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Solubilization of phosphorus by low molecular weight organic acids and amino acids in calcareous soils

In order for plants to perform well in nutrient-deficient calcareous soils, they have an efficient adaptive technique of root exudate secretion, which contains low molecular weight organic acids. They enhance  nutrient release and thereby increase the nutrient availability in calcareous soils. The present study aimed to investigate the effect of concentration and time of incubation of low molecular weight organic acids on P solubilization from calcareous soils collected from various locations of Coimbatore district with varying levels of calcareousness. An incubation experiment was conducted with five calcareous soils with varying levels of free CaCO3 viz., (1, 7.5, 12.5, 17.5 & 21.5%) by incubating with seven different concentrations (0, 20, 40, 60, 80 & 100 mM) of four organic (citric, malic, oxalic and acetic acid) and two amino acids (glycine and lysine) for nine incubation time intervals (5, 10, 20, 30, 60, 120, 240, 960 & 1440 mins) on a factorial experiment based on completely randomized design (CRD). Available P was analyzed to find the solubilization efficiency of various organic and amino acids. The organic acids were more efficient when compared to amino acids in P solubilization, especially citric acid followed by oxalic and malic acids, at 100 mM concentration incubated for 1440 mins. Also, the solubilization increased with increasing concentration and incubation time, irrespective of the soil calcareousness, but the magnitude of phosphorus extraction decreased with increasing soil calcareousness. Incubating the calcareous soils with 100 mM of citric acid for 1440 min  solubilized more amount of phosphorus. Hence it can be concluded that addition of 100 mM citric acid will influence the phosphorus release even from highly calcareous soils.