An empirical formula was suggested to evaluate the effects of different treatments applied under the rhizosphere conditions. These effects could be indexed by determining the Efficiency of Rhizosphere treatment [E. R. T] i. e., the net effect of rhizosphere treatment divided by the net effect of the same treatment in root-free soil. Organic amendment [0.2% maize stalks] was used as a substrate in this investigation. The formula was applied on two plants maize and wheat grown under two different environmental conditions. The rhizosphere effect and the E. R. T. Were periodically determined for the plants grown in unamended and amended soil, respectively. The changes in populations of total microbial flora, Azotobacter spp., Azospirillum spp., the rates of CO2 evolution, the organic carbon and total nitrogen contents were used as microbiological and chemical parameters under these conditions. The results of this study were presented and discussed