WATER CONDUCTIVITY OF SOILS. 



149 



(4) Tlie l-apidity of drainage iu a grauular soil i.s indepeudeut of the size of the 

 grain. 



The experiments were made with soils of varying grain in tubes 110 centimeters 

 deep, the water drojjpiug on top constant] j"; the results ai'c exhibited iu the follow- 

 ing two tables : 



Water conductivit}) in soil with varying size of grain. 



Water conductivity in granular soils. 



Soila. 



Loam powder : 



to 0.25 millimeters. 

 0.5 to 1.0 millimeters 



Loam grannlfs : 



1 to 2 millimeters 



2 to 4 millimeters 



4 to 6.75 millimeters- 

 6.75 to 9 millimeters - 

 jUixturo 



Water sank to a depth of- 



Afterone 

 half hour. 



Cm. 

 9.0 



18.8 



After 1 

 liour. 



Cm. 

 32.1 

 32.2 



After 3 

 hours. 



Cm. 

 20.2 



82.4 



83.1 

 81.5 

 77.5 

 80.5 

 11.0 



After 4 

 hours. 



Cm. 

 23.4 

 100.0 



100.0 

 100.0 



99.6 

 100. 



19.5 



After 23 

 hours. 



Cm. 

 57.4 



After 59 

 hours. 



Cm. 



97.6 



24.1 



100.0 



According to Fesca the downward movement proceeds quickest in a 

 dry dust, only slowly in clay soils; tlie same amount of water being 

 drained through the former in one hour which it took two days to drain 

 through the latter. 



The influence of a soil cover on the physical condition of soils has 

 been investigated directly by Wollny ; he comes to the result that veg- 

 etation and cover with dead material (straw, litter, etc.) tend to i)re- 

 serve the loose granular structure of the soil. 



The forest cover, then, has a tendency to preserve the granular, porous 

 structure of the soil, which is favorable to tiltration ; and as, moreover, 

 the roots furnish cliannels for unimpeded drainage, it must have the 

 tendency, other things being equal, to allow a more rapid tiltration 

 than the naked, mostly compacted soil, or even that of a field of crops 

 after cultivation ceases. 



The temperature, too, appears to have an influence favorable to rapid 

 filtration in the forest; for, according to Pfaff", in the field during winter 

 three-quarters of the precipitation will sink to 2 feet depth in the soil, 

 and not more than 10 to 30 per cent in summer. 



Unless, therefore, the forest cover itself had a tendency to retard 



