THE SOIL. 



from the original rock. This carbon dioxide is set 

 free by the decomposition of vegetable matter, so that 

 the presence of considerable decomposing vegetable 

 matter is essential to the fertility of most soils. More- 

 over the vegetable matter itself contains more or less 

 of the same chemical elements which had been used 

 in the growth of plants from which it was formed. 

 These soluble salts accumulating in the soil constitute 

 the immediately available plant food. 



ANIMAL PRODUCTS 

 TO MARKET 



LOST BY 

 LEACH1N6 



GRAIN AND VEGETABLES 

 MARKET 



COMMERCIAL FERTILIZER 



ATMOSPHERIC NITROGEN 

 LOSS OF CO, TO 

 ATMOSPHERE 



MINERAL BASE OF SOIL oVV 



FlG. 2. 



The Revolving Fund of Soil Fertility. Figure 2 is 

 constructed to show the various factors which are con- 

 cerned in soil fertility. As illustrated in this figure a 

 considerable quantity of material accumulates in the 

 soil from the decomposition of the mineral bases, from 

 the residue of roots and other portions of vegetation 

 growing on the ground, and from manure and other 

 fertilizers added. All of these together constitute the 

 revolving fund of soil fertility. From this the crop 

 largely derives its supply of the essential elements 



