REMOVAL OF NUTRIENTS FROM THE SOIL 303 



tion the ash is almost entirely returned, while there is a large 

 gain of organic matter and often an increase in nitrogen as 

 well. Under natural conditions the soil usually increases in 

 fertility; for, while there is some loss through drainage and 

 other sources, this is more than counterbalanced by the action 

 of the natural agencies of disintegration and decomposition, 

 while the fixation of atmospheric nitrogen affords a constant, 

 though small, supply of that important soil ingredient. 



When land is placed under cultivation a very different 

 condition is presented. Crops are removed and only par- 

 tially returned at best to the soil as manure and crop resi- 

 due. A certain proportion of the soil nutrients are, therefore, 

 permanently withdrawn. The point of vital importance, 

 however, is that only a part of the total supply of soil con- 

 stituents will ever become available, the portion withdrawn 

 each year by cropping being a more serious consideration 

 than is generally supposed. 



The following table, computed by Warington, 1 shows the 

 quantities of nitrogen, potash, phosphoric acid, lime and sulfur 

 trioxide 2 removed from an acre of soil by some of the common 

 crops. The entire harvested crop is included. 



Table LXVI 



Crop 



Wheat 



Barley 



Oats 



Maize 



Meadow Hay 

 Red Clover . < 

 Potatoes. . . . 



Yield 



30 bushels 

 40 bushels 

 45 bushels 

 30 bushels 

 V/ 2 tons 

 2 tons 

 6 tons 



so 3 



(LBS.) 



15.7 

 14.3 

 19.7 

 12.0 

 11.3 

 15.4 

 11.5 



1 Warington, E., Chemistry of the Farm; pp. 64-65, London, 1894. 



"From Hart, E. B., and Peterson, W. H., Sulphur Requirements of 

 Farm Crops in Relation to the Soil and Air Supply; Wis. Agr. Exp. Sta., 

 Res. Bui. 14, 1911. 



