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Adsorption of phosphate and organic matter on metal (hydr)oxides in arable and forest soil: a mechanistic modelling study
Author(s) -
Regelink I. C.,
Weng L.,
Lair G. J.,
Comans R. N. J.
Publication year - 2015
Publication title -
european journal of soil science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.244
H-Index - 111
eISSN - 1365-2389
pISSN - 1351-0754
DOI - 10.1111/ejss.12285
Subject(s) - chemistry , adsorption , calcareous , organic matter , solubility , environmental chemistry , desorption , phosphate , soil water , total organic carbon , soil carbon , soil chemistry , soil ph , arable land , soil organic matter , soil science , geology , ecology , paleontology , organic chemistry , biology , agriculture
Summary Phosphate ( PO 4 ) and organic matter ( OM ) compete for adsorption to metal (hydr)oxides. Our objective was to quantify the effect of OM on PO 4 solubility in forest and arable soil by desorption experiments and surface complexation ( SC ) modelling. We sampled different types of soil along an age gradient (≈50–2500 years) and from different depths (0–80 cm). The soil types are calcareous and cover a range of soil organic carbon ( SOC ) contents (5.6–43.5 g kg −1 ), PO 4 contents (0.2–5.9 mmol kg −1 ) and water‐soluble PO 4 concentrations (0.03–13.4 µ m ). Assuming that PO 4 concentrations are controlled by desorption, PO 4 concentrations were expected to correlate with the PO 4 loading on metal‐(hydr)oxide surfaces. However, we show that the PO 4 loading alone is a poor predictor of PO 4 solubility because its solubility increases with increasing SOC content. These data were explained by SC modelling, which shows a decrease in the apparent adsorption affinity of PO 4 with increasing OM loading on to the metal (hydr)oxides. As a consequence, if the competition with OM is disregarded in SC modelling, it results in underestimation of the PO 4 concentration by several orders of magnitude. For forest soil, predicted OM loadings increase slightly with increasing soil age. For arable soil, however, OM loadings were much smaller, which we explain by the replacement of PO 4 with OM . Overall, adsorption interactions strongly affect PO 4 solubility and levels of OM and PO 4 stabilization in soil.