This week I met with Mike Deibel regarding soil fertility measurements. One of the primary accepted ways to measure soil fertility is the combustion method. We don’t want to do that. Other alternatives are spectroscopy of the soil directly (requires infrared electromagnetic range) or of a soil solution after a reaction (can be done in the visible light range, but requires reagents and possibly a flow-injection system). For the munsell color test, a visible-range spectrometer that uses fiber optic cables to transmit signal could be used.

NIR spec focuses on the infrared region of the electromagnetic spectrum. Building a NIR spectrometer is tricky because a lot of things absorb infrared wavelengths and because I would have to build some sort of detector that scans through individual wavelengths very precisely. This isn’t impossible, but it isn’t trivial – so I’m still looking into it. There are a large number of DIY spectrophotometers projects out there but few of them dip very far into the IR range, precisely because it is so difficult.

There is a nice DIY solution for flow-injection analysis (a stream of reagent is merged with a stream of sample and the mixture is analyzed). [3D printed syringe pump] [Nitrate quantification]

For the munsell color test, things are a lot simpler because we only need to deal with the visible light range. Reverse-engineering a visible light spectrometer like this one is not at all an unreasonable thing to do.