical, chemical, and mineralogical changes resulting from heating three soils up to 600° C for 48 hours were determined in the laboratory in an attempt to explain the effects of the “guie” (soil burning) practice common of Ethiopia. Heating to 200° C did not affect soil color, particle size distribution or clay mineralogy. Heating to 400 and 600° C changed colors to redder hues, the textures from clayey to sandy, produced the collapse of layer‐silicate clay minerals and probably fused clay particles into sand‐sized particles. Organic C started to decompose between 100 and 200° C and was essentially eliminated at 400° C. Total N decreased by half at 400 and 600° C. Ammonium nitrogen increased sharply at 200° C heating but decreased at higher temperatures. Soil pH values increased with heating temperature in acid soils but decreased in the alkaline soil up to 400° C. Changes in exchangeable Ca, Mg, K, Al, and available Fe, Mn, Cu, and Zn varied with soil properties. The most pronounced chemical change was a marked increase in available P in all soils when heated at 200° C or above. Although the different layers in the “guie” heaps are heated to different temperatures, the main beneficial effect of heating in the amorphous Ethiopian soils seems related to increases in available NH4+‐N and P at temperatures low enough to prevent drastic changes in particle size distribution or organic matter content.