SOILS AND THEIR MANAGEMENT 195 



strontium, zinc, etc., but more usually these are absent. 

 The analysis by your chemist friend will show that some 

 of the twelve elements in the list are only present in very 

 small quantities. The prevailing elements in a good loamy 

 soil are Calcium, Potassium, Aluminium, Silicon, and 

 Carbon. These are grouped together to form the following 

 ingredients of soils : clay (silicate of aluminium and potas- 

 sium), sand (oxide of silicon), chalk (carbonate of calcium). 

 And in addition to these mineral compounds we have 

 humus which is organic. 



Different Kinds of Soils : Everyone must have noticed 

 that there are many different kinds of soil. It may be 

 very light and sandy, composed largely of red sand, or of 

 yellowish sand ; or of clay containing iron (distinguished 

 by its reddish appearance) ; or of clay containing no iron 

 (usually grey or very yellow) ; or of really good black 

 earth. These are only a few of the many kinds of soils 

 he will meet. Two others I must mention are limey 

 or chalky soils containing as much as one-fifth of their 

 weight of carbonate of lime ; and humic soils containing 

 over much vegetable or animal humus. The nature of the 

 underlying rocks has, of course, much to do with the 

 nature of the soil. If they are of chalk or limestone the 

 soil will be chalky or limey, if of sandstone it will be sandy, 

 if of clay it will be clayey. 



What the Soil Provides : Now it will be evident that 

 the soil provides both board and lodging for our plants. 

 The soluble ingredients provide the board, or food of plants, 

 and are sucked up by the roots and used for building up 

 tissue. But plants also absorb carbon dioxide from the 

 air by their leaves, and some few also nitrogen for building 

 up root nodules. Nitrogen and carbon dioxide are found 

 in the air, so we may say that plants feed on the air as 

 well as the soil. 



The insoluble portion of the soil, whether mineral or 

 organic, provides lodging for the plants, and if the lodging 

 is not in a suitable friable condition, the roots of our plants 

 cannot work in it. Thus it is evident we must cultivate 



