No. 6. 



DEPARTMENT OF AGRICULTURE. 



843 



sidered more in detail in connection %Yith the results of some experi- 

 ments treated of later in this bulletin, but a brief summary of the 

 principal points will be given in the following paragraphs. 



THE INFLUENCE OF THE CHARACTER OF THE SOIL UPON THE 



AVAILABILITY. 



The kind and character of the soil may influence the ease and 

 rate at which plants may be able to use the phosphate which is ap- 

 plied. A soil which is open and porous, and which admits of a freje 

 circulation of air and water, presents more favorable conditions for 

 the crops using the phosphates than on a close, compact soil. 



There is a marked dili'erence in the availability of phosphate 

 dependent upon the origin of the soil, and, hence, upon the chemical 

 and physical properties. Many phosphates will act well on clay 

 soils that are poorly adapted to the sandy soils, and some difference 

 is manifestly due to the different chemical properties of various 

 clay and sandy soils, dependent upon their origin. 



THE EFFECT OF ORGANIC MATTER UPON THE AVAILABILITY OF 



PHOSPHATES. 



Organic matter exerts a marked influence upon the physical 

 properties of a soil and, hence, in this way alone, may aid in making 

 applications of phosphate available. The formation of humic acid 

 and humates also works beneficial results. Again, the organic 

 matter is constantly undergoing more or less decomposition and 

 thus giving oft' carbonic acid gas, which unites with the soil water. 

 Water so charged has a greater dissolving action upon phosphates 

 than ordinary rain water, hence, the presence of organic matter 

 may render many phosphates available which would be entirely use- 

 less in the same soil without the organic matter. 



Some experiments conducted by Bretschneider to determine the 

 relative solubility of some phosphates in pure water and water 

 charged with carbonic acid show that one part of phosphoric acid 

 was dissolved in the several substances as follows 



Precipitated tri-ealcium phosphate, fresh. . 

 Precipitated tri-oalcium phn=ph;ite. ignited. 

 Precipitated di-calclum phosphate, fresh. . 



Ammonia and magnesia phosphate 



Precipitated Iron phosphate, fresh, 



Precipitated Iron phosphate, Ignited 



Bone black finely powdered 



87.K!2 



159 .^2 



29.S30 



21 957 



160.625 



732,958 



18.181 



13.321 



S.916 



1,969 



146.570 



782.958 



249,480 



