58 Effective Farming 



richer than others and will last longer, but even very rich 

 soils will wear out in time unless the supply of plant-food is 

 replenished. 



The growing of legumes is one method of helping to main- 

 tain soil fertility, but, as the legumes are instrumental in adding 

 only nitrogen to the soil, some other way must be found 

 to supply phosphorus and potassium. To this end certain 

 fertilizer materials containing these elements must be added 

 to the soil. A list and descriptions of these are given on sub- 

 sequent pages. 



Investigation by means of chemical analyses and practical 

 field tests can determine whether or not certain elements are 

 lacking in a soil. The experiment stations in most states have 

 made these tests for the important soil types and their officers 

 are able and willing to give information about the various needs 

 of the soils in their state. Often it will pay farmers to write 

 to these men concerning the best practice to follow in main- 

 taining the fertility of their farms. 



Removal of plant-food from the soil. Plant-food is removed 

 from the soil in several ways, chiefly by cropping, by soil 

 washing, and by leaching. A hundred-bushel crop of corn will 

 remove from an acre approximately 148 pounds of nitrogen, 

 23 pounds of phosphorus, and 71 pounds of potassium. A 

 fifty-bushel crop of wheat requires 71 pounds of nitrogen, 12 

 pounds of phosphorus, and 13 pounds of potassium. A four- 

 ton crop of red clover takes 160 pounds of nitrogen, 20 pounds 

 of phosphorus, and 120 pounds of potassium. From these 

 figures it will be seen that cropping, with the plants sold off 

 the farm, will soon remove much plant-food from the soil. 

 It has also been determined that only about 2 per cent of the 

 nitrogen, 1 per cent of the phosphorus, and ^ per cent of the 

 potassium in a soil is likely to be available for a crop in a season. 

 Experiments show that in one of the rich soil types of Illinois, 

 if hundred-bushel corn crops were removed each year, there 

 would be nitrogen enough in the soil to last thirty-four years ; 



