Solubility and Phosphorus‐31 Magic Angle Spinning Nuclear Magnetic Resonance of Phosphorus in Sludge‐Amended Soils

The solubility of P in two sludge‐amended soils was studied. Solubility and activity ratio diagrams for P in sludge‐amended soils were constructed and were compared with those of selected Ca‐P, Fe‐P, and Al‐P minerals. The solid phase controlling P solubility in the sludge‐amended soils appeared to be a carbonated apatite formed through coprecipitation. The 31 P magic angle spinning nuclear magnetic resonance ( 31 P MAS NMR) examinations confirmed that P in the sludge‐amended soils was in form of calcium phosphate. The resonant peak [at isotropic chemical shift (δ lso ) = 3.1 ppm] is indicative of an apatitic calcium phosphate environment characterized by carbonate substitution. Additionally, pyrophosphate was detected by the presence of a peak at δ lso = −9 ppm.