Variations on soil carbon dioxide flux with land-use type and selected soil properties in the hardveld of Botswana

Abstract

The dynamics of carbon dioxide (CO₂) flux in the hardveld regions of Botswana are poorly understood, with previous studies having concentrated on sandveld and pan environments. In particular, soil organic carbon (SOC) has a positive influence on CO₂ emissions to the atmosphere. To examine the effects on soil CO₂ flux of land use, namely conventional tillage, horticultural and grazing land uses, measurements were carried out in sites having similar climatic conditions. To enhance the understanding of soil carbon dynamics in these typical land uses, an investigation on the influence of soil pH, moisture content, organic carbon and temperature on CO₂ flux rates was carried out. The results showed a relatively stronger dependence of CO₂ flux rates on soil temperature for conventional tillage (R 2 = 0.71) and grazing (R 2 = 0.56) compared with horticultural land use (R 2 = 0.05). High SOC content in the grazing and horticultural land uses was due to increased oxidation of organic matter following soil disturbance. High organic matter turnover was probably from animal wastes and plant decomposition. Similarly, a decrease in CO₂ flux with pH in the conventional tillage and grazing land uses suggests there is clear potential for these land uses to become carbon sources depending on the acidity of the soil.