One familiar gripe from tenants who are asked to switch to cash rent from shares or have to compete with strong cash rent bidders is that cash renters mine the soil. This actually one way I try to argue for longer term contracts, since there would an obvious incentive to take care of fertility if you are reasonably assured you will be there in 10 years or so.
As Illinois is one of the leading cash rent states, a recent study may add some strength to that argument.
The most consistent P declines since 2005 occurred across the Corn Belt and Central Great Plains. The median P level for the 12 major Corn Belt states plus Ontario declined from 28 ppm in 2005 to 22 in 2010. This decline has major agronomic significance since a high percentage of samples from this region now test below critical levels (Figure 3). Considering that soil P levels are highly buffered, such large declines for a population of over 3 million samples over a 5-year period are surprising. The high sample volume and limited diversity in cropping systems of the Corn Belt offers opportunities for additional evaluation of aggregate data to gain insights into the cause of these declines. [More (pdf)]Consider these maps:
Of course, there are several other reasons why P1 tests are dropping, but as the article points out, this is about the best data we can come up with. And the study was done by the fertilizer industry, so the point of view must be taken into consideration. Even with those sampling flaws and disclaimers, I think there is some cause to be concerned.
The report also details the drops in K as well as micronutrients, but it was the phosphorus that stuck out in my mind. Checking our own tests, I can't see it, but soil tests can wander all over a wide range.
Still maybe our tests aren't dropping because we haven't enjoyed the killer yield increases that all the other farmers seem to be getting. Seriously, since it takes considerable time to correct soil deficiencies, I think owners and farmers both should be paying closer attention to what is happening with fertility.