ABSTRACTS 561 



Studies on Soil Protozoa. Selman A. Waksman. (Soil Science, 1916, 



1, 135-153.) 



The author found that no flagellates could be found in a living condi- 

 tion before sixteen minutes and no ciliates until after sixty-two minutes 

 in a soil which was covered with water during these periods. The 

 longer time allows a closer observation among the soil particles and a 

 more thorough examination of the field. There is no doubt that there 

 is a minimum moisture content for each soil below which protozoa can- 

 not be found in a living condition. 



Four soils were selected which varied in humus content and were 

 under crops or orchard. Examinations were made every day for ten 

 days in succession during which period several rains occurred. The 

 moisture content proved to be a limiting factor but not the only one as 

 the structure and humus content of the soil hkewise play an important 

 part. The protozoa found were all flagellates. 



Another experiment with three different soils under different mois- 

 ture conditions, part sterilized and part unsterilized, the latter plus dried 

 blood, to each of which cultures of protozoa were added, brings out the 

 fact that the sterilization of soil and addition of easily soluble organic 

 matter will make the conditions optimum for protozoan activities at a 

 lower moisture content than in corresponding unsterilized or untreated 

 soils. 



Protozoa (flagellates) found in the first inch of three cultivated soils 

 varied in numbers from 1000 to 10,000 per gram of soil; at four inches, 

 from 100 to 5000; at eight inches from 100 to 5000; at twelve inches 

 from 10 to 100. None were found at a depth of twenty or thirty inches. 

 The fourth soil, an acid forest soil, contained from 10 to 100 flagellates 

 at a depth of one inch and at four inches; at eight inches only 1 to 10 

 were found and below that none. Ciliates and amoebae were not re- 

 corded as they occurred only occasionally. 



Flagellates are present in greatest numbers at a depth of 1 inch where 

 conditions favor microorganic activities, ciliates and large flagellates in 

 largest numbers at a depth of 4 inches where the moisture conditions 

 may be more favorable for their development. A hst of the common 

 types is given. 



The flagellates are at once the most common and the largest group of 

 soil protozoa. 



Ammonification by bacteria is not influenced appreciably by soil 

 protozoa although their presence acts detrimentally upon bacterial 

 numbers. 



This might be explained by one of the following assumptions: (1) if 

 the protozoa destroy bacteria, they destroy non-ammonifying organ- 

 isms ; 2) the protozoa themselves take part in the process of ammonifica- 

 tion; (3) the disintegration of the bacterial cells results in decomposi- 

 tion products which might be responsible for high ammonia produc- 

 tion.— Z. N. 



