An asset purchased for business (the production of income) is a deductable item. In short, an ATV purchased for pulling aerators, wagons etc. used in the production of income is deductable. In fact, I am considering such equipment for spray applications. The main thing to remember is to keep the purchases ordinary and necessary for business (is the asset used in the production of income?) The IRS is generally more liberal in interpretation of deductability when there is a bona fide business earning a profit.
One caveat, don't try too much of a stretch when defining "business assets". For example you wouldn't want to try to deduct a D5 dozier when you'er in a small lawncare business, unless you're prepared to show it's used regularly in servicing clients and producing income.