Soil optical transducer for NPK nutrients detection

Hey guys, did anyone here try to build optical sensor based on this research?Detection of NPK nutirents in the soil using optical transducer

I want to construct one, but have doubts after looking at schematics. The light detection part (LDR sensor) used for reading & detecting values from RGB LED seems to be enough to attain measured nutrient level from the soil sample.

However, after watching this video I can't decide which one to try and construct.
I need to have this sensor implemented as crucial component of my system. Please give me some advice or guidelines, I'm currently in a dead end :fearful: