“I understand that,” said the Deacon, “but if the weeds are left on the land, and the useful plants are sold, the farmer who keeps his land clean would exhaust his land faster than the careless farmer who lets his land lie until it is overrun with thistles, briars, and pig-weed. You agricultural writers, who are constantly urging us to farm better and grow larger crops, seem to overlook this point. As you know, I do not take much stock in chemical theories as applied to agriculture, but as you do, here is a little extract I cut from an agricultural paper, that seems to prove that the better you work your land, and the larger crops you raise, the sooner you exhaust your land.”
The Deacon put on his spectacles, drew his chair nearer the lamp on the table, and read the following:
“There is, on an average, about one-fourth of a pound of potash to every one hundred pounds of soil, and about one-eighth of a pound of phosphoric acid, and one-sixteenth of a pound of sulphuric acid. If the potatoes and the tops are continually removed from the soil, it will soon exhaust the potash. If the wheat and straw are removed, it will soon exhaust the phosphate of lime; if corn and the stalks, it will soon exhaust the sulphuric acid. Unless there is a rotation, or the material the plant requires is supplied from abroad, your crops will soon run out, though the soil will continue rich for other plants.”
“That extract,” said I, “carries one back twenty-five years. We used to have article after article in this strain. We were told that ‘always taking meal out of the tub soon comes to the bottom,’ and always taking potash and phosphoric acid from the soil will soon exhaust the supply. But, practically, there is really little danger of our exhausting the land. It does not pay. The farmer’s resources will be exhausted long before he can exhaust his farm.”
“Assuming,” said the Doctor, who is fond of an argument, “that the above statement is true, let us look at the facts. An acre of soil, 12 inches deep, would weigh about 1,600 tons; and if, as the writer quoted by the Deacon states, the soil contains 4 ozs. of potash in every 100 lbs. of soil, it follows that an acre of soil, 12 inches deep, contains 8,000 lbs. of potash. Now, potatoes contain about 20 per cent of dry matter, and this dry matter contains say, 4 per cent of ash, half of which is potash. It follows, therefore, that 250 bushels of potatoes contain about 60 lbs. of potash. If we reckon that the tops contain 20 lbs. more, or 80 lbs. in all, it follows that the acre of soil contains potash enough to grow an annual crop of 250 bushels of potatoes per acre for one hundred years.”
“I know farmers,” said Charley, “who do not get over 50 bushels of potatoes per acre, and in that case the potash would last five hundred years, as the weeds grown with the crop are left on the land, and do not, according to the Deacon, exhaust the soil.”
“Good for you, Charley,” said the Doctor. “Now let us see about the phosphoric acid, of which the soil, according to the above statement, contains only half as much as it contains of potash, or 4,000 lbs. per acre.
“A crop of wheat of 30 bushels per acre,” continued the Doctor, “contains in the grain about 26 lbs. of ash, and we will say that half of this ash is phosphoric acid, or 13 lbs. Allowing that the straw, chaff, etc., contain 7 lbs. more, we remove from the soil in a crop of wheat of 30 bushels per acre, 20 lbs. of phosphoric acid, and so, according to the above estimate, an acre of soil contains phosphoric acid to produce annually a crop of wheat and straw of 30 bushels per acre for two hundred years.
“The writer of the paragraph quoted by the Deacon,” continued the Doctor, “selected the crops and elements best suited to his purpose, and yet, according to his own estimate, there is sufficient potash and phosphoric acid in the first 12 inches of the soil to enable us to raise unusually large crops until the next Centennial in 1976.
“But let us take another view of the subject,” continued the Doctor. “No intelligent farmer removes all the potatoes and tops, all the wheat, straw, and chaff, or all the corn and stalks from his farm. According to Dr. Salisbury, a crop of corn of 75 bushels per acre removes from the soil 600 lbs. of ash, but the grain contains only 46 lbs. The other 554 lbs. is contained in the stalks, etc., all of which are usually retained on the farm. It follows from this, that when only the grain is sold off the farm, it takes more than thirteen crops to remove as much mineral matter from the soil as is contained in the whole of one crop. Again, the ash of the grain contains less than 3 per cent of sulphuric acid, so that the 46 lbs. of ash, in 75 bushels of corn, contains less than 1½ lbs. of sulphuric acid, and thus, if an acre of soil contains 2,000 lbs. of sulphuric acid, we have sufficient for an annual crop of 75 bushels per acre for fifteen hundred years!