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Phosphate (P) fertilisers produced from waste recycling (e.g., struvite) are considered to be more sustainable than those conventionally produced from the processing of rock P (e.g., highly soluble triple superphosphate, TSP). In this study, we used 33P to monitor struvite dissolution and P diffusion into the soil in comparison to TSP. We evaluated three distinct chemical formulations of struvite, namely: (1) Crystal Green® (CG) produced in an industrial process from sewage sludge; (2) natural struvite (NS) precipitated in swine manure pipelines; and (3) laboratory precipitated struvite (PS) from chicken manure by a new process of P recovery. P diffusion was evaluated in soil columns over a 21-day period. This was complimented with a pot experiment in which wheat and soybean were cultivated in a Eutric Cambisol for 38 days in the presence of either struvite or TSP. P fertilisers were applied at a dose equivalent to 17.5 kg P ha−1 and fertiliser solubility determined by recovering soil solution. All three types of struvite tested showed reduced P solubility and mobility relative to TSP, but a comparison of the three struvites has shown that their P solubilities differed by a factor of two, with the greatest P release (up to 85% of total P) obtained from a struvite recovered from poultry manure and containing other useful nutrients (K, S and Ca). All struvites enhanced crop growth and P uptake of wheat and soybean relative to a nil P control, with up to 80% P recovery compared to TSP. These results further support the more widespread use of struvite as a sustainable source of P to plants despite its low water solubility.

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