Sept. ii, 1916 



Bacteriological Studies of a Soil 



967 



differences, whether the nitrate-forming power is low or high. Table 

 VII gives the relative rank of the different plots at each analysis. Fig- 

 ure 1 illustrates very clearly the low and the high nitrate-forming power 

 at different periods. 



Table VII. — Average nitrate formation without addition of calcium carbonate (Table V) 

 of seven fertility plots studied in igij and IQ14, together with their relative rank at 

 each sampling 



Since the addition of calcium carbonate has to such a large extent 

 eliminated the differences in nitrate formation when testing in the soil 

 itself, it is interesting to ascertain whether this can be traced to an 

 elimination of acid conditions. Dr. P. F. Trowbridge, of the Depart- 

 ment of Agricultural Chemistry, Missouri Experiment Station, has 

 furnished us with the following data regarding the lime requirements 

 of some of the plots. The figures are in pounds per acre-foot; basis, 

 3,000,000 pounds per acre: Plot 2, 7,900; plot 13, 7,200; plot 17, 7,900; 

 plot 18, 2,400; plot 22, 2,400; plot 23, 7,200 pounds. 



It will be noted that, so far as the crop is concerned, the differences 

 in lime requirements are very slight (plots 13, 17, and 23 or 18 and 22). 

 Manure kept the acidity low (plots 18 and 22). Commercial fertilizers 

 have had no appreciable effect upon acidity (plot 2). Nevertheless, 

 continuous corn soil with a lime requirement not materially different 

 from that of timothy, the rotation, or continuous wheat receiving com- 

 mercial fertilizers produced only about one-half the amount of nitrates 

 as these soils. It will be shown later that transferring the organisms 

 to a common pabulum containing an abundance of calcium carbonate 

 does not eliminate the large differences. In this connection, as a sug- 

 gested explanation of one of the effects of lime when added to the soil, 

 we call attention to the work of Schreiner and Reed (16), who have 

 demonstrated the stimulative effect of calcium carbonate upon oxidases. 

 It is not impossible that soil conditions are sometimes such as to permit 

 the accumulation of nit rate -forming oxidases, while other conditions 



