Effect of soil heating on the dynamics of soil available nutrients in the rhizosphere

The effect of soil heating on the dynamics of soil available nutrients in t he rhizosphere was evaluated. A pot experiment was carried out by using a r hizobox; a pot which enables to sample soils and soil solutions not only te mporally with plant growth but also spatially depending on the distance fro m the root-accumulating compartment. The experiment consisted of 4 treatmen ts; soils with or without heating treatment (150 degreesC, 3 h), each of wh ich was either planted with maize (Zea mays L.) or not. During the 17-d exp eriment, soil solutions at; 0-2 mm from the root-accumulating compartment w ere collected 5 times. Soils depending on the distance from the root-accumu lating compartment and plants were also collected after the experiment. The ionic concentrations of the soil solutions and soil water extracts, and th e nutrient contents of plants were analyzed. Immediately after soil heating , the concentrations of cations, SO42-, Cl-, water-soluble P, and water-sol uble organic carbon increased significantly. With plant growth, the total i onic concentration in the rhizosphere soil solution increased for heated so il, whereas it decreased for:unheated soil. The increase of the concentrati ons of cations and SO42- in the rhizosphere of heated soil was appreciable, suggesting that the movement of cations such as Ca2+ and Mg2+ by mass flow was regulated by that of SO42-. Moreover soil heating inhibited nitrificat ion, resulting in the supply of N mainly in the form of NH4+ within 10 mm f rom the root-accumulating compartment. As a result, the soil pH decreased i n the rhizosphere of heated soil. The amount of nutrients absorbed by plant s, on the other hand, did not change significantly by soil heating except f or an increase of P uptake. The increase of P uptake could be explained not only by the; immediate increase of the water-soluble P concentration but a lso by the dissolution of Ca-bound P and.the hydrolysis of water-soluble or ganic P in the rhizosphere.