The extent of the rhizosphere was investigated by using root volume and root length in ten replications. The experiment was conducted using split cylindrical pots, 23 cm long and 7.5 cm in diameter. Sorghum (Sorghum bicolor) plants were grown in a calcareous soil of low phosphorus (P) status. Fertilized soil (750 g soil and 250 g sand) was placed in a closed-bottom PVC tube. At harvest, plant roots were gently removed from the pots and the roots were shaken five times in order to reduce variation between samples. The soil that was easily shaken from the root surface was assumed to be non-rhizosphere soil, and the soil adhering to the root segment after a gentle shake was considered to be rhizosphere soil. The rhizosphere thickness was found to have a range of 0.39 to 0.64 mm from the root surface (0.51 mm average thickness). Rhizosphere soil mass was also calculated and found to be on average 22% of the total soil mass.