EFFECT OF PROPERTIES OF SOIL 131 



6. It has been repeatedly demonstrated by many workers that 

 both heat and antiseptics destroy all or part of the protozoa found 

 in the soil, depending on the degree of heat applied or the strength 

 of antiseptic used. 



7. Some workers have found antiseptics and heat to depress 

 denitrifi cation in soil. Both Wagner and Morgan found that carbon 

 bisulphid kills denitrifying organisms. 



8. Especially significant is the fact that there is a considerable 

 increase in the soluble matter in the heated soil, not only of inorganic 

 matter, as phosphorus and potash, but even more in the organic 

 matter made soluble. Stoklasa holds that the plants are able to get 

 more phosphate-ions from a soil as a result of the disintegration of 

 the bacteria killed by the treatment with carbon bisulphid. 



Fred found that the application of carbon bisulphid to a soil 

 increases the insoluble compounds of nitrogen and sulphur as well as 

 the bacterial activities. Lyon and Bizzell determined the effect of 

 sterilizing soils by steam on the water-soluble material and found 

 that steaming the soil at two atmospheres reduced the nitrates to 

 nitrites and ammonia, but that most of the ammonia is formed from 

 organic nitrogen in the soil . 



9. Although the majority of workers report an increase in nitrogen 

 fixed in a soil treated with carbon bisulphid, yet Koch reports cases 

 in which carbon bisulphid added to a soil containing fairly large 

 quantities of cane sugar has resulted in a weakening rather than in 

 a strengthening of their nitrogen-fixing powers. The increase in 

 nitrogen fixation may at times be very pronounced, as may be 

 seen from the following experiments in which tumblers containing 

 soil were all carefully sterilized and half of them placed in the 

 incubator in the sterile condition. To the others was added a soil 

 extract prepared by shaking one part of soil with two parts of sterile 

 distilled water for three minutes. After standing for about five 

 minutes the liquid was decanted and 10 c.c. portions were used to 

 inoculate the soil. Before inoculating, this extract was placed in 

 thin- walled test-tubes in 10 c.c. portions and then kept at the 

 required temperature for exactly fifteen minutes before adding to 

 the soil. The moisture content was made up to 18 per cent, and 

 the whole incubated for twenty days. The milligrams of nitrogen 

 fixed under the varying treatments were as follows: 



Milligrams 

 Temperature of soil extract ( C.). nitrogen-fixed. 



Room 5.11 



50 . 9.00 



55 .. 14.14 



60 . . 16.38 



65 ... 14.42 



70 . . 13.02 



75 ... 11.34 



80 ... 12.66 



85 10-36 



