Journal of Agricultural Research 



Vol. VI. No. 1 



EXPERIMENTAL METHODS 



Commercial carbon bisulphid was poured into small holes in the soil, 

 and these were covered immediately. The soil Vv'as sieved and potted in 

 2-gallon jars and the moisture maintained at half saturation. Changes in 

 the soil flora were determined at regular intervals by plate counts of the 

 number of bacteria and dilution counts of the number of active protozoa. 

 The formation.of ammonia and nitrates was measured at regular intervals. 



The following plants were used: Buckwheat {Fagopyrum fagopyrum), 

 clover (Trifolium pratense), corn (Zeamays), mustard (Sinapis alba), oats 

 (Avena sativa), and rape {Brassica napus). In many of the experiments 

 a first and a second crop were grown. 



EFFECT OF CARBON BISULPHID ON THE NUMBER AND ACTIVITY OF 



SOIL ORGANISMS 



Eight jars were filled with Miami silt-loam soil from the Experiment 

 Station farm. These were arranged in duplicate and treated as follows: 

 (i) Control, untreated; (2) 2 per cent of carbon bisulphid; (3) 2 per cent 

 of carbon bisulphid, evaporated; (4) 2 per cent of carbon bisulphid, 

 evaporated, and reinoculated with 5 per cent of the original soil. 



Twenty-four hours after treatment the soil in the evaporated series 

 was spread out on sterile paper and the volatile antiseptic allowed to 

 escape. At the end of the second 24-hour period the soil was put back 

 into the jars. In order to prevent any contamination, the jars were 

 covered with a double layer of cheesecloth and nonabsorbent cotton. 

 This cover should allow free access of air without much danger of con- 

 tamination. At regular intervals the covers were removed and samples 

 drawn for analysis. The results of these determinations are presented 

 in Tables I and II. 



NUMBER OF ORGANISMS 



Bacteria. — In Table I are shown the number of bacteria in i gm. of 

 soil at different times and under the different conditions. 



TabIvE I. — Effect of carbon bisulphid on number of bacteria 



Time. 



Bacteria per gram of dry soil. 



Control. 



2 per cent of 

 carbon bisul- 

 phid. 



2 per cent of 

 carbon bisul- 

 phid evapo- 

 rated. 



2 per cent of 

 carbon bisul- 

 phid evapo- 

 rated + 5 per 



cent of soil 

 from control. 



Days 

 I 



3 



5 



9 



13 



21 



25 



29 



60 



II, 496, 000 

 22, 010, 000 

 20, 635, 000 

 14, 739. 000 

 16, 115, 000 

 19, 508, 000 

 18, 272, 000 

 15.346,000 

 12, 372, 000 



I, 965, 000 



23.975.000 

 25.253,000 

 36, 651, 000 

 90. 473. 000 

 60, 149, 000 

 68, 276, 000 

 90, 645, 000 

 58, loi, 000 



2, 260, 000 

 8, 254, 000 

 27, 416, 000 

 61, 904, 000 

 98, 850, 000 

 71, 257, 000 

 86, 483, 000 

 84, 272, 000 

 60, 000, 000 



2,358,000 

 12, 480, 000 

 95. 499. 000 



80, 420, 000 

 52, 495, 000 

 64, 570, 000 

 38, 495, 000 

 30, 000, 000 



