54 THE POPULAR SCIENCE MONTHLY 



But the other five elements require careful consideration if lands are to 

 be kept fertile. These are potassium, magnesium, calcium, phosphorus 

 and nitrogen; and every landowner ought to be as well acquainted with 

 these five elements as he is with his five nearest neighbors. 



Instead of making this acquaintance and gaining a knowledge of 

 important facts and principles, the average farmer in the older states, 

 with failing fertility, has made the acquaintance of the fertilizer agent ; 

 and instead of purchasing what he needs for the permanent improve- 

 ment of his soil, he buys what the agent wants to sell, with the common 

 result that the seller is enriched while the soil is merely stimulated to 

 greater poverty. 



Potassium. — A careful study of the facts shows that potassium is 

 one of the abundant elements in nature; that the average crust of the 

 earth contains 2^ per cent, of this element, and that normal soils bear 

 some relation in composition to the average of the earth's crust. 



If normal soil had the same percentage, then the plowed soil of an 

 acre 6§ inches deep (corresponding to 2 million pounds of soil) 

 would contain 50,000 pounds of potassium. In Illinois, the normal soils 

 actually do contain from 25,000 to 45,000 pounds per acre of this plant- 

 food element in the first 6| inches, while less than 4 pounds of potassium 

 would be added in an application of 200 pounds of the most common 

 commercial fertilizer. The Illinois system of permanent fertility does 

 not provide for the purchase of potassium for normal soils, but it does 

 provide for the liberation of an abundance of that element from the 

 practically inexhaustible supply in the soil. This liberation is accom- 

 plished 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 susceptible of 

 liberation, as is the case with some sand soils and with most peaty swamp 

 lands, need potassium be purchased in permanent systems of either 

 grain farming or live-stock farming; but in market gardening or in 

 raising timothy hay for the market commercial potassium may be re- 

 quired ; and, on some worn soils especially deficient in decaying matter, 

 temporary use of kainit is often advisable. 



Magnesium and Calcium. — As a general average, normal soils con- 

 tain more than four times as much potassium as magnesium, while the 

 loss by leaching and cropping in rational systems of grain or live-stock 

 farming may be actually greater for magnesium than for potassium, so 

 that magnesium is more likely to become deficient in soils than is po- 

 tassium. 



The calcium supply in normal soils is also only one fourth that of po- 

 tassium, while the average loss by cropping and leaching is four times 

 as great, so that 16 to 1 expresses the relative importance of calcium 

 and potassium in the problem of permanent fertility on normal soils. 



All limestones contain calcium ; and the common dolomitic limestone 



