Phosphate-coated nanoparticles as mobile P carriers in soil: fate study

In tropical soils, low P bioavailability is a major plant nutritional problem. Responses to fertilizer application are low and transient due to strong fixation of P by Fe- and Al-oxyhydroxides. Recently, it was shown that supplementing a low-P nutrient solution with phosphate-coated Al-nanoparticles (NPs) enhances P bioavailability to plants. The aim of this study was to assess if phosphate-coated NPs can also be used in tropical soils as a carrier of P. The mobility of P-coated NPs in soil and the P mobilisation potential of the NPs was tested with three different soils: sand (control) and a P fixing Ferralsol and Andosol. Four different types of Fe- or Al-based NPs were added to the soils in two set-ups: either NPs loaded with 33PO4 added to non-labelled soil or non-labelled NPs added to 33PO4 labelled soil. After 7 days incubation with soil, dissolved 33P was measured in soil extracts (0.01M CaCl2, S:L 1/1 water and S:L 1/10 water) with liquid scintillation counting and Fe & Al with ICP-MS. Finally, advanced characterisation of the different types of NPs used, was performed with Asymmetric Flow Field Flow Fractionation (AF4)-ICP-MS and with single particle ICP-MS. In the 1/10 water extracts, 33P solubility increased by the addition of 33PO4-labelled NPs but this was generally not found when the ionic strength of the extracts was higher. There was no significant increase in the mobilisation of 33P by the NPs with 33PO4 labelled soils. Other formulations of NPs are required with higher colloidal stability at the prevailing ionic strength in soils to mobilise PO4 with NPs.status: publishe