362 HANDY-BOOK OF HUSBANDRY. 



lbs. 



First 6 inches 2,613,600 



Second " 2,657,1 60 



Third " 2,746,280 



" No great error, therefore, will be made if we assume in the 

 subsequent calculations that 6 inches of this soil weigh 2^ millions 

 of pounds per acre. 



" An acre of land, according to the preceding determinations, 

 contains : — 



1st 6 inches. 2d 6 inches. }d 6 inches, 



lbs. lbs. lbs. 



Phosphoric acid 4)95° .... 2,725 .... 3)575 



Nitrogen 3>350 •••• '1875 .... i»325 



Equal to ammonia 4)05o .... 2,275 • • • • 1,600 



" The proportion of phosphoric acid in 6 inches of surface 

 soil, it will be seen, amounted to about two-tenths per cent. ; a 

 proportion of the whole soil so small that it may appear insuffi- 

 cient for the production of a good corn-crop. However, when 

 calculated to the acre, we find that 6 inches of surface soil, in an 

 acre of land, actually contain over 2 tons of phosphoric acid. An 

 average crop of wheat, assumed to be 25 bushels of grain, at 60 

 lbs. per bushel, and 3,000 lbs. of straw, removes from the land on 

 which it is giown 20 lbs. of phosphoric acid. The clover-soil, 

 analyzed by me, consequently contains an amount of phosphoric 

 acid in a depth or only 6 inches, which is equal to that present in 

 2474- average crops of wheat ; or supposing that, by good cultiva 

 tion and in favorable seasons, the average yield of wheat could be 

 doubled, and 50 bushels of grain at 60 lbs. a bushel and 6,000 lbs. 

 of straw could be raised, 124 of such heavy wheat-crops would 

 contain no more phosphoric acid than actually occurred in 6 

 inches of this^clover-soil per acre. 



'■'• The mere presence of such an amount of phosphoric acid in 

 a soil, however, by no means proves its sufficiency for the produc- 

 tion of so many crops of wheat ; for, in the first place, it cannot 

 be shown that the whole of the phosphoric acid found by analysis 

 occuis in the soil in a readily available combination; and, in the 

 second place, it is quite certain that the root-fibers of the wheat- 

 plant cannot reach and pick up, so to speak, every particle of 

 phosphoric acid, even supposing it to occur in the soil in a form 

 most conducive to "ready assimilation by the plant." 



" The calculation is not given in proof of a conclusion which 

 would be manifestly absurd, but simply as an illustration of the 



