. 1994. Towards a minimum data set to asseis soil organic matter quatity ii agricultural soils. Can. J. Soil Sci. 74 [367][368][369][370][371][372][373][374][375][376][377][378][379][380][381][382][383][384][385]. Soil quality is a composite measure of both a soil's ability to funct-ion and how welt it functions, relative to a specific use. Soil quality can beassessed using a minimum data set comprisingioil attributes such as texture, organic matter, pH, bulk density, and rooting depth. Soit organic matter has particular significa-nce for soil quality as it can influenie many different soil properties including other attributes of the minimum data set. Asiessment of soil organii matter is a valuable step towards identifying the overall quality of a soil and may be so informative as to be included in minimum data sets used to evaluate the world's soils.In this review, soil organic matter is considered to encompass a set of attributes rather than being a single entity. Included among the attributes and discussed here are total soil organiciarbon and nitrogen, light fraction and macroorganic (particulate) mattei, mineralizable carbon and nitrogen, microbial biomass, soil carbohydrates and enzymes. These attributes are involved in various soil processes, such as those related to nutrient storage, biological activity, and soil structure, and can be used to establish different minimum data sets for the evaluation of soil organic matter quality.Key words: Biological activity, minimum data set, nutrient storage, soil organic matter, soil quality, soil structure (Fig' l). The relationships between cumulative mineralization during 22 wk and 3 or l0 wk, although highly significant (P < 0.0001), were less close for N (Fig. 2) than C (Fie. 1).Mineralizable-C and N may be determined simultaneously in a single incubation, but combined data are rarely reported (Table 3). Under optimal conditions in the laboratory. rates of C mineralization typically range fr-om ] to 30 pg I -' d -' in mineral soils and 150-800 pE g-| d -' in organic layers'Corresoonding rates of N mineralization range from 0'3 to -2.5 is.s-rt-r in mineral soils and from 3.0 to 15 pg g-r d-T in organic layers (Table 3). Carter and Rennie (fSAZ) reported greater rates of C and N mineralization in thin layeis of surface soil under zero tillage compared to conventional tillage because crop residues were concentrated at the surface ofzero-tilled soils. Janzen's (1987b) comparisons of crop rotations indicated that the proportions of the total store of C and N in the mineralizable fractions decreased with increasing frequency of fallow, suggesting that fallow was detrimental to organic matter quality (Table 3). In another study, the amounts of mineralizable C and N were greater in fertilized than unfertilized soils, but the proportions of total soil organic C and N in the mineralizable fractions were similar, because fertilized soils also contained greater amounts of total C and N (Janzen 1987a