ASSIMILATION OF NITROGEN 73 



Recent technical advance has made it possible to obtain larger amounts of 

 nitrogen compounds from atmospheric nitrogen. By oxidation of the latter, 

 with the electric current, nitric acid is obtained on a large scale. By passing 

 nitrogen through glowing calcium carbide, calcium cyanamide is formed, accord- 

 ing to the equation: CaC 2 + 2N = CaCN 2 + C. The German commercial 

 name of this product in the raw state is " Kalks ticks toff "* and it is used as a 

 nitrogen fertilizer. 



What has been attained by man only after much travail is commonly ac- 

 complished by plants, however, for we now know a number of plants that can 

 assimilate atmospheric nitrogen. 



§5. Fixation of Atmospheric Nitrogen by the Leguminosae. — All legumes are 

 able to develop normally, producing a rich harvest with a high nitrogen content, 

 without the addition of any nitrogenous compounds to the soil, as the exact 

 studies of Lawes and Gilbert* have shown. If we cultivate some sort of grain 

 or legume for many years in succession on the same field without applying fer- 

 tilizer, the nitrogen content of the crop finally reaches a certain minimum, 

 beyond which it does not alter. Addition of mineral fertilizers without nitrogen 

 is almost without effect upon the yield of grain, the nitrogen content remaining 

 almost the same as before. This is entirely different in the case of the legumes; 

 the same mineral fertilizer without nitrogen produces a marked increase in the 

 nitrogen content of this crop. 



Two series of experiments by P. Wagner 2 are illustrated in Figs. 44 and 45, 

 one with peas and the other with oats, the experimental conditions being the 

 same in both cases. The containers marked O contained no fertilizer at all, 

 those marked KP contained potassium and phosphoric acid (P0 4 ), and those 

 marked KPN contained potassium, phosphoric acid and nitrogen as nitrate. 

 Comparison of these figures reveals a distinct difference between the legumes and 

 the grains in their relation to fertilizers. The growth of oat plants is seen to 

 be very slight in the unfertilized culture, and the addition of potassium and 

 phosphoric acid produces no improvement; while the addition of these together 

 with potassium nitrate produces excellent growth (Fig. 44). The behavior of 

 the pea plants is entirely different. These do not need nitrate fertilizer, addition 



1 Frank, A., Die Nutzbarmachung des freien Stickstoffs der Luft fur Landwirtschaft und Industrie. 

 Zeitsch. angew. Chem. 16: 536-539. 1903. Gerlach, M., Die Nutzbarmachung des atmospharischen 

 Stickstoffes. Illustr. landw. Zeitg. 1904. Nos. 5 and 7.* Review by Vogel in: Centralbl. Bakt. //, 12 : 

 495-497. 1904. [See also review in: Exp. sta. rec. 15 : 25. 1903-04.] 



2 Wagner, P., Ergebnisse von Diinungungsversuchen in Lichtdruckbildern mit erlauterndem Vortrage 

 iiber die rationelle Dungung der land wirtschaftlichen Kulturpflanzen. 2te Aufl. Darmstadt, 1891. 



i Lawes, J. B., and Gilbert, J. H., The sources of the nitrogen of our leguminous crops. 

 Jour. Roy. Agric. Soc. England 77/, 2: 657-702. London, 1891. Idem, The Rothamsted 

 memoirs on agricultural chemistry and physiology, 7 v. London, 1886-1899. Idem, same 

 title. 3 v. London, 1890-1893. Hall, A. D., The book of the Rothamsted experiments. 294 p. 

 New York, 1905. For a brief discussion of this whole matter see: Russell, E. J., Soil condi- 

 tions and plant growth. 4th ed. London and New York 406 p., 1921. Russell's excellent 

 bibliography includes references to a number of the papers of Lawes and Gilbert. These 

 papers have all been collected and published in the Rothamsted Memoirs, and Lawes and 

 Gilbert's results are summarized by Hall. — Ed. 



