ABSTRACT
Concerns over environmental effects of intensive agriculture, such as soil organic matter loss and degradation of soil-water-air resources, have promoted consideration of change from the prevailing high-input agricultural systems to crop management systems that are more diverse, require less tillage and purchased inputs, and enhance biological diversity (Doran et al., 1996; Lupwayi et al., 1998). Soil health, productivity, and sustainability are affected by numerous complex interactions between physicochemical and biological factors. New monitoring approaches to determine simultaneous changes in soil physical, chemical and biological properties are needed to evaluate system function and sustainability of the soil resource. Soil organic matter (SOM) is a major determinant of soil condition and an important source of inorganic nutrients for plant production. Soil organic matter components that are responsive to management practices such as particulate organic matter (POM), mineralizable N, and microbial biomass need to be evaluated as soil quality attributes for assessing soil function and system sustainability (Jenkinson and Ladd, 1981; Doran, 1987; Jenkinson, 1988; Cambardella and Elliott, 1992; Sparling, 1992; Kaiser, 1994; Doran and Parkin, 1996). Particulate organic matter, that part of SOM greater than 0.050 mm in size, has been identified as the organic matter fraction most sensitive to changes in soil management practices (Cambardella and Elliott, 1992). Increases in surface SOM are closely associated with increases in microbial biomass in the surface 5 to 7.5 cm of soil for no-tillage management as compared to previously tilled systems (Doran, 1987; Gupta et al., 1994). Soil microbial biomass C and N contents, mineralizable C and N levels, and respiration may be useful measures and sensitive indicators of change in SOM dynamics (Anderson and Domsch, 1989; Sparling, 1992; Parkin et al., 1996).
