SOIL ACIDITY 241 



Table XII. — Amount of CaO Removed by Various Crops 



(Expressed in pounds per acre.) 



Alfalfa 212 



Cabbage 95 



Corn 12 



Clover 90 



Oats 11 



Potatoes 31 



Timothy 14 



Tobacco 83 



Wheat 8 



In many cases, it is true, sufficient calcium is added in 

 the ordinary fertilizers to feed crops. Table XIII gives the 

 estimated amount of calcium oxide in 100 pounds of various 

 fertilizers. 



Table XIII. — Amount of CaO in Various Fertilizers 



Fertilizer. Form of Calcium. Per cent. CaO. 



Acid phosphate Phosphate and sulphate .... 21 



Basic slag Phosphate, silicate, and oxide . . 48 



Bone meal Phosphate 27 



Rock phosphate Phosphate and carbonate ... 42 



Wood ashes Carbonate and phosphate . . . 34 



It may happen, however, that a fertilizer application 

 does not add calcium and the crop becomes starved for lack 

 of this essential element. Particularlv may this be true in 

 the case of clover and alfalfa, as mentioned above. An 

 application of lime, then, has the added benefit of feeding 

 the crop. 



ISO. Soil Acidity. — One of the most important effects of 

 adding lime to the soil is the neutralization of soil acidity— or 

 to "sweeten a sour soil." This condition in the soil is very 

 common, may occur in all kinds of soils, and in fact is the 

 natural result of cropping. Its bad effect on crops is fre- 

 quently exaggerated, some crops preferring an acid soil and 

 even refusing to grow in neutral or alkaline soils. For 

 ordinary crops, however, in the usual farm rotation, a soil 

 which is neutral or slightly alkaline is preferable and should 

 be maintained. 



The primary cause of soil acidity is the production of 

 acids or acid salts. These acids may be organic or inorganic 

 in nature and may vary in their harmful effect on crops. 

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