Effect of Rice Straw on Potassium Availability in Illite Containing Soils of Central Plain, Thailand

Abstract

Soil potassium (K) in various forms and the effect of rice straw on soil K release were studied in lowland soils containing illite clay minerals. Surface soils of 2 Inceptisols and 2 Alfisols were collected to study. Soil samples were incubated for 120 days with rice straw incorporation at different rates (0, 3,125, 6,250, and 9,375 kg/ha), and various forms of K in soils were determined at various times during the period of incubation. The results showed that the readily available K content (water-soluble K + exchangeable K) of the studied soils increased with the increasing rate of rice straw incorporation. In addition, non-exchangeable K content also increased with the increasing rate of rice straw incorporation by fixation process for all soils. The maximum increase of water-soluble K content of the studied soils was observed on the 4th day of incubation for all treatments, corresponding to the decrease of exchangeable K content at the same time. This result indicated that water-soluble K and exchangeable K were in equilibrium. Changes of non-exchangeable K content during the period of incubation through alternate release and fixation processes were observed monthly. This result suggested that most of the readily available K enhanced by rice straw incorporation would be beneficial for K uptake by the plant.