312 ILLINOIS STATE ACADEMY OF SCIENCE 



It would be of fundamental importance to know : What 

 becomes of phosphorus when phosphatic fertilizer is ap- 

 plied to the soil? What reactions take place? To what 

 extent is phosphorus "available" when "water soluble" 

 acid phosphate is incorporated with the moist soil mass? 



As generally known, one of the strongest claims of 

 acid phosphate advocates is that acid phosphate is water 

 soluble and that when it is applied to the soil, it becomes 

 available immediately for the use of plants, while phos- 

 phorus in the rock phosphate is so insoluble that its avail- 

 ability is too low for the immediate use of growing crops, 

 The validity of this contention is often doubted, for it 

 was observed that phosphorus of water soluble acid phos- 

 phate could not be extracted from the soil to which it was 

 previously added. It is often argued, that although this 

 phosphorus can not be extracted with water, it is ab- 

 sorbed or even adsorbed by the soil particles, and loosely 

 held thereby. This phosphorus, however, is in such state 

 that plant roots are able to extract it far more easily 

 than the phosphorus of the insoluble rock phosphate. 

 The data presented in this paper will tend to show that 

 this general contention is also of questionable validitv: 

 that phosphorus of acid phosphate or even of double acid 

 phosphate (super phosphate), after this material is ap- 

 plied to some agricultural soils, becomes very insoluble ; 

 and its solubility is not to any extent greater than the 

 solubility of phosphorus from natural rock phosphate 

 added to the same soil and under the same conditions. 



EXPEKIMENTAL 



The present investigation was carried out on many soil 

 types, the soils in the majority of cases being obtained 

 f-rom Champaign county, Illinois. The phosphatic fer- 

 tilizers used were three different rock phosphates; five 

 slags; ground apatite; iron and aluminium phosphates; 

 steamed bone meal and acid and double acid phosphates. 

 The composition of these phosphatic fertilizers is pre- 

 sented in Table 1. 



The comparative work on different soils was carried 

 out with Tennessee rock phosphate, as a representative 

 of insoluble rock phosphate, and with double acid phos- 

 phate, as easily soluble phosphatic fertilizer. 



