A highly significant quadratic relationship of SBQ with SQI suggested that among the soil biological, chemical and physical quality indices, the SBQ is a consistent, sensitive, and early indicator of changes in SQ long before the changes are detected in other SQ indicator properties. The SBQ is greatly responsible, among other properties, for decomposition of organic residues, facilitating nutrient cycling, metabolizing labile C, synthesizing humic substances, enhancing macro aggregation and structural stability, and protection of organic matter as POM (Dexter, 2004, Aziz et al., 2009 and Melero et al., 2009). Therefore, improvement in soil biological properties relates to improvement in soil chemical and physical properties, and ultimately soil quality. A significant relationship of SBQ with SCQ and SPQ justified the role of soil biology to improve other soil properties. Parkin et al. (1996) reported that changes in biological activities or biochemical processes may be used as indicators of SQ. Furthermore, a significant linear relationship between SQI and Cindex supported our hypothesis that improved SQ will facilitate soil C sequestration or vice versa. Therefore, a routine evaluation of SBQ can be used as an early and sensitive indicator of both soil quality and C sequestration.