In general agriculture in Illinois, whether it be grain farming or
ordinary livestock farming, the growing of legumes is absolutely
essential as a part of any economic system which shall maintain the
fertility of the soil; and for the successful growing of legumes the
presence and assistance of the proper species of nitrogen-gathering
bacteria are also absolutely essential. These facts being granted, it
certainly follows that when sowing any legume on land, where the same
legume has never been grown before, or perhaps where it has not been
successfully grown within recent years, we should always consider the
matter of inoculation; and, unless there is good reason to believe that
the soil has been inoculated by the washing from other higher lying
land where these bacteria are known to be present or by applications of
manure made from that legume, or by some other such incidental means; or
unless there is evidence that the bacteria are carried with the seed in
sufficient quantity to effect a satisfactory inoculation (as appears to
be the case with the cowpea), then we should inoculate the soil directly
with the specific bacteria required by the legume which we desire to grow.
While some Illinois soils are becoming deficient in phosphorus and
in lime, especially in the southern part of the state, and while
phosphorus[8] and ground limestone can be applied to such soils with
marked benefit and profit, especially for the growing of legumes, there
is abundant evidence that one of the dominant causes for the failure
or unsatisfactory growth of some of our most valuable legumes, and on
some soils the sole cause of failure, is the absence of the proper
nitrogen-gathering bacteria.
There is no reason to believe that any of the different species of
nitrogen-gathering bacteria will live in the soil for more than a few
years[9] in the entire absence of any legume upon which they naturally
live, and the accumulating evidence strongly indicates that the bacteria
which are present in places in our soils, such as the red clover
bacteria, now found abundantly in many places in the state, especially
in northern and central Illinois, the cowpea bacteria more common in
southern Illinois, and the alfalfa or sweet clover bacteria, which are
becoming prevalent in some sections—that all these have been, and are
being, gradually introduced and extended almost entirely by mere chance.
Of course if the wagon-wheel, which carries the mud along the road,
carries with it sweet clover seed from one place to another, it may also
carry the sweet clover bacteria which live on the sweet clover roots.
It now seems absurd to suppose that there were red clover bacteria in
Illinois soil before red clover itself was grown on Illinois soil, unless
the same bacteria live also upon some other legume which was native to
our soils. There is some evidence that the vetch bacteria are native to
our soil, possibly living upon the native wild vetches. At any rate,
tubercles commonly develop on vetch roots without artificial inoculation.
Investigations are in progress to ascertain whether the notorious failure
of crimson clover in Illinois may not be due in part, at least, to the
absence of the proper bacteria. (It has been stated by some writers that
the bacteria of crimson clover and those of red clover are identical, but
we already have some reason to doubt the accuracy of this statement.)