SOILS AM) FERTILIZERS 



CHAPTER I 



SOIL AS A MEDIUM FOR PLANT GROWTH 



The farmer's interest in the soil is due chiefly to what 

 it contributes to plant production. In this respect it per- 

 forms several functions : (1) it acts as a mechanical support 

 for plants by furnishing a foothold comprising many open- 

 ings through which plant roots ramify and hold the plant 

 in place; (2) it- serves as a receptacle in which water is 

 held in a convenient way for roots to appropriate ; (3) it is 

 composed, in part, of substances that dissolve in the water 

 which it holds and are absorbed from solution by roots, and 

 utilized by plants as food material ; (4) its porous nature 

 allows air to circulate within it, thus supplying plant roots 

 witl), air. 



These are the contributions that soils make to plant growth. 

 Before proceeding with a more detailed study of soil it will 

 be desirable to consider briefly the needs of the plant as 

 supplied by the soil. 



1. Soil as a mechanical support for plants. — Land plants 

 need anchorage, for they must have some permanent supply 

 of water and other food material, which is not to be had 

 from the atmosphere. The soil serves, at once, as anchor- 

 age and food reservoir. One property of soil that adapts 

 b 1 ' 



