MICROBIOLOGICAL ANALYSIS OF SOIL 



723 



stances of the soil). After prolonged incubation, following the addition 

 of CaC0 3 , a definite favorable effect was evidenced. 



A marked correlation between crop yield, nitrate accumulation and 

 bacterial numbers, but not between crop yield and ammonia accumu- 

 lation, is shown in figure 61 where the bacterial activities of limed and 

 unlimed soils are compared. 27 The soil (1 kgm.) may be placed in a 

 pot which is then covered with a bell-jar using the suction apparatus 

 described elsewhere. 



One can differentiate between the formation of C0 2 in untreated soil 

 and the formation of C0 2 from glucose or other available organic matter 



CROP YIELDS 

 COj PRODUCTION 

 NC3 ACCUMULATION 

 BACTERIAL NUMBERS 

 NH3 ACCUMULATION 



7T3TT" TxTTZ 7TTT3 



Unlimed 

 Plots 11A and 21 



Limed 

 Plots 11B and 24 



Fig. 61. The correlation between crop yields, C02-producing power of the soil, 

 bacterial numbers, NH 3 and N0 3 accumulation in soil from limed and unlimed 

 plots (from Neller). 



added to the soil. 28 In the first instance, a definite amount of soil is 

 placed under optimum conditions of moisture and temperature and the 

 amount of CO2 formed in a definite period of time is measured. This 

 was found (Stoklasa) to depend upon (1) the number and kind of 

 microorganisms present, (2) the amount of organic matter in the soil, 

 (3) the composition of this organic matter and the degree of its decom- 



27 Neller, 1920 (p. 712). 



28 Waksman, S. A., and Starkey, R. L. Microbiological analysis of soils as 

 an index of soil fertility. VII. Carbon dioxide evolution. Soil Sci., 17: 141— 

 161. 1924. 



