62 GENERAL CONSIDERATIONS 



time for growing one or more crops for sale and at 

 least one crop every year for enriching the soil. 



Any kind of fermentable vegetable matter is useful 

 when incorporated in the soil. The stalks, straw, or 

 other unused portions of all crops should be left in 

 the field to be plowed under. Even unsightly weeds 

 will have their usefulness if plowed into the land. 

 Grasses of all kinds are also useful. The richness of 

 well-rotted sod land is proverbial. Crops of the 

 small grains like rye or oats or of fodder corn plowed 

 into the land are also helpful. In the Southern states 

 cotton and corn land should when possible be seeded 

 down to winter oats or rye in the fall, since these 

 crops prevent washing during the heavy winter rains 

 and when plowed down in the spring add consider- 

 ably to the fertility of the soil. All such green crops 

 are beneficial, however, only for the organic matter 

 which they contain and their consequent effect on the 

 mechanical and biological condition of the soil. They 

 add no important chemical elements, since all the ni- 

 trogen, phosphoric acid, and potash they contain was 

 taken directly from the soil, and they, therefore, only 

 return what they have already taken. The marvelous 

 power has already been mentioned possessed by plants 

 belonging to the Leguminosoe^ of seizing and fixing 

 the atmospheric nitrogen through the agency of the 

 tubercle-forming bacteria that dwell in their roots. 

 This overshadowingly important fact indicates clearly 

 that some leguminous crop should if possible always 

 be chosen for green manuring. A well-grown crop of 

 clover, cowpeas, velvet beans, or beggar weed, turned 

 into the soil, adds as much nitrogen as would be con- 



