I'm not familiar with your machine, but it's almost certainly a draft control. Draft controls work by varying the depth of a ground-engaging implement (e.g. a plow) to maintain a certain amount of pull (or "draft" force). If the soil gets harder in a certain spot, the draft control will raise the implement to keep the tractor from stalling or just spinning the wheels and "digging in".
For a lot more info on them, how they're used, when they're handy to have, etc. do a Search here on TBN for draft control (using the phrase method). Or just ask for what you want to know again in this thread.
