Fig. 4. High-power decoupling with magic angle spinning (HPDec–MAS) nuclear magnetic resonance (NMR) (A) and cross polarization with magic angle spinning (CP–MAS) (B) spectra of Soil 3 before extraction (control) and after extraction with either 0.01 M CaCl₂ or water. Dashed and solid peaks represent Ca-P and Al-P species, respectively (see Fig. 3a, Table 2). Resonances marked ssb are spinning sidebands.