30 AGRICULTURE 



earth-crust as the source of plant food, and it is these which supply 

 that food. 



In Nature's vast storehouse, most of the elements needed by 

 plants are placed within their reach, in bountiful quantities, 

 but sometimes one or more are lacking. The farmer who under- 

 stands this subject can supply the needed elements, and by thus 

 feeding his crop or fertilizing it, as we say can increase its yield. 



Let us consider, then, some of the elements in the earth- crust. 



Metallic Elements. Six important elements of the soil are 

 metallic, iron, cSl'ci um, mag ne'si um, po tas'si um, so'di um, 

 and al u min'i um. 



Iron is an important element everywhere abundant. It forms 

 from one to four per cent of the soil. 



Calcium is a yellowish metal. It is found in limestone. 



Magnesium is a hard, white metal. 



Potassium is a soft, whitish metal. With ox'y gen it forms 

 pot'ash, which is a compound of great importance in agriculture. 



Sodium is a soft, light metal, resembling potassium in appearance. 



Aluminium is a hard, white metal, like silver in appearance. 



Nonmetallic Elements. The most important and abundant 

 nonmetallic elements of the soil are sil'i con, sul'phur, phos'- 

 phor us, chlo'rine, oxygen, hy'dro gen, m'tro gen, and car'bon. 



Silicon is the second most abundant element in the earth's 

 crust, of which it forms from one fourth to one third. 



Sulphur is a pale yellow substance. 



Phosphorus is a soft, yellowish substance. It is usually found in 

 small quantities in the soil, and its lack is soon felt by plants. 



Chlorine is a gas of yellowish green color and disagreeable odor. 



Oxygen is a colorless gas, the most plentiful element in nature. 

 It forms one half of the earth-crust, one fifth of the air, and eight 

 ninths of the water. 



