Life Science Journal, 2011:8(S2) http://www.lifesciencesite.com 33 Soil biological properties beneath canopies of Acacia erioloba (syn. Acacia giraffae) trees under different land- use practices in a South African semi-arid environment S.A. Materechera 1 and R.N. Murovhi 2 1 Faculty of Agriculture, Science & Technology, North-West University (Mafikeng Campus), P/B X2046, Mmabatho 2735, South Africa 2 Agricultural Research Council (Institute for Tropical and Sub-tropical Crops), Private Bag X 11208, Nelspruit, 1200, South Africa Corresponding author email: albert.materechera@uniwest.ac.za Abstract: The study was conducted to quantify the biological properties of soil beneath the canopies of Acacia erioloba trees growing under three dominant local land-use practices in a semi-arid environment of South Africa. The results showed that all biological properties were significantly different (p<0.05) from one land-use practice to another. Fallow land was found to have significantly higher (p<0.05) organic carbon (OC), particulate organic matter fraction (POM), microbial biomass carbon (MBc) and microbial biomass nitrogen (MBn) than grazing and bare land-use practices. The order of rating for all the measured properties was fallow >grazing > bare land. Bare land had the lowest of all the measured properties signifying limited biological activity. Significant higher (p<0.05) values of OC and POM were found in soils that were collected under fallow while MBc and MBn were higher under grazing land-use practice. In both canopy locations, all biological properties were significantly higher (p<0.05) in soils that were collected at 0-10 cm compared to those that were collected at 10-20 cm. High organic matter content under fallow and grazing land was attributed to three possible sources, namely: leaf litter from Acacia erioloba trees, grass and turnover of roots and also dung from grazing animals. The major contributing factor under grazing land was considered to be the large amount of organic materials that are returned to the soil, especially that from animal dung and turnover of grass roots. It was concluded that the quantity and quality of soil organic matter and microbial activity was enhanced by the micro environment beneath the canopy of Acacia erioloba tress. This was attributed to higher decomposition of soil organic matter that takes place on the surface layer of the soil where most of the organic materials are deposited. [S.A. Materechera and R.N. Murovhi. Soil biological properties beneath canopies of Acacia erioloba (syn. Acacia giraffae) trees under different land-use practices in a South African semi-arid environment. Life Science Journal. 2011;8(S2):33-39] (ISSN: 1097 – 8135). http://www.lifesciencesite.com . Key words: Agroforestry, Land-use, microbial biomass, soil quality, organic matter Introduction Acacia erioloba (synonym: Acacia giraffae) is an indigenous leguminous tree of the dry savanna environments of Southern Africa and other tropical areas of West Africa (Carr, 1976). It is an ecologically important tree because of its multipurpose roles in nature as well as the roles it plays in the ecosystem (Palgrave, 1991). Being a leguminous plant, the roots of the A. erioloba tree harbor rhizobium bacteria that fix nitrogen into the soil (Palgrave, 1991). A combination of leaf-fall, root nodulation and continuous presence of livestock near the trees in dry environments greatly enhances the microbial activity and cycling of plant nutrients underneath the canopy of A. erioloba trees (Murovhi and Materechera, 2006). A canopy of Acacia erioloba tree creates a microclimate beneath the tree that can alter the composition and activity of soil biota. Consequently, the agroforestry roles of A. erioloba trees are well established and appreciated in many rural and peri-urban communities of the semi-arid areas of the North West Province in South Africa where the trees are planted or deliberately maintained in the homestead, cropland and grazing land (Materechera, 1999). Soil biological activity is largely concentrated in the topsoil and it normally decreases greatly with depth, as does, soil organic matter content (Haynes and Graham, 2004). Soil biota is the main driving force behind nutrient and energy transformations in soils (Banerjee et al., 1999). Soil microbial activity affect nitrogen availability to plants by transforming organically held nitrogen into inorganic plant-available forms (Roper and Gupta, 1995). Soil organisms and their activities strongly affect soil properties and processes, and their abundance is largely to be affected by land-use and management practices, thus they serve as important indicators of soil quality (Karlen et al., 1997). Soil quality is defined as the capacity of a specific soil to function, within natural or managed ecosystem boundaries.