Feb. as; 19x8 Influence of Carbonates on Soil Bacteria 469 



The calcium-carbonate requirement of the acid soils was determined 

 according to the Truog barium-hydroxid method. In calculating the 

 amount of acid in each soil only the active acidity was considered. For 

 every 100 gm. of Colby silt loam on the dry basis 1.05 gm. of calcium 

 carbonate were required to correct the active acidity, and for 100 gm. of 

 Plainfield sand 0.21 gm. Three different bases were used to neutralize 

 the acidity in these soils — namely, pure precipitated calcium carbonate, 

 pure precipitated magnesium carbonate, and commercial ground lime- 

 stone. The limestone, the analysis of which showed 53 per cent of calcium 

 oxid and 43 per cent of magnesium oxid, was ground to pass through a 

 loo-mesh sieve. 



Aside from the compounds just named, monocalcium phosphate was 

 used in certain experiments. The phosphate was employed to find out 

 whether or not the calcium of this phosphate salt would serve in a like 

 capacity as that of calcium carbonate. Accordingly the monocalcium 

 phosphate was added to the soil alone and in various mixtures with cal- 

 cium carbonate. 



The calcium carbonate, magnesium carbonate, and limestone were 

 added in amounts sufficient to satisfy one-fourth, one-half, and full cal- 

 cium-carbonate requirement — that is, to neutralize one-fourth, one-half, 

 and the total active acidity. The phosphate was added in varying 

 amounts. After the bases and phosphate were thoroughly mixed with 

 the soil, the latter was then poured into earthenware jars and the moisture 

 content raised to one-half saturation with distilled water. At definite 

 intervals samples were drawn and plate counts made. The soil of each 

 jar, after the sample had been drawn, was poured on sterile paper, thor- 

 oughly mixed, and returned to the original jar. In order to reduce evapo- 

 ration and to prevent outside contamination, the jars were covered with 

 cheesecloth. The entire series of jars was incubated in the greenhouse 

 at approximately 22° C. 



At regular intervals the effect of these compounds on the total number 

 of bacteria in the soil, on ammonification, and on nitrification was 

 studied. 



INFLUENCE OF CALCIUM CARBONATE, LIMESTONE, AND MONOCALCIUM 

 PHOSPHATE ON THE NUMBER OF BACTERIA IN SOIL 



Colby silt loam. — Two-kgm. portions of soil were treated as outlined 

 in Table I and incubated for a period of five months. During this time 

 eight plate counts were made with Heyden-Nahrstoflf agar. These plates 

 were incubated at 27° C. for 10 days. The influence of monocalcium 

 phosphate on the number of bacteria in the soil was tested simultaneously 

 with that of the carbonates. The data of this experiment are given in 

 Table I. 



