Moreover these crops help land in another way. They send a multitude of roots deep into the ground. These roots loosen and pulverize the soil, and their decay, at the end of the growing season, leaves much humus in the soil. Land will rarely become worn out if legumes are regularly and wisely grown. From the fact that they do well in so many different sections and in so many different climates, the following are the most useful legumes: alfalfa, clovers, cowpeas, vetches, and soy beans. =Alfalfa.= Alfalfa is primarily a hay crop. It thrives in the Far West, in the Middle West, in the North, and in the South. In fact, it will do well wherever the soil is rich, moist, deep, and underlaid by an open subsoil. The vast areas given to this valuable crop are yearly increasing in every section of the United States. Alfalfa, however, unlike the cowpea, does not take to poor land. For its cultivation, therefore, good fertile land that is moist but not water-soaked should be selected. Good farmers are partial to alfalfa for three reasons. First, it yields a heavy crop of forage or hay. Second, being a legume, it improves the soil. Third, one seeding lasts a long time. This length of life may, however, be destroyed by pasturing or abusing the alfalfa. [Illustration: FIG. 231. SHEEP FATTENING ON ALFALFA STUBBLE] Alfalfa is different from most plants in this respect: the soil in which it grows must have certain kinds of bacteria in it. These cause the growth of tubercles on the roots. These bacteria, however, are not always present in land that has not been planted in alfalfa. Hence if this plant is to be grown successfully these helpful bacteria must sometimes be supplied artificially. There are two very easy ways of supplying the germs. First, fine soil from an alfalfa field may be scattered broadcast over the fields to be seeded. Second, a small mass of alfalfa tubercle germs may be put into a liquid containing proper food to make these germs multiply and grow; then the seeds to be planted are soaked in this liquid in order that the germs may fasten on the seeds. Before the seeds are sowed the soil should be mellowed. Over this well-prepared land about twenty pounds of seed to the acre should be scattered. The seed may be scattered by hand or by a seed-sower. Cover with a light harrow. The time of planting varies somewhat with the climate. Except where the winters are too severe the seed may be sowed either in the spring or in the fall. In the South sow only in the fall. [Illustration: FIG. 232. HERD OF DAIRY CATTLE GRAZING ON ALFALFA STUBBLE] During the first season one mowing, perhaps more, is necessary to insure a good stand and also to keep down the weeds. When the first blossoms appear in the early summer, it is time to start the mower. After this the alfalfa should be cut every two, three, or four weeks. The number of times depends on the rapidity of growth.