Circular economies: using DGT to assess the release kinetics of phosphorus in soils treated with waste-based fertilizer alternatives

Abstract

Phosphorus (P) is essential to assure world food security since it cannot be replaced for other elements as a fertilizer in agriculture. The estimations on the amount of remaining phosphate in the world are conflicting. Recycling P from urban waste shows up as an alternative to the dependence of P from the external market. Struvite is the most recovered P product with similar fertilizer performance compared to the chemical triple-super-phosphate (TSP). However, there are concerns about its application in forest soils due to the faster leaching of P in acidic environments, which can lead to eutrophication. A sustainable way of increasing soil pH is mixing struvite with industrially-produced urban biowaste composts generating a composite here called COM-VITE. This new composite is being tested to be a sustainable and safe alternative to chemical fertilizers in Irish forest soils. This project aims to evaluate whether COM-VITE provides a longer-term release of P with less run-off and leaching than chemical fertilizers in acidic forest soils using the diffusive gradients in thin films (DGT) technique. Intact forest soils from Irish sites will be amended with COM-VITE, struvite, urban waste compost, and chemical fertilizer. Flat DGT probes will be deployed vertically to map P and associated elements at a millimeter spatial resolution. The experiments will be repeated in the same samples periodically within a 9-month time window to assess the effectiveness of each soil amendment with the time regarding the mobility of P. DIFS (DGT Induced Fluxes in Sediments) model will allow quantitative interpretation of DGT measurements in terms of kinetic and equilibrium resupply parameters in soils during in situ DGT deployments. (AU)