Effect of plant growth on the distribution and forms of soil nutrients in the rhizosphere

The effect of plant growth on the distribution and forms of soil nutrients in the rhizosphere was studied by growing plants in rhizoboxes. An experime nt was carried out in a growth chamber for 17 d with three treatments, i.e. maize (Zea mays L.), kidney bean (Phaseolus vulgaris L.), and no plants. A fter the experiment, soil samples were collected up to about 50 mm from the central compartment (C.C.) in which roots were allowed to grow, and analyz ed for the soluble, exchangeable, and total amounts of nutrients. Plant sam ples were also analyzed for their nutrient; contents. The pattern of nutrient distribution in the rhizosphere varied among the ty pes and forms of elements. In both maize and kidney bean, the concentration s of soluble P, K, and N decreased significantly at the C.C., up to 4 mm an d up to 10 mm from the C.C., respectively. The magnitude of their depletion reflected their rate of diffusion in soil. The concentration of exchangeab le K decreased significantly up to 2 mm from the C.C., whereas those of exc hangeable Ca and Mg increased within 1 mm from the C.C. The total amount of nutrients, however, did not change significantly for each element. The dep letion of soluble P and K mainly around the C.C. indicated the presence of their diffusion toward the root surface. Their uptake was larger than the a pparent decrease of their soluble forms, suggesting that their depletion wa s compensated by intensive replenishment from the soil solid phase. The con centrations of N, Ca, and Mg, on the other hand, markedly decreased up to t he end of the rhizobox, indicating the presence of mass dow. The depletion was proportional to the rate of transpiration by plants.