You read/hear about tenant farmers mining the soil. Here, you are suggesting the landowner mine the soil in his own fields.  

At the very least, I would apply enough potash to meet typical potassium removal rates for the crops.  Initially, I was thinking I would apply Sulfur as well.  But, to me, applying the potassium would be more important.  I am of the opinion that he will see benefit in the same year that the potash is applied.