"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 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."