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

Phosphate reactions and retention in the soil are of paramount importance from the perspective of plant nutrition and fertilizer use efficiency. The objective of this work was to investigate the effect of some low molecular weight organic acids (LMWOAs) on phosphorus release kinetic and its availability in calcareous soil. Experiments were conducted in laboratory. Soil-limestone mixtures were prepared to achieve highly calcareous samples (i.e. 50% CaCO3). The prepared samples were mixed thoroughly with phosphate fertilizers i.e. Triple super phosphate (TSP) and Monoammonium Phosphate (MAP) and watered with distilled water only (CK), with citric acid solution (CA) and with oxalic acid solution (OA). The treatments were arranged in a CRD with three replications and incubated at 25 ± 2°C and 80% soil moisture for a period of 960 h. The parabolic model was used for describing the decrease in P with time. As a result, all treatments showed a significant decrease in available P with time. Using LMWOAs showed important results and combination of phosphate fertilizers with both LMWOAs solutions exerted a very favorable effect on P availability in soil. The parabolic diffusion equation used was fitted well to experimental data. Addition of LMWOAs decreased loss in extractability of P with increasing soil available phosphorus fraction. Moreover, treatments irrigated by LMWOAs solutions released a lot of phosphorus compared to untreated treatments.

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Movements of Phosphorus Between its Biologically Important Forms in Lake Water

Journal of the Fisheries Research Board of Canada ◽

10.1139/f73-242 ◽

1973 ◽

Vol 30 (10) ◽

pp. 1525-1536 ◽

Cited By ~ 106

Author(s):

D. R. S. Lean

Keyword(s):

Molecular Weight ◽

Lake Water ◽

Membrane Filtration ◽

Organic Phosphorus ◽

Gel Filtration ◽

Particulate Fraction ◽

Low Molecular Weight ◽

Radioactive Phosphorus ◽

Dissolved Phosphorus ◽

Kinetics Of

A model consistent with the kinetics of phosphorus in epilimnetic lake water was developed. Adding 32PO4 to lake water and separating the major forms of dissolved phosphorus by Sephadex gel filtration showed that the exchange mechanism between inorganic phosphate and the particulate fraction predominates. At the same time, a low-molecular-weight phosphorus compound is excreted which combines with colloids in lake water, releasing phosphate from the colloid and making the phosphate available for "transfer" again. This rapid cycling of phosphorus between the four principal forms — the particulate fraction, the low-molecular-weight P compound, colloidal P, and phosphate — appears to contribute to formation of colloids in lake water. No direct complexing of phosphate to the colloid was observed. Only in the presence of algae, bacteria, and other particulate matter did the radioactive phosphorus move to the low-molecular weight and the colloidal forms. The low-molecular-weight compound is negatively charged, as is the colloidal P, but to a lesser degree. Both are removed by anion exchange materials along with phosphate, but the rate that they move into the fraction removed by membrane filtration is different from that for phosphate. When filtrate is refiltered a large amount of the colloidal P is retained by the filter. This complicates measurements of transfer and makes previous studies on utilization of dissolved organic phosphorus of doubtful value since corrections for filter retention were rarely, if ever, made.

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