PHYSICAL PROPERTIES OF SOILS II 



3. Weight. — Soils differ in weight according to 

 the composition and size of the particles. Fine sandy 

 soils weigh heaviest, while peaty soils are lightest in 

 w r eight. But when saturated with water, a cubic foot 

 of peaty soil weighs more than a cubic foot of sandy 

 soil. Clay soils weigh less per cubic foot than sandy 

 soils. The larger the amount of organic matter in a 

 soil the less the weight. Pasture land, for exam- 

 ple, weighs less per cubic foot than arable land. 

 Weight is an important property to consider when the 

 total amounts of plant food in two soils are compared. 

 For example, a peaty soil containing 1 per cent, of 

 nitrogen and weighing 30 pounds per cubic foot has 

 less total nitrogen than a soil containing 0.40 per cent, 

 of nitrogen and weighing 80 pounds per cubic foot. 



(1) The weight of soils per cubic foot is approxi- 

 mately as follows : 5 



Pounds. 



Clay soil 70 to 75 



Fine sandy soil 95 to 1 10 



Loam soil 75 to 90 



Peaty soil 25 to 60 



Average prairie soil 75 



Uncultivated prairie soil 65 



Figures for the weight per cubic foot or specific 

 gravity of soils are on the basis of the dry soil. When 

 taken from the field the weight per cubic foot varies 

 with the amount of water present. 



(2) The volume of a soil varies with the conditions 



