12 



THE SOIkfAND THE PLANT 



i * * * 



soil, which is generally! called; humus. The soil water and 

 soil air occupy the pores in 'the soil. 



Kinds of Soils. -- There are three classes of soils on 



Fig. i. A rich soil containing much humus. 



the basis of the size of the soil particles. Soils made up 

 wholly of very fine particles are called clay soils. Those 

 composed largely of particles of sand are called sandy 

 soils. Soils consisting of large amounts of both clay and 

 sand are called loams. Loams are the most satisfactory 

 soils for most crops, because they are easily cultivated, do 

 not bake, and hold moisture well. Sandy soils dry out 

 rapidly and clay soils bake in the hot sun after heavy 

 rains. The special methods for handling these soils are 

 taken up later in this text in connection with the respective 

 crops best adapted to them. 



Color of Soils. The color of soils is due to decaying 

 organic matter and to mineral substances which they con- 

 tain. The black color of soil is due mainly to the de- 

 caying vegetable matter. Even the red clays turn black 

 when fertilized with barnyard manure for some time. 



