Mar. II, i9i8 Nitrifying Bactevla and Triccdcium Phosphate 68 1 



the phosphoric acid. The results of many studies on the concentration 

 of nitric nitrogen in soils supporting growing crops show, for example 

 that diffusion is an important force in maintaining equilibrium in soils. 



Tricalcium phosphate can not be converted into monocalcium phos- 

 phate (the water-soluble form) without active acidity being developed.^ 

 Nor are acids neutralized by converting tricalcium phosphate into mono- 

 calcium phosphate, since the latter is an acid compound. But when the 

 acidity necessary to the solution of tricalcium phosphate is neutralized, 

 the phosphoric acid will be precipitated. If it be desirable that a con- 

 dition either of neutrality or slight alkalinity obtain in soils, as has been 

 widely taught, it is difficult to see how more than traces of monocalcium 

 phosphate can exist therein at the same time. 



It should also be recalled that untreated rock phosphate generally 

 contains considerable amounts of calcium carbonate intimately com- 

 mingled with the phosphate. Before dilute acids, formed by the action 

 of bacteria or otherwise, can dissolve the phosphate, the carbonate must 

 first be neutralized, as is commonly recognized in the commercial pro- 

 cesses employed in the manufacture of acid phosphate. 



It seems possible, however, that the nitrifying bacteria may dissolve 

 limited amounts of rock phosphate in acid soils. The soil used in this 

 investigation, although low in carbonate, was not acidic, and more active 

 solution of tricalcium phosphate would probably take place in an acid 

 soil. But, in any case, with the possible exception of very sandy types 

 of soil, it is probable that phosphoric acid, made soluble by the nitrifying 

 bacteria, would tend to become fixed through being brought into con- 

 tact with other soil constituents by diffusion. Many investigations have 

 shown, for example, that acid phosphate soon becomes fixed, even in 

 acid soils. 



From these investigations it seems, therefore, that while the nitrite 

 bacteria are capable of effecting the solution of tricalcium phosphate 

 under restricted conditions, they are not the potent agents in the solu- 

 tion of rock phosphate in the field that Hopkins and Whiting were led to 

 infer from their experiments with solution cultures. 



In the opinion of the author the results obtained in this investigation 

 should not be interpreted as being definitely opposed to the use of un- 

 treated rock phosphate as a fertilizer. It is true that the means by which 

 tricalcium phosphate is made soluble in soil have not been definitely 

 determined, but the important fact remains that in various localities 

 beneficial effects on the growth of crops have frequently been produced 

 by rock phosphate. It therefore remains for further investigation to 

 lay bare the reasons. The suggestions offered by Truog (9) in this con- 

 nection seem to be deserving of special consideration. 



• It is, of course, understood that hydrolysis is excepted in this case. The absolute increases in soluble 

 phosphoric acid in soib resulting from the hydrolysis of tricaldum phosphate are probably quite small. 



