86 REPORT OF THE AGRICULTURAL RESEARCH 



the 8th and 12th weeks of the process in the laboratory; a 

 considerable amount of work has been done with the object 

 of discovering whether this loss could be accounted for by- 

 correlating it with the gradual evaporation of soil water; 

 the enquiry is not yet sufficiently complete for conclusive 

 report, but it seems certain that the change noted is due to 

 variation in the water content of the soil rather than to 

 seasonal variation in the functions of the soil flora. 



Experiments were made to determine the effect upon 

 nitrification of varying the quantity of nitrogen as organic 

 matter added to the soil; it was considered probable that 

 any excess above the optimum would retard or even inhibit 

 nitrification, but that the optimum might vary considerably 

 with different soils, and also in the same soil under different 

 conditions. An unexpectedly high optimum was found for 

 mustard cake in Pusa soil, namely, one per cent, of the soil 

 weight, but it was shown that the high lime content of this 

 soil was mainly responsible for this high figure, and that 

 in soils such as the average tea soils of Assam, with less 

 than one per cent, of lime, a much smaller quantity of cake 

 would fail to nitrify at the normal rate. A study was made 

 of the progress of decomposition of cake in soils varying in 

 lime content, by periodic estimations of the loss on ignition, 

 humus, ammonia and nitrates; it was found that decom- 

 position was rapid in proportion to high lime content, 

 although in time the soil lower in lime attained the same 

 nitrate concentration. 



Isolation of nitrifying organisms from Indian soils was 

 continued with special reference to a nitrite forming 

 organism hitherto undescribed, the isolation of which by 

 Mr. Joshi, 1st Assistant, is still in hand. 



Azotobacter. — A number of soils was examined for 

 Azotobacter, which was found in those from Naupada, 

 Vizianagram, Waltair, Tuni, Samalkota, Ellore, Walajah 

 Road, Bowringpet, Jalarpet, Bangalore, Darjeeling and 

 Cawnpore. 



A series of determinations of amounts of nitrogen fixed 

 in liquid culture media inoculated with Pusa soil week by 



