Recycled nutrients supply phosphorus and improve ryegrass yields on phosphorus-depleted soil

Recycling phosphorus (P) within the food system is fundamental to long-term sustainability. This greenhouse study compared three sources of recycled P - struvite precipitated from municipal wastewater, black soldier fly frass from food waste, and anaerobic digestate of food waste - to mono-ammonium phosphate (MAP), com- post, and a control. Italian ryegrass (Lolium multiflorum) was harvested four times during a 123 d trial from P-depleted soil. In nitrogen (N) sufficient conditions, all amendments significantly increased cumulative ryegrass yields compared with the control and were not significantly different from MAP. Relative P supply was frass = MAP > struvite >= compost >= digestate >> control. The recycled nutrient sources tested show promise as sustainable P sources.