Long-Term Kinetics of Phosphate Release from Soil

Abstract

Long-term phosphate (P) desorption from soil is described using two discrete P "pools" in the soil: one available and one strongly fixed pool. The P release kinetics for each pool are described with a firstorder rate equation. A new desorption method is used with hydrous iron oxide inside dialysis tubing acting as a P sink. The widely used iron-impregnated filter paper desorption method overestimates initial P desorption by a factor of up to 4 and underestimates the quantitative progression of desorption as a function of time. P desorption continued with substantial rates for periods longer than 1600 h. A wide range in P desorbability was observed: 15-70% of oxalateextractable P (Pox) desorbed after 1600 h. P desorbability decreased with increasing Feox + Alox content of the sample. The relative size of the quickly desorbing pool increased with increasing initial degree of P saturation oto = P0X/[Fe0X + Alox] of the soils. This fact is of direct importance for the estimation of P losses from phosphate-rich soils. This study furthermore provides evidence that all oxalate-extractable P potentially is desorbable: no irreversibly fixed Pox exists.

Soil phosphorus saturation degree: Review of some indices and their suitability for P management in Québec, Canada

“…pool will increase (Lookman et al 1995b). This has been confirmed by many studies reporting a significant positive relationship between soil P solubility and saturation index ( Table 1).…”

“…Similarly, Van der Zee et al (1988) reported that "the degree of saturation of soil with P may be expressed with the ratio α = F/ME", in which F may be assessed with P ox and ME = Al ox + Fe ox (expressed in mmol kg -1 ). Lookman et al (1995b) also refered to the molar ratio of P ox /(Al ox + Fe ox ) as an estimator for the initial degree of P saturation of the binding sites in slightly acidic to acidic sandy soils.…”

Phosphorus Sorption Kinetics in Reclaimed Lignite Mine Soils under Different Age Stands ofRobinia pseudoacaciaL. in Northeast Germany

“…In contrast, for soil under R14 plantation longer period is expected to complete the desorption process. As noted by Lookman et al [96], for sandy soils with low sum of Fe ox and Al ox , the P desorption attains more than 90% of P ox on a long time scale (200 days). The Spearman correlation shows significant ( < 0.01) negative correlation between all investigated sites and the Fe ox and Al ox .…”

“…Moreover, by using a sink with concentration gradient, the desorption process is forced, and it is independent of extraction solution. However, the desorption amount based on this technique may tend to overestimate the initial desorbed P or underestimate the quantitative progression of desorption, leading to the impression that desorption stability level is reached after some time [96]. Additionally, the adhesion of fine soil particles to the paper strips can cause adsorption errors.…”

Phosphorus forms and response to changes in pH in acid-sensitive soils on the Precambrian Shield

“…Both Al ox and Fe ox are important sorbents for phosphate and other anions (Freese et al 1992;Lookman et al 1995;Kanˇa and Kopa´cˇek 2006) and soils with high Al ox and Fe ox concentrations have a high capacity for P sorption (Yuan and Lavkulich 1994). Decreasing soil pH also increases the positive charge around Al and Fe oxides and thereby increases anion adsorption (Muljadi et al 1966;Bowden et al 1980).…”