266 



ually been shown by Riimpler's experiments and later those of Schloszing 

 Such processes are constantly present and show how quickly a soil can be 

 leached by continued abundant precipitation, or can be impoverished in the 

 supply of its other valuable food stuffs by a one-sided supply of fertiUzer. 



The addition of fertilizer and the consequent increase of nutriment does 

 not always give the expected increase in the yield. This occurs especially in 

 rich soils and is explained by the fact that such a soil is no longer in a con- 

 dition to absorb, as a direct result of its wealth of nutriment. Soils poor in 

 clay are especially able to cause such phenomena because of their small ab- 

 sorptive power. 



A further painful surprise, connected with absorption, is the poisoning 

 of the soil from metallic salts. All heavy metals combine actively and, on 

 this account, for example, the failure of crops, observable near smelting 

 works, may not always be ascribed to the sulfuric acid of the fuel alone, but 

 often also to the larger accumulations of metalUc compounds. The fact, as 

 shown by experience, that plants will live In soil containing small quantities 

 of copper, lead, zinc, etc., has, up to the present, prevented paying the neces- 

 sary attention to this kind of soil poisoning. 



With potassium and ammonium, both of which combine actively, ab- 

 sorption often takes place by exchange in equivalent amounts (3 parts KgO 

 for I part NH3), whereby sodium, calcium and magnesia pass over into 

 solution. The easily dissolved, salt- forming sodium is only weakly absorbed 

 and, to a still lesser degree, the calcium, present in the form of its humate, 

 carbonate or phosphate, which can easily be replaced in the silicates by other 

 bases. Magnesium acts similarly. Acids are combined only when they form 

 insoluble salts. This is especially the case with phosphoric acid, which 

 forms insoluble compounds with calcium, magnesium, ferruginous earth and 

 aluminum oxid. Sulfuric acid is very weakly absorbed, nitric acid and 

 chlorin not at all. The latter case deserves consideration in the chlorin 

 poisoning near hydrochloric acid factories. 



By the different absorptive capacity and the constant exchange of nu- 

 tritive substances is explained the effect of many fertilisers which have a 

 two-fold action, — disintegrating and thereby increasing nutriment and ex- 

 hausting the supplies. Thus an abundant supply of potassium salts and 

 Chih saltpetre exhausts the calcium and magnesium in the soils. The ex- 

 pression, "soil impoverished from marling" indicates that marl, as well as 

 g}^psum, can prematurely exhaust the nutritive stores in the soil by a disin- 

 tegrating action. In this disintegration lies also the value of sodium chlorid 

 (common salt). A greater source of poor production is found in the acid 

 content, especially in the abundance of humic acids which greatly weaken 

 the absorption and are in a condition to dissolve all the elements in the soil. 

 This subject has been treated more thoroughly under the disadvantages of 

 moor soils and under the formation of swamp ore. 



