a dressing of 50 lbs. per acre pays
better than a dressing of 100 lbs. per acre. I wish Mr. Lawes had sown
75 lbs. on one plot."

I wish so, too, but it is quite probable that in our climate, 50 lbs. of
available ammonia per acre is all that it will usually be profitable to
apply per acre to the barley crop. It is equal to a dressing of 500 lbs.
guaranteed Peruvian guano, or 275 lbs. nitrate of soda. --"Or to how
much manure?" asked the Deacon.

To about 5 tons of average stable-manure, or say three tons of good,
well-rotted manure from grain-fed animals.

"And yet," said the Deacon, "Mr. Lawes put on 14 tons of yard manure per
acre, and the yield of barley was not as much as from the 50 lbs. of
ammonia alone. How do you account for that?"

Simply because the ammonia in the manure is _not_ ammonia. It is what
the chemists used to call "potential ammonia." A good deal of it is in
the form of undigested straw and hay. The nitrogenous matter of the food
which has been digested by the animal and thrown off in the liquid
excrements, is in such a form that it will readily ferment and produce
ammonia, while the nitrogenous matter in the undigested food and in the
straw used for bedding, decomposes slowly even under the most favorable
conditions; and if buried while fresh in a clay soil, it probably would
not all decompose in many years. But we will not discuss this at
present.

"The superphosphate does not seem to have done much good," said the
Deacon; "3-1/2 cwt. per acre gives an increase of less than two bushels
per acre. And I suppose it was _good_ superphosphate."

There need be no doubt on that point. Better superphosphate of lime
cannot be made. But you must recollect that this is pure superphosphate
made from burnt bones. It contains no ammonia or organic matter.
Commercial superphosphates contain more or less ammonia, and had they
been used in these experiments, they would have shown a better result
than the pure article. They would have done good in proportion to the
available nitrogen they contained. If these experiments prove anything,
they clearly indicate that superphosphate alone is a very poor manure
for either wheat or barley.

The _second_ year, the unmanured plot gave 25-3/4 bushels per acre.
Potash, soda, and magnesia, (or what the Deacon calls "ashes,") 27-5/8
bushels; superphosphate 33-1/2, and "ashes" and superphosphate, nearly
36 bushels per acre.

50 lbs. of ammonia, alone, gives nearly 39 b