91 



i 



a soil, it is safe to say that the soil is not greatly deficient 

 in phosphorus, although a 1,000 pound application might still 

 be a profitable investment. At any rate, it can never do 

 any harm. 



How TO BUY PHOSPHORUS 



Phosphorus can be purchased in the form of bone meal, 

 acid cut rock phosphate, and raw rock phosphate. The results 

 of various experiments made at the Illinois Agricultural Ex- 

 periment Station at Urbana, prove conclusively that the most 

 economical method of increasing the phosphorus content of 

 the soil is by the application of finely ground rock phosphate 

 with stable manure, preferably spread on clover land. 



A good grade of rock phosphate should contain from ten 

 to twelve per cent of phosphorus. Since the phosphorus is 

 the only part of the rock that is of value to the soil, it should 

 be purchased on the basis of the phosphorus it contains. 

 The phosphorus is chemically locked up in the rock and 

 requires the action of some acid to liberate it and make it 

 available for plant use. For this reason it is best to apply 

 it with manure on clover fields. 



The acids in the manure and clover plant will set free 

 the phosphorus much more quickly than when applied to 

 some grain crop. The rock phosphate should be ground fine 

 enough so that at least 90 per cent of it will pass through 

 a one-hundred mesh screen. The finer it is ground the more 

 quickly it will be acted on by the acids in the soil. 



APPLICATION 



A good time to apply rock phosphate is in the fall. If 

 as much as twelve tons are needed, it is well to purchase it 

 in bulk by the carload. By getting a minimum carload, it is 

 much cheaper than buying in bags. A good method of 



