Release of potassium from some heated calcareous soils to different solutions

Abstract

ABSTRACT Top soil burning may occur in shifting cultivation in hills, forest fire or burning of agricultural straw. It may affect the mechanisms of potassium (K) release by different extractants. Cumulative K release from six calcareous soils before and after heating (at 350°C) during 10 times extraction with 0.025 M CaCl2, HCl, oxalic and citric acids was determined. Initial K release was increased from 8–23 mg kg−1 to 13–47 mg kg−1 by heating the soils. Citric acid extracted more K than other solutions in the initial stage of K release. Cumulative K release ranged from 61 mg kg−1 for Torriorthents (containing high calcium carbonate and low clay) to 248 mg kg−1 for Haploxererts (containing low calcium carbonate and high illitic clay). Citric and oxalic acids extracted more K than CaCl2 and HCl. Heated soils released more K than unheated soils to the different extractants (62, 86, 112 and 105% increase for CaCl2, HCl, oxalic and citric acids, respectively). It is concluded that presence of calcium carbonate in soil affects the mechanisms of K release; in highly calcareous soils, exchange reactions were the main mechanism, while in slightly calcareous soils, exchange reactions and mineral dissolution were involved in the K release.