The burning of brush is permitted for agricultural purposes, with a permit, only on the first full weekend of each month. The permit must be applied for by 3pm the Friday before the burning weekend (if monthly).
Monthly - $15
Yearly (Calendar year) - $50
The burning pile must also be no closer then 100 feet from any structure and this will be verified at the time of your application.
Permits can be obtained at the Township building. For more information please see the Open Burning Ordinance. (link is to off-site codification page)