Alfalfa is a legume or nitrogen gathering plant. An examination of the
roots of leguminous plants reveals numerous bacteria nodules which vary
in size, shape and number according to the kind and age of the plant. A
very close relation has been found to exist between leguminous plants
and the bacteria existing within these nodules. The plant furnishes the
nourishment required by the bacteria while the bacteria in turn draw
nitrogen from the air and render it available for the use of the plant.
Nitrogen is essential to plant life. The plowing under and resulting
decay of legume plants releases vast quantities of nitrogen into the
soil where it may be absorbed and assimilated by succeeding crops.
The accompanying illustration shows the nodule development on the roots
of a two-months-old legume plant.