CHANGES IN MICROBIAL BIOMASS AND PROTEASE ACTIVITIES OF SOIL ASSOCIATED WITH LONG-TERM SUGAR-CANE MONOCULTURE

As part of a broader study, the aim of which is to identify soil facto rs that might be associated with yield decline of sugar cane, microbia l biomass and protease activities were examined in soil samples collec ted from seven paired old and new land sites in three cane-growing dis tricts of north Queensland. No consistent changes in soil protease act ivities were observed, although some sites exhibited specific effects, as a result of extensive periods of sugar cane monoculture. Soil micr obial biomass, however, was significantly lower in those soils where s ugar cane had been grown for extended periods. The implications of a l owering of soil microbial biomass on sugar cane yields and sustainabil ity are discussed.