Interrelationship of pH, organic acids, and phosphorus concentration in soil solution of rhizosphere and non-rhizosphere of wheat and rice crops

To study the interrelationship of pH, soil solution phosphorus (P) and organic acids concentrations in rhizosphere and non-rhizosphere of wheat and rice, plants were grown in plastic funnels (150 mm diameter) containing 500g of three types of soils, namely, Alfisol, Vertisol, and Inceptisol under greenhouse conditions. Soil solutions were collected by water displacement methods, 21 and 50 days after sowing. Eight different organic acids, viz., valeric, malic, benzoic, tartaric, citric, oxalic, acetic, and butyric were identified and quantified in rice rhizosphere. On the other hand only five (malic, tartaric, benzoic, citric, and butyric) acids were found in wheat rhizosphere. Organic acids were found to be more in rhizosphere and at initial stages of crop growth (21 DAS). Most of the acids showed negative relationship with solution P concentration, which indicated more secretion of organic acids from roots in P stressed condition in soil. Due to higher dissolution capacity of citric acid from non-labile P from soil constituents showed a positive relationship with soil solution P in both the crops in Vertisol. More occurrence and greater interrelationship of organic acids with P concentration were found in Alfisol having relatively lower pH and less solution P concentration.