CHAPTER 



/- Soil as a Medium for 

 Plant Growth 



EMIL TRUOG 



o 



ur best soils provide a well-nigh perfect medium for 

 the growth of crop plants. Why should this be the case? Were soils 

 specifically designed and created to support plants of the type we now 

 have? More likely the correct answer is that plants by evolution gradu- 

 ally adapted themselves to grow on the soils as they happened to exist. 

 This is substantiated by the belief that the first or primitive plants 

 lived in water from whence one or more species migrated to the land, 

 and there, by evolution, gradually developed into the many forms of 

 land plants which today, as regards number of species, far surpass 

 those of the ocean. 



Whatever the answers may be to the questions just raised, the fact 

 that nearly all our food and clothing and much of our housing come 

 directly or indirectly from the soil provides ample reason and incentive 

 for learning why some soils are good and many are poor media for crop 

 growth, and how the poor soils may be made better and all good soils 

 conserved indefinitely. Of the natural resources which are easily subject 

 to serious deterioration and even complete destruction, soil is the most 

 precious of all. To be sure, sunshine and water are just as important 

 or even more so than soil, but fortunately neither is subject to destruc- 

 tion by the carelessness of man, although inland water resources may 

 be greatly impaired through improper soil management practices. 



The soil may, of course, be studied from several standpoints. The 

 pedologist thinks of soils primarily in terms of their origin, form or 

 morphology (profile characteristics), and classification. The soil physi- 

 cist, the soil chemist, the soil microbiologist, and the soil conservationist 

 each has his own field of special interest and study. A well-rounded 



