Estimation of phosphate extractability in flooded soils: Effect of solid-solution ratio and bicarbonate concentration

• Published in: Chemosphere (Oxford) Vol. 303; no. Pt 3; p. 135188
• Main Authors: Amini, Mitra, Antelo, Juan, Fiol, Sarah, Rahnemaie, Rasoul
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01.09.2022
• Subjects: Anoxic conditions; Extractable phosphate; Iron (hydr)oxides; Organic carbon; Surface complexation modeling; Iron (hydr)oxides; Organic carbon; Anoxic conditions; Surface complexation modeling; Extractable phosphate
• ISSN: 0045-6535; 1879-1298
• DOI: 10.1016/j.chemosphere.2022.135188

The Olsen method is widely used to determine bioavailable phosphate (P) in upland soils. It is also used in flooded soils, although different estimates of extractable-P are obtained under anoxic and oxic conditions. In this study, variations in extractable-P in three soils under different redox conditions were evaluated as a function of solid to solution ratio (SSR) (1:5–1:200) and bicarbonate concentration (0.1–1 M). The parameterized CD-MUSIC model was used to describe the data, with optimization of reactive surface area (RSA) and reversibly adsorbed-P (R–PO4). The RSA may vary due to the reductive dissolution of iron minerals and/or the formation of new reactive surfaces upon the establishment of reducing conditions. Changes in SSR and bicarbonate concentration significantly affected extractable-P under both oxic and anoxic conditions; more P was extracted under anoxic than under oxic conditions. The difference was 1.5–2 times greater for the highest SSR considered. In the soil samples with higher organic carbon content, the effect of bicarbonate concentration on extractable-P was remarkable. The large differences in extractable-P under oxic and anoxic conditions were probably due to differences in iron (hydr)oxide content. The CD-MUSIC model successfully predicted the effect of SSR on extractable-P under both conditions. R–PO4 data were fitted for oxic conditions and assumed unchanged for anoxic samples, while RSA data were fitted for both conditions. The RSA values were lower in anoxic than in oxic samples. Overall, our data and model calculations indicate that using wet soil samples obtained in-situ for evaluation of Olsen-P in submerged soils lead to a higher estimation of extractable-P than estimated in oxic soils. If soil testing in the presence of target plants confirms the reliability of in-situ sampling for Olsen-P estimation, the P fertilizer dose applied to submerged soils could be reduced, which is very important from environmental and economic perspectives. [Display omitted] •Effects of SSR and NaHCO3 on PO4 release is larger in anoxic than in oxic soils.•Low P buffering capacity enlarges difference in P release between oxic and anoxic soils.•Decrease in redox potential decreases soil reactive surface area.•Model parameters derived in oxic conditions simulate data in anoxic conditions.•P-Olsen decreases by increasing SSA in both oxic and anoxic condition.