farm field or strip mine?

in the documentary "king corn" curt ellis and ian cheny say that 32% of the corn crop they raised went to export or to the ethanol industry and that more than half went to be used as feed for cattle in confined animal feeding operations (cafo)...which leaves about ten percent to be refined into industrial food, but value added isn't what we're on about here...the ethanol industry and cattle feed are linked in that a by-product of the ethanol process is wet corn gluten feed which cafos use...the cafos also use high moisture field corn stripped from the cobs by the combines at harvest....and they also use the entire corn plant run through choppers and called corn silage...a lot like meat packers using "every part of the pig except the oink"...which i suppose is efficient in a capitalist sort of way but what does it do to the field? you can see by the photos that the corn field i tracked all summer was reduced to stubble at harvest...sure the inefficiencies of the combine left some cobs with kernels out there but the vast majority were stripped clean and discarded...the whole process removes the sugars, starches, and the nutrients used by the plants to build the stalks and leaves that support the crop from the field and deposits it somewhere else...mining the fertility of the soil and forcing the farmer to rely more and more on petrochemical inputs in the form of ( among many others ) anhydrous ammonia ( not in itself a petrochemical but a substance that relies heavily on natural gas as a feedstock in its production by the haber/bosch method)...cafos have a build up of nutrients mined form fields that collect in toxic amounts a sludge from animal waste which never make their way back to the fields...even when a farmer plants a cover crop it isn't geared toward nutrient replacement...the field of winter wheat by the supermarket was a soybean field a few months ago and those beans are long gone being processed into soy burgers and whatever else comes from them...the wheat isn't adding anything...it's just holding the soil together...true it will probably be turned under in spring to make way for a new crop but it won't be adding anything...it just won't be taking anything away...that will be achieved by the next crop...industrial agriculture has utterly disrupted anything that resembles a nutrient cycle in the fields...no natural economy will allow unrelenting extraction and as the cost of petrochemical inputs rises ( as the surely will ) so will the cost of what passes for food...this disruption imperils the dollar menu at macdonalds not to mention the natural cycle of local ecosystems.