>5 



THE FORESTER. 



November, 



investigations found the ground-water of a 

 valley passing partly straight down the 

 valley in conformity with the surface con- 

 figuration and partly turning more or less 

 abruptly and passing under the hills and 

 coming out on the further slope. 



The capacity of the earth to receive and 

 convey water is all-important to us. 

 Whatever agencies give the rain freer ac- 

 cess to the earth should be well studied. 

 The condition of the ground-surface is of 

 vital importance and it is here that forests 

 exercise one of their most beneficent func- 

 tions a quality which in itself is more 

 than sufficient to justify our constant ef- 

 forts in preserving and extending our 

 wooded areas. 



All soils are dependent upon their top 

 surface as to whether they absorb water or 

 not. Take an extreme case : sand cov- 

 ered by an asphalt pavement, a great ca- 

 pacity for water but no mouth to take it 

 in. Take an ordinary case, as exempli- 

 fied by tests made at Colby, Kansas, by 

 the U. S. Department of Agriculture. 

 Comparative measurements of the moist- 

 ure in soil were made at a depth of twelve 

 inches under three separate conditions : 

 First, a covering of natural prairie sod ; 

 secondly, bare soil, top cultivated ; third, 

 bare soil, sub-cultivated. The tests were 

 continued daily throughout the months of 

 June, July, August and September. 

 Throughout the tests the cultivated soils 

 showed over twice the moisture in the 

 soil under the natural prairie top. 



It has been suggested that the chief 

 cause of the difference may have been clue 

 to the water taken up and evaporated by 

 the grasses. A study of the record at 

 times of rainfall, when there could have 

 been no evaporation to speak of, does not, 

 however, support any such assumption. 

 In fact it is of interest to note that evapor- 

 ation from plants which derive their water 

 supply from the capillaries of the soil does 

 not necessarily reduce the moisture of that 

 soil at any time ; that depends upon whetljer 

 the sub-water is ample to keep up the de- 

 mands of the capillaries. If the supply is 

 good, a pipe does not show less water be- 

 cause the faucet at the end is open. 



The percolation gauges at Rothamsted, 



the place previously spoken of, gave as an 

 average for 20 years that 47^ per cent, of 

 the total rainfall percolated through 20 

 inches of soil and 44.9 per cent, through 

 60 inches. The surface of the soil was 

 kept clear of vegetation. 



The capacity of sand for receiving and 

 transmitting water can be well illustrated 

 by the water supply of The Hague, cap- 

 ital of the Netherlands. The city is situ- 

 ated about two miles inland from the 

 North Sea and has a population of 190,000. 

 Its domestic water-supply is drawn from a 

 tract of uncultivated country lying near the 

 sea and covered with sand dunes, similar to 

 portions of the New Jersey coast. The 

 sand is described as very pure and white. 

 The water is fresh to a depth of 66 feet be- 

 low the sea. It is gathei'ed by infiltration 

 pipes and pumped to its destination. 



Through the courtesy of Mr. Corey, the 

 United States Consul at Amsterdam, I am 

 able to give the percentage of percolating 

 water as about 40 per cent, of the rainfall. 

 According to other information, from 30 

 to 50 per cent, of the rainfall can be col- 

 lected, the variation being according to the 

 season of the year. In summer a loss is- 

 stated . to take place by reason of vegeta- 

 tion. This draws attention to the point 

 that whether vegetation aids ground stor- 

 age or not depends largely upon the nature 

 of the soil. In the case of sand, such as 

 described, it is detrimental inasmuch as it 

 impedes penetration and aids the extrac- 

 tion of moisture. 



The water conductivity and capacity of 

 various soils have received much attention 

 at the hands of forest experimenters. By 

 conductivity is meant the capacity to 

 transmit water, and by capacity the quan- 

 tity that a given volume of soil can be 

 caused to receive into its interstitial spaces, 

 generally spoken of as its voids. Of the 

 quantity that can be thus introduced into 

 dry soil, part can be removed only by 

 processes of evaporation. It is held with- 

 in the capillaries and as films around the 

 grains, and will not yield to gravitation. 

 The texture of the soil is the governing 

 factor in rate of conductivity. It ranges 

 from well-rounded pebbles through the gra- 

 dations of sand and loam to clay. It requires 



