This study estimates a system of supply equations for major field crops in Turkey and evaluates alternative agricultural policies for crop supply control. The supply of major field crops in Turkey responds significantly to both own-price and substitute price changes. The Turkish wheat price or gross return is the most important factor determining area allocation in Turkish field crops. Moreover, adopting measures that improve the growth of wheat yields also affect the substitute crops supply unless the price or gross return ratio is readjusted between substitute crops.