Soil Microbial Biomass in Semi-Arid Communal Sandy Rangelands in the Western Bophirima District, South Africa

Abstract

Abstract. Soil microbial biomass is considered as an important early indicator of changes that may occur in the long term with regard to soil fertility and constitutes an important source and sink of nutrients. In South Africa, rangeland monitoring has mostly focused on assessing changes of aboveground vegetation in response to land uses effects, but the associated changes at belowground soil level remain a topic of further research. The aim of this study was to explore soil microbial biomass at three sites under communal grazing management. Soils from grazed and adjacent ungrazed rangeland plots were collected at a depth of 0-25 cm towards the end of the rainy season in April 2005. The soil microbial biomass was characterized by analyzing the phospholipids ester-linked fatty acids. Soils were also analyzed for organic carbon, pH, and total phosphorus. Results showed no statistically significant differences in organic carbon and soil microbial biomass between the grazed and ungrazed plots at any of the sites. Both organic carbon and soil microbial biomass were low, ranging from 0.06 to 0.11% and 489.28 pmol g -1 to 1823.04 pmol g -1 , respectively. Fourteen grass species were recorded during the vegetation surveys, and most occurred in low abundance. Plants supply organic materials as energy sources for microbial growth, so the low soil microbial biomass could be a reflection of the low vegetation abundance. This study provides essential baseline information regarding soil microbial activity never reported before in these rangelands. Further investigations are required for in-depth understanding of the underlying processes that regulate soil microbial biomass dynamics at these sites.

Impact of enclosure management on soil properties and microbial biomass in a restored semi-arid rangeland, Kenya

“…Range rehabilitation promotes litter and organic matter supply by reducing soil disturbance, restoring herbaceous vegetation and increasing biomass production (Verdoodt et al, 2010;Mekuria and Aynekulu, 2011). Holt (1997) and Raiesi and Asadi (2006) reported a reduction in C mic under long-term grazing compared to adjacent ungrazed sites in Australia and Iran, respectively, whereas Moussa et al (2007) found non-significant differences in C mic between grazed and ungrazed plots in the semi-arid rangeland of South Africa. The microbial biomasses recorded in the restored rangeland in the Njemps Flats (73 to 156 µg/g soil) are relatively low compared to the literature data for the tropics.…”

An assessment of the potential for carbon finance in rangelands ICRAF Working Paper no. 68

“…Because grazing may be beneficial for vegetation production and C allocation to soils, it has also been found that exclosure of livestock does not benefit grassland soil C sequestration in some semi-arid rangeland (Nosetto et al 2006;Shresta & Stahl 2008) and savanna contexts (Moussa et al 2007). Enclosure of grasslands from livestock grazing may also restrict the access of livestock keepers to functional grazing lands, adversely affect herders' incomes and displace grazing intensity onto unenclosed lands (Williams 1996).…”

Exclosures backed up with community-based soil and water conservation practices increased soil organic carbon stock and microbial biomass carbon distribution, in the northern highlands of Ethiopia

“…It also acts as biological early indicator of changes [22,23]. It makes up 1-5% of total SOC [24] and acts as the most active component in the biochemical process of SOC turnover [25].…”