CAUSES OF FERTILITY. 



221 



Sect. 4. arcumstances upon which the Fertility of Soil 

 depends. 



Having in a previous section, given the mode of analysis, 

 by which the substances which have been described are ob- 

 tained, this section will be devoted to an examination of soils^ 

 with a view of ascertaining, if possible, the reason or source 

 of their fertility. This will enable us to understand those 

 various methods of improvement which will be hereafter 

 described. 



In order therefore, to give ?i practical value to the various 

 topics treated of in this chapter, it will be necessary to make 

 some calculations, as to the absolute quantity of the various 

 ingredients in the soil, that we may infer what the soil re- 

 quires, as a condition of fertility. The first example which 

 we will introduce for this purpose, is the analysis by Berze- 

 lius of two soils, from Russia and Siberia. 



A, soil never cultivated. B, long cultivated, and said to 

 be in an exhausted condition. C, sub-soil of the field B. 



f Sand, . 

 Silica, , 

 Alumina, 

 Perox. of iron, 

 Aluminous matter, <[ Carbonate of lime 

 Magnesia, 

 Water, 



Phosphoric acid, 

 ^ Crenic acid, 

 Acids combined f Apocrenic acid, 

 with peroxide ofJ ^^^ic acid, 

 iron & alumina, f^^tract of humus, 

 Humin and rootlets. 



52.77 

 18.65 



8.85 

 5.33 

 1.13 



.67 

 4.04 



.46 

 2.56 

 1.87 

 1.87 



.00 

 1.66 



I 99.84 I 99.86 | 99.86 

 It will be seen by inspection of these soils, that they do not 

 differ m the quamity of silica, alumina and oxide of iron. 

 The difference in fertility, therefore, is not due to these in- 

 gredients. Let us examine further, and see if we can dis- 

 cover the true cause of it. 



19 



