44 ALKALIES IN SOIL. 



per acre, for 7400 years ; for at twenty bushels per 

 acre, and at 50 pounds per bushel, each acre would 

 afford 1000 pounds of grain, which contain nearly 

 1-2 lb. of lime, or *049, (Schrceder,) dividing 3626 

 by this, the quotient 7400 is the number of years the 

 lfme would supply the grain. Wheat will not differ 

 much from rye, and if the time is diminished, by the 

 amount of lime contained in the straw, it will be 

 seen, that the actual amount of lime and potash, in 

 what is called poor soil, will hardly begin to di- 

 minish at the end of a long lease, cropping every 

 year, 30 bushels of wheat. Allowing thus, for ex- 

 ample, the proportion of straw which such a crop 

 would afford, to be about 5000 pounds, and this is 

 not far from the truth ; the straw gives 0*044 of its 

 weight of ashes, or 220 lbs. of which, one-fifth is 

 soluble in water, and consists of one-half of that dis- 

 solved, of potash. The spent ashes, or that part 

 not soluble in water, contains 5*80 percent, of lime. 

 On these data, an acre of wheat straw, or 2 1-2 tons 

 will give 220 lbs. of ashes, containing 22 lbs. of 

 potash, and 10 lbs. of lime. The potash will last 

 at this rate for the straw, three thousand years ! It 

 will be hereafter shown, that when the lime fails, the 

 crop will not. 



75. Were similar calculations extended to soil 



