484 Journal of Agricultural Research voi. xii.no. s 



phate. The dibasic magnesium phosphate increased the number of 

 bacteria to about the same degree as an application of one-half magne- 

 sium carbonate. A combination of each phosphate with each carbonate 

 did not prove beneficial in augmenting the number of bacteria in Miami 

 silt loam beyond that caused by each carbonate when used alone. It is 

 evident from the foregoing data, as shown in figure 9, that the relative 

 increase of the number of bacteria from the use of carbonates of calcium 

 and magnesium in Miami silt loam was not so great as when Colby silt 

 loam was treated with the same compounds. However, the phosphate 

 gave a greater relative increase in the neutral Miami silt loam than in 

 the acid Colby silt-loam soil. 



INFlvUENCS 0]P MAGNESIUM CARBONATE, CAI^CIUM CARBONATE, LIMESTONE, 

 AND MONOCALCIUM PHOSPHATE ON THE BACTERIA IN SOIL, 



Another series of jars was filled with Colby silt loam treated with 

 magnesium carbonate; a second series with the same soil treated with 

 calcium carbonate; a third series with limestone, and a fourth with 

 monocalcium phosphate. All jars were placed in the greenhouse and 

 the soil moisture maintained at half saturation. After one, two, and 

 three months samples of this soil were drawn and tested for ammonifying 

 power, for nitrate content, and for the number of bacteria. 



The ammonifying power was determined by mixing 2 per cent of 

 dried blood, which contained 13.4 per cent of nitrogen, with 100 gm. of 

 soil. After adding the dried blood meal, the soil was placed in tumblers, 

 the proper amount of water added, the tumblers covered with petri-dish 

 covers, and incubated at 27° C. for six days. The ammonia was deter- 

 mined by the steam-distillation method. 



In order to measure the nitrification in the treated and untreated soil, 

 samples were taken from the jars and the nitrate content determined 

 immediately. This was simply a study of nitrate accumulation in 

 the soil; no nitrogenous substance was added. Nitrates were deter- 

 mined by the phenol-disulphonic acid method. The data for the experi- 

 ments with Colby silt loam and Plainfield sand are shown in Tables 

 VIII to XI, inclusive. 



From the data in Table VIII it will be seen that after one month the 

 increase in the number of bacteria in Colby soil, in conformity with 

 previous tests, was greatest with the magnesium-carbonate treatment. 

 The increase was very marked, about five times greater than that de- 

 rived from the use of calcium carbonate or limestone. The favorable 

 effect of the magnesium carbonate was noted after both the 2- and 

 3-month periods. In most cases the calcium carbonate and limestone 

 increased the number of bacteria, notably after two months. The 

 monocalcium phosphate apparently exerted no effect in increasing the 



