Abstract
^<15>N tracer experiments in the experimental field of Hokuriku National Agricultural Experiment Station were carried out. the effects of compost and rice straw application on the fate of mineralized soil nitrogen were examined. Seven plots were set up, namely, a non-application plot, a standard rate of compost application (compost 1 ton/10a) and higher rates of compost application (compost 2 and 3 ton/10a) plots, a standard rate of rice straw application (rice straw 0.6 ton /10a) and higher rates of rice straw application (rice straw 1.2 and 1.8 ton/10a) plots. At each time of planting, active tillering, young panicle initiation and booting, nitrogen was applied at the rate 3 g/m^2. The results obtained are summarized as follows: 1) Immobilization, denitrification, and absorption by rice plants of the mineralized soil nitrogen NH_4-H existed at each time. (1) Immobilization: Percentage of immobilization at the time of planting was in the following order: higher rates of rice straw application > standard rate of rice straw application > higher rates of compost application > standard rate of compost application > non-application. The amount at the time of active tillering showed that higher rates of rice straw application was higher than other plots. However, the amount of each plot at the time of young panicle initiation and booting was nearly the same. (2) Denitrification: Percentage of denitrification at the time of planting was in the following order: rice straw 1.8 plot > rice straw 1.2 > rice straw 0.6 > compost application > non-application. However, the amount of each plot at the time of active tillering, young panicle initiation and booting was nearly the same. (3) Plant recoveries: Ratio of absorption by rice plants increased with the advance of plant growth. Effect of compost and rice straw application showed a tendency that the ratio of those at the active tillering time was low by the higher rates of rice straw application plots. 2) Transfer from mineralized soil nitrogen to immobilization, denitrification, and absorption by rice plants. The total amount of nitrogen transferred from mineralized soil nitrogen was 19.4 g in the non-application, 21.0 g in the standard rate of compost, 19.7-21.9g in the higher rate of compost, and 17.7-18.2 g/m^2 in the rice straw plots. The total amount of nitrogen immobilized increased with compost and rice straw application. The total amount of nitrogen immobilized increased with compost and rice straw application. The total amount of nitrogen absorbed by rice plants increased with compost application and decreased with rice straw application. The total amount of nitrogen denitrified decreased with rice straw application.
