“There is not much doubt,” said the Deacon, “that you will get a good crop of clover, if you will keep the sheep off of the land this fall. But I do not see what you mean by the clover-plants finding food enough for 40 bushels of wheat, while in point of fact, if you had sown the field again to wheat this fall, you would not, as you say, probably get more than 12 or 15 bushels of wheat.”
“He means this,” said the Doctor. “If he had sown the land to wheat this fall, without manure, he would probably not get over 15 bushels of wheat per acre, and yet you both agree that the land will, in all probability, produce next year, if mown twice, three tons of clover-hay per acre, without any manure.
“Now, if we admit that the clover gets no more nitrogen from the rain and dews, and from the atmosphere, than the wheat will get, then it follows that this soil, which will only produce 15 bushels of wheat per acre, does, in point of fact, contain plant-food enough for 40 bushels of wheat, and the usual proportion of straw.
“The two crops take up from the soil as follows:
| Phosphoric acid. | Potash. | Nitrogen. | |
|---|---|---|---|
| 15 bushels wheat and straw | 10¼ lbs. | 11¼ lbs. | 22 lbs. |
| 3 tons clover-hay | 33 ” | 90 ” | 150 ” |
“These facts and figures,” continued the Doctor, “are worth looking at and thinking about. Why can not the wheat get as much phosphoric acid out of the soil as the clover?”
“Because,” said the Deacon, “the roots of the clover go down deeper into the subsoil than the roots of wheat.”
“That is a very good reason, so far as it goes,” said I, “but does not include all the facts. I have no sort of doubt, that if I had sown this land to wheat, and put on 75 lbs. of nitrogen per acre, I should have got a wheat-crop containing, in grain and straw, 30 lbs. of phosphoric acid. And so the reason I got 15 bushels of wheat per acre, instead of 40 bushels, is not because the roots of wheat do not go deep enough to find sufficient soluble phosphoric acid.”
“Possibly,” said the Doctor, “the nitrogen you apply may render the phosphoric acid in the soil more soluble.”
“That is true,” said I; “and this was the answer Liebig gave to Mr. Lawes. Of which more at some future time. But this answer, like the Deacon’s, does not cover all the facts of the case; for a supply of soluble phosphoric acid would not, in all probability, give me a large crop of wheat. I will give you some facts presently bearing on this point.