hierarchical approach to the study of organic C, N, P, and S in western Canadian soils

Abstract only Organic C, N, P, and S contents in soil are thought to be the result of interactions among soil-forming processes, which occur in all soils but to different degrees. To test this hypothesis, the effect of climate, vegetation and topography on the organic matter composition in cultivated soil profiles was examined along an environmental gradient, from semiarid to subhumid regions in Saskatchewan. This transect encompasses a narrow environmental gradient of decreasing evapotranspiration and increasing precipitation (350–450 mm). Representative catenas selected from Brown, Dark Brown, Black and Gray Luvisol soil zones showed changes in the quantity and composition of organic matter. Concentrations of organic C, N, P and S progressively increased from the Brown to the Black soils and then decreased substantially in the Gray soils. Nutrient concentrations also increased from the upper to the lower slope positions of the catenas and decreased with depth in the soil profile. However, the distribution of organic elements across the soil zones, relative to each other (i.e. C:N, C:P, or C:N:P:S ratios), did not follow the same trends as concentration of the individual elements. The most consistent trends were observed in the lower slope soils, where organic C:N (9.8 to 12.5:1), C:P (48 to 78:1) and C:N:P:S (68:6.9:1.4:1 to 145:11.6:1.8:1) ratios widened from the Brown to the Gray soils. Within any one catena, organic C:N:P:S ratios narrowed with depth in the soil profile, often showing a several-fold decrease relative to the C:N:P:S ratios of the surface horizons. This study demonstrates the value of recognizing integrative relationships among soil processes. It provides a mechanism for better understanding and explaining the patterns of distribution and behavior of various soil chemical, physical and biological properties. Key words: Catenary sequence, Chernozem, Luvisol, hierarchical relationships