FORTY-FIRST ANNUAL CONVENTION 339 



the past fifteen years, and also in harmony with the general prac- 

 tice of soil improvement in Illinois. 



The normal soils of Illinois actually contain from 25,00a 

 to 45,000 pounds of potassium per acre in the first 6 2-3 -inches, 

 corresponding to two million pounds of soil; while 200 pouhds 

 of the most common commercial fertilizer would add less than 

 4 pounds of potassium to an acre of land. 



The Illinois system of permanent fertility does not provide 

 for the purchase of potassium for normal soils, but it does pro^ 

 vide for the liberation of abundance of potassium from the praci* 

 tically inexhaustible supply in the soil. This liberation is ac- 

 complished by the action of decaying organic matter plowed 

 under in the form of farm manure or crop residues, including' 

 clover or other legumes. 



Only where the soil is positively deficient in potassium sus- 

 ceptible of liberation need potassium be purchased in permanent 

 systems of grain or live-stock farming. Such are some sand 

 soils and most peaty swamp lands. In market gardening and in 

 some other special types of farming, commercial potassium^may 

 be required; and on some worn soils especially deficient in de- 

 caying organic matter temporary use of kainit often is advis- 

 able. 



As a general average the normal soils of Illinois contain 

 more than four times as much potassium as magnesium, while 

 the loss by leaching and cropping in rational systems of grain 

 farming or live-stock farming may be greater for magnesium 

 than for potassium, so that magnesium is more likely to become 

 deficient in such soils than is potassium. The calcium supply in 

 normal soil is also only one-fourth that of potassium, while the 

 average loss by cropping and leaching is four times as great ; so 

 that 16 to I expresses the relative -importance of calcium and 

 potassium in the problem of permanent fertility on normal Illi- 

 nois soils. 



All limestones contain calcium; and the dolomitic limestone 

 in the almost measureless deposits of northern Illinois contains 

 both calcium and magnesium in very suitable form both for 

 plant food and for correcting or preventing soil acidity. In the 



