A solution can become supersaturated with an ion (i.e. > 100% or SI > 0) if the conditions are right. I started to write a long reply explaining why this is not as simple as you are trying to make it, and some of it is just wrong, but instead I will just point you to the docs I have previously referenced. http://lawr.ucdavis.edu/classes/ssc102/ Pay particular attention to sections 3, 6-8. With respect to P, please check up on solubility constants of different P species/compounds and how that may or may not affect availability at low pH. Once again, these micro/macro nutrient problems with respect to high soil P are mostly associated with high pH soils, not low, as is the case here. SOC (soil organic carbon) is not comprised of strictly humus (humic compounds). Also, you cannot compare a "soil" comprised strictly of humus to one that is a mix of humus and mineral components. Where are you getting this information? Also your same inputs and productivity example does not pan out. Why would you apply the same inputs on a soil with a higher CEC (i.e. nutrient retention) as a soil with low CEC? I think the more important relationship to draw is fewer inputs are required to get the same level of productivity in soils with higher CEC/SOM strictly due to better nutrient retention, soil structure, etc.... If anything, I would expect a decline in productivity in a strictly humus soil if fertilized at the same rate as, say a sandy soil, due to the potential for nutrient toxicity over time. @Bill Just because no "visible" improvement is noted does not mean there is not an improvement. More likely that not, a "visible" improvement was not noted because there were no limiting nutrients (i.e. luxury consumption was the case) or limiting conditions, not because the SOM was at 9%. While we are at it, please define "enough available OM". Available for what?