SOIL i oi 



These are alluvial. It is the alluvial soil of the Mississippi 

 and Missouri valleys which have made their farms famous 

 the world around. Another thing which adds to the 

 agricultural value of such land is its levelness. 



For agricultural purposes a mixture of sand, clay, and 

 humus is desirable. Pure sand dries too quickly, while 

 pure clay does not dry quickly enough. When wet, clay 

 becomes compact, difficult to plow, and difficult for roots 

 to penetrate. Clay mixed with sand makes a soil easy to 

 work, easy for plants to grow in, and with about the right 

 capacity for holding moisture. Alluvial soils usually 

 contain sand and clay mixed in a proportion which is very 

 favorable to plant growth. The humus part of soil is also 

 very important. It adds to the mineral constituents 

 material which is rich in substances used by plants, and it 

 also contains that hidden, microscopic life of the soil 

 which is very important to the life of green plants. Soil 

 composed of a mixture of sand, clay, and humus is called 

 loam; in some parts of the country this term is also used 

 to describe mixtures of sand and clay which contain little if 

 any humus. The proportions of sand and clay in common 

 agricultural soils are given in Dryer as follows : — 



Sandy soil 80% sand 10% clay 



Sandy loam 60-70% sand 10-25% cla y 



Loam 40-60% sand 15-3°% clay 



Clay loam 10-35% sand 30-50% clay 



Clay . . • 10% sand 60-90% clay 



B. Soil and Food. — We have said that the soil is as 

 necessary to plants as plants are necessary to us. We get 

 substances from plants upon which our life depends, and the 

 plants get substances from the soil upon which their life 



