Herstellung und Verwendung 33P-markierter Carbonatfluorapatite zur Untersuchung der Wirkung rohphosphathaltiger Düngemittel

Preparation and use of ³³P labelled carbonate fluorapatite in studies on the effect of phosphate rock containing fertilizers For a precise evaluation of the effectiveness of the different phosphate fractions in partially acidulated phosphate rocks these fractions were alternatively labelled. For this purpose a technique was developed to prepare synthetic, ³³P labelled carbonate fluorapatite (francolite type). A labelled (NH₄)₂HPO₄ solution (+ Na₂CO₃, NH₄F) was poured into a Ca(NO₃)₂ × 4H₂O solution (pH 12) and the washed precipitate heated until the aimed solubility was reached (e.g. 2 h 400°C + 1.5 h 600°C). After grinding this mother phosphate rock was acidulated with sulphuric acid to fully acidulated superphosphate and partially acidulated phosphate rock. The nonacidulated rock residue was extracted from the partially acidulated phosphate rock. In an identical procedure phosphate rock was prepared without addition of ³³P and in part acidulated to superphosphate. Mixing of labelled phosphate rock and not labelled superphosphate (and vice versa) gave two fertilizer mixtures with alternate labelled fractions equivalent to the fully labelled partially acidulated phosphate rock. Mineralogical properties of the synthetic phosphate fertilizers and their turnover in pot experiments with rye grass were corresponding to that of commercial products. The reactivity of the nonacidulated rock residue was inferior to that of the original phosphate rock after the process of partial acidulation. Fertilizer utilization was determined by use of isotopes (³³P) and total P uptake method. P utilization as determined by total P uptake method was significantly higher compared to the real fertilizer effectiveness measured by ³³P labelling.