Experiments on t/tc Growth of Wheat. 
41 
srcutive years. Tlie incroaso of straw by each of those manures, 
used scjiarately, was, however, greater in th(! Kent experiments 
than at Kothamsted. The edect was ahogetlier different when 
the mineral and nitrogenous manures were used ti)g(;ther ; — the 
combination yiehling an average annual increase of about 21 
bushels of corn and 22^ cwts. of straw at Kothamsted, against 
only 8 bushels of corn and 21 cwts. of straw at Rodmersham. 
Not only was the annual increase of both corn and straw the 
greater at Kothamsted, but the actual produce per acre, per 
annum, of dressed corn, was greater by about 5^ bushels ; though 
that of the straw was about 13 cwts. less. 
In both localities, then, the mixed mineral and ammoniacal 
manure greatly increased the crop, and the increase was greater 
when tire two were used together than when each was used 
separately. But at Kodmersham, where the land was in compara- 
tively high condition, the heavy manuring tended to over- 
luxuiiance, and excessive proportion of straw ; whereas, at 
Kothamsted, with an average of about half a ton less total pro- 
duce per acre per annum, there was a considerably greater actual 
amount of corn, and of course a greater proportion of corn to 
straw, and also a greater increase of both corn and straw. 
Plot 5. Guano. — The guano employed supplied a large 
quantity of phosphate of lime, small quantities of alkaline salts, 
and rather more than four-fifths as much ammonia or nitrogen 
as the quantity of ammonia-salts of experiments 3 and 4. It 
yielded an average annual increase of about 1^ bushel of dressed 
corn, and 4|- cwts. of straw more than the ammonia-salts alone ; 
and only about ^ bushel of dressed corn and 3J cwts. of straw 
less than the mixed mineral manure and ammonia-salts together. 
It will presently be seen that the guano gave far more increase, 
in proportion to its cost, than any of the other manures. 
Plot 6. Mape-cake. — The amount of rape-cake employed would 
contain rather more nitrogen than the ammonia-salts of experi- 
ments 3 and 4, but in a condition in which it would be more 
slowly rendered available for the plant ; it would contain a con- 
siderable quantity of mineral constituents ; also a lai-ge amount of 
carbonaceous matter, yielding carbonic acid in the soil. It gave 
only the same average annual increase of corn (about 8 bushels), 
and 6f cwts. less straw than the mixed mineral manure and 
ammonia-salts (plot 4), which contained a less total amount of 
nitrogen, and no carbonaceous matter whatever. This is per- 
fectly consistent with results obtained at Kothamsted, which show 
the non-utility of supplying carbonaceous manure for wheat and 
other grain-crops. 
Plot 7. Farimjard Manure. — The quantity employed would 
contain more of every constituent, mineral and organic, than the 
