138 THE FORAGE AND FIBER CROPS IN AMERICA 



that the poorer the soil is in nitrates and hence the greater 

 the need of soil and plant for nitrogen the greater the supply 

 obtained from the atmosphere. (132) 



5. The organic matter left in the soil improves the physical 

 condition of most soils. Probably the most important physical 

 property is that with reference to the retention and passage 

 of water in the soil. The decay of deep-growing tap roots of 

 red clover and alfalfa in the sub-soil may assist drainage mate- 

 rially by offering an opening for the passage of water. On the 

 other hand, the decay of large amounts of vegetable matter 

 in the surface soil enables the water to enter the soil more 

 freely rather than running off the surface, and also enables 

 the soil to hold the optimum amount of water. The influence 

 which these factors may have on the time that must elapse 

 before land can be cultivated after heavy rains, and on the num- 

 ber of days in the year that it is possible to cultivate the land is 

 often extremely important. 



6. The introduction of leguminous plants has offered op- 

 portunity for a better system of rotation not alone for reasons 

 just stated, but because it brought into the rotation a plant 

 not subject to the same insect enemies and fungous diseases of 

 cereals and grasses, and perhaps for other reasons not well 

 understood. The introduction of red clover, together with root 

 crops, resulting in the Norfolk system of rotation, revolutionized 

 the agriculture of Great Britain and had a profound influence 

 indirectly upon the colonists of North America. "Red clover 

 has contributed even more to the progress of agriculture than 

 the potato itself, and has had no inconsiderable influence on 

 European civilization. Its cultivation has led to an increased 

 production of stock as food for man, and in this way has 

 fostered and advanced commerce, industry, and science." 1 



143. COLLATERAL READING. H. W. Conn: Agricultural Bacteriology, pp 

 76-108; 130-162. Philadelphia: P. Blakiston's Son & Co., 1901. 



1 Stebler and Schroter: The Best Forage Plants, p. 123. 



