524 
Report of Experiments- witJf different Manures 
stable or farmyard-manure. Taking into account the other con- 
stituents at the same time thus supplied, silica and potass are 
more advantageously and economicallv provided in this form 
than in any other ; and, as the results with the farmvard-manure 
show, the increase which a given quantity annuallv vields, 
removes but a small amomit of mineral constituents compared 
with that which it supplies, so that the effects extend over several 
years, causing, unless specially nitrogenous manures be also 
applied, an accumulation within, rarther than an exhaustion of 
the soil. When farmyard-manure is so emploved, a further 
increase of crop may, without detriment to the land, be annuallv 
obtained by the moderate application of the current artificial 
manures containing nitrogen and phosphoric acid ; but to this 
point we shall recur presently. 
Produce of Nitrogen per Acre. 
Table Vm. (p. 537) shows the acreage amounts of nitrogen 
taken off in the crop of each plot, in each of the last four years, 
also the average annual yield, and the average annual increase of 
it, over the last four, and over the whole seven years. A compari- 
son of the two columns, giving the annual average yield, shows 
that, in the majority of cases, it was almost identical over the 
last four, and the whole seven years. The agreement was the 
less close where the large amounts of ammonia were used in 
conjunction with mineral manure, by which very large crops 
were obtained. It is, however, only in the case of Plot 13(7, 
where the very excessive amount of ammonia-salts was applied 
in the first, second, third, and seventh years, that the average 
vield of nitrogen is at all matcriallv reduced during the last four, 
as compared with the seven years (98'3 lbs. to 85'8 lbs.). But, 
as the supply of nitrogen in the manure was reduced by one- 
half in three years out of the four, this is only what might be 
expected ; and it is seen that, in the seventh year, when the larger 
amount of ammonia-salt was again employed, the yield of nitrdgen 
per acre in the crop was considerably increased. 
Taking the average over the seven years, the result is — that the 
vield of nitrogen per acre without manure was within a fraction 
of 40 lbs., or about 1^ time as much as has been annually taken 
from an acre of ubmanured land in either wheat or barley ; that 
mineral manures alone increased the yield bv nearly one-half, the 
increase being then due to the large amount per acre, and propor- 
tion in the produce, of the highly nitrogenized Leguminous 
herbage ; that ammonia-salts alone (or nitrate of soda con- 
taining about an equal amount of nitrogen) increased it more 
than mineral manures alone, though Leguminous plants were then 
almost excluded, and the produce was almost wholly Grami- 
