for the ammonia."

"Yes, I see how that might be, but I don't see why the guarantee
should be two per cent. of ammonia instead of one and two-thirds per
cent. of nitrogen, when the nitrogen is all that gives it value."

"There is no good reason for it," said Percy. "It is one of those
customs that are conceived in ignorance and continued in
selfishness. It is very much simpler to consider the whole subject
on the basis of actual plant food elements, and I am glad to say
that many of the state laws already require the nitrogen to be
guaranteed in terms of the actual element, a few states now require
the phosphorus and potassium also to be reported on the element
basis."

"That is hopeful, at least," said Mr. Thornton. "Now, if I am not
asking too many questions or keeping you here too long, I shall be
glad to have you explain two more points that come to my mind:
First, how much of that two hundred pounds of nitrogen can I put
back in the manure produced on the farm; and, second, just what is
meant by potash and phosphoric acid?"

Percy made a few computations and then replied: "If you sell the
wheat; feed all the corn, oats, and cowpea hay and half of the straw
and corn fodder, and use the other half for bedding; and, if you
save absolutely all of the manure produced, including both the solid
and liquid excrement; then it would be possible to recover and
return to the land about 173 pounds of nitrogen during the four
years, compared with the 200 pounds taken from the soil."