Phosphorus speciation and fertiliser performance characteristics: A comparison of waste recovered struvites from global sources

Abstract Our immediate and future food security agenda requires sustainable phosphorus (P) management, and recovered P products such a struvite form part of the solution. Waste recovered struvite is generated from different waste streams and precipitation technologies. In this study, we compare P speciation and bioavailability of nine struvite products with traditional/granulated chemical fertilisers to investigate performance characteristics across soil types in the Irish ecoregion. Elemental-analysis/P-speciation of the struvites was examined by ICP-OES, 31P solid state NMR, PXRD and P-solubility tests. The fertiliser dose effect and bioavailability of the different struvite products were tested in 4-week and 3-month rhizotron experiments with perennial ryegrass (Lolium perenne). In addition to calculating plant-P offtake, bioavailability was assessed by Olsen-P and Diffusive-Gradients-in-Thin-Films (DGT). The struvites differed markedly in colour/appearance, texture, metal content and solubility. Struvites all had similar P-speciation, but minor impurity phases were detected. There was no significant difference between the struvite samples and triple-super-phosphate (TSP) with respect to either plant growth performance or P-bioavailability. The struvite products are produced from different wastewater streams/processes, yet possess a uniformity in overall fertilising performance within our experiments. Encouragingly, no appreciable agronomic difference in terms of yield was observed between the struvite and chemical fertilisers, which provides further evidence in support of struvite as a sustainable alternative to mined rock-phosphate derived products. Importantly the struvite samples analysed within this study contained both significantly fewer impurities than TSP and lower concentrations of toxic metals such as cadmium.