“Now, if you were going to compound a manure for wheat, say 100 lbs., consisting of potash and phosphoric acid, what would be the proportions?”
The Deacon figured for a few moments, and then produced the following table:
| Wheat manure. | Turnip manure. | |
|---|---|---|
| Phosphoric acid | 42½ lbs. | 18⅓ lbs. |
| Potash | 57½ lbs. | 81⅔ lbs. |
| 100 lbs. | 100 lbs. |
“Exactly,” said the Doctor, “and yet the experiments of Lawes and Gilbert clearly prove that a soil needs to be richer in available phosphoric acid, to produce even a fair crop of turnips, than to produce a large crop of wheat. And the experience of farmers everywhere tends in the same direction. England is the greatest turnip-growing country in the world, and you will find that where one farmer applies potash to turnips, or superphosphate to wheat, a hundred farmers use superphosphate as a special manure for the turnip crop.”
“And we are certainly warranted in saying,” continued the Doctor, “that the composition of a plant affords, in practical agriculture, and on ordinary cultivated soils, no sort of indication as to the composition of the manure it is best to apply to the crop.”
“Again,” continued the Doctor, “if the theory was a correct one, it would follow that those crops which contained the most nitrogen, would require the most nitrogen in the manure. Beans, peas, and clover would require a soil or a manure richer in available nitrogen than wheat, barley, or oats. We know that the very reverse is true—know it from actual, and repeated, and long-continued experiments like those of Lawes and Gilbert, and from the common experience of farmers everywhere.”
“You need not get excited,” said the Deacon, “the theory is a very plausible one, and while I cannot dispute your facts, I must confess I cannot see why it is not reasonable to suppose that a plant which contains a large amount of nitrogen should not want a manure specially rich in nitrogen; or why turnips which contain so much potash should not want a soil or manure specially rich in potash.”
“Do you recollect,” said I, “that crop of turnips I raised on a poor blowing-sand?”
“Yes,” said the Deacon, “it was the best crop of turnips I ever saw grow.”
“That crop of turnips,” said I, “was due to a dressing of superphosphate of lime, with little or no potash in it.”