262 



SOIL CONDITIONS AND PLANT GRO WTH 



nitrates produced after a certain time are determined. By 

 working under uniform conditions (which each investigator 

 fixes for himself) the results obtained are comparable for the 

 series of soils under investigation.^ The amount of nitrate 

 produced by unit weight of soil is called the " nitrifying 

 power ". The actual figure is obviously arbitrary, depending 

 on the conditions selected, and it has meaning only in relation 

 to the other soils in the same set of experiments. Several 

 investigators, however, have found that nitrifying power shows 

 some relation to plant growth, the soils most favourable to 

 plants having, on the whole, the highest nitrifying power. 

 This result has been obtained by Gainey in Kansas ^ ; C. B. 

 Lipman in California ^ ; G. P. Given in Pennsylvania * ; Percy 

 Brown in Iowa (60^); P. S. Burgess in Hawaii (63); at 

 Rothamsted by Ashby (jd) ; and at Fallon, Nevada, by Keller- 

 man and Allen ^ ; some of the data are given in Table LXVII. 



Table LXVII. — Nitrifying Powers of Various Soils of Known 

 Productiveness. 



Withers and Fraps (313) have modified the method, and 

 use sterilised soil as the medium for the growth of the 



^ For a statistical study of the magnitude of the error see D. D. Waynick, 

 IJniv. Calif. Pub. Ag. Set., 1918, 3, 243. 



'■^ Soil Sci., 1917, 3, 339-416. 



^Proc. Soc. Prom. Agr. Set., 1914, 33-39, and Cal. Bull., 260, 107-127. 



* Penn. Rept., 1912-13, 204-206. 



5 Bacteriologieal Studies of the Soil of the True kee-C arson Irrigation Project, 

 Karl F. Kellerman and E. R. Allen (U.S. Dept. of Agric. Bureau of Plant In- 

 dustry, Bull. No. 211, 1911). See also Ehrenberg (936). 



