290 SOIL CONDITIONS AND PLANT GROWTH 



by D. W. Cutler and Miss L. M. Crump at Rothamsted, by 

 Waksman at the Rutgers College (292^), by Kopeloff, Lint 

 and Coleman at the New Jersey Experiment Station (152), 

 and by others, for estimating their numbers and activities.^ 



There has been much discussion as to whether protozoa 

 are normally active in the soil or whether they are simply 

 there as cysts. Waksman (292^) recognises a trophic fauna, 

 Sherman (261), Koch,^ Moore,^ Fellers and Allison,'^ consider 

 the protozoa are not active because they cannot be seen when 

 soil is examined under a microscope. 



D. W. Cutler (73^) has, however, found a satisfactory 

 explanation of the difficulty of seeing living protozoa in the soil. 

 He finds that the organisms rigidly adhere to the soil particles 

 and indeed up to a certain limit they can be completely 

 removed from a suspension by shaking for a few minutes with 

 soil. The saturation capacity of the soil is high ; at Rotham- 

 sted it is 1,500,000 or 2,000,000 per grm., a figure consider- 

 ably in excess of the numbers present, and only in exceptional 

 cases can organisms be dislodged sufficiently readily to be 

 recognised under the microscope. 



At Rothamsted frequent estimations are made of the 

 number of protozoa found in certain arable soils. The method 

 (73(^) discriminates between cysts and active forms, and 9 species 

 of flagellates, 5 of amoebae, 2 of thecamoebae, and 3 of ciliates 

 are enumerated. Table LXXIX. shows the order of values 

 frequently obtained. It is difficult to explain these high 

 values if they simply represented cysts blown in from ponds. 



The numbers are considerably higher in autumn and spring 

 than in summer, and they are higher in summer than in winter, 

 and they are much higher on the plot receiving dung than on 

 that continuously unmanuftd. 



^ See N. Kopeloff and D. A. Coleman for a review of the investigations 

 up to 1917 (Sot7 Set., 1917, 3, 197-269). 



"G. P. Koch, jfourn. Agric, Research, 1915, 4, 511 ; Soil Sci., 1916, 2, 

 163. 



^G. T. Moore, Science, N.S., Nov, 8th, 1912; see also E. J. Russell, Science, 

 N.S,, April 4th, 1913, 



*C. R. -Fellers and F. E, Allison, Soil Set., 1920, 0, i. 



