Rotation of Crops. 
645 
Very much the same may be said of maize as grown as a 
fodder-crop in America, as of roots as grown in rotation in other 
countries. Thus, there can be no doubt that the maize derives 
its nitrogen from the soil, collecting some time longer than 
wheat, and availing itself of the nitrates formed after the col- 
lection by the wheat has ceased. But, so far as the product is 
consumed on the farm, much of its nitrogen is recovered in the 
manure — the more when the food is used for growing or fatten- 
ing stock, and the less when for the production of milk. 
The still more highly nitrogenous leguminous crops, on the 
other hand, although not characteristically benefited by nitro- 
genous manures, nevertheless contribute much more nitrogen to 
the total produce of the rotation than any of the other crops 
comprised in it. It is also certain that, at any rate a large 
proportion of the nitrogen of these crops is obtained from the 
soil and subsoil ; though recent investigations have proved that 
some of their nitrogen, and sometimes much of it, may be 
derived indirectly from the free nitrogen of the atmosphere, 
brought into combination under the influence of micro- 
organisms within the nodules on the roots of the plants. 
It is the leguminous fodder crops, and among them 
especially clover, which has a much more extended period ol 
growth, and much more extended range of collection within the 
soil and subsoil, than any of the other crops of the rotation, that 
yield in their produce the largest amount of nitrogen per acre. 
Much of this is doubtless taken up as nitrate ; yet, the direct 
application of nitrate of soda has comparatively little beneficial 
influence on their growth. The nitric acid is probably taken 
up chiefly as nitrate of lime, but probably as nitrate of potash 
also, and it is not without significance that the high nitrogen- 
yielding clover takes up, or at least retains, very little soda. 
The general result is, then, that although undoubtedly the 
clover takes up a good deal of its nitrogen as nitrate, this would 
seem to be derived from accumulations within the soil, which 
are brought into suitable conditions of combination, and 
distributed through a wide range of soil and subsoil. 
So much then for the benefits of rotation, so far as the 
requirements, the habits of growth, and the capabilities of 
gathering and assimilating the various mineral constituents, and 
the nitrogen, of the different crops, are concerned. It cannot be 
doubted that the difference in the amounts, in the conditions of 
combination, and in the distribution within the soil, of the 
various mineral constituents, is at least an element in the 
explanation of the benefits of alternation ; nor, on the other 
