CHAPTER VI 



ENRICHING THE SOIL COMMERCIAL 

 RESOURCES 



G. W. GAVANAUGH 



1. The Elements in the Soil 



127. Chemically, a fertile soil is one con- 

 taining an abundance of available plant- food. 

 The substances which are necessary for the 

 growth and welfare of plants are called plant- 

 foods. There are about ten essential elements 

 of plant- food. Six of these are derived from 

 the mineral part of the soil, phosphorus 

 sulfur, iron, calcium, magnesium and potas- 

 sium. Nitrogen is contained in the humus. 

 Water supplies the hydrogen and oxygen 

 to the roots. Carbon comes from the air. For- 

 tunately, the greater part of the plant-food ele- 

 ments of the soil always exist in quantities more 

 than sufficient to supply any possible need of 

 the plants. 



128. Three of these elements are often de- 

 ficient in the soil ; or, if present, they may not 



(87) 



