2 7 6 



SOIL CONDITIONS AND PLANT GRO WTH 



As in the laboratory experiments (p. 272) the bacterial 

 numbers show no relation to the temperature and moisture 

 content of the soil. Numerous counts were made by Hiltner 

 and Stormer (135^) from plots of cropped ground, and of un- 

 manured and dunged fallows. Some of these are recorded in 

 Table LXXIII. 



TABLE LXXIII. BACTERIA IN CROPPED AND FALLOW SOILS, MILLIONS PER 

 GRAM. HILTNER AND STORMER (135^). 



The only marked effect is that of the dung ; the net result 

 of the clover and grass has only been small in spite of the 

 organic residues shed by the roots. On no plot has the 

 warm summer weather increased the bacterial numbers. 



Later on Engberding (94) made a more extensive series of 

 counts of the bacteria in plots of ground under known treat- 

 ment and published his results in very complete form, giving 

 details of temperature, moisture content, etc. Here again no 

 connection could be traced between temperature or moisture 

 content and bacterial numbers. A very similar result was 

 obtained by W. E. King and Doryland (148). Neither tem- 

 perature nor moisture changes explained the observed fluc- 

 tuations in bacterial numbers. 2 



Some of Waksman's results (292*2) with a garden soil at 

 New Jersey are given in Table LXXIV. 



Russell and Appleyard (241^) have studied the problem 

 in some detail at Rothamsted, and have determined the 

 bacterial numbers, and the nitrate in the soil, and the amount 



1 Dung applied in July at the rate of 130 to 140 Centner pro Morgen (10 to 

 ii tons per acre). 



2 In these experiments, however, one cubic millimetre only of the soil sus- 

 pension was used for the plate cultures. 



