One of the best TED talks I've seen: Dramatic reverses of desertification by simply concentrating and rotating livestock. This mimics the huge, ever-moving herds that grasslands co-evolved with. Overgrazing is avoided, and it can revitalise even highly-marginal land.
By trampling (and fertilising) the existing grass and breaking up the ground, the herds create a natural mulch that retains much more water and maintains a beneficial micro-climate that breaks down methane and fixes nutrients into the soil. The results appear rapid and impressive. And importantly, newly growing grasslands can suck enormous amounts of carbon from the atmosphere, which has crucial implications for climate change.