Factors Affecting Solubilization of Rock Phosphates in Soils

The aim of this work was to conduct laboratory and pot experiments to study the ability of plant roots on solubilizing various sources of rock phosphate and factors that may facilitate or inhibit their activity. The effect of adding organic matter or sulphur in solubilizing rock phosphate added to alkaline and calcareous soil was studied. A split medium – split root technique experiment was conducted to study also the effect of N form, soil type, source and nature of rock phosphate on the pH, P solubility in the medium and P uptake by bean plants (Vicia faba var. balady). Results show that the highest NaHCO3 extractable P of incubation experiment were found for both soils treated with superphosphate. The behavior of rock phosphates in the two soils indicated slight solubilization in the alluvial soil and no remarkable change of extractable P in the calcareous soil as compared to the control. Regarding the effect of N form and P on growth and root exudates of bean plants, results indicated that the highest recorded total dry weight was found when both N forms were applied in the ratio of 1:4 : or alone. Results of root exudate analyses for amino acid content indicated the presence of several amino acids and variations in the amount were only with lysine. The highest content (115 μδ/100 ml) was in the root exudate of the complete nutrient solution (Hoagland solution) and the lowest value (24 μδ/100 ml) in the exudates of bean plants fed with as the only N form. The rock phosphate from Abou zaabal gave the highest P content in acid soil in the presence of plant. The highest drop in pH value in the collected solutions was when NH4+ alone was the N source.