Nano andfine colloids suspended in the soil solution regulate phosphorusdesorption and lability in organic fertiliser-amended soils br

Mobile colloids impact phosphorus (P) binding and transport in agroecosystems. However, their relationship to P-lability and their relative importance to P-bioavailability is unclear. In soils amended with organic fertilisers, we inves-tigated the effects of nano (NC; 1-20 nm),fine (FC; 20-220 nm), and medium (MC; 220-450 nm) colloids suspendedin soil solution on soil P-desorption and lability. The underlying hypothesis is that mobile colloids of different sizes,i.e., NC, FC, and MC, may contribute differently to P-lability in soils enriched with organic fertiliser. NC- and Fc bound Pcollwere positively correlated with P-lability parameters from diffusive gradient in thinfilms (DGTA-labile Pconcentration,r >= 0.88; and DGTA-effective P concentration,r >= 0.87). The corresponding relations with MC-bound Pcollare weaker (r values of 0.50 and 0.51). NC- and FC-bound Pcollwere also strongly correlated with soil P-resupply (r >= 0.64) and desorption (r >= 0.79) parameters during DGTAdeployment, and the mobility of these colloidswas corroborated by electron microscopy of DGTAgels. MC-bound Pcollwas negatively correlated with the solid-to-solution distribution coefficient (r=-0.42), indicating this fraction is unlikely to be the source of P-release fromthe solid phase after P-depletion from the soil solution. We conclude that NC and FC mainly contribute to regulatingsoil desorbable-P supply to the soil solution in the DGTAdepletion zone (in vitroproxy for plant rhizosphere), andconsequently may act as critical conditioners of P-bioavailability, whereas MC tends to form complexes that lead toP-occlusion rather than labilit