l6 FE;R'riUTY AND FERTILIZER HINTS 



exceedingly valuable but ordinarily field trials with crops prove 

 the better way of determining productiveness. 



The Essential Elements. — In the preceding chapter the elements 

 needed by plants were discussed and the composition of plants 

 given. From the composition of plants aided by field experi- 

 ments it has been possible to learn that certain elements are 

 necessary for plant growth. From this data it has been ascer- 

 tained that only three and sometimes four elements are required 

 to be furnished the plant for its complete development, as the 

 other elements are fortunately present in sufficient quantities in 

 the air and the soil so that we do not consider them. Nitrogen, 

 (N) phosphorus (phosphoric acid, PioO-,) and potassium (potash. 

 K2O) are the elements usually exhausted most readily from 

 the soil, and occasionally calcium (lime, CaO). Because of the 

 necessity of adding nitrogen, phosphoric acid and potash for the 

 growth of most crops, the name "essential" is applied to these 

 elements, and the remaining elements are termed ''unessential." 

 The essential elements, nitrogen, phosphoric acid and potash are 

 usually found in larger amounts in plants and in smaller quanti- 

 ties in soils than the other elements. Nitrogen and phosphoric 

 acid are usually more Hable to be deficient than potash, and lime 

 is only occasionally lacking. The term fertilizers is applied to 

 materials containing any or all of these essential elements, in 

 available form, and are supposed to make up for the deficiencies 

 in the soil. Fertilizers may contain other elements as magnesia, 

 sulphuric acid, etc., though needed by the plant are unessential as 

 the soil contains a sufficient amount for crops. 



The fifteen elements used by plants may be classified as: 

 Elements sometimes lack- Elements obtained from Elements that are pres- 

 in the soil the air or water ent usually in suffi- 



cient amounts 

 Nitrogen Hydrogen Calcium (usually) 



Phosphorus Oxygen Iron 



Potassium Carbon Sulphur 



Calcium (occasionally) Nitrogen (sometimes) Magnesium 



Silicon 

 Sodium 

 Chlorine 

 Manganese 

 Aluminium 



