Kinetics of inorganic and organic phosphorus release influenced by low molecular weight organic acids in calcareous, neutral and acidic soils

Abstract

Low molecular weight organic acids exuded by plants roots enhance inorganic P i release into soil solution and thereby increases plant-available Pi in soils. Low molecular weight organic acids may also induce organic P (P o ) release into soil solution, but kinetics of both Pi and Po displacement from the soil matrix into soil solution of agricultural soils is poorly understood, and the mechanism for P o release is not well explained. This study used kinetic experiments to determine the concentrations and release rates of P i and P o induced by oxalic acid, citric acid, and malic acid in calcareous, neutral and acidic soils. Kinetic data were well described by Elovich (r 2 = 0.801-0.993, P < 0.001) and power functions models (r 2 = 0.721-0.977, P < 0.001). Low molecular weight organic acids at 10 mmol kg -1 soil induced the exponential release of both P i and P o , which reached a plateau approx. 480-2,880 min after the start of the experiment. Cumulative P o release induced by low molecular weight organic acids was ranked as oxalic acid (0.63-3.17 mg kg -1 ) > citric acid (0.61-2.82 mg kg -1 ) > malic acid (0.52-1.76 mg kg -1 ) and mainly resulted from the release of labile P o (NaHCO 3 -P o ) regardless of soil type. By contrast, oxalic acid was most effective in enhancing P i release from the HCl-P i (Ca-P i ) fraction of the calcareous soil, and citric acid was most effective in releasing P i from the NaOH-P i (Fe/Al-P i ) fraction of the neutral and acidic soils. Therefore, the mechanism for the kinetics of P o release induced by low molecular weight organic acids is ascribed to their ability to mobilize the labile P o (NaHCO 3 -P o ) rather than their ability to chelate cations (i.e., Fe 3+ , Al 3+ ) bound to P o in soil.

Crystallization of single and binary iron‐ and aluminum hydroxides affect phosphorus desorption

“…The time‐dependent phosphorus desorption data were modeled with the Elovich, Exponential, and Parabolic functions and, based on R 2 , the data fitted better to the Elovich equation, followed by the Exponential equation. This suggests that phosphorus was desorbed from Fe‐ and Al‐hydroxides by chemisorption reactions, which corroborated previous studies with phosphorus desorption from soils ( Steffens , ; Shariatmadari et al., ; Wang et al., ). For CaCl 2 , CaSO 4, and humic acid the calculated kinetics parameters showed a fast initial desorption step, followed by a slow reaction phase.…”

How functional is a trait? Phosphorus mobilization through root exudates differs little between Carex species with and without specialized dauciform roots

“…Second, citrate exudation by DRs did not improve plant growth with iron phosphate although citrate is the most powerful carboxylate at mobilizing iron‐associated P (Gerke et al ., ; Wang et al ., ). Again, the DRs of our species were small and scattered on the root system.…”

“…This inhibition is the likely reason why P diesters can accumulate through time in acidic forest soils, where they may represent a substantial fraction of organic soil P (Turner et al ., ). Oxalic acid is particularly effective at mobilizing organic P (Wang et al ., ), which may have compensated the lower diesterase activity in species without DRs.…”

Synthetic Humic Acids Solubilize Otherwise Insoluble Phosphates to Improve Soil Fertility

“…Organic acids, including humic and fulvic acids, can inhibit the precipitation of phosphate minerals, enhance the P bioavailability, and increase the availability of micronutrients . Organic acids have also been shown to induce high P mobilization, as they interact with multivalent metal cations and thus compete with PO 4 3− for cation binding . Martinez et al .…”