CHAPTER III. 



UNFAVORABLE CHEAllCAL SOIL CONSTITUTION. 



I. Relation of the Food Stuffs to the Soil Structure. 



A. Soil Absorption Resulting from Chemico-physical Processes. 



Injuries to vegetation can take place either because the capital of nu- 

 tritive substances in the soil takes a form quantitatively or qualitatively un- 

 favorable for the nutrition of the plants, or because, with an abundant sup- 

 ply and normal composition of the nutritive substances, the plant's capacity 

 for taking them up will be arrested by other factors of growth. Thus, either 

 a lack or an excess of the nutritive substances can make itself felt, or, be- 

 cause of modified conditions of absorption, one single nutritive substance 

 can be present in amounts too scanty or too great for effectiveness, and thus 

 disturb the equilibrium in the organism. This second form of nutritive 

 disturbance will be treated in the following division under the headings, 

 "Lack of moisture and nutritive substances" and "Excess of moisture and 

 nutritive substances." 



The consideration of the supply of water in this connection, together 

 with nutritive substances, is justified by the fact that the water not only 

 furnishes these by its decomposition in the plant body, but also, as 

 a transporting medium, causes weak or strong concentrations of the 

 nutrient solutions according to the amount of water present, thus influencing 

 beneficially or disadvantageously the process of nutrition. In view of the 

 constantly changing concentrations, the influence of the water will therefore 

 have to be taken into consideration, when studying the relation of the nutri- 

 tive substances to the soil structure. 



The soluble salts produced by the decomposition of the minerals or in- 

 troduced by fertilization, serve as a basis for soil absorption. The retention 

 and giving up of the salts, as also their transformations continually taking 

 place in the soil, were thought at first to be predominantly physical processes, 

 while they now, in substance, are considered chemical processes^ In any 



1 See Ramann, Bodenkunde, 2nd. Edition, p. 21, Berlin, 1905, Jul. Springer. In the 

 remainder of this section, if other authors are not cited, we relj' chiefly on the work 

 here named. 



