our exhausting the
land. It does not pay. The farmer's resources will be exhausted long
before he can exhaust his farm."

"Assuming," said the Doctor, who is fond of an argument, "that the above
statement is true, let us look at the facts. An acre of soil, 12 inches
deep, would weigh about 1,600 tons; and if, as the writer quoted by the
Deacon states, the soil contains 4 ozs. of potash in every 100 lbs. of
soil, it follows that an acre of soil, 12 inches deep, contains 8,000
lbs. of potash. Now, potatoes contain about 20 per cent of dry matter,
and this dry matter contains say, 4 per cent of ash, half of which is
potash. It follows, therefore, that 250 bushels of potatoes contain
about 60 lbs. of potash. If we reckon that the tops contain 20 lbs.
more, or 80 lbs. in all, it follows that the acre of soil contains
potash enough to grow an _annual_ crop of 250 bushels of potatoes per
acre for one hundred years."

"I know farmers," said Charley, "who do not get over 50 bushels of
potatoes per acre, and in that case the potash would last five hundred
years, as the weeds grown with the crop are left on the land, and do
not, according to the Deacon, exhaust the soil."

"Good for you, Charley," said the Doctor. "Now let us see about the
phosphoric acid, of which the soil, according to the above statement,
contains only half as much as it contains of potash, or 4,000 lbs. per
acre.

"A crop of wheat of 30 bushels per acre," continued the Doctor,
"contains in the grain about 26 lbs. of ash, and we will say that half
of this ash is phosphoric acid, or 13 lbs. Allowing that the straw,
chaff, etc., contain 7 lbs. more, we remove from the soil in a crop of
wheat of 30 bushels per acre, 20 lbs. of phosphoric acid, and so,
according to the above estimate, an acre of soil contains phosphoric
acid to produce annually a crop of wheat and straw of 30 bushels per
acre for _two hundred years_.

"The writer of the paragraph quoted by the Deacon," continued the
Doctor, "selected the crops and elements best suited to his purpose, and
yet, according to his own estimate, there is sufficient potash and
phosphoric acid in the first 12 inches of the soil to enable us to raise
unusually large crops until the next Centennial in 1976.

"But let us take another view of the subject," continued the Doctor. "No
intelligent farmer removes all the potatoes _and tops_, all the wheat,
straw, and chaff, or all the corn and stalks from his farm. Accordin