The underlying principle in the use of the term “soil health” is that soil is not just an inert, lifeless growing medium, which modern farming tends to represent, rather it is a living, dynamic and ever-so-subtly changing whole environment. It turns out that soils highly fertile from the point of view of crop productivity are also lively from a biological point of view. It is now commonly recognized that soil microbial biomass is large: in temperate grassland soil the bacterial and fungal biomass have been documented to be 1–2 t (2.0 long tons; 2.2 short tons)/hectare and 2–5 t (4.9 long tons; 5.5 short tons)/ha, respectively.[3] Some microbiologists now believe that 80% of soil nutrient functions are essentially controlled by microbes.[4][5] If this is consistently true, than the prevailing Liebig nutrient theory model, and Mitscherlich modifications of it, all which exclude biology, are perhaps dangerously incorrect for managing soil fertility sustainably for the future.