Energy, fossil fuel and electrical, is a high proportion of the input costs in conventional agriculture, a point missed by many. To harvest the sun's energy as plants, tillage, irrigation and harvesting require a lot of horsepower. A typical farm tractor used in tillage or harvesting is 100 HP to 400 HP (and cost $800 or so per hp - think of a typical tractor as 2 nice Beamers or a Mercedes).

http://www.deere.com/en_US/ProductCatalog/FR/category/FR_TRACTORS.html (not the utility tractors)

Forage choppers and combines are even higher hp:
http://www.deere.com/en_US/ProductCatalog/FR/series/spfh_forage_harvesters.html

In typical use, a tractor burns about 4.4 gallons of diesel per hour per 100 Hp in size. Then there is the cost of fertilzer, irrigation power, crop drying costs, transportation to market and so on. Historically 40% of the on-farm costs for alfalfa, a major feed crop for cows, is the direct or indirect cost of energy. For milk production the cost of feed is about half the input costs. The increasing production of biofuels displaces the production of either human or animal food, reducing their supply and thus increasing their prices as inputs. IMO, increasing energy prices are a double whammy for food agriculture (animal or human) and ultimately the cost of food.