422 EXPEEIMEXT STATION RECORD. 



Activity of soil protozoa, G. P. Kocii {U. S. Dept. Agr.. Jour. Agr. Research, 

 5 {1915), No. 11, pp. 477-JtSS). — Experiments with field and greenhouse soils con- 

 ducted at the New Jersey Experiment Stations are reported, the purpose of 

 which was to study (1) protozoan activity in soils of different moisture con- 

 tent and under constant and variable temperatures, (2) the effect of moisture on 

 the activity of soil protozoa under constant and variable temperatures, and (3) 

 the period of excystment of soil protozoa. It was found that direct examina- 

 tion of the soil to which a little water was added was the most satisfactory 

 methd of determining the presence of motile protozoa. 



It was found that "under ordinary gi*eenhouse conditions small ciliates, 

 flagellates, and amebte are active in some soils, but their presence is very lim- 

 ited. Active protozoa (.small ciliates, large ciliates, flagellates, and amebce) do 

 not seem to be present in field soils with a normal moisture content and even 

 when the moisture content is slightly supernormal. . . . 



All field soils contain cysts of protozoa the organisms of which become 

 active when conditions become favorable. The moisture content of the soil 

 is the primary influencing factor which determines the presence or absence of 

 the active protozoa in the soil, while the temperature, the presence of organic 

 matter, and the physical properties of the soil are secondary factors. Soon 

 after standing water is accumulated, as after a heavy rain, some protozoa will 

 excyst and be active as long as the moisture content is favorable. Active pro- 

 tozoa seem to be always present in free standing .soil water [and] in water- 

 logged soils at constant and variable temperatures. Under normal conditions 

 it would seem that protozoa can not excyst in 2 minutes. Small ciliates can 

 excyst in 1 to 2 hours at 22 to 24° C. At the same temperature flagellates can 

 excyst in 6 to 8 hours and large ciliates can excyst in 40 hours." 



A list of references to cited laterature is appended. 



Azotobacter and nitrogen fixation in Indian soils, .1. II. Walton (ilcm. 

 Dept. Agr. India, Bact. Ser., 1 (1915), Xo. 4. pp. 97-112, pis. 5, figs. 2).— Pre- 

 liminary studies on the optimum conditions for nitrogen flxation by Azotobacter 

 in Indian soils are reported. 



Using Ashby's nutrient solution (E. S. R., 18. p. 721) it was found that 

 with Pusa field soil the best length of incubation period for nitrogen fixation 

 by Azotobacter was from 10 to 14 days. A higher nitrogen fixation per gram 

 of mannite was obtained with 10 gm. of mannite per liter of solution than 

 with 12 or 20 gm. The addition of basic .slag did not influence nitrogen flxation. 

 The addition of ferric chlorid or ammonium sulphate depre.ssed fixation, while 

 the substitution of magnesium carbonate for calcium carbonate only slightly 

 increased it. 



With Pusa soil nitrogen fixation was lowest between October and January 

 and highest between June and September. Low fixation coincided with the 

 drying of the soil and lowering of the temperature, while high fixation accom- 

 panied abundant moisture and fairly high temperature. 



In 11 out of 17 cases nitrogen fixation in liquid cultures was greater at 30 

 than at 20° C. In soil cultures nitrogen fixation was Increased by cultivation 

 and the addition of suitable carbohydrate material. Pure cultures of Azoto- 

 bacter isolated from different Indian soils varied In nitrogen-fixing power and 

 In morphological and cultural characters, the latter being constant in any par- 

 ticular variety. 



Additions of basic slag, filter paper, sterilized soil, and humus to p;ire cul- 

 tures of Azotobacter were all beneficial to nitrogen fixation, but additions of 

 different nitrogenous substances had little effect. 



It is concluded from these results that proper soil management should in- 

 clude the provision of conditions favorable to the physiological activity of 



