Understanding the role of grain legumes in N cycling of agroecosystems

Summary

Grain legumes have three major functions in a cropping systems: 1) to produce feed and food protein, 2) the unique feature of being able to contribute N to the cropping system via symbiotic N2 fixation, and 3) to serve as a break-crop in cereal-rich rotations. Depending on the farming system concept these functions have different priorities. In conventional systems the priority may be for feed and food protein and the break-crop effect whereas in organic farming systems all the three functions are of immense importance.
Symbiotic N2 fixation (SNF) is a unique biological process, but it is influenced by many environmental factors and optimising SNF requires an understanding of the many factors controlling this process. The effect of grain legumes on the N cycling in the cropping system is mainly via some of the species low ability to utilize the available soil N sources, and via the high N concentration of crop residues. High amount of autumn available N may enhance N losses via leaching to ground and surface waters in some agroecological environments with high surplus precipitation during winter, but this nitrogen can also be conserved for subsequent crops via appropriate management.
In this paper we discuss recent progress in understanding the effects of some environmental factors on N2 fixation and grain legume yield. We discuss the latest findings regarding grain legumes on soil N cycling post cropping, with emphasis on determining root derived N, about N losses by leaching in and their prevention.