118 A YEAR IN AGRICULTURE 



at once reduced to a consideration of the other elements, 

 nitrogen, potassium, phosphorus, calcium, and magnesium. 



The Illinois system of permanent soil fertility recognizes 

 that there is an inexhaustible supply of nitrogen in the air, 

 and provides for its utilization as needed; also that there is 

 an inexhaustible supply of potassium in the soil which may 

 also be liberated and utilized as needed. It also recognizes 

 that the supply of phosphorus in the common Illinois soil 

 is very limited, that phosphorus is contained neither in the 

 air nor in the rain, and consequently that phosphorus must 

 be purchased and applied to the soil in larger amounts than 

 are removed in crops if the productive power of the soil is 

 to be increased and permanently maintained. The Illinois 

 system also recognizes that soils should be sweet, not acid 

 or sour, and that ground limestone will destroy acidity and 

 also provide calcium, Avhich is sometimes deficient ; and, finally, 

 that if magnesium is also deficient in the soil, which is rarely 

 the case, it, too, may be provided, together with calcium, in 

 dolomitic limestone, which is the most common limestone of 

 northern Illinois, and which consists of the double carbonate 

 of calcium and magnesium. 



These are the simple basic facts which every man should 

 make a part of his ready knowledge, and then proceed to 

 make use of in his farm practice. 



There is no one order of procedure that is best under all 

 conditions, and the step which should be taken first in one 

 season may not be best in another season. However, these 

 are minor matters, the same as the time of plowing, the time 



