A simple digital imaging method for estimating black-soil organic matter under visible spectrum

Soil organic matter (SOM) plays a key role in soil, and is used to determine soil quality. Conventional soil property analysis is relatively slow, expensive and laborious. Although using a spectrometer can quickly assess a large amount of organic matter content, it is an expensive, complex and undefined process. This article presents a potential simple method for estimating black-SOM that uses a digital camera that is cheaper and easier to operate than a spectrometer. RGB (red, green and blue) image-intensity values of the soil from a digital camera were measured, to research the relationship between black-SOM and RGB. The results show the red image-intensity values provide the greatest correlation with SOM, with a correlation coefficient (r) reaching 0.73. A comparison with spectrometer results for SOM predictions shows that the best prediction result for the digital camera (R2 = 0.72, root-mean-square error [RMSE] = 0.40) is slightly better than the spectrometer (R2 = 0.65, RMSE = 0.45) at certain band points. Thus, a low-cost digital camera that is easy to operate can be used as an alternative tool for the rapid and accurate estimation of black-SOM content.