THE EXPERIMENT STATION. 



135 



Percolation in Damp Soils. 



The time required for water to flow through air-dry soil, and the quantity 

 required to wet them is hardly a fair test, because we never find 35 inches 

 depth of such dry soils in lands used for farming in this climate. After the 

 soil in these tubes had been thoroughly wet, the tubes were left freely 

 exposed to the air in a room, well ventilated, for 33 days of hot and drying 

 weather. Evaporation could, only take place at the top of the closed tubes, 

 representing a soil where only surface evaporation is possible, while evapora- 

 tion could freely take place in the perforated tubes from both top and 

 bottom, representing in an exaggerated degree a tiled field. 



At the close of this " drought " of 33 days the tubes were again weighed to 

 determine the loss of water by evaporation and the amount still retained in 

 the soil. The following table exhibits the results : 



Loss by Evaporation from Drained and Undrained Soils. 



Air Dry Soil in 



Open tubes... 

 Closed tubes. 



Average Weight of Water Re- 

 tained by Soil. 



At Beginning of 



33 Days' Drought. 



' Grammes. 



323.43 

 358.15 



At End of 



33 Days' Drought. 



Grammes. 



223.76 



288.80 



Evaporation. 

 Grammes. 



99.67 

 69.35 



On drenching these soils it was found that the moist garden soils in per- 

 forated tubes required 4.45 inches in vertical column of water to saturate 

 them, and the average time for water to percolate through 36 inches of this 

 moist soil was 9£ hours ; while the soils in the closed tubes required for satura- 

 tion a vertical column of 2.35 inches, and 11 hours time. It will be noted 

 that soils in the closed tubes required only about half as much water to wet 

 them down as the soils in the perforated tubes, though it required a longer 

 time. The rapidity with which a drained soil takes up the rain when it 

 falls after a dry spell is not to be overlooked in discussing tile-draining. 

 This singular fact came out in these experiments that at the second wetting 

 of these soils after 33 days of dry weather as regards the soil in the tubes, 

 the drained soils absorbed and retained by capillary action an average of 

 34.47 grammes (or .67 inch vertical column) more water than at the first 

 wetting of the air-dry soil, while the soils in the closed tubes could not take 

 up as much water by capillary action as at the first wetting, the loss of 

 capillary power being 8.57 grammes (.17 inch vertical column of water). It 

 thus appears in this experiment that the underdrained soil has an increase 

 of 12.6 per cent of capillary power over the soil destitute of drainage. The 

 draining and the non-draining of the soils in these experimental tubes are 

 both in exaggerated form. But even if we estimate this increase of absorp- 

 tive power in a tile-drained field at only one-third of the amount found in 

 these tube experiments, this will enable the tiled field to take up and retain 

 after a dry spell, one-fifth of an inch of rainfall more than the field 

 destitute of drainage, in case of copious rainfall that comes in a short 



