Earthworms affect reactive surface area and thereby phosphate solubility in iron-(hydr)oxide dominated soils

Sustainability of agricultural systems is at stake, as phosphorus (P) a non-renewable resource while its global reserves are limited. Stimulating earthworm activity can be technology to increase the level readily plant-available phosphate (PO4). However, conclusive evidence on mechanisms underlying an earthworm-enhanced PO4 solubility yet missing. This study aimed reveal possibly overlooked pathways by which earthworms affect solubility, and quantify relative importance all contributing mechanisms. Therefore, we set up greenhouse pot experiment in investigated large water-extractable casts three species (Lumbricus rubellus, Aporrectodea caliginosa, Lumbricus terrestris) soils with either predominantly Fe- or Al-(hydr)oxides. Oxalate-extractable was increased compared bulk soil attributed mineralisation natural organic matter (NOM). Surface complexation modelling used elucidate that control solubility. The results our showed pH affects only minor extent. Besides NOM mineralisation, two major (i) decrease reactive surface area (RSA) metal-(hydr)oxide fraction; (ii) competition between for binding sites metal-(hydr)oxides. As newly discovered RSA found Fe-(hydr)oxide-dominated soils, have largest potential enhance those soils.