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 the rhizosphere was evaluated. A pot experiment was carried out by using a rhizobox; a pot which enables to sample soils and soil solutions not only temporally with plant growth but also spatially depending on the distance from the root-accumulating compartment. The experiment consisted of 4 treatments; soils with or without heating treatment (150 degreesC, 3 h), each of which was either planted with maize (Zea mays L.) or not. During the 17-d experiment, soil solutions at; 0-2 mm from the root-accumulating compartment were collected 5 times. Soils depending on the distance from the root-accumulating compartment and plants were also collected after the experiment. The ionic concentrations of the soil solutions and soil water extracts, and the nutrient contents of plants were analyzed. Immediately after soil heating, the concentrations of cations, SO42-, Cl-, water-soluble P, and water-soluble organic carbon increased significantly. With plant growth, the total ionic concentration in the rhizosphere soil solution increased for heated soil, whereas it decreased for:unheated soil. The increase of the concentrations 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 nitrification, resulting in the supply of N mainly in the form of NH4+ within 10 mm from the root-accumulating compartment. As a result, the soil pH decreased in the rhizosphere of heated soil. The amount of nutrients absorbed by plants, on the other hand, did not change significantly by soil heating except for 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 also by the dissolution of Ca-bound P and.the hydrolysis of water-soluble organic P in the rhizosphere.