216 EXPERIMENT STATION RECOED. [Vol.36 



of preparing a seed bed for wheat on yield, soil moisture, and soil nitrates. 

 Plats were selected which were representative of the extremes in treatment in 

 the previous experiments. 



It was found that " the differences in nitrate content reported by Call can 

 not be attributed to a difference in the bacterial content. Some nonbiological 

 condition existing in certain plats, under field conditions, prevents the normal 

 activity of the bacterial flora. Among the factors controlling bacterial activity 

 the available moisture probably plays a paramount role." 



Four references to literature bearing on the subject are appended. 



Studies on the actiAdty of soil protozoa, G. P. Koch {Soil Sci., 2 {1916), 

 No. 2, pp. 163-181, fig. J).— In a further contribution (E. S. A., 34, p. 422) 

 experiments conducted at Rutgers College with sandy loam and clay soil to 

 determine the influence of moisture content, organic matter, and physical prop- 

 erties of soil on the presence of protozoa in soils in the active state are reported. 



It was found that " the direct examination of the soil under the microscope 

 for a period of 15 to 20 minutes (taking three or four samples), gives a fair 

 indication as to the relative extent of active protozoa in the soil. Practically 

 all of the protozoa as found in the soil can be observed under the low power 

 of the microscope. 



" The addition of organic matter to the Sassafras sandy loam soil encour- 

 aged a greater protozoan development than where none had been added. Addi- 

 tions of dried blood to the Penn clay loam soil increased the number of active 

 protozoa but very little, while cow manure had no effect on the protozoan 

 activity of this soil. 



" Increasing the porosity and aeration of the soils by the addition of sand 

 did not increase the number of motile protozoa. 



" In the Sassafras soil to which cow manure had been added flagellates were 

 noted on the first day, while with the other samples they were not seen until 

 the second or third and, in some cases, the fourth day. The maximum numbers 

 were recorded on the fourth and sixth days, after which there was a marlied 

 decrease, so that on the twenty-first and twenty-eighth days practically none 

 were found to be in the active state. This would indicate that the destructive 

 ability . . . would be present for only a limited period, namely, the early stages 

 of organic decomposition. 



" Flagellates were the first protozoa to excyst ; later, on the third and fourth 

 days, small ciliates appeared. On the fourteenth, twenty-first, and twenty- 

 eighth days small ciliates were more numerous than flagellates. With these 

 soils the largest number of protozoa was recorded where the moisture was 

 highest. The Penn clay loam soil seemed to be a very undesirable medium for 

 protozoa, as very few of these organisms were noted in any of the samples 

 compared with those found in the Sassafras soil. 



"At the lowest moisture content (one-third of the optimum), protozoa did 

 not become active. With these soils moisture seemed to be the primary limit- 

 ing factor which determined the presence or absence of active protozoa. 



" With one exception, no correlation between the presence of protozoa in the 

 active condition and the numbers of bacteria could be seen. Increased numbers 

 of bacteria were observed irrespective of the presence or absence of living 

 protozoa. On the fourteenth day in the soils, even where no protozoa were 

 found in the active condition, there was a great decrease in bacterial numbers. 



" Inasmuch as the numbers of protozoa in comparison with the bacterial 

 numbers are so small, even in the presence of such abnormal quantities of 

 organic matter as were used, it hardly seems that they would be of very great 

 importance in agricultural practices." 



A list of 19 references to literature bearing on the subject is appended. 



