THE PHYSICAL PEOPERTIES OF SOILS 



layers because they are more compact, contain less humus, 

 and, often, more stones. In trials made at Eothamsted the 

 following results were obtained : 



Calculating from the volume weights given above, the 

 mass of an acre of sand 9 inches deep would be 

 2,950,101 Ibs., of clay, 2,058,210 Ibs. In the case of the 

 old pasture land at Eothamsted the mass of the first 

 9 inches would be 2,328,973 Ibs., and of the fourth 

 layer 3,343,737 Ibs. per acre. In round figures the mass 

 of an acre of land 9 inches deep may be from two to 

 three million pounds. 



MOISTURE. 



Importance of Soil Moisture. One of the most impor- 

 tant functions of soils is to supply water to the crops. 

 Fertility depends upon their capacity to adequately per- 

 form this, without interference with other functions, 

 perhaps more largely than upon any other single condition. 

 It is well known to farmers that a wet or a dry spot in a 

 field makes more difference to the crops than any manure 

 or treatment that can be applied to it. The capacity of 

 the soil to provide the necessary water depends upon the 

 climate and the physical properties mainly the size and 

 arrangement of the particles of the soil. 



