I don't have up to date information on what the effect of the subsidy would be on increasing overall emissions from the sector, but in the context of mechanization of agriculture, it's possible that getting rid of the clunkers and changing up for new vehicles will help in the short term, at least. (greenleapforward.com)
NPK and fossil fuel based fertilizer along with mechanization of harvesting (the hardest most labour intensive part of agriculture) get the lions share of the credit (IMHO). (wattsupwiththat.com)
Texas Chainsaw Massacre also updates the notion of encroaching mechanization in the American production industry from Upton Sinclair's classic novel The Jungle. (slantmagazine.com)