Agronomic Evaluation of Recovered Phosphorus and Related Solids from Layer Manure

The recovery of phosphorus (P) from layer manure can contribute to closing nutrient cycles while reducing dependence on mineral P fertilizers. This study evaluated the agronomic performance of recovered phosphorus products (RP) and recovered solids (RS) obtained from layer manure using three different P extractants. Therefore, three RP products from extraction using (1) sulfuric acid, (2) oxalic acid, or (3) grape pomace combined with sulfuric acid, and their corresponding RS fractions, were evaluated in two greenhouse pot experiments with ryegrass (Lolium multiflorum). P and nitrogen (N) uptake, P recovery efficiency (PRE), N recovery efficiency (NRE), and changes in soil nutrient availability were assessed including N and P commercial fertilizers. In Experiment 1, all P-fertilized treatments increased ryegrass biomass, while RP showed P uptake comparable to commercial P fertilizer. P uptake was more strongly associated with application rate than RP source. In Experiment 2, urea produced the highest biomass, N uptake, and NRE, whereas layer manure and RS showed limited short-term N availability. Overall, RP showed promise as a short-term P fertilizer, whereas RS may be better suited for longer-term nutrient release. These results support the potential of layer manure-derived products as recovered fertilizers within circular nutrient management strategies.