Fast and Non-Destructive Determination of N, P, and K in Sorghum, Oat, and Corn Residue Using Near-Infrared Spectroscopy

A fast and non-destructive method is reported to nitrogen, phosphorus and potassium quantification in sorghum, oat, and maize residues. The reflectance spectra of 261 litter plant samples using near-infrared spectroscopy were obtained with integrating sphere and sampling rotator. Second derivative spectra and Partial Least Squares were used to develop calibration and validation models. The cross-validation (leave-one-out) technique was used to evaluate the performance of the calibration and validation models, based on analytical parameters, root-mean-square error of estimation, determination coefficient, number of latent variables, residual prediction deviation, root-mean-square error of cross-validation. It was concluded that near-infrared spectroscopy and chemometric tools are a fast and non-destructive alternative to determine nitrogen and phosphorus content in sorghum, oat, and maize residues using calibration and validation models developed according to values obtained from traditional chemical methods. For potassium content, the results indicate the low quality (imprecision) of the calibration and validation models.