Efficiency of soil and fertilizer phosphorus use in time : a comparison between recovered struvite, FePO4-sludge, digestate, animal manure, and synthetic fertilizer

The aim of this study was to evaluate the phosphorus use efficiency (PUE) based on the plant reaction and changes in soil P bioavailability status in time by land application of recovered bio-based fertilizers, including struvite, FePO4-sludge, digestate, and animal manure, compared to synthetic triple super phosphate (TSP). First, product characteristics and P fractionations were assessed. Then, a greenhouse experiment was set up to evaluate plant growth and P uptake, as well as changes in P availability on sandy soils with both high and low P status. P soil fractions were determined in extracts with water (Pw), ammonium lactate (PAl), and CaCl2 (P-PAE) and in soil solution sampled with Rhizon samplers (Prhizon). Struvite demonstrated potential as a slow release, mixed nutrient fertilizer, providing a high P availability in the beginning of the growing season, as well as a stock for delayed, slow release. The addition of FePO4-sludge was not interesting in terms of P release, but resulted in the highest PUE regarding biomass yields. The conversion of animal manure by anaerobic (co)digestion and subsequent soil application of digestate improved the PUE. Finally, the additional use of Rhizon samplers is proposed for better understanding and categorization of different inorganic and organic P fertilizers in environmental legislation