AN INTRODUCTION TO THE STUDY OF 

 THE SOIL SOLUTION. 



Chapter I. 



THE SOIL. 



The soil, or that part of the land surface of the earth 

 adapted to the growth and support of crops, is a heterogeneous 

 mixture composed of solids, gases and a liquid, and containing 

 living organisms. There are present : mineral debris from rock 

 degradation and decomposition; organic matter from the degra- 

 dation and decomposition of former plant and animal tissues; 

 the soil atmosphere, always richer in carbon dioxide and water 

 vapor and possibly other gases than the atmosphere above the 

 soil; living organisms, such as various kinds of bacteria and 

 fungi, with the products of their activities, notably the "nitrogen 

 carriers" and the enzymes ; and finally the soil moisture, a solu- 

 tion of products yielded by the above components and in equili- 

 brium or approaching equilibrium with the solids and gases with 

 which it is in contact. 



In its relation to crop plants, 1 that part of the soil of imme- 

 diate importance is the soil moisture. From this solution the 

 plants, through their roots, draw all the material involved in 

 their growth, except the carbon dioxide absorbed through their 

 leaves. The soil solution is the natural nutrient medium from 

 which the plants absorb the mineral constituents which have 

 been shown to be absolutely essential to their continued exist- 

 ence and development. And from this solution plants some- 

 times absorb dissolved organic substances, but such absorptions 

 are probably adventitious and incidental to the growth of the 

 t plant in a particular environment. While it appears certain that 



1 By crop plants are meant the ordinary green plants employed in agri- 

 culture. As is well known, the fungi as well as certain parasitic and 

 saprophytic non-green seed plants obtain their nutriment in a very differ- 

 ent way from ordinary green crop plants. 



