LESSON V 

 FERTILITY OF THE SOIL 



Fertile soil. The chemical composition and the 

 physical condition of the soil determine its fertility. 

 In order to be fertile a soil must have the mineral and 

 organic matter which gives food to the plants; and 

 it must also be in such a condition that the growing 

 plants can secure their food. 



Plant foods. The food of plants consists mainly 

 of carbon dioxide, water, oxygen, and compounds of 

 nitrogen, phosphorus, potassium, and calcium. Many 

 other substances furnish plant food, but these are of 

 greatest importance. Plants get carbon dioxide from 

 the air, water from the soil, and oxygen from the air 

 and the soil. The other food materials come from the 

 organic and mineral matter in the soil. 



Nitrogen is one of the most important elements in 

 plant food, and the securing of the needed supply of 

 nitrogen compounds is always one of the greatest 

 problems to the farmer. Although four fifths of the 

 air is nitrogen, yet plants cannot take nitrogen directly 

 from the air. They must obtain it from the nitrogen 

 compounds in the soil. Salts, called nitrates, are the 

 best nitrogen-giving foods for plants. These salts 

 and the organic matter in the soil furnish nitrogen. 



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