Abstract

The status and spatial variability of organic C levels in soils that were never cultivated but were grazed are a function of environmental and inherent soil properties. The organic C content in South African soils was therefore quantified using existing data with reference to master horizon classification and soil-forming factors. Data from 7079 soil profiles covering the whole of South Africa, including land type survey modal profiles and profiles from other soil surveys, were used in this study. All profiles were analyzed for physical and chemical properties including organic C. The average organic C content ranged from 16% in the O horizon to 0.3% in the C horizons and decreased in the sequence O > A > G > B > E > C. The organic C content was correlated to the soil-forming factors climate (rainfall, evaporation, and aridity index), topography (terrain morphological units, slope percentage, slope type, and slope aspect), and soil texture (clay content). There was therefore a circular influence among topography, master horizons, and organic C contents. A regression was further done to correlate organic C per master horizon with rainfall, evaporation, slope aspect, aridity index, and clay content. Unfortunately most of the R2 values were too low for the equations to be used to estimate organic C content in the master horizons of South African soils.

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