Effect of application of inorganic and organic fertilizers on the dynamicsof soil nutrients in the rhizosphere

The effect of fertilizer application on the dynamics of soil-available nutr ients in the rhizosphere was studied in a pot experiment. A rhizobox equipp ed with a soil solution sampler was used to collect soil solutions and soil s in the rhizosphere. The experiment consisted of 6 treatments; soils with application of inorganic fertilizer (NH4NO3, NaH2PO4, KCl), organic fertili zer (rice bran), and without fertilizer application, each of which was eith er planted or not with maize (Zea mays L,), During the 17-d experiment, soi l solutions in the rhizosphere were collected 5 times. After the experiment , soils in the rhizosphere and plants were also sampled. The ionic concentr ations of the soil solution and soil extracts with deionized water and the nutrient contents of the plants were then determined. The application of in organic and organic fertilizers immediately increased the total ionic conce ntration of the soil solution. As the plant grew, the total ionic concentra tion of the soil solution in the rhizosphere increased in the inorganic fer tilizer treatment mainly due to the accumulation of Cl- in the rhizosphere, whereas it decreased in the others. After the experiment, the concentratio ns of water-soluble N, P, and K decreased in the rhizosphere in all the tre atments. The decrease in the concentrations of N, P, and K in the treatment without fertilizer extended significantly until 10, 0, and 2 mm from the r oot surface, respectively. The decrease was generally larger for the fertil izer treatments. From these results, the amounts of apparent decrease of N, P, and K in water-soluble forms within or beyond 10 mm from the root surfa ce were calculated, and they were related to the amount of plant uptake. As a result, although the difference among the treatments was not as apprecia ble as that among elements, the contribution of the net supply of N, P, and K by the replenishment from the soil solid phase was higher for the organi c fertilizer treatment than for the inorganic fertilizer treatment.