“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.”

“I can’t understand that,” said Mr. Thornton.  “How can that be when one of the crops is cowpeas?”

“In average live-stock and dairy farming,” Percy continued, “about one-fourth of the nitrogen contained in the food consumed is retained in the milk and animal growth, and you can make the computations for yourself.  It should be kept in mind, moreover, that much of the manure produced on the average farm is wasted.  More than half of the nitrogen is in the liquid excrement, and it is extremely difficult to prevent loss of the liquid manure.  There is also large loss of nitrogen from the fermentation of manure in piles; and when you smell ammonia in the stable, see the manure pile steaming, or colored liquid soaking into the ground beneath, or flowing away in rainy weather, you may know that nitrogen is being lost.  How many tons of manure can you apply to your land under such a system of farming as we have been discussing?”