Now, three tons of clover-hay contain about 33 lbs. of phosphoric acid,
90 lbs. of potash, and 150 lbs. of nitrogen.

The last crop of wheat, of 22 bushels per acre, and say 1,500 lbs. of
straw, would contain:

In the grain. In the straw. In total crop.
Phosphoric acid 11-1/2 lbs. 3-3/4 lbs. 15-1/4 lbs.
Potash 6-3/4 " 9-3/4 " 16-1/2 "
Nitrogen 23 " 9-1/2 " 32-1/2 "

It seems very unkind in the wheat-plants not to give me more than 22
bushels per acre, when the clover-plants coming after will find
phosphoric acid enough for 40 bushels of wheat, and potash and nitrogen
enough for nearly 100 bushels of wheat per acre. And these are the three
important constituents of plant-food.

Why, then, did I get only 22 bushels of wheat per acre? I got 23 bushels
on the same land the year previous, and it is not improbable that if I
had sown the same land to wheat again this fall, I should get 12 or 15
bushels per acre again next year. But the clover will find plant-food
enough for 40 bushels of wheat.

"There is not much doubt," said the Deacon, "that you will get a good
crop of clover, if you will keep the sheep off of the land this fall.
But I do not see what you mean by the clover-plants finding food enough
for 40 bushels of wheat, while in point of fact, if you had sown the
field again to wheat this fall, you would not, as you say, probably get
more than 12 or 15 bushels of wheat."

"He means this," said the Doctor. "If he had sown the land to wheat this
fall, without manure, he would probably not get over 15 bushels of wheat
per acre, and yet you both agree that the land will, in all probability,
produce next year, if mown twice, three tons of clover-hay per acre,
without any manure.

"Now, if we admit that the clover gets no more nitrogen from the rain
and dews, and from the atmosphere, than the wheat will get, then it
follows that this soil, which will only produce 15 bushels of wheat per
acre, does, in point of fact, contain plant-food enough for 40 bushels
of wheat, and the usual proportion of straw.

"The two crops take up from the soil as follows:

Phosphoric acid. Potash. Nitrogen.
15 bushels wheat and straw 10-1/4 lbs. 11-1/4 lbs. 22 lbs.
3 tons clover-hay 33 " 90 " 150 "

"These facts and figures," continued the Docto