)18 STATE BOARD OF AGRICULTURE. 



"(lew is formed from the vapor rising from the warmer soil into a colder 

 atmosphere" is wrong, and those who proposed and adhere to this theory 

 seem to be laboring under misapprehension of facts. 



MOVEMENT OF MOISTURE FROM MOIST AND WARM COLUMN TO DRY AND COLD 



COLUMN OF SOIL^ AND FROM TNIOIST AND COLD COLUMN TO 



DRY AND WARM COLUMN OF SOIL. 



The soil moisture under field conditions exists during the warm period 

 of the year, nearly always in a gradient form. During a long drought 

 the upper surface even dries out, either by its own accord or aided by 

 artificial means. This layer of di\y soil formed at the surface is known 

 as mulch. To this mulch is ascribed the important function of conserv- 

 ing the moisture in the soil by its ability to reduce evaporation of water 

 at the surface. It accomplishes this conservation of moisture, it is 

 claimed, by producing a change or break in the capillary connections be- 

 tween itself and the moist soil below. 



Since, on account of the kinetic energy, the absorptive and adhesive 

 forces of the solid substances decrease with rise in temperature, the inter- 

 esting question arose whether the dry mulch with an excessively high 

 temperature would absorb moisture from a moist soil with low tempera- 

 ture, even when the capillary connections were ideal. The desire to 

 secure information upon this important and exceedingly interesting 

 point led to the execution of the following experiments: Brass tubes de- 

 scribed in the preceding sections, were filled one-half with dry soil and 

 the other half with moist soil, and the two columns were separated only 

 by a circular piece of cheese-cloth in order to facilitate separation of 

 the two columns for moisture movement determinations. The tubes were 

 then inserted in the boxes shown in figure 1, and that portion of the 

 tubes containing the moist soil was kept at 20° and 40° C, and that 

 part which held the dry soil was maintained at 0° C. In another set of 

 tubes these temperatures were reversed. The soils employed were the 

 same as those previously described, namely : quartz sand, light and heavy 

 Miami sandy loam, Miami silt loam, Clyde silt loam and Miami clay. 

 There were three different moisture contents used for each soil, desig- 

 nated as, low, medium, and high. The duration of all experiments was 

 about 8 hours. The numerical data obtained are shown in table 4 below. 

 The accompanying figure 3 represents these same data graphically. Each 

 soil has two charts, the one to the left is for the temperature amplitude 

 of 40° C. and the one to the right is for the temperature range of 20° C. 

 The abscissas, in every case, represent percentage of moisture content, and 

 the ordinates, percentage of water moved either from the moist and warm 

 column to the dry and cold column of soil, or from the moist and cold 

 column to the dry and warm column of soil. The upper curves of each 

 chart represent the percentage of water movement that took place from 

 the moist and warm soil to the dry and cold soil, and the lower curves 

 show the movement of water that occurred from the moist and cold soil 

 to the dry and warm soil. As in the preceding case, the percentage of raois- 



