IX, A, 1 Cox and Argilelles: Soils of Luzon 9 



About thirty years ago, Berthelot observed that nitrogen 

 fixation takes place in bare and uncultivated soils and attributed 

 such gain to the activity of certain forms of microorganism,^' 

 and Garlach and Vogel, Koch, Vorhees and Lipman, and other 

 investigators have conclusively shown that members of the 

 azotobacter group of aerobic bacilli can fix nitrogen. However, 

 further investigation would be necessary before the certainty 

 of the value ^° to practical agriculture of nonsymbiotic bacteria 

 can be definitely established. 



The fixation of nitrogen by bacteria within root tubercles is 

 of comparatively recent development. Hellriegel" first dis- 

 covered that legume tubercles are due to bacterial activity and 

 that the root tubercles contain the atmospheric nitrogen stored 

 up by bacteria. Where tubercles develop in the legumes and 

 soil conditions are satisfactory to bacterial growth, experiments 

 have shown the fixation of as much as 200 pounds of nitrogen 

 per acre in the case of crimson clover. This is amply con- 

 firmed by similar experiments in the different experimental 

 stations where proper soil conditions have been established. 



Some soils do not contain the necessary bacteria for desirable 

 legumes to be grown, and therefore the help of bacteria cannot 

 be utilized to increase the supply of nitrogen. This can be 

 remedied when proper soil conditions are attained by inocu- 

 lating the seed with the desired bacteria. 



For each class of bacteria there are optimum conditions of 

 temperature, moisture, aeration, alkalinity, etc. for the greatest 

 activity.^^ In neutral or acid soils the activity of nitrification 

 bacteria is stopped. A sufficient quantity or an excess of a 

 base must be present to unite with the acids formed by the 

 oxidation of ammonia. The most favorable substances for this 

 purpose are limestone and dolomite, an excess of which does 

 no harm. These principal conditions inducing bacterial activity 

 have had practical application in modem agriculture and have 

 given beneficial returns by increased production of crops. One 

 of the most striking is the common practice of inoculating the 



"76tU, 81. 



"° Hopkins, Soil fertility and Permanent Agriculture. Ginn & Co., N. Y. 

 (1910), 225. 



"Tagebl. 59. Versamml. deut. Naturf. u. Aerzte. Berlin (1886), No. 7, 

 290; Bull. U. S. Dept. Agr., Off. Exp. Sta. (1907), 194, 89. 



"R. Warington [Trans. Chem. Soc. (1878), 44; (1879), 429; (1884), 

 637; (1891), 484] has investigated the conditions affecting the activity of 

 some of the organized ferments. 



