Studies on Cessation of Grazing in Permanent Pasture Ecosystem : 4. Effect of cessation of grazing on soil microorganisms

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 the numbers of microorganisms in 0-10cm soil layer of the following three experimental plots; Control plot: managed by rotational grazing; Ca-exclosure plot: no gazing 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 properties of soil microorganisms in each plot were compared with that in 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. The number of bacteria in control plot showed the positive correlation with soil moisture, and the number increased gradually from spring and reached maximum in autumn. In both exclosure plot, however, such correlation and seasonal change as seen in control plot were found slightly in the second year of the period, but not at all in the fifth year. 2. There was no correlation between the changes in the numbers of actinomycetes and fungi and those of soil moisture in the all plots examined. 3. No significant differences in the numbers of soil microorganisms were observed among the all plots, except that the number of fungi in Ca-exclosure plot decreased in the fifth year as compared with that in control plot. 4. There was no relationship between the numbers of microorganisms and moisture in the forest soil. Such a property of microorganisms in the forest soil was like that in both exclosure plots at the fifth year. These results were discussed in relation to applying fertilizer and grazing of cattle.