PHOSPHORUS AND LIMESTONE 93 



these bacteria, it is impossible for clover, soy beans, cowpeas, 

 etc., to secure nitrogen from the air. If soil is very acid 

 (sour), legumes can not be grown until it has first been 

 sweetened by the application of limestone. Thousands of 

 acres of land in southern Illinois are now growing clover 

 where it was once thought such crops could not be grown. 

 In these cases, clover crops were made possible by the appli- 

 cation of limestone. 



To determine the acidity of soil, place blue litmus paper 

 between two layers of soil to be tested. If the paper turns 

 red in a few minutes the soil may be considered acid and the 

 application of from one to three tons per acre would prob- 

 ably be a very profitable investment. Ground limestone costs 

 from one to three dollars per ton, delivered at most Illinois 

 points. This difference in price is due largely to the differ- 

 ence in freight charges. (The state penitentiary at Chester 

 is the source of a considerable supply of crushed limestone.) 



Our soil is only very slightly acid. For this reason we 

 have never used any limestone on our own farms. However, 

 we intend to apply it to our alfalfa fields next year. 



POTASSIUM 



So far, we have said nothing about the plant food element, 

 potassium, for the reason that the common prairie soils con- 

 tain enough of this element to last for generations to come. 

 On the other hand, bottom lands, subject to overflow, already 

 show a shortage of potassium. Potassium is usually supplied 

 by applying muriate of potash. When muriate of potash is 

 applied to land that is not deficient in potassium it acts as 

 a crop stimulant rather than as a soil builder. Germany 

 is the principal source of potash. 



