The copper era and Morenci leader., 1912-01-05
ESCAPE OF MOISTURE
Conditions of the Evaporation of
 Water From Soil.
Under Ordinary Conditions 1t Is I'm possible to Remove All Liquid Mat ter, for Small Quantity Is
 Strongly Attracted.

Evaporation does not alone occur from the surface of free water All wet or moist substances lose by evap- oration most of the water that they hold, providing the conditions of tenn perature and relative humidity are fa- vorable. Thus, from a wet soil, evap- oration is continually removing wa ter. Yet, under ordinary conditions, it is impossible to remove all the water, for small quantity is attract ed so strongly by the soil particles that only temperature above the boiling point of water will drive it out This part of the soil is the hygroscopic moisture.
 Moreover, it must be kept in mind that evaporation does not occur as rapidly from wet soil as from water surface, unless all the soil pores are. so completely filled with water that the soil surface is practically water surface The reason for this reduced evaporation from wet soil Is almost sel1-evident. There is a comparative ly strong attraction between the soil and water which enables the moist ure to cling as thin capillary film around the soil particles, against the force of gravity. Ordinarily only cap Hilary water is found in well-tilled soil, and the force causing evapora- ton must be strong enough to over come this attraction besides chang ing the water into vapor.
 The less water there is in the soil, the thinner the water film, and the more firmly is the water held. Hence. the rate of evaporation decreases with the decrease of soil moisture. | This law is confirmed by actual field tests. For instance, in an average of 274 trials made at the Utah sta | tion, it was found that three soils. l otherwise alike, that contained respec- lively, 22.63 per cent, 17.14 per cent, and 12.75 per cent. of water lost in two weeks to a depth of eight feet. respectively, 21.0, I'll, and 100 pounds i of water per square foot. Similar experiments conducted elsewhere also furnish proof of the correctness of this principle. From this point of view the dry farmer does not want his soils to be unnecessarily moist The dry farmer can reduce the per cent. of water in the soil without di minishing the total amount of water | by so treating the soil that the water will distribute itself to considerable depths. This brings into prominence again the practice of fall blowing
 deep blowing, sub-soiling, and the choice of deep soils for dry farming.
 Very much for the same reasons evaporation goes on more slowly from water in which salt or other sub stances have been dissolved. The at traction between the water and the enough to resist partially the force causing evaporation. Soil water al ways contains some of the soil ingre dients in solution, and consequently under the given conditions, evapora tion occurs more slowly from soi water Now, the more fertile the soil is, that is, the more soluble
 plant food it contains, the more ma
 terial will be dissolved in the soi
 water, and as result the more slow ly will evaporation take place. Fol lowing, cultivation thorough blowing
 and maturing, which increase thu
 store of soluble plant food, all tent : to diminish evaporation. While thes , conditions may have little value il . the eyes of the farmer who is unde
 an abundant rainfall, they are o
 great importance to the dry farmer . It is only by utilizing every posst l bility of conserving water and fer 3 tility that dry farming may be made : perfectly safe practice.