Chicken Tractor - How much pasture does a chicken consume in a day?

I'd like to get my hands on some chickens to clear a field/prepare land for me. I expect to built a tractor with a large footprint, something like 8-10ft wide and 10-12ft long. I would like to only need to move the tractor twice a week or so, I will supplement their feed as required for a balanced diet.

If I have 100sqft of pasture inside the tractor, so roughly 30sqft/day, how many chickens should I put in there?

If you're using them to clear the field, instead of maintaining a groundcover, and you plan to supplement their diet, you could have as many as 25 in a 100 square foot pen, in my opinion. Joel Salatin http://www.polyfacefarms.com/ put 75 - 100 birds in a 10' x 12' pasture pen but he raised Cornish Cross who do not forage actively, and the pen was moved daily. Personally I would put no more than 25. Keep in mind if you have predators, not moving the pen can increase danger of predators digging under the edge.