Fred, Edwin Broun; Baldwin, Ira Lawrence; McCoy, Elizabeth / Root nodule bacteria and leguminous plants
Chapter 12: Economic importance of leguminous crops, pp. 210-228 ff.
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 210
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