SUPERPHOSPHATES AND El'I^ECT OE PHOSPHORIC ACID 89 



distribution takes place before the insoluble compounds are 

 formed. Soils rich in lime readily fix phosphoric acid and a 

 certain amount is probably fixed in combination with iron and 

 alumina. Experiments show that phosphoric acid is not carried 

 away by leaching to any extent. All soils are not of equal fixa- 

 tion value ; most soils fix phosphoric acid but some are better 

 equipped to perform this process than others. Clay soils rich in 

 lime fix phosphoric acid very rapidly while soils deficient in lime 

 act much slower in this respect. Sandy and gravel soils, lacking 

 in organic matter and clay, do not fix the phosphoric acid rapidly.* 



Functions of Phosphoric Acid. — Phosphoric acid hastens maturi- 

 ty of crops. It has a ripening effect and seems to hasten grain 

 and fruit formation ; it increases the yield of grain ; it stimulates 

 root development in young plants. 



Phosphoric acid helps in transferring substances from the 

 stalks, leaves, and other growing parts to the seed. Certain sub- 

 stances are aided by phosphoric acid by being rendered soluble 

 enough to pass through the plant tissues. 



Phosphoric acid helps to build up protein substances in the 

 plant as certain proteid bodies require phosphoric acid for their 

 complete development. Therefore a lack of phosphoric acid 

 would necessarily cause the plant to suffer.* 



The kind af phosphate to use depends upon the crop and the 

 soil. As a general rule the best immediate results are secured 

 from those phosphates that are acidulated and the raw phosphates 

 are slower acting and not so suitable for weak feeding crops. 

 To get the full benefit from raw products sometimes requires 

 two or three seasons, so that a farmer employing slowly avail- 

 able products should plan to add enough each year to supply 

 the crop with sufficient available phosphoric acid.* 



