"There are a few important facts to be kept in mind regarding
nitrogen:

"A fifty-bushel crop of corn takes 75 pounds of nitrogen from the
soil. Of this amount about 50 pounds are in the grain, 24 pounds are
in the stalks, and 1 pound in the cobs. A fifty-bushel crop of oats
takes 48 pounds of nitrogen from the soil, 33 pounds in the grain,
and 15 in the straw. A twenty-five bushel crop of wheat also takes
48 pounds of nitrogen from the soil, 36 pounds in the grain and 12
in the straw.

"These amounts will vary to some extent with the quality of the
crops, just as the weight of a bushel of wheat varies from perhaps
56 to 64 pounds, although as an average wheat weighs 60 pounds to
the bushel."

"You surely remember figures well," remarked Mr. Thornton as he made
some notations.

"It is easy to remember what we think about much and often," said
Percy; "as easy to remember that a ton of cowpea hay contains 43
pounds of nitrogen as that Blairville is 53 miles from Richmond."

"I have added those figures together," continued Mr. Thornton, "and
I find that the three crops, corn, oats, and wheat, would require
171 pounds of nitrogen. Now suppose we raise a crop of cowpeas the
fourth year, how much nitrogen would be added to the soil in the
roots and stubble?"

"Not any."