How much fertilizer do we really need?

Denny, this is no small question. I have a Conservation Innovation Grant (CIG) that I am running with 5 farmers at the moment. The idea is that we are (1) building soil with cover crops and (2) measuring the nutrient benefits/credits through the Haney-Brinton CO2 burst respiration test and (3) got the farmers to split their fields into standard and low nitrogen applications (on average, we saw about 40lb/ac of mineralizable N in the soils) . We don't have the harvest data yet, but it look like there were small only small differences in yields of cotton (1 field), corn (2 fields) and grain sorghum (1 field) - my expectation that if the reduction in nitrogen inputs more than paid for any loss in yield. On the implications toward fertilizer producers, I believe in this last year the National Ag Statistics Service said that farmers planted 10 million acres of cover crops (land which would have otherwise been fallow). The potential in my mind is that by doing so, farmers may save up to $150 an acre on fertilizers, let alone savings on chemicals as their soils build up (this can be in a short space of time). What many farmers lack are the tools to evaluate what the value (in "fertility") of the increased organic activity in their soils is to them, b/c most ag services do not provide this information. What we are doing is making use of the services that are available to figure out how much is in the organic/biologic component soil, and then also evaluate how much we have in the cover crop. These sources are typically ignored in most production but once the farmer is aware of them, he can pull the trigger on going with much less fertilizer. So going back to the fertilizer companies, I think this movement represents a potential shift in the transfer of wealth from the farmer to the corporation, where the farmer will benefit. The big growth industry right now will be the cover crop seed folks and riding. The motivation for the farmer should be profit (often times yield is more important than profit. With corn and other commodity prices dropping in 2014, however, farmers may be paying more attention to this. Hope I am making sense. I will be occupied today, but will take your advice and get some lab notes up!