The Bulletin 7 



able opportunity Itceii given tor ALL of the i)liosphoric aeid, not quickly 

 utilized by the plants, to combine with the iron and aluniinuni oxides." 

 Dr. Wheeler further states, in E. S. K., Vol. 18, No. 7, that "In soils 

 deficient in or devoid of carbonate of lime, but well sup]di<'(l with the 

 o.xides of iron and aluminum, LIME MAY EXTEND THE PERIOD 

 OF EFFICIENCY OF TJIE SOLUBLE PIIOSPIFATES, POSSI- 

 BLY BY COMBINING WITH .MFCll OF TIIK PHOSPHORIC 

 ACID AT ONCE, AND THUS HOLDING IT IN A MOKE AS- 

 SIMILABLE COMBINATION THAN IF IT WERE POSSIBLE 

 FOR IT ALL TO UNITE HIMEDIATELY WITH THE IKON 

 AND ALUMINUM OXIDES." 



Professor Hilgard, in discussing the relative availabilities of certain 

 forms of phosphorus, states : "On soils containing large amounts of iron 

 and aluminum oxides a high per cent of lime carbonate may offset the 

 small ])er cent of phos))horic acid, a]>|»arentlv, bv bringing about 

 GKEATEK AVAILABILITY. In general, we'find\hat a lower per- 

 centage of potash, phosphoric acid, and nitrogen are adequate when a 

 large proporition of lime carbonate is present. On the other hand, 

 VERY LARGE PERCENTAGES OF FINELY DIVIDED FER- 

 RIC^ HYDRATE, ESPECIALLY IN THE ABSENCE OF LIME 

 CARBONATE, RENDERS EVEN^ LARGE SUPPLIES OF PHOS- 

 PHORIC ACID INERT AND USELESS BY^ THE FORMATION 

 OF IN^SOLUBLE FERRIC PHOSPHATES. ALUMINUM HY- 

 DRATE ACTS IN A SIMILAR MANNER." 



Lucius L. Van Slyke, of the Geneva Experiment Station, New York, 

 says: "Calcium compounds, especially hydrates and carbonates, change 

 insoluble phos])hates into forms that can be more readily utilized as 

 plant food. This action is based on the following chemical facts: the 

 phosphates of iron and aluminum are more or less prevalent in the 

 soil. These compounds become soluble only with extreme slowness 

 under ordinary conditions. Calcium compounds, especially hydrates 

 and carbonates, change these insoluble phosidiates into tricalcium ])hos- 

 phates which are more readily siduble in water containing carbon di- 

 oxide, as in the case of ordinary soil water. The api)lication of the 

 calcium compounds mentioned is, therefore, of marked value in this 

 way in case of soils rich in iron and aluminum compounds and poor in 

 calcium carbonate." 



The al>ove is the exact condition found in most of the soils of North 

 Carolina. They are low in lime carbonate content and high in iron and 

 aluminum oxide content. 



Dr. Van Slyke further states: "The extent and value of the change 

 involved in this action of certain calcium compounds has not been suffi- 

 ciently appreciated. !Most agricultural writers advise against the use 

 of calcium compounds in soils where s(duble calcium phosphate (super- 

 phosphate) is used on the ground that PHOSPHORIC ACID AV I LL . 

 BE RENDERED LESS EFFICIENT AS PLANT FOOD. This 



