Its a location thing.  Im guessing your ground is over 1.5% organic matter.   Ive heard some ground in michigan is so high it can catch on fire in a drought (peat).  The climate and rainfall amounts combined with low drainage slows the mineralization of the soil.   In arid climates the opposite is true and the plow accelerates soil OM decline and water holding capacity which is a very bad thing in those climates.   Disclamer: I have 6 plows but notill everything "here".