Mar. II, 1918 Nitrifying Bacteria and Tricalcium Phosphate 673 



EXPERIMENTAL RESULTS 



The soil used in this investigation was drawn from one of the plots 

 (F) now being used in a fertilizer experiment with Citrus trees. This 

 plot has been treated annually for 10 years with light applications of 

 stable manure, but no commercial fertilizer or lime has been applied 

 to it. The soil is a light sandy loam of granitic origin, the coarser par- 

 ticles of which are composed largely of granite. It contained 8.5 p. p. m. 

 of nitric nitrogen, and 0.188 per cent of total phosphorus pentoxid 

 (P2O5), of which 17.4 p. p. m. were soluble in water when the experiment 

 was begun. The total carbonate (CO3), as determined by the Gaither 

 (2) method, amounted to 0.03 per cent, but the sample was free from 

 water-soluble carbonate (CO3). 



Portions of 2,000 gm. each of fresh soil were weighed into half -gall on 

 (1.89 Hters) fruit jars. A solution of ammonium sulphate (c. p.) was 

 added to certain portions at rates supplying o.oi gm. of nitrogen per 

 100 gm. of dry soil. To other portions an equal quantity of nitrogen was 

 added in the fonr) of dried blood. Still other portions were employed with- 

 out the addition of any nitrogenous substance. Baker's analyzed trical- 

 cium phosphate was added in certain cases at the rate of o.io gm. per 100 

 gm. of soil and calcium carbonate (c. p.) at the rate of 0.25 gm. per 100 

 gm. of soil. The experiments were made in duplicate. After a thorough 

 mixing, adding suitable amounts of water and mixing again, the jars 

 were loosely covered and incubated at room temperature. 



It is, of course, well known that the purest tricalcium phosphate is 

 somewhat soluble in water and that ammonium sulphate affects the 

 solubility of certain soil constituents, notably calcium, without the inter- 

 vention of bacteria. Consequently it was deemed necessary to deter- 

 mine the solubility of calcium and phosphoric acid after the above- 

 named substances had been mixed with the soil, but before sufficient time 

 had elapsed to permit measurable bacterial action. It is obvious that 

 the amounts of soluble calcium and phosphoric acid present in the soil 

 at the beginning of the experiment should not be considered as having 

 been dissolved by subsequent bacterial action. Accordingly portions of 

 soil each containing 200 gm. were placed in flasks, the same relative 

 proportions of tricalcium phosphate, calcium carbonate, and ammonium 

 sulphate added as in the incubated series, and the contents thoroughly 

 mixed. Distilled water was added at the rate of 250 parts per 100 

 parts of dry soil, and the contents were vigorously shaken once every 

 10 minutes during an hour, and were then filtered through Chamberland- 

 Pasteur filters. Calcium was determined in the filtrates by the volu- 

 metric permanganate method and phosphoric acid by the Pemberton 

 volumetric method. The average results obtained from closely agreeing 

 duplicate solutions, expressed in parts per million of dry soil, are sub- 

 mitted in Table I. 



