Lupin can be seen as a biological plow. Its roots dig very deep and fix nitrogen that increases fertility of the soil.
Gallery
Tiny lupin plants
Young lupin in winter
Lupin in my garden. The plants you see are one row of plants, over 1 meter high and 1 m wide. They are also excellent for green manure or animal fodder. Rye almost ripe at the right, yarrow at the left.