VI. SOIL INGREDIENTS 



THE most important ingredients of soil are sand, clay, lime, 

 and organic matter. 



Sand. Quartz sand is composed chiefly of silica. It contains 

 very little nutriment for the plant, but it makes soils porous and 

 loose, so that air and moisture may reach the roots of the plant. It 

 also raises the temperature of the soil, as it is rapidly heated by the 

 sun's rays. Water works its way very easily through sand and 

 dissolves no appreciable amount of it. Hence it holds but little 

 moisture and soon dries out. This being the case, it is not sur- 

 prising that very sandy soils are poorly adapted to plant growth. 



Cla^ consists of very fine particles of certain rocks. Ordinarily 

 it contains a mixture of silica and alumina with certain impurities, 

 especially potash. Although not a valuable plant food, clay has 

 the important property of absorbing and retaining phosphoric 

 acid, ammonia, lime, and other substances which are needed in 

 plant nutrition. Pure clay has no grit in it, but feels smooth and 

 velvety. When mixed with water it becomes sticky and forms a 

 pasty mass like putty. Silt is like clay in composition but its 

 particles are larger. 



Sand and Clay Compared. If we examine sand and clay 

 closely, we find many points of difference. Moist clay sticks closely 

 together and may be molded into almost any form, while sand 

 readily falls apart. Water readily passes through sand, while 

 clay retains it. The sun's rays are more readily absorbed by sand 

 than by clay, and hence a soil containing sand is always warmer 

 than one containing clay. If you have a thermometer, compare 

 the temperature of a pint of sand with the temperature of a pint 

 of pulverized clay. Then place each sample in a tomato can and 

 after pouring a moderate quantity of water on each see which one 

 dries out first. 



Loam. A soil containing a mixture of sand and clay is called 

 a loam. If the clay predominates, it is known as a clay loam. 

 If the sand is largely in excess, it is called a sandy loam. 



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