THE FOOD OF PLANTS. 279 



growing spontaneously. To obtain a clear under- 

 standing of the needs of the soil, it may be stated 

 that an acre of wheat producing $5 bushels of 

 grain, and 3,000 pounds of straw, removes about 

 40 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 100 bushels to the acre, removes in kernel 

 and stalk 150 pounds of potash and 80 pounds of 

 phosphoric acid. We cannot raise large crops of 

 corn without furnishing potash in some assimilable 

 form, for a small crop of fifty bushels to the acre 

 requires about 75 pounds of the agent. A fair crop 

 of oats, say 50 bushels to the acre, removes only 

 about 13 pounds of potash. Barley and rye re- 

 move not far from 30 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 de- 

 crease of tubers ? Can science, can chemistry 

 point out the reason, or aid in remedying the diffi- 

 culty ? I think it can, and in order to understand 

 the matter it is necessary to understand the kind 



