480 



Journal of Agricultural Research 



Vol. V. No. II 



Table I. — Extent of protozoan activity in greenhouse soil 



oS.C.=small ciliates; l,.C.= large ciUates; F.= flagellates; A.= anieb3e; t=few; tt= several ; ttt= many. 



FIELD SOILS 



The extent of protozoan activity in field soils was studied in the same 

 manner as the greenhouse soils. Samples of 14 field soils of different 

 texture and tillage treatment were collected at a depth of 3 inches from 

 the surface and brought to the laboratory in flasks. The temperature 

 was in all cases noted. These were examined at once, each for half an 

 hour, a new sample being placed on the slide every two minutes, as in 

 the case of greenhouse soils. The moisture content was likewise deter- 

 mined. The soils were sampled and examined under normal conditions, 

 again two days after a fall of 1.69 inches of rain, and a third time five 

 days after 1.69 inches of rainfall. The second sampling was made at 

 that period, since it allowed the organisms sufficient time to excyst, if 

 possible, when the moisture content of the soil was increased. Like- 

 wise, the third examination was made five days after the heavy rainfall, 

 for if the protozoa excysted and were washed to a lower level in the 

 soil, this lapse of time allowed them to return to their normal level in 

 the soil. Each soil was subjected to a half-hour's examination at every 



