1752 



The Cornell Reading-Courses 



the soil, and should supply the food required for plant development. 

 These conditions should be maintained as evenly as possible. Not only 

 are changes injurious in themselves, but one unfavorable condition will 

 induce another. 



That layer of soil in which the roots of plants are distributed and in 

 which all the physical, chemical, and biological processes are most active 

 is termed the root-zone. (Fig. 87.) For crops most commonly grown the 

 root-zone should have a depth of at least three feet. 



Fig. 87. — Section of soil showing natural structure and the distribution of grass roots. 

 It shows, also, ideal plowing; the action of the moldboard in hoisting the furrow 

 slice; and the action of the jointer in turning under the edge of. the furrow. Rather 

 large spaces occur between the furrow slices adjacent to the subsoil. At the lower right 

 hand side is an enlarged view of a section of the subsoil showing distribution of cracks, 

 root cavities, and burrows of worms 



TILTH 



The factor that most often determines the adjustment of all these 

 conditions of the soil is physical structure. Soil is a frame- work of particles 

 of rock and organic matter through which many small spaces or pores are 

 distributed. By their size, volume, and distribution, the spaces regulate 

 the other properties of the soil. If the particles are small, the open spaces 



