for Twenty Years in succession on the same Land. 309 
straw, than with the previous too heavy dressings. Tlioie was, 
moreover, not only more corn and more straw by the super- 
phosphate and the reduced amount of ammonia-salts, but also 
more where ammonia-salts = only 41 lbs. of nitrogen had been 
used from the commencement, than by the superphosphate and 
the rape-cake. 
The nitrogen of the nitrogenous organic matter of the rape- 
cake would doubtless be much less rapidly available than that 
supplied in ammonia-salts ; and analysis of the soil has shown 
that the rape-cake has left a considerable residue of nitrogen 
near the surface ; nor can there be any doubt that, since the 
excessive dressings of both ammonia-salts and rape-cake have 
been stopped, there has annually been some effect due to the 
unexhausted residue of nitrogen previously applied. 
The general result is, that about 9 cwts. of rape-cake per 
acre per annum have given a produce exceeding the average crop 
of the country, but not quite a maximum yield for the soil and 
seasons in question. The mineral constituents of the rape-cake 
doubtless serve to render effective the nitrogen associated with 
them ; though there can be little doubt that the increase yielded is 
mainly dependent on the amount of nitrogen rendered available by 
the decomposition of the nitrogenous organic matter of the rape- 
cake. But since the effect is less for a given quantity of nitrogen 
supplied, than when ammonia-salts or nitrate of soda is used, 
it is impossible to decide absolutely whether, or in what degree, 
the carbonaceous organic matter has been of service. It Avould 
yield by decomposition carbonic acid and other products. The 
increased supply of carbonic acid in the soil would, it must be 
concluded, not only serve as a source of carbon, but aid the 
solution and distribution of other plant-food, and so far further 
growth. But that any such supply is essential for the successful 
growth of either wheat or barley is clearly disproved by the fact 
that maximum crops of both have been grown for 20 years or 
more by means of mineral manures and ammonia-salts, without 
any return to the soil of carbonaceous organic matter. The 
carbonaceous organic matter of farmyard manure is obviously 
equally unessential, so far as the successful growth of the cereals 
is concerned. 
Suifimary of the Results obtained on the Growth of Barley for 
20 Years in succession on the same land, without Manure, and 
hy different descriptions of Manure. 
1. Without manure, the average annual produce of barley over 
20 years was about 21 bushels of dressed corn, and 12 cwts. of 
straw. The qualitv, indicated by the weight per bushel of grain, 
Y 2 
