Soil improvement
Alfalfa is an N-fixing legume and does not require added N fertilizer. In unfavourable soil conditions or when the crop is first grown, inoculation with Rhizobium meliloti may be necessary for good N fixation (Ecocrop, 2009). As a perennial legume, alfalfa may be used as a cover crop: its roots improve soil texture and its leaves add organic matter to the soil. The leaf canopy prevents soil erosion (Suttie, 2000). Alfalfa often increases the yield of succeeding crops. However, when alfalfa is ploughed under, care must be taken to prevent N losses due to the mineralisation of plant residues. N release occurs within 18 months after alfalfa removal and it is thus recommended to sow the following crop as soon as possible after ploughing. If the next crop cannot be sown before winter, alfalfa should not be cut in the autumn (Justes et al., 2001).
Biodiversity
The melliferous flowers of alfalfa attract bees and birds and enhance biodiversity. The crop is valued for honey production (Duke, 1983).
Genetically modified alfalfa
Genetically modified glyphosate-resistant alfalfa has been developed. Planting started in the USA in 2005 but was regulated in 2007 when a District Court found that risks of cross-contamination with non-GM alfalfa had not been sufficiently assessed by the USDA. The ban was reversed in June 2010 by the US Supreme Court and planting resumed in January 2011.