Mar. II, 1918 Nitrifying Bacteria and Tricalcium Phosphate 677 



was accompanied by increases in the solubility of the calcium present.* 

 This was noted to some extent in the portions to which no nitrogenous 

 additions were made ; was considerably greater when dried blood was sup- 

 plied; and was greatest with the addition of ammonium sulphate. The 

 data show, however, that the concentration of soluble calcium was not 

 increased as a result of adding tricalcium phosphate. On the other hand, 

 soluble calcium was considerably increased in a number of cases by the 

 addition of calcium carbonate. It would seem, therefore, that calcium, 

 in the form either of the carbonate or of such silicates as occur in this 

 soil, will be dissolved by the biochemical oxidation products in preference 

 to tricalcium phosphate. 



In contrast to the effects on the solubility of calcium, the data show 

 that nitrification of the soil nitrogen and that added as dried blood was 

 accompanied in each case by a well-defined decrease in soluble phos- 

 phoric acid. Where ammonium sulphate was added alone, the amounts 

 of soluble phosphoric acid found at the 28- and 57-day periods were 

 approximately the same as found at the beginning of the experiment. 

 It would appear, therefore, that the solvent action of the bacteria in 

 this case was almost exactly equal to the precipitating action that evi- 

 dently took place in the control and dried-blood portions. After 157 

 days, however, more than half of the soluble phosphoric acid originally 

 present in this portion had disappeared. It is also shown that, while 

 larger amounts of soluble phosphoric acid were found where tricalcium 

 phosphate had been added than in the control portions, the increases 

 can not be definitely ascribed to the action of bacteria in any case except 

 where ammonium sulphate was also added, and then only without the 

 addition of calcium carbonate. For in all other cases the solubility 

 immediately after adding tricalcium phosphate was equal to or greater 

 than that at the end of the incubation periods. 



In the absence of calcium carbonate, however, the oxidation of am- 

 monium sulphate dissolved tricalcium phosphate, as shown by the fact 

 that the concentration of soluble phosphoric acid was increased in 28 

 days from 24.2 to 52.1 p. p. m. Later the solubility steadily declined 

 until at the end of 157 days the concentration had been reduced to 

 30 p„ p. m. 



Assuming in this case that the increase in nitric nitrogen over the 

 amounts found in the controls was due to the oxidation of ammonium 

 sulphate, we find that the oxidation of 78.0 p. p. m. of nitrogen resulted 



' It should be clearly understood that the results obtained in this investigation represent the algebraic 

 sumanddifferenceoi the results of a number offerees. In the first placeit is highly probable that biochem- 

 ical agent"! other than the nitrif jTng organisms are capable of affecting the solubility of calcium and phos- 

 phoric add in soils. A part of this effect may be referred to as positive and a part as negative, since, on the 

 one hand, carbonic acid, formed in the life process of bacteria, is a solvent for calcium and phosolioric acid, 

 andon the other hand, the organisms themselves absorb phosphoric acid {8). in the second place diffusion 

 tends to bring about more or les^ fixation in soils. The concentration at a given moment, therefore, is 

 really dependent on the Interaction of a number of forces. Consequently a full explanation of the results 

 obtained is not possible at present. 



