404 



SOIL PHYSICS AND MANAGEMENT 



free acids will inhibit the action. Chemical combination takes 

 place and calcium nitrites and nitrates are formed, the latter of 

 which are available for the use of plants. 



FIG. 194. Corn on peaty swamp land, 1903. Lime and phosphorus at top, yield 0. 

 Lime and potassium at bottom, yield 72.5 bushels per acre. (Bulletin 157, Illinois Agri- 

 cultural Experiment Station.) 



The element calcium is used by plants as food, as shown by the 

 table on page 390, and there is little doubt but that it may be limit- 

 ing the size of the crops on some soils. 



Soils frequently are acid or become so after long cropping, 

 bringing about conditions unfavorable for the growth of many 

 legumes. This acidity may be removed by the use of lime, lime- 

 stone, or some other carbonate. Many bacteria cannot develop in 

 an acid soil. 



