Phosphor fertilization effects of phosphorus recycling products

P uptake from different P products of P recycling were tested in pot experiments: 17 products of recycled sewage sludge ashes (SSA), 1 meat and bone meal ash, 1 sinter product of meat and bone meal, 1 cupola furnace slag, 9 Ca phosphates from Ca crystallization on CSH substrates or from precipitation by Ca(OH) 2 and CaCl2 such as P-ROC, Fix-P, SESAL, Pasch, Seaborne-Ca-phosphates, Seaborne-Mg-phosphate and struvites from 3 institutions. These P products were tested in comparison with simple super phosphate (SSP) or triple super phosphate (TSP), and row phosphate. Sandy and loamy soils (pH: 4,7-6,8; CAL-P: 33-49 ppm) were used. Maize was used predominantly as the test plant. The P uptake from super phosphate (P amount of plants with P fertilizer minus P amount of plants without P) was set as the reference value (= 100 %) for all P products. The following results were found: (1) plants took up less than 25 % P in 65 % of all SSA (15 products). (2) 6 products (26 %) resulted in P uptake of 25 and 50 % relatively to TSP. In only one Mg product P uptake reached 67 %. With cupola furnace slag 24 % P uptake was reached on sandy soil and nearly the same value as TSP on loamy soil. The uptake results of Ca phosphates were between 0 and 50 %. Mg products from precipitation processes consistently showed a better P supply in relation to comparable Ca compounds. With struvite the same P uptake as TSP was reached. Reasons for the different P efficiency of recycling products and perspectives of their use are discussed.