g6 THE SOIL SOLUTION 



r 



Agroceric acid, C 21 H 42 O 3 . 

 Paraffinic acid, C 24 H 48 O 2 . 

 Lignoceric acid, C 24 H 48 O 2 . 

 Phytosterol, C 26 H 44 O.H 2 O. 

 Pentosan, C 5 H 8 O 4 . 

 Agrosterol, C 26 H 44 O.H 2 O. 

 Picoline carboxylic acid, C 7 H 7 O 2 N. 

 Histidine, C 6 H 9 O 2 N 3 . 

 Arginine, C H 14 O 2 N 4 . 

 Cytosine, C 4 H 5 ON 3 .H 2 O. 

 Xanthine, C 5 H 4 O 2 N 4 . 

 Hypoxanthine, C 5 H 4 ON 4 . 

 Glycerides, resin acids, etc. 



Some of these, picoline carboxylic acid, dihydroxystearic acid 

 and the pentosan just cited, are toxic to growing plants; others 

 are not. The origin and mode of production of these substances 

 in the soil is, generally speaking, uncertain and obscure, and is 

 yet one of the important fundamental problems confronting the 

 soil chemist. 



It is important to note that the organic substances thus far 

 isolated from soils are of widely varying types, and with very 

 different chemical characteristics. As pointed out above, almost 

 any type of organic substance is likely to be found in soils, and 

 the effects of any of them on growing plants can hardly be pre- 

 dicted from a priori considerations. 



It has been found that as a general rule the continued growth 

 of one crop in any soil results in a low crop production. Pot 

 cultures have given even more pronounced results in the same 

 direction. The explanation long accepted is that the soil has, 

 as a result of continued cropping, become deficient in some one 

 or more of the "available" mineral nutrients. Pot experiments, 

 where the garnered crop was returned to the soil and still a 

 diminished yield was obtained, throw doubt on this explanation. 

 Still further doubt results from water-cultures which, by grow- 

 ing a crop in them, become "poor" for subsequent crops, although 



