Rotation of Crops. 
639 
acid, which will be converted into carbonic acid in the incinera- 
tion, and be found as such in the ash, if not expelled by an 
excess of fixed acid, or by silica. 
In the case of the cereals of the rotation, it is probable that 
most if not all of their comparatively small amount of nitrogen 
is taken up as nitrate. Potash is by far the predominating base 
in the ash of the grain, straw, and total produce; lime is in 
much less amount, both actually and in equivalency ; and 
magnesia is in less amount still, though it is a characteristic 
constituent of the grain-ashes. There is practically no carbonic 
acid in either wheat or barley grain-ash, and but little in the 
straw-ash ; and if there have been organic acid salts formed with 
the base of the nitrate, the carbonic acid may have been expelled 
in the incineration, by the excess of fixed acid in the grain- 
ash, or by silica in the straw-ash. 
Taking the produce by the mixed manure as the most 
normal, the root-crops of the rotation come next in amount ot 
nitrogen assimilated over a given area. Potash and lime are 
the predominating bases. There is much more potash than 
lime in the more definite product — the root ; but the proportion 
of lime to potash is much greater in the leaf-ash, as would be 
expected if the nitrogen had been taken up chiefly as calcium 
nitrate, and the nitric acid subjected to decomposition in the 
leaves. 
Lastly come the Leguminosas, with their much higher 
amounts of nitrogen assimilated. These plants also doubtless 
derive at any rate much nitrogen from nitrates in the soil and 
subsoil ; and it has been shown that their great assimilation of 
nitrogen is associated with very large amounts of lime and 
carbonic acid in their ashes. 
Referring to the results with the rotation beans grown by 
the mixed manure, calculation shows that, taking the total 
crop, corn and sti'aw together, it contained very much less lime 
than would be required if the whole of its nitrogen had been 
taken up as calcium nitrate ; so that, either part of the nitrogen 
must have been taken up as nitrate of some other base, or in 
some quite different state of combination, or as free nitrogen ; or 
some of the lime must have been eliminated from the above- 
ground parts of the plant into the roots, and possibly some of it 
passed from them into the soil. Again, the amount of carbonic 
acid found in the ashes of the crop for 100 of nitrogen in it, 
would require about one-and-a-half time as much lime as was 
found in association with it ; indicating the probability that part 
of the nitrogen taken up as nitric acid was as the nitrate of some 
other base — potash, and possibly to some extent soda also. 
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