A feasibility quantitative analysis of NIR spectroscopy coupled Si-PLS to predict coco-peat available nitrogen from rapid measurements

Abstract Available nitrogen was an important index to evaluate the supply capacity of nitrogen fertilizer in planting environment. The study of coco-peat available nitrogen content rapid detection technology was of great significance for instructing scientific fertilization. In this study, near infrared (NIR) spectroscopy was used to realize rapid quantitative detection of available nitrogen in coco-peat. Seven different spectral pretreatment methods were adopted to pre-process spectral data with detection band range of 1000–2500 nm (full-band), and synergy interval partial least squares (Si-PLS) was used to screen the optimum combination sub-intervals reflecting coco-peat available nitrogen content from the original full-band spectral data and various pre-treated spectral data. The spectral prediction models of coco-peat available nitrogen based on full-band spectral data and optimal combined sub-intervals spectral data were respectively established, the improvement effects of different pretreatment methods on the accuracy of coco-peat available nitrogen spectral prediction models were analyzed, and the performances of the optimal full-band spectral prediction model and combined sub-intervals prediction model were compared. By analysis and comparison, the first derivative combined with Savitzky-Golay (S-G) smoothing was used to pre-process spectral data, Si-PLS was used to screen the spectral data of 1724–1784 nm, 1852–1922 nm, 1923–1999 nm and 2175–2272 nm, and then the optimal spectral prediction model of available nitrogen content in coco-peat could be established by using the four bands spectral data. For the optimal model, the correlation coefficient and root mean square error of calibration set were 0.994 and 6.998 mg/100 g respectively, the correlation coefficient and root mean square error of prediction set were 0.993 and 7.390 mg/100 g respectively, and the RPD was 8.062. It showed that the combination of NIR spectroscopy and Si-PLS could realize coco-peat available nitrogen quickly and accurately quantitative detection, Si-PLS could effectively reduce the input variables of the established model and simplify the complexity of the model. It also provided a reference for development of a coco-peat available nitrogen content rapid detection device based on characteristic band sub-intervals spectral data.