176 



SOIL CONDITIONS AND PLANT GRO WTH 



traces of antiseptics. It shows a general increase up to a 

 certain point with the amounts of moisture, organic matter 

 and calcium carbonate present, although no sharp proportion- 

 ality exists. It is related to productiveness ; in a series of 

 similar soils under similar climatic and other external cir- 

 cumstances the respective rates of oxidation were found to 

 vary in the same way as the values for productiveness (Table 

 XLVIL). 



Table XLVII. — Rates of Oxidation, Order of Productiveness, and 

 Analytical Data for Certain Woburn Soils. Russell (241a). 



The reasons for the connection between oxidation and 

 fertility will become more evident as we proceed. In so far 

 as oxidation is due to micro-organisms, its velocity obviously 

 affords a measure of their activity ; Wollny and later van 

 Suchtelen ^ used the CO2 evolution for the same purpose. 

 But there is a more fundamental relationship. Oxidation 

 affords, so far as is known, the chief source of energy for the 

 numerous micro-organisms of the soil. Gillespie ^ has sug- 



1 Van Suchtelen, Cent. Bakt. Par., 1910, 28, 45- 

 y. Am. Soc. Agron., 1918, 10, 281. 

 "^Soil Set., 1920, 9, 199. 



See also F. G. Merkle, 



