GRAZING PRESSURE AND SOIL CARBON, MICROBIAL BIOMASS AND ENZYME-ACTIVITIES IN SEMIARID NORTHEASTERN AUSTRALIA

The effects of cattle grazing pressure on total carbon, microbial biom ass carbon levels and selected enzyme activities of the soils at sever al sites in northeastern Australia have been examined. No changes in o rganic carbon levels were detected, but a significant reduction in soi l microbial biomass carbon levels (approximately 24% and 51%) occurred at two tropical semi-arid woodland sites after 6 and 8 years of an ex perimentally imposed heavy grazing strategy. Peptidase and amidase act ivities were also significantly reduced in the soils of the heavily gr azed treatments at one of these sites. A comparison of soils in areas where poor grazing management over a period of at least 10 years had g iven rise to pastures in poor condition with similar soils from nearby well managed areas supporting pasture in good condition was also made . Both total carbon and microbial biomass carbon were lower in the soi ls of the area that had been subjected to poor grazing management. Und er poor management regimes, soil microbial biomass may provide an earl ier indication of changes in organic matter status than total carbon. (C) 1997 Elsevier Science B.V.