Soil properties as influenced by cultivation of the aromatic shrub Artemisia afra

Abstract

The herbaceous aromatic shrub African wormwood (Artemisia afra) is thought to be indigenous to the Eastern Cape region of South Africa. In the natural environment, wherever the plant grows, patches of hard, bare ground develop around the plant. To investigate whether the growth of the plant directly affects the physical and chemical properties of the soil, we compared selected properties of soil from the bare patches beneath the canopy of the shrub with those from contiguous land with the same soil but where Artemisia had never been grown (control). The results showed that soil from under A. afra had significantly (p < 0.01) higher stability of aggregates (2.0–5.6 mm) than the control, in spite of the fact that the organic C and bulk density did not differ significantly between the two soils. There was no significant difference in the pH, Bray 1-P, electrical conductivity and exchangeable cations (Ca, Mg, K & Na) content of the two soils. Analysis of the organic compounds present in the A. afra extracts indicated that it contained a mixture of unsaturated hydrocarbons, carboxyls and benzene, which were either absent or present only in very small amounts in the control soils. It is considered that these compounds contributed to the increased stability of aggregates in A. afra soil. The findings of this study are significant because the observed increase in aggregate stability would lead to reduction in soil erodibility, so that the introduction of A. afra on cultivated agricultural lands could be beneficial from both the economic and soil management stand points.