Chapter VT 



ENRICllINc; THK SOIL— COMMERCIAL 

 RESOIRC^ES 



O. W. CAVANAVQH 



1. riic i.lrtuiHts ni tilt Soil 



127. Cheinically, a fertile soil is one con- 

 taining an al)uu<lanee of availal)!*' i»lant-foo<l. 

 The substances which air iifffssary U^y tho 

 uTowth an<l welfare of plants are called plant- 

 foods. Tiiere are about ten essential dements 

 of plant- food. Six of these are <leriveil from 

 thf mineral jtart of the soil, — phosphorus 

 sulfur, iron, calfium, magnesium and potas- 

 sium. Nitrogen is contained in the humus. 

 Water sup|)lies the hydrogen an«l oxygen 

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

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

 ments of the soil always exist in quantities more 

 than suflieient to supply any possible iiimmI of 

 the j)lants. 



I'JH. Three of tiiese elements are often de- 

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



(87) 



