and yet
3 cwt. of Peruvian guano on Plot 13, only produced an increase of two
bushels and 643 lbs. of straw per acre. The guano at $60 per ton, would
cost $9.00 per acre. This will not pay."

This is an unusually small increase. The reason, probably, is to be
found in the fact that the manure and seed were not sown until March,
instead of in the autumn. The salts of ammonia are quite soluble and act
quickly; while the Peruvian guano has to decompose in the soil, and
consequently needs to be applied earlier, especially on clay land.

"I do not want you," said the Deacon, "to dodge the question why an
application of 14 tons of farmyard-manure per acre, every year for over
thirty years, does not make the land too rich for wheat."

"Possibly," said I, "on light, sandy soil, such an annual dressing of
manure _would_ in the course of a few years make the land too rich for
wheat. But on a clayey soil, such is evidently not the case. And the
fact is a very important one. When we apply manure, our object should be
to make it as available as possible. Nature preserves or conserves the
food of plants. The object of agriculture is to use the food of plants
for our own advantage."

"Please be a little more definite," said the Deacon, "for I must confess
I do not quite see the significance of your remarks."

"What he means," said the Doctor, "is this: If you put a quantity of
soluble and available manure on land, and do not sow any crop, the
manure will not be wasted. The soil will retain it. It will change it
from a soluble into a comparatively insoluble form. Had a crop been sown
the first year, the manure would do far more good than it will the next
year, and yet it may be that none of the manure is lost. It is merely
locked up in the soil in such a form as will prevent it from running to
waste. If it was not for this principle, our lands would have been long
ago exhausted of all their available plant-food."

"I think I understand," said the Deacon; "but if what you say is true,
it upsets many of our old notions. We have thought it desirable to plow
under manure, in order to prevent the ammonia from escaping. You claim,
I believe, that there is little danger of any loss from spreading manure
on the surface, and I suppose you would have us conclude that we make a
mistake in plowing it under, as the soil renders it insoluble."

"It depends a good deal," said I, "on the character of the soil.
A light, sandy soil will not prese