“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!