468 



Journal of Agricultural Research 



Vol. XII, No. 8 



Fischer (/d) obtained a better growth of Bacillus azotobacter from limed 

 than from unlimed clay soil. On the other hand, Koch, Litzendorf , KruU, 

 and Alves (32) reported that lime retarded free-nitrogen fixation. Kriiger 

 (5j) treated soil with lime and obtained an increase in nitrogen fixation. 



Purer and better film growth of Bacillus azotobacter was obtained by 

 Ashby (2) with magnesium carbonate than with calcium carbonate. 



The effect of calcium carbonate and magnesium carbonate on the 

 fixation of nitrogen by Bacillus azotobacter, both in liquid cultures and in 

 soil, was studied by Lipman and Burgess (40). In every case magnesium 

 carbonate alone proved toxic. These authors observed that when 15 

 parts of calcium carbonate were mixed with i part of magnesium car- 

 bonate, the latter was no longer toxic to this organism. 



SUMMARY OF LITERATURE 



From the citations just given it appears that the addition of calcium 

 and magnesium, either in the form of oxid or carbonate, to soil, and 

 especially to acid soil, brings about conditions favorable to the growth 

 of certain groups of microorganisms. There are many factors which have 

 been given little or no consideration — for instance, what relationship 

 exists between the total number of bacteria in soil and the quantity of 

 soil acid neutraHzed? With few exceptions, little attention has been 

 directed toward the relative effect of calcium and magnesium carbonates 

 on the soil flora. There exists a diversity of opinion with regard to the 

 relation of bacteria to these two compounds. This lack of harmony may 

 be due to the difference in the soil types which have been studied. 



Again, it seems that no one has tried to measure the effect of calcium 

 and magnesium carbonates on pure cultures of bacteria in sterihzed 

 acid soil. To obtain information with regard to these points, a series of 

 experiments was planned. 



EXPERIMENTAL WORK 



For this study three Wisconsin soils, acid Colby silt loam, acid Plain- 

 field sand, and neutral Miami silt loam, were used. The Colby silt loam 

 was collected near Marshfield, the Plainiield sand from Hancock, and 

 the Miami silt loam from Madison. At the laboratory each soil was 

 passed through a 4-mm. sieve and thoroughly mixed. 



The percentage composition of these soils is given below : 



Constituent. 



Colby silt 

 loam. 



Miami silt 

 loam. 



Plainfield 

 sand. 



Potassium 



Nitrogen 



Phosphorous. .. 

 Calcium oxid . . 

 Organic matter 



I- 51 

 . 198 

 . 072 

 . 0907 



3-91 



2. 16 

 •IS 



•IS 



.185 



2.74 



0-93 

 .09 

 .032 

 . 0023 



I. 41 



