Application of Ftir-Photoacoustic Spectroscopy for Rapid Assessment of Phosphorus Availability in Digestates and Digestate-Amended Soils

Digestate is the anaerobic digestion by-product from biogas plants that can be used as a phosphorus (P) fertilizer. In this study, FTIR-photoacoustic spectroscopy (FTIR-PAS) combined with multivariate analysis was applied to predict water-extractable P (WEP) in 45 digestate samples and plant-available P (determined by the diffusive gradients in thin films (DGT) technique) in 57 digestate-amended soil samples. The model developed to predict WEP showed a coefficient of determination (R2) of 0.80 and a root mean square error (RMSE) of 0.78 g kg-1 by cross-validation (CV). The predictive model of P concentrations on the surface of the DGT (CDGT) in digestate-amended soils exhibited R2 of 0.70 and RMSE of 134.09 µg P L-1 by CV. Furthermore, regression coefficients with a significant contribution from the CDGT predictive model were identified, indicating that FTIR-PAS has good potential to predict P availability in digestate-amended soils and correlate spectra information with related chemical bonds