“And yet we are told,” said the Deacon, “that potatoes contain no end of potash.”
“And the same is true,” said I, “of root-crops, such as mangel-wurzel, turnips, etc., but the fact has no other significance than this: If you grow potatoes for many years on the same land and manure them with nitrogenous manures, the soil is likely to be speedily impoverished of potash.”
“But suppose,” said the Deacon, “that you grow potatoes on the same land without manure of any kind, would not the soil become equally poor in potash?”
“No,” said I, “because you would, in such a case, get very small crops—small, not from lack of potash, but from lack of nitrogen. If I had land which had grown corn, potatoes, wheat, oats, and hay, for many years without manure, or an occasional dressing of our common barnyard-manure, and wanted it to produce a good crop of potatoes, I should not expect to get it by simply applying potash. The soil might be poor in potash, but it is almost certain to be still poorer in nitrogen and phosphoric acid.”
Land that has been manured with farm-yard or stable-manure for years, no matter how it has been cropped, is not likely to need potash. The manure is richer in potash than in nitrogen and phosphoric acid. And the same may be said of the soil.
If a farmer uses nitrogenous and phosphatic manures on his clayey or loamy land that is usually relatively rich in potash, and will apply his common manure to the sandy parts of the farm, he will rarely need to purchase manures containing potash.