160 AGRICULTURAL ECONOMICS 



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. 



With phosphorus at 3 cents a pound, 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 

 station 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 f or 1 2 to 1 5 cents in acid phosphate. It can be used with 

 profit in any of these forms, but the data thus far secured in compara- 

 tive experiments plainly indicate that, with equal amounts of money 

 invested, the natural rock phosphate will give the greatest profit in 

 rational permanent systems, At least 1,000 pounds per acre every 

 four years should be applied, and for the first application even 3 or 4 

 tons per acre is not considered too much phosphate by those who best 

 understand the need and value of phosphorus on normal Illinois land. 



Nitrogen and organic matter. There is a rather common opinion 

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

 people even believe that clover in crop rotation will maintain the 

 fertility of the soil. Such opinions are largely erroneous. The mere 

 growing of clover on normal land does not enrich it. Even the 

 nitrogen is not increased unless the clover crop is returned to the soil, 

 either directly or in farm manure. Rotation with such crops as corn, 

 oats, and clover depletes the soil of all important elements of fertility, 

 and on normal soils always results ultimately in land ruin unless 

 some system of restoration is practiced. Clover takes large amounts 

 of calcium and phosphorus from the soil, and does not increase the 

 nitrogen content if only the roots and stubble are left, because they 

 contain no more nitrogen than the clover itself will take from soils of 

 normal productive power. 



To increase or maintain the nitrogen and organic matter of the 

 the greatest practical problem in American agriculture. In an 

 hour's time one can spread enough limestone or phosphate on an acre 

 of land to provide for large crops of wheat, corn, oats, and clover for 

 ten or twenty years, while to supply the nitrogen for the same length 

 of time would require from 20 to 40 tons of clover or from 80 to 160 

 tons of farm manure to be added to the same acre of land even though 

 one of the four crops harvested secured its nitrogen from the air. 



