Evaluation of the nutrient metal content in Chinese animal manure compost using near infrared spectroscopy (NIRS)

This study explored the feasibility of determining the content of several nutrient metals (K, Ca, Mg, Fe and Zn) in animal manure compost products in China using near infrared spectroscopy (NIRS). Samples of 120 compost products were collected from 22 provinces in China. The spectra were scanned obtained with a FT–NIRS system. For fresh samples, the validation coefficient of determination (r2), standard error of prediction (SEP) and the ratio of the standard deviation in the validation set to the standard error of prediction (RPD) were 0.69, 5.08 g/kg and 1.83 for K, 0.46, 17.99 g/kg and 1.33 for Ca, 0.54, 1.73 g/kg and 1.42 for Mg, 0.86, 1.14 g/kg and 2.55 for Fe and 0.65, 62.95 mg/kg and 1.71 for Zn, respectively. For dried samples, the r2, SEP and RPD were 0.68, 5.68 g/kg and 1.79 for K, 0.78, 15.34 g/kg and 2.12 for Ca, 0.72, 2.07 g/kg and 1.81 for Mg, 0.84, 1.49 g/kg and 2.27 for Fe and 0.57, 86.32 mg/kg and 1.52 for Zn, respectively. The results showed that the NIRS technique is a potential method for predicting nutrient metal content of animal manure compost products. However, further research is needed to improve the prediction precision of calibration models by enlarging the number of samples and using other chemometric methods.