AGGREGATE STRUCTURE AND CARBON, NITROGEN, AND PHOSPHORUS IN NATIVE AND CULTIVATED SOILS

This work corroborates the hierarchical conceptual model for soil aggregate structure presented by Tisdall and Oades (1982), extends it to North American grassland soils, and elaborates on the aspects relating to the influence of cultivation upon losses of soil organic matter. Aggregate size distributions observed for our soils are very similar to those of Australian soils, indicating that the microaggregate-macroaggregate model may hold for a wide array of grassland soils from around the world. The use of two wetting treatments prior to sieving demonstrated that the native sod soil had the same general structural characteristics as cultivated soil but the macroaggregates were more stable. The macroaggregate-microaggregate conceptual model is applied to help explain accumulation of soil organic matter under native conditions and its loss upon cultivation.