144 



FOREST INFLUENCES. 



WATER CAPACITY AND WATER CONDUCTIVITY OF SOILS AND SOIL-COVERS. 



We must discern two kinds of water capacity in soils, namely, the 

 absolute or minimum water capacity and tlie full or maximum water 

 capacity. The former, also called ''moisture coefficient" in soil analy- 

 ses, is that water quantity which the soil will retain, no matter what 

 the drainage conditions, provided the supply is not deticient. It is this 

 water retained in the capillaries which determines the designation of 

 the soil as moist, wet, or dry, which latter is only comparatively so. If 

 the drainage is impeded by an impermeable layer underlying a porous, 

 permeable surface soil, and if the slope of the impermeable layer does 

 not favor rapid drainage, then if additional supplies reach the soil, all 

 interstices and h^rgest capillaries will fill up and the amounts of water 

 then contained in the soil represent its greatest (full or maximum) 

 water capacity. Any surplus above this greatest water capacity is 

 bound to drain ofl" at once either superficially or subterraneously. 



Absolute or minivium water capacity of soils according to Von Elenze. 

 [Volume unit, 3.5 cm. diam. by 10 cm. height.] 



Soil. 



Sand, loose.... \ 



Loau), fine, loose \ 



[ 



Humose lime sand, loose, fine I 



Height 

 of layer 

 in centi- 

 meters. 



10 



20 

 .30 

 40 

 10 

 20 

 30 

 40 

 10 

 20 

 30 

 40 



Weight of 

 water ab- 

 sorbed in 

 grams. 



44.6 



68.0 



83.8 



92.9 



43. ,5 



76.2 



106.8 



138. 2 



48.2 



79. 2 



113.1 



129.2 



Volume. 



Per cent. 

 20.99 

 24. 04 

 20. 37 

 17.58 

 48.27 

 47. 59 

 42. 08 

 38. 42 

 49.13 

 47.37 

 45.11 

 43.60 



Relation 

 of weight 

 to volume. 



44.0 

 34.0 

 27.2 

 23.2 

 43.5 

 38.1 

 35. 6 

 34.5 

 48.2 

 39.6 

 37.7 

 32.3 



Full or maximum ivater capacity of soils according to Meister. 

 [Volume unit 1 cubic foot]. 



Soils. 



Clay 



Loam 



Humus 



Peat 



Garden mold 



Lime 



Chalk 



Sand (82 per cent) 

 Sand (04 per cent) 

 Quartz sand 



Weight of 



water 

 absorbed. 



Povndg. 

 21.99 

 26. 40 

 30.90 

 27.99 

 30. 33 

 . 24.09 

 21.74 

 19. 94 

 28.67 

 20. 42 



Volume. 



Per cent. 

 50.0 

 60.1 

 70.3 

 63.7 

 69.0 

 54.9 

 49.5 

 45.4 

 6.5.2 

 46.4 



From the above tables it appears that with the depth of the soil the 

 minimum water capacity varies greatly, and the same may be expected 

 for the maximum water capacity. In sand it may sink within 15 inches 



