ARS | Publication request: N fixation versus N uptake in alfalfa

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: February 22, 2011
Publication Date: February 22, 2011
Citation: Lamb, J.F. 2011. N fixation versus N uptake in alfalfa [abstract]. Idaho Alfalfa and Forage Conference, February 22-23, 2011, Burley, Idaho. Available: www.idahohay.com/Lamb_NFixation.pdf.

Technical Abstract: Fertilizer N is the single most expensive input in nearly all crop-production systems and has been implicated in declining groundwater quality due to nitrate contamination. Commercial alfalfas are highly productive in the absence of nitrogen inputs because of the symbiotic association with soil bacteria that fixes atmospheric N2 into a form of N that the plant can utilize. The biologically fixed nitrogen produced can replace all or most of the N fertilizer needed by subsequent cereal crops following alfalfa in a rotation system. Indirect evidence such as reduced soil nitrate under alfalfa in dry and sub-humid environments and minimal nitrate leaching losses under tile-drained alfalfa has demonstrated that alfalfa is also efficient at removing sub-soil N and can be used to prevent groundwater contamination. Nitrogen fixation rates in alfalfa are influenced by the presence of N in the sub-soil. Alfalfa evaluated under high annual N application rates still obtained 20 to 25% of its N supply from biological N fixation. Plant breeding strategies for alfalfa should include methods to improve N fixation rates for a sustainable N supply for subsequent crops in rotation as well as alfalfas sensitive to the presence of nitrates to remediate high soil nitrate situations to protect groundwater quality. Alfalfas to improve N cycling and increase the efficient use of biologically fixed N could have a marked effect on the economic and environmental impacts of agricultural systems.