on Permanent Meadow Land. 
523 
equal in nitrogen to the ammonia-salts of Plot 9 (Plot 15), the 
quantity of mineral constituents taken from the land was some- 
what less. , 
Lastly on this point : by means of an annual dressing of farm- 
yard-manure, doubtless supplying much more of every mineral 
constituent than was contained in the crop yielded, rather under 
3 cwts. of incombustible constituents were annually taken from 
the land ; and, when to the farmyard-manure ammonia-salts were 
added, the amount was raised by only 43i lbs. — that is, from 
328f to 372^ lbs., or to less than when the artificial mixtures of 
mineral manure and ammonia-salts were employed. 
The result is, then, that without manure the land yielded, 
over seven vears, about 1^ cwt. of mineral constituents per acre 
per annum, the amount increasing rather than diminishing in the 
later vears ; that farmyard-manure supplying, besides other 
matters, more of every mineral constituent than the produce 
obtained by its use, gave a crop containing about twice as much ; 
and that artificial mixtures containing both mineral constituents* 
and ammonia-salts gave a still larger yield, even when no sili- 
cates were supplied in the manure. 
It is obvious, that when purchased nitrogenous and phosphatie 
manures, such as Peruvian guano, or mixtures of ammonia-salts 
or nitrate of soda and superphosphate of lime, are alone relied 
upon for the increased crop of hay, the drain of potass and avail- 
able silica from the soil must be very great. This was illustrated 
in some detail in our former report, by reference to the analvses of 
the ashes of the hay grown by the different manures ; and con- 
firmatory evidence of the injurious effects of such exhaustion will 
be found on comparing the average annual amounts of mineral 
matter taken from each plot over the seven with that over the last 
four years. Thus, whilst without manure, with mixed mineral 
manure, and with farmvard-manure, the average amount of 
mineral constituents annually taken from the land was greater 
during the later years than during the whole period of the experi- 
ments, it was (with one exception) less in the later years wherever 
large quantities of ammonia-salts were employed. A similar 
result is not as yet observable when nitrate of soda has been 
used ; but, as already explained, it is probable that some of the 
plants then developed would draw their nutriment from a more 
extended range within the soil ; and, if so, a diminution in the 
annual yield may be only a little postponed. 
These results in regard to the mineral constituents taken from 
the land in the hay crop, clearly show how important it is that 
due restoration should be made, if the character of the herbage 
and the amount of crop are to be maintained. This is best 
accomplished in practice by an occasional dressing of well rotted 
