176 SOILS AND FERTILIZERS 



fertilized with phosphoric acid have been found, in a number 

 of experiments conducted in Great Britain, to be more vigor- 

 ous and to develop faster than when no phosphoric acid was 

 applied. 



By balancing the effect of nitrogen, phosphoric acid pre- 

 vents an undue formation of straw, at the same time making 

 it stronger ; on the other hand, it increases the production of 

 grain in cereal crops. In the same way it increases resistance 

 to disease, probably by producing a more normal develop- 

 ment of the plant cells. 



An insufficient supply of phosphoric acid is less easy to de- 

 tect than is an inadequate supply of nitrogen, because its ef- 

 fect is exercised on the production of grain or other seeds, 

 rather than on the height and color of the plants. It re- 

 quires some care, therefore, to detect a lack of phosphoric 

 acid. * 



230. Plants particularly benefited by phosphoric acid. — 

 The crops that respond particularly well to applications of 

 phosphoric acid are turnips, barley, cabbage and other plants 

 of that family, beets, spinach, radishes and lettuce. Corn is 

 said to be well qualified to secure its phosphoric acid from the 

 natural phosphates, as are also some of the legumes. 



QUESTIONS 



1. Name the natural phosphate fertilizers. 



2. Why should natural phosphates be finely ground, when ap- 

 plied to the soil ? 



3. How does basic slag compare in availability with rock phos- 

 phate ? 



4. How is acid phosphate made, and how does it compare 

 in availability with the natural phosphates ? 



5. What is reverted phosphoric acid ? 



6. Why is soluble phosphoric acid not readily leached out of soil 

 after being applied as a fertilizer ? 



7. What phosphoric acid fertilizers may be used for top dressing 

 grass or other crops ? 



