THE AMOUNTS OF DISSOLVED ORGANIC CARBON IN THE SOIL SOLUTIONS OF A FOREST AND A FARM SOIL IN SITU

Abstract

Field studies are described on the amounts of dissolved organic carbon (DOC) X in the soil solutions of a mixed forest and an intensive farm in situ on the campus of Tokyo Univ. of Agri. & Tech., Fuchu, Tokyo. Diurnal and seasonal fluctuations in the amount X of the two soils at a depth of 5 cm were almost independent of the changes in the soil temperature, the contents of soil water, the amounts of ammonium and those of nitrate ion in the soil solutions. The average amount X (g C/m^2,to a depth of 10 cm) and the coefficient of variation (%) throughout the year was 0.328 and 28.0 in the forest soil, and 0.160 and 36.3 in the farm, respectively. Being controlled strongly by the temperature, the rate of CO_2 evolution Y (g C/m^2/day) at 5 and 25℃, for example, was 0.73 and 2.13 for the forest excluding the respiration of root and macrofauna, and 0.51 and 1.22 for the farm, respectively. Assuming that the DOC was the respiratory substrate for the soil microbes, the higher rate Y of the forest than that of the farm was attributed to the difference in the amounts X between the two soils. Furthermore, the turnover rates per day of the amount X (ratio of the rate Y to the amount X) were calculated, assuming that all the CO_2 was evolved from the upper layer to a depth of 10 cm. Being controlled by the temperature, the turnover rate at 5 and 25℃, for example, was 2.2 and 6.5 for the forest, and 3.2 and 7.6 for the farm, respectively. The high turnover rate suggests the active production and consumption of DOC