SOILS AND FERTILIZERS 443 



it is important that the farmer should know whether it is the 

 soil or the plant that needs the food. The food may be in the soil, 

 but not in a condition that the plants can make use of it. In that 

 case a fertilizer that will release the food and make it available is 

 needed. 



FERTILIZER REQUIREMENTS OP DIFFERENT SOILS AND CROPS. 



Nitrogen, phosphoric acid, and potash are the constituents most 

 likely to be deficient in soils or most quickly exhausted by the pro- 

 duction and removal of crops. They are known as essential fertiliz- 

 ing constituents, and the value of a commercial fertilizer is deter- 

 mined most exclusively by the amount and form of the nitrogen, 

 phosphoric acid, and potash which it contains. It does not follow, 

 however, that all soils or crops will respond equally to applications 

 of materials containing these elements, for the needs of soils and the 

 requirements of crops vary. 



Soils differ as to their needs for specific fertility elements, owing 

 to their methods of formation or to their management and cropping. 

 A sandy soil is usually deficient in all the essential plant-food consti- 

 tuents nitrogen, phosphoric acid, and potash while a clayey soil 

 usually contains the mineral elements in abundance particularly 

 potash. On the other hand, a soil very rich in vegetable matter is 

 frequently deficient in mineral matter, while a limestone soil is 

 likely to contain considerable proportions of phosphoric acid. These 

 are tne indications in a general way, and they explain why it is that 

 different kinds of soil that have not been cropped differ as to their 

 need of the different fertilizing constituents. 



The soils of no two farms are alike neither are the soils of two 

 fields on the same farm exactly alike. The total plant-food in one field 

 differs from that of the adjoining field; the amount of decaying or- 

 ganic matter (humus) differs in different fields; the degree of coarse- 

 ness or fineness of the soil particles varies greatly ; the moisture con- 

 ditions of no two fields are identical ; neither are other physical con- 

 ditions, nor texture of the soil exactly alike in two different fields 

 and so on with an almost infinite number of conditions, each having 

 more or less influence upon the fertility or productivity of the soil, 

 each having its influence upon plant growth. 



Every observing farmer is familiar with the fact that while he 

 can raise from seventy-five to one hundred bushels of corn per acre 

 upon one part of his farm, another part of the farm will produce only 

 from fifteen to twenty-five bushels per acre. He is also painfully 

 cognizant of the fact that it requires more labor to produce the less 

 number of bushels than it does to produce the greater. There are 

 many causes for these failures, such as too much, or too little mois- 

 ture, compactness of the soil, and other physical conditions, which 

 incapacitates the plant for taking its food, or rendering the plant 

 food contained in the soil unavailable. It is not, by any means, an 

 easy task to overcome these difficulties. 



The results of experiments made at the various Experiment 

 Stations bring out in a striking manner the fact that soils vary widely 



