MICROORGANISMS AS A FACTOR IN SOIL FERTILITY 313 



soils. It was also used by Schloesing and Muntz and their followers in 

 similar studies on nitrate' formation. A method somewhat similar in 

 principle but different in its apphcation was proposed by Remy in 

 1902. He suggested the use of special media for the quantitative 

 estimation of different physiological reactions; thus, making a i per 

 cent solution of peptone and inoculating with equivalent quantities of 

 soil, he caused the decomposition of the peptone and the formation of 

 ammonia, and secured comparisons of the ammonifying power of 

 different soils. In a similar manner he used special solutions for .com- 

 paring quantitatively the transformation accomplished by nitrifying, 

 denitrifying or nitrogen-fixing bacteria. 



Remy's method has been extensively tested by Lohnis, Ehrenberg, 

 Lipman and -others. It has been shown to possess a serious defect in 

 that it deals with conditions unhke those occurring in the soil itself. 

 For this reason more recent investigations have been carried on in 

 weighed portions of soil rather than in culture solutions inoculated with 

 10 per cent of soil as is done in Remy's method. 



Rate of Oxidation of Carbon. — ^The rate of decomposition of 

 humus or of other organic matter in the soil may be measured, as was 

 done by Wollny, by determining the amount of carbon dioxide evolved 

 in weighed quantities of material kept under definite conditions. The 

 influence of temperature, moisture, aeration, organic matter, anti- 

 septics, etc., has been determined in this manner. The same method 

 may be used in studying decay, and factors influencing decay, in soils 

 in the field. 



More recently Russell and his associates have modified the method 

 in that they have determined the rate of oxidation of carbon not by 

 measuring the carbon dioxide evolved, but by estimating the amount of 

 oxygen absorbed. In either case decay is measured from the carbon 

 standpoint. The method based on this principle should find wide 

 application in future soil fertility investigations. 



Rate of Oxidation of Nitrogen. — Another method or series of 

 methods for studying deconiposition processes in the soil may be based 

 on the determination of nitrogen compounds formed in the breaking 

 down of proteins. Two of the derivatives of protein, namely, ammonia 

 and nitrate, have been used successfully to gauge the decomposition of 

 organic matter in the soil. The recent results secured by Lipman and 

 his associates demonstrate that ammonia formation from dried blood in 



