POTASH REQUIRED BY CROPS. 89 



crops. Formerly there were but two sources of supply, that 

 from manure or animal excrement, and that from the bones of 

 animals ; but now we have a third source in the phosphatic de- 

 posits found upon the coast of South Carolina. From these 

 substances what are popularly known as superphosphates are 

 made and sold largely in the market. 



Potash holds a most important place in the list of substances 

 consumed by plants, and hitherto much anxiety has been mani- 

 fested regarding a supply equal to our wants. A few years ago 

 we were acquainted with no sources of the agent save that of 

 the ash of plants ; and as mineral coal came into use for fur- 

 nishing household warmth, wood ashes and the potash salts 

 obtained from them became very scarce and costly. Every year 

 the farmer removed from the soil large quantities of potash in 

 his crops which he could not return again through the excre- 

 ment of his animals, and therefore it was evident his lands 

 were becoming impoverished to an alarming extent. High cul- 

 tivation, as respects potash, increases this impoverishment, as 

 all cultivated plants are richer in this substance than those 

 growing spontaneously. To obtain a clear understanding of 

 the needs of the soil, it may be stated that an acre of wheat pro- 

 ducing twenty-five bushels of grain and three thousand pounds 

 of straw, removes about forty pounds of potash in the crop. 

 Can any farmer conceive of that amount of potash existing in 

 the soil of any one acre of land upon his farm ? We know it 

 must be present and within easy reach of the plants, else not a 

 blade of wheat can grow and mature the seed. Nearly all soils 

 of course contain potash, but the quantity is often insufficient 

 for crops of any of the cereal grains. A crop of corn of one 

 hundred bushels to the acre removes, in kernel and stalk, one 

 hundred and fifty pounds of potash and eighty pounds of phos- 

 phoric acid. We cannot raise large crops of corn without fur- 

 nishing potash in some assimilable form ; for a small crop of 

 fifty bushels to the acre requires about seventy-five pounds of 

 the agent. A fair crop of oats, say fifty bushels to the acre, 

 removes only about thirteen pounds of potash. Barley and rye 

 remove not far from thirty pounds each. 



Now we have observed the great deterioration in our potato 

 crops during the past ten or twenty years ; and what is the 

 cause of this alarming decrease of tubers ? Can chemistry 

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