g to
Dr. Salisbury, a crop of corn of 75 bushels per acre removes from the
soil 600 lbs. of ash, but the _grain_ contains only 46 lbs. The other
554 lbs. is contained in the stalks, etc., all of which are usually
retained on the farm. It follows from this, that when only the grain is
sold off the farm, it takes more than thirteen crops to remove as much
mineral matter from the soil as is contained in the whole of one crop.
Again, the ash of the grain contains less than 3 per cent of sulphuric
acid, so that the 46 lbs. of ash, in 75 bushels of corn, contains less
than 1-1/2 lbs. of sulphuric acid, and thus, if an acre of soil contains
2,000 lbs. of sulphuric acid, we have sufficient for an annual crop of
75 bushels per acre for fifteen hundred years!

"As I said before," continued the Doctor, "intelligent farmers seldom
sell their straw, and they frequently purchase and consume on the farm
nearly as much bran, shorts, etc., as is sent to market with the grain
they sell. In the 'Natural History of New York,' it is stated that an
acre of wheat in Western New York, of 30 bushels per acre, including
straw, chaff, etc., removes from the soil 144 lbs. of mineral matter.
Genesee wheat usually yields about 80 per cent. of flour. This flour
contains only 0.7 per cent of mineral matter, while fine middlings
contain 4 per cent; coarse middlings, 5-1/2 per cent; shorts, 8 per
cent, and bran 8-1/2 per cent of mineral matter or ash. It follows from
this, that out of the 144 lbs. of mineral matter in the crop of wheat,
less than 10 lbs. is contained in the flour. The remaining 134 lbs. is
found in the straw, chaff, bran, shorts, etc., which a good farmer is
almost sure to feed out on his farm. But even if the farmer feeds out
none of his wheat-bran, but sells it all with his wheat, the 30 bushels
of wheat remove from the soil only 26 lbs. of mineral matter; and it
would take more than five crops to remove as much mineral matter as one
crop of wheat and straw contains. Allowing that half the ash of wheat is
phosphoric acid, 30 bushels remove only 13 lbs. from the soil, and if
the soil contains 4,000 lbs., it will take three hundred and seven
crops, of 30 bushels each, to exhaust it."

"That is to say," said Charley, "if all the straw and chaff is retained
on the farm, and is returned to the land without loss of phosphoric
acid."

"Yes," said the Doctor, "and if all the bran and shorts, etc., were
retained on the farm, it would take e