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.