10 SOILS AND FERTILIZERS 



weight. 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 example, 

 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. A 

 peaty soil containing i per cent, of nitrogen and 

 weighing 30 pounds per cubic foot has less total nitro- 

 gen than a soil containing 0.40 per cent, of nitrogen 

 and weighing 80 pounds per cubic foot. 



The weight of soils per cubic foot is approximately 

 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 and 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. 



The volume of a soil varies with the conditions to 

 which it has been subjected. Usually about 50 per 

 cent, of the volume is air space. A cubic foot of soil 

 from a field which has been well cultivated weighs 

 less than from a field where the soil has been com- 

 pacted. Hence it is that soils have both a real and 

 an apparent specific gravity. The apparent specific 



