Combining diffusive gradients in thin-films (DGT) and 31P NMR spectroscopy to determine phosphorus species in soil

The diffusive gradients in thin-films (DGT) technique shows in many publications a superior correlation to the amount of plant-available phosphorus (P) in soil. However, this technique cannot give information on the plant-available P species in soil. Therefore, we combined DGT with solution P-31 nuclear magnetic resonance (NMR) spectroscopy. This was achieved by using a modified DGT device in which the diffusive layer had a larger pore size, the binding layer incorporated an adsorption material with a higher capacity, and the device had a larger exposure area. The spectroscopic investigation was undertaken after elution of the deployed DGT binding layer in a NaOH solution. Adsorption tests using solutions of known organic P compounds showed that a sufficient amount of these compounds could be adsorbed on the binding layer in order for them to be analyzed by solution P-31 NMR spectroscopy. Furthermore, various intermediates of the hydrolysis of trimetaphosphate in soil could be also analyzed over time. Core Ideas We show a promising combination of DGT technique and solution P-31 NMR spectroscopy. This technique combination can identify organic phosphorus species in solutions. Modified DGT device can analyze the hydrolysis of trimetaphosphate in soil.