No. 6. DEPARTMENT OF AGRICULTURE. 167 



(5.45) inches, and a tube one-thousandth of an inch in diameter will 

 lift it over tifty-four (54.o6) inches. If there are any subsoils that 

 maintain a giouud water level (full saturation) within four feet 

 of the surface, then capillary water would rise from this water level 

 into the soil above to a height that will be proportioned to the fine- 

 ness of the soil particles, and if so fine that the spaces between will 

 be at all points not less than one-thousandth of an inch in .-...meter, 

 then the water will rise into the soil above this ground water level 

 fifty-four inches, or within six inches of the surface. As this degree 

 of fineness rarely exists at all points under natural conditions, the 

 capillary rise is more frequently within the limit of one or two feet. 

 This would bring the capillary water within two or three feet of the 

 surface. Where the surface soil holds water in excess, and requires 

 drainage, to remove the surplus and fit the supply to the needs of 

 plant life, then the height to which capillary water will rise may 

 become important in determining the depth at which to place tile 

 drains. For instance, if the subsoil is of suMciently fine texture 

 to lift the capillary water three feet, then a tile laid at the depth of 

 four feet would lower the ground water to that level, and the capil- 

 lary water would come to within one foot of the surface, furnishing^ 

 a fixed supply of moisture to the deeper roots of growing vegeta- 

 tion, so long as that ground water level was maintained. If, however, 

 the subsoil is of a texture that could lift water but two feet, then 

 the tile drain should be placed at the depth of three feet to bring the 

 capillary water equally near the surface. But this condition can 

 apply to a very limited area. The more prevalent condition after 

 June first is a ground water level so deep that the capillary rise 

 from it can never benefit the deepest rooting trees or- plants. Our 

 surplus water disposes itself by simply thickening the films to half 

 saturation, as far down in the soil as the supply will go, 



SURFACE TENSION. 



The majority of farmers are now familiar with the capillary rLse 

 of water from ground water level, but the movement of the water 

 when the .soil is less than half saturated, and no ground water level 

 within available distance, is less understood, but most important to 

 understand, because it is the only water available to the plant, the 

 water most easily lost and most under control of the tiller of the 

 soil. 



I hold in my hand a rubber band. I stretch one-half to its fullest 

 limit. You will notice that the farther the rubber is stretched, the 

 thinner it gets, and the tighter it grips over my thumb. The other 

 half of the rubber is of normal thickness, and presses lightly against 

 the finger. By holding my hands the same distance apart and freeing 

 the center of the band, you will notice that the tension has been dis- 

 tributed equally at all points, and the band is of equal thickness at 

 all points. This does not illustrate the principle that moves the 

 water over the surfaces of the soil grains, but it does illustrate the 

 method. When the film water is thinnest it is held with the greatest 

 force against the exposed surfaces, and where thickest, it is held 

 with least force. The greater tension of the thinnest film is all 

 the time drawing water from the films that are thicker in an effort 

 to adjust the differences between the.m and make the tension equal 



