market, such as dried blood or sodium nitrate."

"Well, even that would be eight or ten dollars a year per acre, and
that is as much as the land is worth, and this wouldn't include any
other plant food elements, such as 'phosphoric acid' and potash."

"No, that much would be required for the nitrogen alone if bought in
commercial form. I understand that the farmers who use this common
commercial fertilizer, apply about three hundred pounds of it to the
acre perhaps twice in four years. That would cost about eight
dollars for the four years, and the total nitrogen applied in the
two applications would amount to 10 pounds per acre."

"It is not quite correct to call 'phosphoric acid' and potash plant
food elements. They are not elements but compounds."

"Like ammonia, which is part nitrogen and part hydrogen?"

"The problem is somewhat similar, but not just the same," Percy
replied. "These compounds contain oxygen and not hydrogen."

"Well, I understand that both oxygen and hydrogen are furnished by
natural processes, the oxygen from carbon dioxid in the carbon
cycle, and the hydrogen from the water which falls in rain."

"That is all true, but you really do not buy the hydrogen or oxygen.
While they are included in the two-eight-two guarantee, the price is
adjusted for that. Thus the cost of nitrogen would be just the same
whether you purchase the fertilizer on the basis of seventeen cents
a pound for the actual element nitrogen, or fourteen cents a pound