Corn Production in Many States of the Midwest Is Limited

Multiple Choice

Corn production in many states of the Midwest is limited by nitrogen levels in the soil. Some farmers reduce the need to apply expensive anhydrous ammonia to their fields by rotating corn crops with nitrogen-fixing soybean crops. Using soybeans to add nitrogen to soils is an example of

A) biological augmentation.
B) the biomass pyramid.
C) promoting leaching efficiency.
D) bioremediation.
E) trophic efficiency.