Twenty five to thirty years ago, much was said in regard to special manures. Fertilizers were prepared for the different crops with special reference to the composition of the plants.
“But it was known then, as now,” said the Doctor, “that all our agricultural plants were composed of the same elements.”
“True, but what was claimed was this: Some crops contain, for instance, more phosphoric acid than other crops, and for these a manure rich in phosphoric acid was provided. Others contained a large proportion of potash, and these were called ‘potash crops,’ and the manure prescribed for them was rich in potash. And so with the other ingredients of plants.”
“I recollect it well,” said the Doctor, “and, in truth, for several years I had much faith in the idea. It was advocated with consummate ability by the lamented Liebig, and in fact a patent was taken out by the Musgraves, of Liverpool, for the manufacture of Liebig’s Special Manures, based on this theory. But the manures, though extensively used by the leading farmers of England, and endorsed by the highest authorities, did not in the end stand the test of actual farm practice, and their manufacture was abandoned. And I do not know of any experienced agricultural chemist who now advocates this doctrine of special manures.
“Dr. Vœlcker says: ‘The ash-analyses of plants do not afford a sufficiently trustworthy guide to the practical farmer in selecting the kind of manure which is best applied to each crop.’”
“Never mind the authorities,” said the Deacon; “what we want are facts.”
“Well,” replied the Doctor, “take the wheat and turnip crop as an illustration.
“We will suppose that there is twice the weight of wheat-straw as of grain; and that to 10 tons of bulbs there is 3 tons of turnip-tops. Now, 100 lbs. each of the ash of these two crops contain:
| Wheat crop. | Turnip crop. | |
|---|---|---|
| Phosphoric acid | 11.44 | 7.33 |
| Potash | 15.44 | 32.75 |
| Sulphuric acid | 2.44 | 11.25 |
| Lime | 5.09 | 19.28 |
| Magnesia | 3.33 | 1.56 |
“There are other ingredients,” continued the Doctor, “but these are the most important.