Over the past few decades, scientists have understood the needs for the exploitation of optical means particularly Vis-NIR spectroscopy to measure agriculture soil properties in real-time. The objective of this study is therefore to
investigate the potential of Vis-NIR spectroscopy for mapping of multiple (19) soil properties using the optical-based
real-time soil sensor (RTSS). For this purpose, Vis-NIR soil reflectance spectra (from 310 to 1700nm) were acquired
using a tractor-mounted RTSS at 2 fields of a commercial farm in Hokkaido, Japan. The RTSS consists of a halogen
lamp, fiber optics, two spectrophotometers, computer, DGPS receiver, and CCD camera. A total of 262 soil samples
were collected subsequently for laboratory chemical analysis. PLSR coupled with full-cross validation was used to
establish the relationship between the pre-treated Vis-NIR spectra with the value of soil properties obtained by chemical
analysis. From this analysis, it was found that the accuracy of the calibration models ranged from R<sub>val</sub><sup>2</sup> of 0.65 to 0.86
and RPD from 1.7 to 2.7, meaning that the accuracy some of the models were excellent and others were almost good.
Moreover, the predicted maps of 19 soil properties were comparable with the measured map. This shows that the RTSS
by means of Vis-NIR spectroscopy can be used for mapping the 19 soil properties.