I43 APPENDIX 144 with organic matter (C and N) contents, and for soils which have received no recent organic substrate amendments activities are poorly correlated with microbial number (Tabatabai, 1977, 1982a; Ladd, 1985). Enzymes related to C, N, P, and S_ cycles in soils Soil enzymes have primarily been involved in the metabolism of carbohydrate-, nitrogen-, phosphorus-containing organic compounds and catalyzing oxidation-reduction processes. Enzymes of special signifi cance in the carbon cycle include amylase, cellulase, glycosidase, and invertase. Metabolism of nitrogenous compounds commonly involves proteinases and peptidases (caseinase, pepsin, and trypsin), deaminases, and araidohydrolases (asparaginase, glutaminase, and urease). Some important enzymes involved in the P cycle include phytase, adenosine triphosphatase, phosphomonoesterase, phosphodiesterase, and pyrophos phatase. The oxido-reductase class of soil enzymes include catalase, dehydrogenase, and peroxidase (Kuprevich and Shcherbakova, 1971). Among the enzymes involved in the sulfur cycle is arylsulfatase. This enzyme is important in the cleavage of sulfate ester bonds in organic matter of soils (Tabatabai and Bremner, 1970a). Among the enzymes involved in carbon metabolism, those acting on glycosyl compounds, including glycoside hydrolases, have been the hydrolases least studied in soils. These enzymes include some important hydrolases like cellulase, amylase, and some glycosidases that catalyze the hydrolysis of disaccharides. Among the glycosidases, a-glucosidase which catalyzes the hydrolysis of aD -glucopyranosides and