The samples of rhizosphere soil were aseptically separated by shaking and washing roots with sterile distilled water to
test soil pH, soil P content, and PSB population densities.
Soil pH was measured in a 1:2.5 soil:water suspension with a pH meter (Model 440, Corning, Tewksbury Massachusetts,
USA).
Available soil P was extracted with sodium bicarbonate (pH 8.5) according to Olsen et al. (1954) and measured
colorimetrically by the Murphy and Riley (1962) method.