During the past two decades one of the most important U.S. agricultural crop production trends has been the movement of corn and soybean plantings into traditional wheat production areas of the western and northern Plains. Kansas, Nebraska, and the Dakotas have now become important producers of corn and soybeans on land that was traditionally planted with wheat.   Three factors have encouraged this shift: 1. Simple economics. Farmers discovered they could make more money growing row crops instead of wheat. Government policies that support ethanol production helped make corn a more attractive crop, and the surge in U.S. and world (Chinese) demand for soybeans helped push production westward. 2. The concurrent development of seed...