490 



Journal of Agricultural Research 



Vol. XII, No. 8 



followed by an increase in assimilation of nitrates. These results agree 

 with those obtained by Fred and Graul (20). 



In the Colby silt loam the full calcium carbonate gave the best results 

 while magnesium carbonate and limestone rank in the order named. 

 The magnesium carbonate when added to the soil with gelatin did not 

 give as good results as calcium carbonate. This difference may be due to 

 the fact that the large increase in the number of bacteria caused by the 

 magnesium carbonate treatment favored a greater assimilation of nitrate 

 by the microorganisms. Plainfield sand apparently gave better results 

 where the one-fourth or one-half neutralization was obtained. Very 

 probably the sand releases more ammonia when neutral than does the 

 Colby silt loam. In both soils the phosphate benefited nitrification but 

 slightly. 



INFLUENCE OF CALCIUM CARBONATE, MAGNESIUM CARBONATE, LIMESTONE, 

 AND MONOCALCIUM PHOSPHATE ON NITROGEN FIXATION IN SOIL 



An effort was made to study the influence which carbonate and phos- 

 phate treatments would have on the independent nitrogen-fixing organ- 

 ism, Bacillus azotobacter chroococcum. Three months after treatment, 

 Colby and Plainfield soils were sampled and the soil placed in large soup 

 plates, I per cent of mannit was added to each plate of soil, which was 

 then inoculated with a culture of B. azotobacter. After incubating for 

 four weeks in the greenhouse, the soils were dried and ground to a very 

 fine powder in a ball mill. Total nitrogen determinations (Kjeldahl 

 method modified to include nitrates) were then made. Duplicate deter- 

 minations were made from each plate and an average of these taken. 

 The results for this experiment are given in Table XIII. 



Table XIII. — Influence of calcium carbonate, magnesium carbonate, limestone, and 

 monocakium phosphate on nitrogen fixation in Colby silt loam and Plainfield sand 

 treated with mannit and inoculated with Bacillus azotobacter 



Treatment. 



None 



One-fourth calcium carbonate 



One-half calcium carbonate 



Full calcium carbonate 



One-fourth limestone 



One-half limestone 



FuU limestone 



One-fourth magnesium carbonate 



' One-half magnesium carbonate 



Full magnesium carbonate 



0.1 per cent monocalcium phosphate. 



0.1 per cent monocalcium phos- 

 phate + one-fourth calcium car- 

 bonate 



0.1 per cent monocalcium phos- 

 phate + full calcium carbonate 



Nitrogen in loo gm. of dry soil. 



Colby silt loam. 



After 4 

 weeks. 



Mgm. 



273.0 

 277. o 

 273.0 

 276.0 

 27S.O 

 273.0 

 278.0 

 277.0 

 278.0 

 275.0 

 274.0 



2 79- o 

 283.0 



Mgm. 



275.0 

 276. o 

 275.0 

 276.0 

 275-0 

 27S-0 

 279. o 

 276.0 

 276.0 

 27S-0 

 276.0 



282. o 

 277. o 



Aver- 

 age. 



Mom. 

 275.0 

 276.5 

 274. o 

 276.0 

 275- o 

 274.0 

 278.5 

 276.5 

 277. o 

 275- o 

 275-0 



280.5 

 280. o 



In- 

 crease. 



Mgm.. 



+ 5-5 

 + S-0 



Plainfield sand. 



After 4 

 weeks. 



Mgm. 

 63.0 

 59- o 

 6i. o 

 64.0 

 6i.o 



61. o 



62. o 

 59- o 

 62. o 

 63.0 

 61. o 



61. o 

 65.0 



Mgm. 

 61. 



59- o 

 65.0 



Aver- 

 age. 



Mgm.. 



60. o 

 65. o 



In- 

 crease. 



Mgm. 



—2.0 



-I-3-0 



