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Lupinus angustifolius is a species of lupin known by many common names, including narrow-leafed lupin and blue lupin. It is native to Eurasia and northern Africa, and it is naturalized in parts of Australia and North America. It is cultivated as a food crop for its edible legume seeds, as a fodder for livestock an for green manure.

Biology
Like other legumes, the narrow-leafed lupin fixes nitrogen in a symbiotic interaction with different bacteria in the rhizosphere. Bacteria living in this rhizosphere include Bradyrhizobium lupinii or the newly discovered species Kribbella lupini.

The narrow-leafed lupin is an erect, branching herb sometimes exceeding one meter. There are reduced-branching cultivars. Each palmate leaf is divided into 5 to 9 linear leaflets under 4 centimeters long. The herbage is slightly hairy in some areas. The inflorescence bears many flowers in shades of blue, violet, pink, or white. The fruit is a legume pod containing seeds of varying colors from dark gray to brown to white, or speckled or mottled.

Agronomy
The narrow-leafed lupin is sown as early as possible in the spring, to have the growing season as long as possible. Another reason for early sowing is its sensitivity to high temperature in spring. Lupins react with a higher yield loss, when they are sown late, than other crops (eg. cereals) do. The optimum seed density depends on the site yield potential and is generally higher in non-branching cultivars than in branching ones. The variance is high, 14 to 138 plants per m2 are an optimal plant density, depending on the yield potential of the site. On most grounds, a plant density around 80 plants per m2 would be the optimum. Lupins are usually sown with technique used for cereals in a depth of about 5 cm.

The narrow-leafed lupin needs to be harvested as soon as the grain reaches a moisture of about 12%. The straw usually isn‘t ripened at this point, but further delay of harvest would increase losses from shattering of the pods and lodging. The harvest is done with machinery used for cereals. Swathing is not widely applied. However, it can be a good alternative to reduce harvest losses in case harvest is delayed.

Lupins are valuable partners in intensive crop rotations, owing to their ability to improve the soil (see Use) and their disease and weed spectrum, that is different from most major crops.

Use
The plant is used as a green manure or as a grain legume for animal feed or human consumption. Through its ability to fix nitrogen and its low nutrient requirement this plant is suitable to be planted on exhausted fields as a soil improver. Additionally, lupins have strong roots, that can reduce the compaction of a soil.

The plant is widely used as a fodder for livestock, due to its high protein and energy content. Lupins contain high levels of fermentable carbohydrates and low levels of starch and are, therefore, an adequate ruminant feed. But lupins are a valuable feed for monogastric animals, because of the high digestibility of the lupin nitrogen and the low level of protease inhibitors.

Lupins have been cultivated for human consumption for over 6000 years. Lupins are consumed as fermented foods, bread and pasta products, milk products or sprouts mainly. In the future, lupins have a great potential as protein producers for processed foods.