Rapid measurement and control of the moisture content of compost using near-infrared spectroscopy

In a compost fermentation of soybean-curd (tofu) refuse, the effects of the moisture content of the compost on the compost reaction were studied. The moisture content of the compost was a very important factor for good fermentation. Near-infrared spectroscopy (NIRS) was applied to the determination of the moisture content of the compost. The reflected rays in the wavelength range between 400 and 2500 nm were measured at 2 nm intervals. The absorption of water was observed at three wavelengths, 960, 1406 and 1888 nm. To formulate a calibration equation, a multiple linear regression analysis was carried out between the near-infrared spectral data at 960 nm (sample number, n = 50) and on the moisture content obtained using a drying method. The values of the simple correlation coefficient and the standard error of calibration were 0.987 and 1.33%, respectively. To validate the calibration equation obtained, the moisture content in the prediction sample set (n = 35) not used for formulating the calibration equation was calculated using the calibration equation, and compared with the values obtained using the drying method. Good agreement was observed between the results of the drying method and those of the NIRS method. The simple correlation coefficient and standard error of prediction were 0.979 and 1.85%, respectively. Then, the NIRS method was applied to a practical situation in which the moisture content was measured and controlled during the compost fermentation, and good results were obtained. The study indicates that NIRS is a useful method for measurement and control of the moisture content in the compost of soybean-curd refuse.