A system for measuring soil constituents having coulter comprising an electromagnetic radiation detector, a source of electromagnetic radiation, and a window transparent to electromagnetic radiation, the source emits radiation through said window to the soil, and the detector receives radiation through said window, reflected from the soil. Typically the source is broad band so the detector provides continuous spectra over the range. The source may be quasimonochromatic to provide Raman scattering, which will also provide continuous spectra over the range. These spectra can be subjected to multivariate analysis and compared to spectra of known constituents to identify the presence and concentration of these constituents.