SOIL carbon and nitrogen in five contrasting biomes of South Africa exposed to different land uses

Abstract

Stocks of soil C to a depth of 50 cm in untransformed, indigenous veld ranged from 21 t ha^-1 in karoo to 168 t ha^-1 in thicket and stocks of N ranged from 3.41 ha^-1 in karoo to 12.8 t ha^-1 in grassland. Mean soil C in thicket (5.6%, 0–10 cm) was approximately five times greater than expected for a semi-arid region. Removal of vegetation due to cultivation, grazing or burning reduced soil C and N at all sites. Soil C under intact thicket was greater than at sites degraded by goats (71 vs 40 t ha^-1, 0–10 cm). Restoration of thicket could potentially sequester -40 t C ha^-1. The sale of this sequestered carbon to the international market may make restoration of thousands of hectares of degraded thicket financially feasible. Soil C under plant cover was greater than In exposed soil in renosterveld (28 vs 15 t ha^-1) and in karoo (7 vs 5 t ha^-1). Parent material was also related to soil C content. In grassland, soil C was greater in dolerite-derived than sandstone-derived soils (54 vs 271 ha^-1); and in bushveld it was greater in basalt-derived than granite-derived soils (28 vs 14 t ha^-1 in unburnt plots). Annual burning in bushveld reduced soil C, particularly at the surface. Soil C in the 0–1 cm layer of unburnt plots was 2 to 3 times greater than in burnt plots.