120 THE SOIL. 



other constituent parts of the soil is enlarged, and on 

 this everything depends as regards the power of the soil 

 to give up to plants the food contained in it. 



A soil on which rye thrives well often proves un- 

 suited for the profitable cultivation of wheat, though 

 both plants take from the soil exactly the same con- 

 stituents. 



It is clear that the failure of wheat on such a soil 

 arises from this cause, that the wheat plants, within the 

 allotted period of their existence, do not find nutriment 

 enough for their full developement in the food-supplying 

 soil about their roots, whilst the quantity supplied is 

 ample for the rye plants. 



Now chemical analysis proves that such a rye soil 

 altogether contains, to a depth of 5 to 10 inches, fifty 

 nay, a hundred times more of the food-elements of the 

 wheat plant than would be required for an abundant 

 crop of wheat ; and yet, in spite of this superabundance, 

 the field will afford no remunerative crop to the agri- 

 culturist. 



If we compare the quantities of phosphoric acid and 

 potash drawn from an area of 2^ acres (hectare), by an 

 average wheat crop (2000 kilogrammes=4400 Ibs. of 

 grain, and 5000 kilogrammes^ 11000 Ibs. of straw) and 

 a rye crop (1600 kilogrammes 3520 Ibs. of grain and 

 3800 kilogrammes =83 60 Ibs. of straw), we find that 

 the two crops severally received from the soil 



The difference in the absolute requirement is there- 

 fore very small. The wheat crop received from the soil 

 only 9 kilogrammes (=20 Ibs.) of phosphoric acid, about 

 12 kilogrammes (=26*4 Ibs.) of potash, and 50 to 60 



