Abstract
A series of field experiments was undertaken to assess changes in some structures of a pasture ecosystem due to cessation of grazing. This report deals with the changes of total C, total N and exchangeable Ca contents in 0-20 cm soil layer of the following three experimental plots ; Control plot: managed by rotational grazing; Ca-exclosure plot: no grazing from 1976 to 1980, with CaCO_3 (2ton/ha) application at the beginning of the period; Exclosure plot: no grazing without application of CaCO_3. Furthermore the chemical characterristics of the soil in each plot were compared with those of the forest soil which was sampled from the adjacent deciduous broadleaved forest dominated by Quercus serrata in 1980. The experimental results obtained were as follows: 1. Total C and total N contents in 0-20cm soil layer increased slowly with the rest period of grazing, and the rate of the increment of total N content was relatively greater than that of total C content. Concequently, C/N ratio in 0-20cm soil layer decreased in both exclosure plots as compared with that in control plot.2. Exchangeable Ca contents in 0-15cm soil layer of both exclosure plots were much higher than that of control plot at the, fifth year, but there were no differences in exchangeable Ca contents of 15-20cm soil layer in the all plots. 3. Total C, total N and exchangeable Ca contents in 0-20cm soil layer of the forest were higher and C/N ratio was lower than each of control plot. Such soil chemical characteristics of the forest were approximate to those of both exclosure plots at the fifth year. From the results in the present and previous reports, it was assumed that each structure of permanent pasture soil might revert to the structures of the forest soil in their peculiar processes, if human activities such as fertilizer application and cattle grazing, which had had maintained the steady-state of the pasture ecosystem, were left off.
