The Potential Environmental Benefits and Risks Derived rom Legumes in Rotations

Humans have approximately doubled the rate at which nitrogen (N) is entering the earth's ecosystems compared with preindustrial times. The two most important sources of N for agriculture are synthetic fertilizers and symbiotic N2 fixation by cultivated legumes. The N2 fixation process in grain legumes contributes directly to food production by providing N that can be accumulated in the fresh pods, seeds, and tubers that are used as vegetables or in the dried grain harvested for human or animal consumption. Some legume species such as pea exhibit lower water use than other crops, and the carry-over of more available soil water after a range of legumes has been identified as an important factor contributing to higher yields by following wheat crops. Furthermore, crops such as pea can be consistent in the efficiency with which they utilize rainfall regardless of the distribution of growing season precipitation