urteenth_ season (1856-7), gives 20 bushels per acre on the
unmanured plot, and 41 bushels on the plot with barn-yard manure. Mixed
mineral manures alone on 5_a_ gives nearly 23 bushels per acre. Mixed
mineral manures and 200 lbs. ammonia-salts, on 6_a_, give 35-1/4
bushels. In other words the ammonia gives us over 12 extra bushels of
wheat, and 1,140 lbs. of straw. Mineral manures and 400 lbs.
ammonia-salts, on 7_b_, give 46-1/4 bushels per acre. Mineral manures
and 600 lbs. ammonia-salts, on 8_b_, give nearly 49 bushels per acre.
Mineral manures and 800 lbs. of ammonia-salts, on 16_b_, give 50 bushels
per acre, and 4,703 lbs. of straw.

"This exceedingly heavy manuring," said the Deacon, "does not pay. For
instance,

"200 lbs. ammonia-salts give an increase of 12-1/4 bushels per acre.
400 " " " " 23-1/4 " "
600 " " " " 26 " "
800 " " " " 27 " "

The Deacon is right, and Mr. Lawes and Dr. Gilbert call especial
attention to this point. The 200 lbs. of ammonia-salts contain about 50
lbs. of ammonia, and the 400 lbs., 100 lbs. of ammonia. And as I have
said, 100 lbs. of ammonia per acre is an unusually heavy dressing. It is
as much ammonia as is contained in 1,000 lbs. of average Peruvian guano.
We will recur to this subject.

The _fifteenth_ season (1857-8,) gives a yield of 18 bushels of wheat
per acre on the continuously unmanured plot, and nearly 39 bushels on
the plot continuously manured with 14 tons of barnyard manure. Mixed
mineral manures on 5_a_ and 5_b_, give a mean yield of less than 19
bushels per acre.

Mixed mineral manures and 100 lbs. ammonia-salts, on plots 21 and 22,
give 23-1/4 bushels per acre. In other words:

25 lbs. ammonia, gives an _increase_ of 4-1/4 bush.
(100 lbs. ammonia-salts)
50 " " , " " " " 10 "
(200 " " " )
100 " " , " " " " 20 "
(400 " " " )
150 " " , " " " " 23 "
(600 " " " )
200 " " , " " " " 23 "
(800 " " " )

"It takes," said the Deacon, "about 5 lbs. of ammonia to produce a
bushel of wheat. And according to this, 500 lbs. of Peruvian guano,
guaranteed to contain 10 per cent of ammonia, would g