Solution Phosphorus-31 Nuclear Magnetic Resonance Spectroscopy of Soils from 2005 to 2013: A Review of Sample Preparation and Experimental Parameters

Phosphorus nuclear magnetic resonance (P-31 NMR) spectroscopy is an important tool for the study of soil P and has significantly advanced our knowledge of soil P forms, particularly organic P; however, it must be used correctly to provide meaningful results. This review covers the P-31 NMR studies of soil published from 2005 to 2013. The first part discusses preparing samples for P-31 NMR, including extractants, pre- and post-extraction treatments, the physical state of the soil sample at the time of extraction, extraction length, the soil/extractant ratio, P recovery, P in residues, methods to concentrate extracts, redissolving samples for P-31 NMR experiments, the use of the internal standard methylene diphosphonic acid, and the potential for degradation with any of these steps. The second part of this review focuses on NMR experiment parameters, including delay times, proton decoupling, and experiment length. Potential concerns in these areas are noted, and suggestions are given for procedures to optimize the information obtained from a P-31 NMR experiment.