40 vermont agricultural report. 



nature; of capillary watlr. 



Before the consideration of the specific tillage operations in 

 their relation to moisture conservation is taken up, a clear idea 

 should be had of the method whereby the soil moisture reaches 

 the surface of the standing water levels as well as of the way in 

 which tillage retards its escape from the surface of the soil. 



It has been said that the soil moisture which is 

 really available for crop growth is that which is known as capil- 

 lary water. The soil is not a solid and impervious mass, but is 

 full of pores ; otherwise water could not sink into it. Different 

 soils contain different proportions of pore space, varying all the 

 way from a quarter to a half of their bulk. Even the hardest 

 Macadam roadway contains some pore space. These openings 

 between the irregularly shaped soil particles are very minute and 

 are of an infinite variety of shapes. They act, so far as soil 

 moisture is concerned, like capillary tubes. A capillary tube, as 

 its name indicates, being derived from a Latin word meaning 

 hair, is a tube of extremely small diameter. In tubes of this 

 character liquids ascend against the force of gravitation to heights 

 which vary as to their diameters, being drawn upwards the higher 

 the smaller the diameter of the tube in which they are confined. 

 Thus, in glass tubes of the diameters mentioned below, water 

 rises above the level to the heights given : 



Diameter o.i inch; water rises above level 0.5 inch. 

 Diameter o.oi inch ; water rises above level 5.4 inches. 

 Diameter o.ooi inch ; water rises above level 54.0 inches. 



This phenomena is caused by the attraction of the glass for 

 the water. That such a force exists anyone can readily demon- 

 strate for oneself with the simplest apparatus, a narrow glass tube 

 and a tumbler of water. The oil in the lamp saturates the wick 

 in this same manner, being pulled upwards through the interstices 

 between the threads, incidentally saturating them in its passage. 

 In the same manner the blotting paper absorbs ink. Now the soil 

 moisture, drawn from the reservoir of the standing water of the 

 lower levels towards and to the surface by this capillary action, 

 passes off into the air — unless its passage is retarded or stopped. 

 It is vaporized by the sun's rays and by the wind. The action is 

 much like that of a lighted lamp. The oil in the lamp represents 

 the water table, i. e., the level of the standing water in the well, 

 the wick represents the soil and the flame the sun's rays. A few 

 hours of illumination and the oil has been drawn up through the 

 wick, burned and the products of combustion vaporized. A few 

 hours of brilliant sunshine and vast quantities of water have been 

 drawn up through the soil and vaporized from its surface. Im- 

 mense amounts, thousands of tons annually per acre, are thus lost 



