Nitrogen and phosphorus losses from legume-supported cropping

The loss of nutrients from agricultural systems is recognized as a major environmental problem, contributing to air pollution and nutrient enrichment in rivers and oceans. The use of legumes within agriculture provides an opportunity to reduce some of these losses in ways which maintain or enhance agricultural productivity. This chapter considers the role of legumes in crop rotations, legumes in intercrops and legume-based green manures in influencing nutrient loss and turnover. Nitrous oxide emissions are particularly important here given that they are the largest contributor to greenhouse gas emissions from many agricultural systems. There are many circumstances in which the use of legume-supported cropping systems can reduce overall nitrous oxide emissions and the biological nitrogen fixation process associated with legumes can replace synthetic nitrogen fertilizer use.