Release of colloid-bound phosphorus in soils: comparing laboratory extraction experiment results with natural soil solution data

International audienceColloids (11000 nm) are important carriers of phosphorus (P) in agricultural soil solutions and have been frequentlystudied by lab extraction experiments. However, little attention has been paid so far to evaluating how theproportion and composition of P-bearing colloids were affected by the water/soil ratio and the ionic strength of theextracting solutions used. Here, we conducted lab extraction of P-bearing colloids on surface soils from two transects(G and K) located in a small agricultural catchment from Western France, at different water/soil ratios (30:1,20:1, 10:1 and 4:1) and different ionic strength (H2O, 0.001M NaCl and 0.01M NaCl), and compared the resultswith colloidal P quantification performed on natural soil solutions from the two same transects. Ultrafiltration combinedwith inductively coupled plasma mass spectrometry (UF-ICP-MS) and XANES spectroscopy were used toevaluate the proportion of colloidal P and the composition of the colloidal carriers. During laboratory extractions,we observed that total dissolved (