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CHAPTER 12
        ECONOMIC IMPORTANCE OF LEGUMINOUS CROPS
   "They not only work for nothing and board themselves, but they pay
for the privilege."
                                                                   -DAVENPORT
    The very fact that leguminous crops have found a place in every known
system of farming is indisputable proof of their importance in the agricultural
economy of the world. It may be said with reason that the extent to which
the
Leguminosae are cultivated is the determining factor in the development and
main-
tenance of a high level of agriculture. If the Leguminosae are raised in
abun-
dance, there is seldom need for artificial building up of soil productivity.
Naturally
if the soil is deficient in calcium, phosphorus, potassium, or other inorganic
con-
stituent, the use of leguminous crops will not supply the lack. How important
the
Leguminosae have been in building up the natural fertility of virgin soils
is an
intriguing question for speculation, but one not easy to answer. Certainly
within
historic times the Leguminosae have constituted a considerable factor in
the
economics of food production and in the complex systems of handling cultivated
soils. Who knows to what extent they have influenced the trend of civilization
itself ?
     Generally speaking, the farmer grows two types of crops, gramineous
and
 leguminous. No better expression of the primary difference between them
can
 be given than that of Schultz-Lupitz, 1881. He designated all cultivated
plants as
 the leguminous or nitrogen accumulators, and the non-leguminous or nitrogen
 consumers. The continued growth of the latter will, of course, deplete the
nitro-
 gen supply of the soil, unless compensated by fertilizers. The Leguminosae,
on the
 contrary, will continue indefinitely to produce large crops and at the same
time to
 maintain or increase the nitrogen supply of the soil. It is now well known
that
 this peculiar quality of the Leguminosae is not a function of the plants
alone, but
 a result of their association with the bacteria of their root nodules. This
will
 be apparent in the following discussion of the plants with and without bacteria.
 The extensive literature on this phase of the subject includes both field
and green-
 house studies with nearly all of the principal leguminous crops.
      Comparison of plants with and without nodule bacteria. The early papers
  of Boussingault, 1838; Lawes, Gilbert, and Pugh, 1861; Schultz-Lupitz,
1881;
  Atwater, 1884 and 1885; and others reported the bare fact that by some
means
  leguminous plants acquire more nitrogen than can be accounted for by straight
  absorption from the substrate. The following year Hellriegel, 1886, achieved
  fame by announcing conclusive proof that the apparent nitrogen-fixation
in the
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