The rhizosphere effect of some wheat cultivars on inorganic phosphorus fractions in a phosphorus-deficient calcareous soil

Knowledge of the distribution and changes of soil phosphorus fractions in the rhizosphere, helps to determine efficiency of different crop cultivars in phosphorus acquisition. This study was conducted in order to evaluate the rhizosphere effect of some wheat cultivars on inorganic phosphorus fractions. A greenhouse experiment as a factorial in completely randomized design was conducted with 10 treatments and 3 replications. Experimental factors were different plant cultivars (4 wheat cultivars and control) and soil-sampling zone (rhizosphere and non-rhizosphere). A rhizobag technique was used to separate rooted and non-rooted inside each pot representing the two soil sampling zones. Based on fractionation results, the order of inorganic phosphorus fractions in the studied soil were apatite-P> OCP-P> DCP-P> Al-P> Fe-P> O-P which were found to be in the order of 830, 123, 17, 16, 14 and 0 g kg-1, respectively. The concentration of the most inorganic phosphorus fractions between rhizosphere and non-rhizosphere soil was significantly different. All plant cultivars decreased inorganic phosphorus forms significantly. This difference was not equal for all cultivars and all fractions. Organic P was significantly higher in the rhizosphere soil compared to non-rhizosphere soil. Soluble phosphorus was not significantly differed between rhizosphere and non-rhizosphere soil. Root induced chemical changes; root morphology, microbial populations, pH changes etc. can be determining factors on phosphorus depletion differences among plant cultivars and soil sampling zone.   Key words: Phosphorus, fractionation, rhizosphere, rhizobag, wheat.