The effect of soil carbon on symbiotic nitrogen fixation and symbiotic Rhizobium populations in soil with Trifolium repens as host plant

Soil organic carbon (SOC) is the main attribute of high-quality soil. The amount of nitrogen fixed by Rhizobium symbiotically with Trifolium repens (white clover) is ultimately determined by the quality of the soil environment. The effect of SOC on the total number of symbiotic and saprophytic rhizobia was determined. Subsequently, the amount of nitrogen (N) fixed was assessed by using the N difference technique. Most Rhizobium was detected between a SOC content of 2.03% to 3.80% in both inoculated and non-inoculated soils. Inoculation increased the number of rhizobia in soil. Most N was fixed in the soil with the lowest SOC content. Although the amount of N fixed increased as the level of SOC decreased, the efficiency of N fixation decreased proportionally to SOC. Subsequently, more N was rhizodeposited. It was concluded that symbiotic rhizobia introduced by the inoculant were more efficient than free-living rhizobia in soils with higher carbon content, which highlights the importance of inoculation in improving the sustainable production of T. repens pastures.Keywords: colony forming units, inoculation, most probable number, plant infection techniqueAfrican Journal of Range & Forage Science 2011, 28(3&4): 121–12

Development of a solar fuels roadmap for South Africa

South Africa is heavily reliant on fossil fuels for energy. Fortunately it has an excellent solar resource which, through solar fuels or high temperature solar applications offers the potential to reduce carbon dioxide emissions, to increase energy security and to optimize fossil fuel resource use. Solar fuels can be defined as solar derived thermochemical processes and can include energy carriers (hydrogen, synthesis gas and liquid fuels), chemical or material commodities (metals, lime, and cement) or thermochemical storage. South Africa is developing a “Roadmap to Solar Fuels” under the guidance of local and SolarPACES experts. This papers aims to provide an overview of the drivers and the process of developing a “Roadmap to Solar Fuels” for South Africa. It will also provide feedback on workshops and interactions with industry and government role players and will provide an overview of the specific solar fuels opportunities that exists for South Africa that can be explored further

Nodulation potential of four Trifolium repens cultivars under field conditions

Four Trifolium repens (white clover) cultivars were evaluated under field conditions to determine the potential of these cultivars to sucessfully develop Rhizobium-associated root nodules. Nodulation of T. repens is often poor, because of suboptimal environmental conditions or absence of host-specific rhizobia. The cultivars Huia, Haifa, Ladino and Regal were selected, as these are popular cultivars available in South Africa. Thousand seed mass (TSM) of each cultivar was measured to determine viability of seed and the possible interaction between TSM and nodulation. Mean TSM values of the cultivars differed significantly, with Huia having the highest TSM followed by Haifa, Ladino and Regal. Biomass production was also measured as an indicator of nitrogen fixation efficiency. The cultivar Huia, with the highest TSM values, resulted in the highest biomass production. Nodulation indices were determined from the size, number and colour of the nodules. All plants, regardless of cultivar, formed nodules within 8 weeks. It was concluded that TSM had no effect on nodulation. Planting date with associated temperature effects and the intrinsic cultivar effect also had no influence on nodulation. It was therefore concluded that nodulation potential of the four cultivars tested was similar under environmental conditions that prevailed during the study.African Journal of Range & Forage Science 2011, 28(2): 51–5