One client of mine told me that he wanted to measure protein and yield as far back as the early 60's.  Spoke with NASA back then and they told him it would cost him a huge sum of money at the time.  Fast forward 40 years and he's on his way to better nutrient management.  He claims there is an easy 20% improvement to be had with site specific techniques and proper feedback (and at his current $100-140k fertilizer bill, that's substantial).  His most interesting find is that some areas of his poorer fields really should get little if no fertilizer as protein content is always higher than the critical percentage, much against his earlier assumptions.... and if he wasnt measuring what he was harvesting, he would never know.