From Waste to Worth: The Art of P Recycling From Secondary Sources

Phosphate from mineable rock is a finite resource. P can be more effectively managed by substituting P-rich secondary resources for mineral phosphorus (P) fertilizer. Substance flow analysis was used to examine Norway’s ability to switch from mineral P fertilizer to total P in secondary resources. In theory, plant-available P in manure alone might meet Norway’s need for P fertilizer, according to the results, which were combined with information on P plant availability in secondary resources. However, the geographical separation of arable farming and animal husbandry results in the poor use of P in manure, which leads to significant P over-application to agricultural soil. The relative agronomic efficiency (RAE) of secondary P products in comparison to mineral fertilizer is crucial for achieving P recycling in practice. In this analysis, eight secondary P products were examined: dairy manure, poultry manure, fish sludge, two digestate products derived from food waste, two biomass ashes, and meat bone meal. In a bioassay including ryegrass ( Lolium multiflorum ), the RAE of these secondary metabolites varied greatly, in part due on the pH of the soil. The solubility of the inorganic P species present in the subsequent products was primarily responsible for the fertilization effects. By combining non-destructive speciation techniques with successive chemical fractionation, it was discovered that P was mostly present as calcium phosphates with varying solubilities.