162 AGRICULTURAL CHEMISTRY 



material which is taken from the soil. In 100 parts of 

 the dry material of any crop, from 5 to 10 parts are 

 derived from the soil while 90 to 95 parts are supplied 

 either directly or indirectly from atmospheric sources. 



210. Importance of Ash Elements. Plant ash is com- 

 posed of potassium, sodium, calcium, magnesium, iron, 

 phosphorus, sulfur, silicon, and chlorin compounds. 

 These elements, with a few others present in small 

 amounts, as aluminum and occasionally manganese, boron, 

 etc. , are the elements which make up the mineral matter 

 of plants. Some of the ash elements, as potassium and 

 phosphorus, are absolutely necessary for the life of the 

 plant, while others, as aluminum and silicon, are, so far 

 as known, unnecessary. The essential ash elements are 

 potassium, calcium, magnesium, iron, phosphorus and 

 sulfur. The non-essential elements are sodium, silicon, 

 chlorin, and aluminum. But in some alkali and sea 

 plants, sodium, chlorin, and other elements are essential 

 for growth. 



Chemically considered, the elements found in the ash 

 of plants are divided into two classes : 



(i) Metals or base-forming (2) Non-metals or acid-forming 



elements. elements. 



Potassium K Phosphorus P 



Sodium Na Sulfur S 



Calcium Ca Silicon Si 



Magnesium Mg Chlorin Cl 



Iron Fe 



Aluminum Al 



To the above list must be added small amounts of 

 other elements occasionally found in the ash of plants, 



