Quantitative topographic analysis of gilgai soil morphology

Abstract

For a gilgai soil complex we estimated the effect of overland and intrasoil substance flows on Vertisol development using concepts of topographic control of lateral substance movement by gravity rather than direct observations and measurements of these processes. First, we studied relationships between gilgai microtopographic characteristics and some Vertisol morphological properties, namely, depth to parent material (C) and calcium carbonate-enriched (B Ca) horizons. Secondly, we checked if microtopographic characteristics of the C horizon surface influence some Vertisol properties by examining the B Ca horizon depth. We used digital models of quantitative topographic variables. We concluded that the dominant mechanism controlling the C horizon depth is pedoturbation. Also, pedoturbation can be important in the development of the B Ca horizons. However, variations in the C and the B Ca horizon depths are not dictated by pedoturbation only. Our analysis showed that key factors influencing the C and the B Ca horizon depths are overland and intrasoil lateral migration and accumulation of water, solution and solid substances. The C horizon depth depends on the landsurface topographic characteristics, namely: horizontal, vertical and mean curvatures, specific catchment area, topographic and stream power indices. The B Ca horizon depth is significantly affected by the same set of topographic attributes of both the landsurface and the C horizon surface. The B Ca and the C horizon depths, as a rule, depend more on specific catchment area, topographic and stream power indices than on horizontal, vertical and mean curvatures of the landsurface and the C horizon surface. This is because specific catchment area, topographic and stream power indices take into account a relative location of a point in a microcatena. Utilization of quantitative topographic variables allows us to explain 82% of variation in the B Ca horizon depth and to suggest that topography is the main factor in the B Ca horizon formation.