CHAPTER XXII 

 SYMBIOTIC FIXATION OF NITROGEN 



Jethro Tull, who wrote a treatise on agriculture 

 in the first half of the eighteenth century, makes some 

 interesting statements concerning sainfoin and lucerne 

 (alfalfa). Himself a good farmer and a careful observer, 

 he added to his knowledge by travels in France and 

 Italy, as well as by the study of ancient writers on the 

 art of agriculture. 



The soil-enriching qualities of legumes had been com- 

 mented on by the Roman writers and Tull could con- 

 firm their observations from his own experience. He 

 contributes excellent testimony as to the efficiency of 

 • legumes in the restoration of depleted soils. The farmers 

 of Europe found in these crops, and particularly in 

 clover, a means for increasing the waning harvests. 

 Previous to its introduction the lands were in a poor 

 condition. 



John Christian Schubert, who introduced clover 

 into Austria, was knighted by Emperor Joseph II for 

 his services to agriculture. Clover rapidly replaced the 

 bare fallow in accordance with the admonition of Schu- 

 bert. 



The limitations of legumes.— The farmers of Europe 

 soon learned, however, that clover was liable to fail 



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