Manures and Fertilizers 123 



fraction of all that is used. Acid phosphate is the prin- 

 cipal source of phosphoric acid in this country, either for 

 factory-mixed fertilizers or for home mixing. The word 

 " acid" has created a foolish prejudice against its use which 

 is not warranted by facts. A very small application of 

 lime will prevent any chance of the soil becoming sour 

 from its use. Ground animal bone and basic slag are 

 valuable sources of phosphoric acid for some other crops, 

 but are too slow acting for the tender potato. Different 

 grades of American acid phosphates vary in the percent- 

 age of phosphoric acid from 12 per cent to 16 per cent or 

 more. Only the highest grades should usually be bought. 

 The price a pound of the phosphoric acid appHed to the 

 land is the real cost. 



In the northern states the price a pound at the rail- 

 road station is usually less in the higher than in the lower 

 grades and in addition there is the cost of hauling to the 

 farm and applying to the land. Three tons of 16 per cent 

 acid phosphate usually cost less than four tons of the 

 12 per cent and the cost of hauling and sowing the extra 

 ton is saved. 



POTASSIUM 



Potassium, usually referred to as "potash" or K2O, is 

 present in large quantities in most American soils. Some 

 of the very sandy soils near the seacoast and the swamp 

 mucks are likely to be deficient in it. Potash helps in the 

 translocation of starch within the potato plant and tends 

 to lengthen the life of the crop. Practically all the com- 

 mercial supply of potash comes from deposits in Germany, 

 controlled by a syndicate there. The principal form used 

 in America is that of muriate of potash containing 47 to 50 

 per cent of actual potash. This is usually the cheapest 



