The Bulletin 19 



On pages 259-60 of "Fertilizers and Manures" Dr. A. D. Hall of the 

 Rotliamsted Experiment Station, England, says : "But nitrogenous com- 

 pounds in the soil are not the only ones rendered more available by the 

 presence of carbonate of lime; both phosphoric acid and potash are 

 thereby kept or brought into a more soluble form. When soluble phos- 

 phates are applied to the land they are precipitated either as dicalcium 

 phosphate, ferric phosphate, or aluminum phosphate ; and on soils con- 

 taining any reasonable amount of calcium carbonate the dicalcium phos- 

 phate will predominate, while iron and aluminum phosphate will pre- 

 dominate on the sands and clays where calcium carbonate is lacking. 

 Now, the effective solubility of iron and aluminum phosphates in soil 

 water is very much below that of the precipitated calcium phosphate; 

 consequently, their phosphoric acid is much slower in reaching the plant, 

 which may remain short of this necessary constituent even though large 

 amounts of phosphates have been applied to the soil. Similarly, a soil 

 may contain considerable amounts of phosphoric acids which, in the 

 absence of lime, is combined with ferric oxide or alumina so as to be 

 in a highly insoluble condition. For example, a soil derived from the 

 marlstone (a geological formation in England) has been found to con- 

 tain 84 hundredths of 1 per cent of phosphoric acid, but yet show great 

 response to phosphatic manures, because, at the same time, it contained 

 over 28 per cent ferric oxide and no calcium carbonate. Applications 

 of calcium carbonate are of great value on these soils because they form 

 a certain amount of calcium phosphate by interaction with the iron or 

 aluminum phosphates, and so increase the proportion of phosphoric 

 acid in the soil water." 



In the annual report of the Virginia Agricultural Experiment Station 

 for 1909-1910 Drs. Ellett and Hill make the following significant ob- 

 servations: "Agricultural chemistry teaches us that the soluble phos- 

 phates are reverted or fixed, and when the combination takes place with 

 the iron and the aluminum compounds the probabilities are that the 

 reversion or fixation which occurs are in forms which remain forever 

 unavailable to plants. If this reversion takes place, it is folly to apply 

 large quantities of sohihle phosphates to the soil in which iron and 

 aluminum predominate over the other bases, as four-fifths of it woidd he 

 forever lost, and would he dead capital on the farmer's hands." 



After conducting some very carefully planned and ingeniously devised 

 experiments to test the matter, these gentlemen had the warning sounded 

 in the above quotation amply confirmed. In discussing the results of 

 their experiments, Drs. Ellett and Hill state, on pages 54-55 of the above 

 named publication, that "A review of these experiments conducted with 

 the solvents used to determine the availability of phosphoric acid in 

 soils and fertilizers show that the substances found in the different soil 

 types fix phosphoric acid from water solutions into compounds of 

 different solubility. The hydroxides of iron and aluminum lock up or 



