The Use of the Freundlich Isotherm for Soil Phosphate Sorption Data

Fitter, A. H.; Sutton, C. D.

doi:10.1111/j.1365-2389.1975.tb01947.x

Cited by 84 publications

(41 citation statements)

References 7 publications

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“…However, in the present study there existed quite a poor association between the water extractable Pin the soil and the term <t B corresponding to the term a of FITTER and SUTTON (1975). This result supports the concept discussed by HARTIKAINEN (1982 b) that, with increasing solution-soil ratio the isotherm expressing the P exchange as a function of final P concentration can be assumed in practice to converge the y-axis without intersecting it.…”

Section: Resultssupporting

confidence: 79%

“…The equation of the isotherm B presented in this study is to some extent similar to the Freunlich sorption isotherm modified by FITTER and SUTTON (1975) into the form AP bC k a, where C stands for the P concentration in the final solution and A P the amount of sorbed P. According to the authors, the third term, a, theoretically represents the phosphate which must be removed in order to reduce P concentration in the final solution to zero, since AP = -a when C = 0. When the equation was fitted to the sorption data, a close relationship was found between a and the resin-P values, with the calcareous and acid soils falling into two distinct groups.…”

Section: Resultsmentioning

confidence: 89%

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Relationship between phosphorus intensity and capacity parameters in Finnish mineral soils: II Sorption-desorption isotherms and their relation to soil characteristics

Hartikainen

1982

AFSci

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Abstract. The relationship between P intensity and capacity parameters in 104 mineral soil samples was studied by means of sorption-desorption isotherms of two types. In the isotherm A the P exchange was expressed as a function of P concentration in the initial solution, in the isotherm B as a function of P concentration in the final equilibrium solution. Both isotherms conformed to the equation y = a + bx, where y stands for the amount of P sorbed or desorbed and x the P concentration in the solution.In the isotherm A the constant a is the intensity factor expressing the amount of water soluble P at a given soil-solution ratio. The term a in the isotherm B, on the contrary, was only poorly related to water solubleP in soil. In both isotherms the slope h of the line seemed to be most effectively affected by oxalate extractable Al. The relative importance of oxalate soluble Fe appeared to be greater in affecting the effectiveness of sorption-desorption reactions than in affecting the buffer reactions. However, the slope b of both isotherms was found to be a semi-intensive parameter: it was quite markedly dependent also on soil characteristics which control the level of water soluble P in soil.The ratio of the term -a to b (termed as EBS or EPC), expressing the zero point of net P exchange, varied from 0.003 to 13.89 mg P per liter, the lowest values tending to be in the heavy clay soils and the highest ones in the non-clay soils. The practical significance of this quantity was discussed.

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Section: Resultssupporting

confidence: 79%

Section: Resultsmentioning

confidence: 89%

Relationship between phosphorus intensity and capacity parameters in Finnish mineral soils: II Sorption-desorption isotherms and their relation to soil characteristics

Hartikainen

1982

AFSci

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“…The particular form of the Freundlich equation that has been most often used in studies of PO 4 -P sorption to soils was originally suggested by Fitter & Sutton (1975):…”

Section: Freundlich Sorption Modellingmentioning

confidence: 99%

The pH dependence of phosphate sorption and desorption in Swedish agricultural soils

2012

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A number of previous studies have reported the existence of a minimum in phosphate solubility between pH 5.5 and 7 in non-calcareous soils. Different hypotheses have been forwarded to explain this phenomenon. In this study, ten soil samples with varying textures and phosphorus status were subjected to batch experiments in which dissolved phosphate was measured as a function of pH and phosphate load. Soil samples with more than 20 % clay all had a minimum phosphate solubility between pH 6 and 7, whereas for samples with < 10 % clay, no such minimum was observed. Further experiments involving additions of phosphate and arsenate showed an increasing adsorption of these anions with decreasing pH also below pH 6 in clay soils, suggesting that the pH dependence on adsorption and desorption in short-term experiments was not the same. Kinetic experiments showed that the increased phosphate desorption at lower pH values in noncalcareous clay soils was a quick process, which is consistent with adsorption/desorption being the most important mechanism governing the retention and release of inorganic P.Moreover, by comparing extraction results with batch experiment results for samples from a long-term fertility experiment, it was concluded that more than 60 % of the accumulated phosphate was occluded, i.e. not reactive within six days. Additional evidence for an important role of occluded phosphate comes from an analysis of the Freundlich sorption isotherms for the studied soils. It is hypothesized that interlayered hydroxy-Al and hydroxy-Fe polymers in clay minerals may be important for P dynamics in clay soils by trapping some of the P in an occluded form. The results also suggest that improved knowledge on the speciation and dynamics of phosphorus in soils is required for consistent mechanistically based modelling of phosphate sorption/desorption reactions.

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“…Net sorption or desorption was calculated from the changes in the DRP concentrations occurring during incubation. The P exchange by sediments was expressed as a Freundlich adsorption isotherm as modified by Fitter & Sutton (1975):…”

Section: Sorption-desorption Experimentsmentioning

confidence: 99%

Bioavailability of phosphorus in agriculturally loaded rivers in southern Finland

Ekholm¹

1994

Hydrobiologia

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The potential bioavailability of phosphorus in agriculturally loaded rivers of southern Finland was determined by an algal bioassay and the release of the potentially bioavailable particulate P was estimated by sorption studies. According to the bioassay 0 to 13.2 per cent (mean 5.1%) of the particulate P in river water samples was potentially bioavailable. Dissolved reactive P (DRP) in river waters appeared to be totally bioavailable whereas the dissolved unreactive P appeared not to be utilized by algae. In addition to river waters two lake sediment samples were also assayed. In these samples 0 and 2.6% of the P was bioavailable. The potential bioavailability of particulate P in agriculturally loaded rivers obtained in this study was lower than that reported in studies from other countries. The difference was assumed to arise partly from methodological factors and partly from the nature of the Finnish soils. The EPC (equilibrium phosphate concentration) values indicated that during the period when most of the agricultural loading enters the lakes in Finland, potentially bioavailable P is not released from the particles because of the relatively high DRP concentration in the receiving waters. However, during the algal production period the DRP concentration in lakes decreases below the EPC and potentially bioavailable particulate P is desorbed. The increase in pH during this period may further enhance the desorption of P.

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The Use of the Freundlich Isotherm for Soil Phosphate Sorption Data

Cited by 84 publications

References 7 publications

Relationship between phosphorus intensity and capacity parameters in Finnish mineral soils: II Sorption-desorption isotherms and their relation to soil characteristics

Relationship between phosphorus intensity and capacity parameters in Finnish mineral soils: II Sorption-desorption isotherms and their relation to soil characteristics

The pH dependence of phosphate sorption and desorption in Swedish agricultural soils

Bioavailability of phosphorus in agriculturally loaded rivers in southern Finland

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