52 SUCCESSFUL FARMING 



decline, but not so rapidly as when nothing is applied. When the need 

 for phosphorus is met, then potash becomes the limiting factor, and large 

 applications of potash may be used in connection with phosphorus with 

 profitable returns. In this way there will always be a limiting factor in 

 crop production. The farmer should ascertain the limiting factors in 

 his crop production, and then supply them most economically. He may 

 find that there are several limiting factors, and that these will vary from 



SOIL FERTILITY PLATS, PENNSYLVANIA AGRICULTURAL EXPERIMENT STATION. 



On left, 200 pounds per acre muriate of potash every other year. 

 In center, dried blood containing 24 pounds nitrogen and dissolved bone-black con- 

 taining 48 pounds phosphoric acid. 



On right, dried blood containing 24 pounds nitrogen, muriate of potash 200 pounds. 



time to time; so the problem of soil fertility is a never-ending problem 

 with which the farmer will always have to contend. 



Fertility an Economic Problem. Soil fertility is a problem of far- 

 reaching economic importance. The principal items of expense in general 

 crop production are labor of men and horses, equipment, seeds and land 

 rental. These cost no more for a productive acre than for one of low 

 productivity. In fact, the productive soils are generally plowed and 

 cultivated at less cost of time and energy than those of low productivity. 

 Every hundredweight of product over that required to meet the cost of 

 production is profit. 



REFERENCES 



"Conservation of Natural Resources." Van Hise. 

 "Soil Fertility and Permanent Agriculture." Hopkins. 

 "Soil Management." King. 

 "First Principles of Soil Fertility." Vivian. 



