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ARS Home » Pacific West Area » Pullman, Washington » Northwest Sustainable Agroecosystems Research » Research » Publications at this Location » Publication #188484
Title: Grain Legumes in Northern Great Plains: Impacts on Selected Biological Soil Processes

Author
item LUPWAYI, NEWTON - AG & AGRI-FOOD CANADA
item Kennedy, Ann

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/7/2005
Publication Date: 7/1/2007
Citation: Lupwayi, N., Kennedy, A.C. 2007. Grain Legumes in Northern Great Plains: Impacts on Selected Biological Soil Processes. Agronomy Journal. 99:1700-1709.

Interpretive Summary: Cropping systems in the Northern Great Plains have shifted from fallow-based to legume-based systems. The introduction of grain legumes such as dry bean, peas, chickpeas soybeans and lentils, has impacted soil organisms and the processes that they perform. The impacts of grain legumes on soil biota begin from the time seed is planted and continue after crop harvest. We investigated the soil biology changes occurring with legumes in rotation. The altered soil biology has mostly beneficial effects to agriculture by adding biologically fixed nitrogen, enhancing nutrient uptake and recycling, reducing greenhouse gas emissions by reducing N fertilizer use, and improving soil structure. Plant pathogens may be introduced through increased microbial diversity and activity, but biological pest control is also enhanced. The microbial and faunal communities found on legume seeds and roots are different from those found on non-legumes. Residue and carbon quality characteristics of the legume also alter the soil microbial community. Inclusion of legumes in a cropping system can greatly alter the biotic component of an ecosystem and leads to mostly beneficial impacts through nitrogen fixation, nutrient uptake, nutrient cycling, reduced greenhouse gas emissions compared to other cropping systems, as well as benefits from biological pest control and improvement of soil structure.

Technical Abstract: Cropping systems in the Northern Great Plains have shifted from fallow-based to legume-based systems. The introduction of grain legumes has impacted soil organisms, including nitrogen fixers, pathogens, mycorrhizae and fauna, and the processes that they perform. Legume seed exudates, rhizosphere exudates, and crop residues impact the soil biotic community. The benefits of legumes in rotation are in part due to the changes occurring in soil biology. The most widely studied legume-microbial association is dinitrogen fixation, which adds plant available nitrogen into the soil system. Many other associations also benefit from the legume in a cropping system. These include, but are not limited to, mycorrhizal associations that improve plant nutrient and water status, changes in the pathogen load and disease development and overall changes in the soil community. The microbial and faunal communities found on legume seeds and roots are different from those found on non-legumes. Residue and carbon quality characteristics of the legume also alter the soil microbial community. Legumes contribute to nitrous oxide emissions during nitrification and denitrification of fixed atmospheric N. Because less fertilizer N is used in legume-based cropping systems, overall greenhouse gas emissions are usually less than those in monoculture cereals. Inclusion of legumes in a cropping system can greatly alter the biotic component of an ecosystem and leads to mostly beneficial impacts.