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

  • PA Swanepoel
  • PR Botha
  • WF Truter
  • AKJ Surridge-Talbot

Abstract

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 technique

African Journal of Range & Forage Science 2011, 28(3&4): 121–127

Author Biographies

PA Swanepoel
Technology, Research and Development, Department of Agriculture: Western Cape, Outeniqua Research Farm, PO Box 249, George 6530, South Africa; Department of Plant Production and Soil Science, University of Pretoria, Pretoria 0002, South Africa
PR Botha
Technology, Research and Development, Department of Agriculture: Western Cape, Outeniqua Research Farm, PO Box 249, George 6530, South Africa
WF Truter
Department of Plant Production and Soil Science, University of Pretoria, Pretoria 0002, South Africa
AKJ Surridge-Talbot
Department of Plant Production and Soil Science, University of Pretoria, Pretoria 0002, South Africa
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Articles

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eISSN: 1727-9380
print ISSN: 1022-0119