I think you're confusing industrial agriculture with capitalist agriculture. I am not with Brenner on seeing property relations as the same thing as collective improvement of agricultural yields. I think it is a confusion of one for the other. Commodity farming certainly had some longstanding effects, but even the small scale studies of enclosure of open fields in England asserted that, for the most part, the apparently advanced yields were really only an upward distribution of income from the workers to the rentiers. As even people at the time realized, there were some efficiency gains to large scale farms (this was part of the program of the Diggers), but there is nothing about that system that necessitates a single owner and multiple landless workers renting land. (unless you want to say that the thing that makes capitalism unique is its ability to discipline labor, making workers work harder and produce more for the profit of the owner--which seems an odd thing to celebrate on a leftist list.)
Maybe there is some better living through chemistry (midcentury Green Revolution stuff) but in many ways this was one of the least capitalist era's of the past 200 years--many of the chemistry gains were achieved (or at least catalyzed) by the wholesale appropriation of patented German technology post WWI, in the context of an advancing the welfare state, extremely progressive taxation, and state run agriculture in the attempt to create some Rostovian "Take Off" to industrialized state. (likewise, much of the early enclosure movement was driven by state imagined plans of Baconian improvement--most of which was the product of careful examination of the work farmers were already doing on the ground, cataloging it, and then making them all more widespread in the context of state run projects of enclosure and expansion.)
In many ways the most perverse period has been the more recent turn to a more pure, market oriented capitalism--where farmers can no longer reuse the most productive seeds, or have to buy proprietary fertilizer or pesticide in order to make it work; where GM seeds have questionable effects on improved yields and unknowable effects on future mutations (as well as problems of monoculture Alan has already mentioned); and where "free trade" is really just a license to dump agriculture abroad and destroy any local projects of improvement before they could even be attempted. This is where the chemical and commodity qualities have been most clearly combined and it is clear that the more naked the capitalist exploitation. Conflating the two, I think, will get you nowhere in explaining the current conjuncture.
s