. You will
recollect that in 1846, one of the plots of wheat (10_b_), which had
received a liberal dressing of salts of ammonia the year previous, was
left without manure, and the yield of wheat on this plot was no greater
than on the plot which was continuously unmanured. In other words, _the
ammonia which was left in the soil from the previous year, had no effect
on the wheat_.

The following table shows the amount of nitrogen furnished by the
manure, and the amount recovered in the crop, when wheat is grown after
wheat for a series of years, and also when barley is grown after barley,
and oats after oats.

Table Showing the Amount of Nitrogen Recovered, and Not Recovered, in
Increase of Produce, for 100 Supplied in Manure.

----+-----------------------------------------+---------------------
| | For 100 Nitrogen
P | | in Manure
l | Manures Per Acre, Per Annum. +----------+----------
o | |Recovered |Not Rec'd
t | | in | in
s | |Increase. |Increase.
----+-----------------------------------------+----------+----------
Wheat--20 Years, 1852-1871.
----+-----------------------------------------+----------+----------
6 |Mixed Mineral Manure and 200 lbs. | |
| Ammonia-salts (= 41 lbs. Nitrogen) | 32.4 | 67.6
7 |Mixed Mineral Manure and 400 lbs. | |
| Ammonia-salts (= 82 lbs. Nitrogen) | 32.9 | 67.1
8 |Mixed Mineral Manure and 600 lbs. | |
| Ammonia-salts (= 123 lbs. Nitrogen) | 31.5 | 68.5
16 |Mixed Mineral Manure and 800 lbs.[1] | |
| Ammonia-salts (= 164 lbs. Nitrogen) | 28.5 | 71.5
9A |Mixed Mineral Manure and 550 lbs.[2] | |
| Nitrate Soda (= 82 lbs. Nitrogen) | 45.3 | 54.7
2 |14 tons Farmyard-Manure every year. | 14.6 | 85.4
----+-----------------------------------------+----------+----------
Barley--20 Years, 1852-1871.
----+-----------------------------------------+----------+----------
4A |Mixed Mineral Manure and 200 lbs. | |
| Ammonia-salts (= 41 lbs. Nitrogen) | 48.1 | 51.9
|