Don't have time to do all the reearch required.

I have seen a figure of 6 EROEI for sunflower oil. That compares with a figure I have seen for ethanol of 1.35 - or maybe even <1. If one rigs up an old-time horse-powered press right on the farm, maybe the EROEI could even be a little better for the sunflowers. Running straight veg oil in cold weather is a problem, but as most farm machinery tasks are in warm weather that should not be much of a problem.

How much acreage would have to be dedicated to growing sunflowers to power a tractor for a year? According to the source below, 1 acre of sunflowers should yield 102 gal of sunflower oil per year; rapeseed does a little better at 127 gal/ac.

http://journeytoforever.org/biodiesel_yield.html

The total amount of fuel needed to run a farm for a year will depend upon the size of a farm, but I would guess that for most farms we are talking about a few acres at most. The source below lists typical farm fuel consumption per acre for most common mechanized tasks.

http://www.extension.iastate.edu/AGDM/crops/html/a3-27.html

Looking at this table, it would appear that the total fuel consumption may run somewhere in the range of 2.5-5 gal/acre, depending upon crop. That would suggest that a single acre of sunflowers should provide enough fuel for at least a 20-40 acre farm. A 160 acre farm may require between 4-8 acres of sunflowers. That would seem to me to leave plenty of acreage for food production.