CONVERSION OF RYE INTO WHEAT SOIL. V2:i 



before us, and were to put the question liow mucli nutri- 

 ment we must add to convert it into a })ermanently jn-o- 

 ductive wlieat soil, the answer would be not hypothetical, 

 but perfectly trustworthy and exact. If 



Hence, to a rye soil of a given condition and productive 

 power, we should have to add, in some form or other, 

 one-half more phosphoric and silicic acid, and one-third 

 more potash, than it already contains, to make it capable 

 of producmg average crops of wheat grain and straw. 



And to obtain permanently from a wheat soil a crop 

 half as large again as an average harvest, we should add 

 one- half more of nutritive substances than it already 

 contains. 



These speculations have no other object than to show 

 that a small difference in the absolute quantity of a nutri- 

 tive element, required by one kind of plant more than 

 by another, presupposes a great excess in the amount of 

 this constituent in the soil. A wheat crop takes from 

 the soil, per hectare (2|- acres), only 8-6 kilogrammes 

 (19 lbs.) more phosphoric acid than a rye crop ; but that 



