40 
Experiments on the Growth of Wheat. 
(Kent). But as a standard by which to compare the effects of 
the different manures during the four years of their application 
in the Kent experiments, it will be necessary to take the average 
of the first four years without manure, which was 25i bushels of 
dressed corn and about 30 cwts. of straw ; against which there j 
were at Rothamsted (Herts), over the same seasons, only 17|- I 
bushels of dressed corn and about 15^ cwts. of straw, or not 
much more than two-thirds as much corn and half as much ' 
straw as at Rodmersham. 
Plot 2. Mixed Minei-al Manure. — This manure supplied 
potass, soda, lime, magnesia, phosphoric acid, and sulphuric 
acid ; in fact, an abundance of nearly all the mineral constituents ' 
required by the crop, excepting silica. The average annual | 
increase it yielded, over the four years of its application, was 1 
about 3 bushels of dressed corn and 5J cwts. of straw. This was j 
almost precisely the same amount of increase of corn as was ' 
yielded by the same manures over the same seasons here at ; 
Rothamsted, but nearly 4 cwts. more straw. : 
Plot 3. Ammonia- Salts alone. — The quantity employed con- < 
tained much more nitrogen than could be taken up by the increase | 
of produce, and quite as much as can be employed for the average | 
of soils and seasons without getting an over-luxuriant and laid 
crop. The average annual increase yielded over the four years ! 
of the application was about 6 bushels of dressed corn and nearly ' 
13 cwts. of straw. This, again, was almost exactly the same ! 
increase of corn, but nearly twice as much increase of straw, as 
Avas obtained by the same manure, in the same seasons at Rotham- 
sted, after their application there for a dozen years consecutively. 
/ Both at Rodmersham and at Rothamsted, then, ammonia-salts I 
alone increased the wheat-crop, for a series of successive years, \ 
considerably more than did mineral manure alone. I 
Plot 4. Mixed Mineral Manure and Ammonia-Salts. — This [ 
manure supplied the same mineral constituents as in experiment 2, ( 
and the same amount of ammonia, or nitrogen, as in experiment | 
3 ; but it contained no carbon, of which about 40 per cent, of the 
dry substance of the crop consists. The average annual increase 
it yielded over the four years was about 8 bushels of dressed corn i 
and 21 cwts. of straw ; or about 5 bushels more corn and 15|- cwts. ' 
more straw than by the mineral manure alone, and about 2 bushels 
more corn and 8 cwts. more straw than by the ammonia-salts 
alone. J 
It has been seen that both mineral manures alone, and ammo- j 
nia-salts alone, yielded almost identically the same amounts of j 
increase of corn over the first four years of the experiments at Rod- j 
mersham (Kent) as they did over the I'same years at Rothamsted 
(Herts), where wheat had been grown for a dozen previous con- i 
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