PERMANENT FERTILITY 55 



in the almost measureless deposits contains both calcium and mag- 

 nesium in very suitable form both for plant food and for correcting or 

 preventing soil acidity. 



In the Illinois system of permanent fertility, ground natural lime- 

 stone is applied., where needed, at the rate of about two tons per acre 

 every four years. With the same price and purity, probably the dolo- 

 mite is preferable to the high calcium stone, although both kinds have 

 been used with very good results. Further data from investigations now 

 in progress are expected to furnish definite information as to the rela- 

 tive value of these materials. 



Phosphorus. — Attention was called to the fact that two million 

 pounds of the average crust of the earth contains 50,000 pounds of po- 

 tassium; but compared with this we find only 2,000 pounds of phos- 

 phorus. Likewise, the plowed soil of an acre of average Illinois land 

 contains about 35,000 pounds of potassium, but less than 1,200 pounds 

 of phosphorus. When grain is. sold from the farm, about equal amounts 

 of phosphorus and potassium are carried away, while in independent 

 systems of live-stock farming much more phosphorus than potassium 

 leaves the farm. 



At 3 cents a pound for phosphorus one can double the amount of that 

 element contained in the plowed soil of our $200 land at a cost of $35 

 an acre,, while to double the potassium in the same stratum would cost 

 more than $1,000 an acre. 



Phosphorus can be purchased, delivered at the farmer's railroad sta- 

 tion in Illinois, for about 3 cents a pound in the form of fine-ground 

 natural rock phosphate, for 10 to 12 cents a pound in steamed bone meal, 

 or for 12 to 15 cents in acid phosphate. It can be used with profit in 

 any of these forms, but the data thus far secured in comparative experi- 

 ments plainly indicate that, with equal amounts of money invested, the 

 natural rock phosphate will give the greatest profit in rational perma- 

 nent systems. At least 1,000 pounds per acre every four years should 

 be applied, and for the first application even three or four tons per acre 

 is not considered too much phosphate by those who best understand the 

 need and value of phosphorus on normal land. 



Nitrogen and Organic Matter. — There is a rather common opinion 

 that the growing of clover enriches the soil in nitrogen, and many even 

 believe that clover in crop rotation will maintain the fertility of the 

 soil. These same people are likely to think that the application of lime- 

 stone and phosphate involves much expense and work, and that the re- 

 turns are much less certain than those from other labor and money in- 

 vestments. 



Such opinions are largely erroneous. The mere growing of clover on 

 normal land does not enrich it. Even the nitrogen is not increased un- 

 less the clover crop is returned to the soil either directly or in farm ma- 

 nure. Eotation with such crops as corn, oats and clover depletes the 



