for my dumb question I found this http://isda.ncsa.illinois.edu/Hyperspectral/hyperAgricultur....
The true place for these chips is university and cooperative extension research. By knowing more about how plants use water they might be able to come up with a more easily measurable metric that farmers can use.
As another poster mentioned, though, spectral analysis shows problems in the leaves of the plant, where it is too late: if your plant is yellowing due to lack of water or nutrients, you've already decreased the potential yield from that plant. It's better to detect deficiencies in the ground.