Potassium Mobilization and Transformation in Red Paddy Soil as Affected by Rice.

A rhizobox experiment was conducted to study the effect of growing rice (Oryza sativa L.) on the movement and transformation of Kin a red paddy soil. Results showed that Kuptake by rice reduced the concentrations of soil water-soluble K (Sol-K), exchangeable K (Ex-K), and non-exchangeable K (Nonex-K) in the root zone. Soil Sol-Kin non-root-zone compartment close to the root zone (0-6 cm) migrated toward the root zone, and soil Ex-K (0-4 cm) and soil Nonex-K (0-3 cm) was released into soil solution. As the rice growth progressed, soil Sol-K, Ex-K, and Nonex-K in the root zone and soil Sol-K in non-root-zone compartment close to the root zone (0-6 cm) continued to decrease. Decreases of soil Ex-K and Nonex-K in non-root-zone compartment extended from the root to 6 and 5 cm into the bulk soil, respectively. At the late grain-filling stage, soil Sol-K concentration in the root zone and non-root-zone compartment (0-6 cm) declined, and then remained stable, whereas Sol-Kin the non-root zone (6-7 cm) kept diffusing toward the root zone. Soil Ex-K and Nonex-K in the root zone and non-root-zone compartment continued to reduce, and the decrease distance of soil Nonex-K was extended to 6 cm. Within the whole season, soil Ex-K and Nonex-K were the main forms of K available to the plants, followed by Sol-K. The information obtained in this study indicated that K fertilizer should be added to the place around the root zone. [ABSTRACT FROM AUTHOR]