Mammoth Red Clover, also called sapling clover and pea-vine clover, closely resembles the red clover, but is ranker in growth and matures two or three weeks later.  It is better adapted to wet land than the red clover.

Crimson Clover, also called German clover and Italian clover, is a valuable green manure crop in the central and southern States east of the Mississippi.  It is a hardy annual in that section and is generally sown from the last of July to the middle of October, either by itself or with cultivated crops at their last working.  Fifteen and twenty pounds of seed are used to the acre.  It makes a good growth during the fall and early winter and is in blossom and ready to cut or plow under in April or May.  It grows at a season when the cowpea will not live.  Crimson clover will grow on soils too light for other clovers.

The Soy Bean, also called soja bean and Japanese pea, is another leguminous crop used for green manuring (Fig. 81).  It was introduced into this country from Japan and in some localities is quite extensively planted.  It grows more upright than the cowpea and produces a large amount of stem and foliage which may be used for fodder or turned under for green manure The seeds are used for food for man and beast.  The soy bean is planted and cared for in the same manner as the cowpea.

The Canadian Field Pea is sometimes grown in the north as a green manure crop.

White Sweet Clover, white melitot or Bokhara clover, grows as a weed from New England to the Gulf of Mexico.  In the Gulf States it is regarded as a valuable forage and green manure plant.  One or two pecks of seed per acre are sown in January or February.

Alfalfa, or lucern, though grown more for a forage crop than for green manuring, should be mentioned here, for wherever grown and for whatever purpose, its effects on the soil are beneficial (Fig. 82).  This plant requires a well prepared soil that is free from weeds.  Twenty to twenty-five pounds of seed are planted per acre.  In the north the seeding is generally done in the spring after danger of frost is past, as frost kills the young plants.  In the South fall seeding is the custom in order to give the young plants a long start ahead of the spring weeds.  One seeding if well cared for lasts for many years.  Alfalfa is pastured or cut for hay, four to eight tons being the yield.  Many fields run out in five or six years and the sod is plowed under.  This plant sends its roots thirteen, sixteen, and even thirty feet into the soil after water and food, and when these roots decay they furnish the lower soil with organic matter and their passages serve as drains and ventilators in the soil.  Alfalfa is grown extensively in the semi-arid regions of the country.

NON-LEGUMINOUS GREEN MANURE PLANTS

Among the non-leguminous green manure plants are rye, wheat, oats, mustard, rape, buckwheat.  Of these the rye and buckwheat are most generally used, the rye being a winter crop and the other a warm weather plant.  They are both strong feeders and can use tough plant food.  They do not add new nitrogen to the soil though they furnish humus and prepare food for the weaker feeders which may follow them.