74 REPORT OF THE AGRICULTURAL RESEARCH 



special attention must be paid to the variations in soil 

 climate previous to the time of sampling, as otherwise 

 erroneous conclusions may be drav^n as to the number of 

 bacteria normally present. For instance, a rainfall of one- 

 tenth of an inch in December has been found to raise the 

 number of bacteria to 100 millions per gram in the course of 

 36 hours, whereas the same soil contained only 5 millions 

 per gram two weeks later. Similarly the rate of decom- 

 position and nitrification of organic matter in Indian soils 

 appears to be very different from that which has been ob- 

 served in Europe, and is no doubt to be correlated with the 

 special conditions of soil and climate of this country. 

 These cases have been referred to as illustrations of the 

 necessity for proceeding with great caution in working out 

 special problems by the application of generally accepted 

 methods. 



A complete series of experiments has been carried out 

 to determine the best means of sterilizing soils, as the 

 majority of experiments on soil bacteriology depend upon 

 work with sterile soil as a medium. Great difficulty has 

 been experienced in obtaining completely sterile soil; inter- 

 mittent steaming in many cases has failed to ensure steri- 

 lity, possibly owing to the rapid formation and germin- 

 ation of spores by some of the numerous spore formers pre- 

 sent, and the use of the autoclave for pots of soil, of which 

 only one can be inserted at a time, makes an experiment 

 involving the use of some 50 pots almost impracticable, 

 owing to the differences in time involved. A sterilizing 

 plant for dealing with a large number of pots simultane- 

 ously is very much needed. 



Samples of Pusa soils have been analysed bacteriologi- 

 caily, pure cultures of the bacteria found have been made, 

 and their physiological functions examined. Special at- 

 tention has been paid to their relative ammonifying power, 

 and the knowledge thus obtained is now being utilized in 

 dealing with special problems. 



A special study has been made of the effect of hot 

 weather ploughing upon the bacterial content of the soil and 



