Using Chickens to maintain a fallow?

In dryland areas, summer fallows are used to store precipitation in the soil for later crops. Traditionally, this involved frequent tilling over the course of the summer to keep down weeds and create a "dust mulch" as a capillary break; this led to problems with erosion. Today, no-till farmers leave crop residue on the soil surface, and use herbicides to suppress growth; this trades erosion for a different set of problems.

Could a chicken tractor be used to maintain a fallow, keeping down weed growth while leaving a light mulch layer on the surface?

Absolutely, Yes!  I use my chicken tractor in my annual garden for exactly this reason.  I divided my garden area in half and the chickens prevent the growth of grass and weeds on the fallow half every year.  I have a rototiller that I still use to stir up more compact parts but I also often just use a digging fork to do the same thing.  I use straw for mulch and litter and I really would not go back to doing the job by myself.   The gardens productivity has increased by leaps and bounds and I can plant more intensively and use less area than before.

Hi Gilbert,
While you can absolutely do this, it does not work well at scale and without inputs. I did it myself. As did Justin Rhodes. Both of us decided there are better ways to use chickens.

Rene mentions putting in straw as mulch. This is an important step. Without it, the ground will get hard pan in my climate. If I leave the chickens long enough to kill all weeds, the ground is hard as a rock when they are done. Without mulch to keep in the moisture, the ground gets hard. Without vegetation and bugs (the result you want for a garden most times) the chickens don't scratch that area, and just poop and walk over it, creating a hard crusty surface. Also, this would be hard to do on anything larger than a home garden, due to the number of chickens needed to keep up with, say even a 1 acre field.

Justin Rhodes started using chickens to keep his gardens clear of weeds and actually switched to tarps instead because it gave a better result. Again, Chickens can create scorched earth, but then it is scorched earth. Without adding mulch to keep the moisture in and keep the chickens scratching... I'm not sure you are going to end up with what you want.