72 SOILS. 



commercial kainit (calculated as K2O) ranges from 16 to 

 35%, while the sulphate frequently ranges from 80 up to 

 95% of the pure sulfate; thus costing materially less in 

 freight charges than the lower-grade kainit. Its potash con- 

 tent ranges from 43 to over 50% of K2O. 



Potash Salts in Alkali Soils. The sulfates and chlorids of 

 potassium, however, occur not only in connection with rock- 

 salt deposits, but are also found in the alkali soils of the arid 

 region. They are, in fact, never absent where such salts 

 occur at all, and their percentage in the total of salts ranges all 

 the way from about 4 to as much as 20% of potash sulphate. 

 In numerous cases it has been found that the content of this 

 salt to the depth of four feet amounts to from 1200 to 1500 

 pounds per acre. In such lands, of course, additional fertiliza- 

 tion with potash salts is totally uncalled for, the more as such 

 soils invariably contain, besides the water-soluble potash, an 

 unusually large percentage of the same in the form of easily 

 decomposable silicates, or zeolites. 



Farmyard or Stable Manure. In connection with the sub- 

 ject of mineral fertilizers, it will be proper to discuss briefly 

 the uses and special merits of stable manure, composts, etc. 

 Up to within the last century, these were practically the only 

 fertilizers known and used, and the exclusive use of this 

 manure might have continued indefinitely but for the dis- 

 covery that as time progressed, stable manure and with it 

 grain crops, for the production of which it was necessary, be- 

 came less and less in amount, so as to threaten bread famines. 

 The cause of this diminution was, of course, the incomplete- 

 ness of the return of the soil-ingredients taken off by the crops, 

 when these were exported to feed the cities or foreign coun- 

 tries. Thus the attention of chemists, and notably that of 

 Liebig, was attracted to the solution of the problem of keeping 

 up production even with an insufficient supply of stable ma- 

 nure; and the discovery of the use of mineral fertilizers was 

 the result of their activity. 



The chemical composition of stable manure does not, alone, 

 suffice to explain its remarkable efficacy and the difficulty 

 of replacing it by any other material. The composition of 

 manure of course differs not only with different animals but 



