SOIL 



Hydrogen in water is necessary for the ab- 

 sorption of mineral salts in the soil and the life 

 processes of animals and plants. 



Phosphorus occurs in the oldest known rocks 

 and has been concentrated from the soil in tis- 

 sues of plants and animals. Deposits of animal 

 remains form valuable sources of commercial 

 fertilizers. 



Nitrogen, which is low in its chemical affini- 

 ties, is most abundant in air as free nitrogen and 

 least abundant in compounds in the earth's crust. 

 It occurs in humus and decaying tissues of ani- 

 mals and plants, and is converted into nitric 

 acid, which is soluble and available to plants. 



Aluminum is abundant in the earth's crust 

 and is a fundamental constituent of true clay 

 derived from feldspar and mica. 



Calcium and magnesium are indispensable to 

 plant-food and collect largely in seeds of plants, 

 as fruit and corn. 



Potash is widely distributed as a constituent 

 of feldspar, mica and kaolin beds. Potash, 

 magnesium and calcium aid in the transfer of 

 starch-forming parts to seed, root and tubers. 

 Plants can not thrive in soil destitute of nitrogen, 

 potash, calcium, magnesium and phosphorus. 



A heavy clay soil allows the threading of 

 roots with difficulty. A light sandy soil admits 

 of an equitable distribution of roots. Light and 



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