Rapid Determination of Total Nitrogen, Ammonium and Nitrate Nitrogen in Vinegar Residue Growing Substrates using Near-Infrared Spectroscopy

The objective of this study was to investigate the feasibility of using Near-Infrared Spectroscopy (NIRS) to determine the total nitrogen, ammonium and nitrate nitrogen in growing substrates of vinegar residues. Samples of 106 substrates were collected from the cultivation experiments of vinegar residue substrates. Spectra of the visible and near infrared region (350-2500 nm) were obtained for all samples after drying and grinding (variant A) or in a moist state (variant B). Across validation was carried out using a partial least square method which was based on the entire spectra. For parameters TN, NO3 and NH4, precisions of the calibration and prediction models were inconsistent between variant A and B. For variant A, the prediction coefficient (r), Root Mean Squared Error of Cross-Validation (RMSECV) and the ratio of standard deviation and RMSECV (RSC) were 0.97, 0.64 g/kg and 4.4 for TN, 0.58, 15.4 mg/kg and 1.2 for NO3, 0.79, 0.75 g/kg and 1.5 for NH4, respectively. For moist samples, the r, RMSECV and RSC were 0.79, 1.81 g/kg and 1.6 for TN, 0.85, 9.95 mg/kg and 1.9 for NO3, 0.92, 0.45 g/kg and 2.5 for NH4, respectively. The results indicate a marked usefulness of NIRS in the nitrogen assessment and management of growing substrates, especially for TN and NH4. However, further research is needed to improve the prediction precision of calibration models by enlarging the number of samples and using other growing substrates.