1356 The Cornell Reading-Courses 



The efficiency of any soil is measured by its capacity to supply plants 

 with the several materials and conditions they require for growth. These 

 include food, water, heat, air, and support; and in addition the soil must 

 be free from various diseases and animal enemies that, in spite of a proper 

 supply of all the essential conditions of growth, may still prevent pro- 

 ductiveness. In proportion as any particular soil supplies all these essen- 

 tial conditions in well-balanced abundance, the largest growth of plants 

 may be obtained. Again, if these conditions are deficient or improperly 

 balanced by the shortage of one of their number, a lower or more simi)le 

 type of plant or a smaller growth will result. Difference in soil conditions 



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FiG. 4. — Seel ion of a soil fanned by glacial ice, slwwing its mixed physical composition 



results in different kinds of plant growth. Thus, wheat is grown on deep, 

 fertile loam, and mosses and ferns on thin, rocky slopes; truck crops are 

 grown on dry, warm sand, and sphagnum or sweet flag on mucky marshes. 

 The great variety in plants is due to the great variety of soil conditions 

 that nature affords. Man's province as a tiller of the soil and grower 

 of plants is to change the conditions of the soil so that they shall be m.ore 

 favorable to the crops he desires to grow. 



The soil is a complex body and is the result of a complex set of pro- 

 cesses, yet we may learn many things about its nature and operation. 

 The fragments of minerals and rocks of which it is chiefly composed have 

 been derived through the operation of many agencies that work together 

 to break down and transport the rocks from which the soils are formed. 



