72 ELEMENTS OF FARM PRACTICE 



are two ways by which moisture is taken from the soil: 

 first, by the growing crops and, second, by evaporation 

 from the surface of the soil. The water that is evaporated 

 is worse than wasted. It is lost to the crop and its evapora- 

 tion tends to make the soil cooler. (Demonstrate this by 

 moistening the hand and exposing it to the air.) The hot 

 sun, the moving air, and the wind, greatly hasten evapora- 

 tion; hence it is evident that, if the part of the soil in which 

 the moisture is held can be separated from the sun and 

 wind, much less moisture will be lost by evaporation. 



Moisture moves in the soil by capillary force. For 

 example, two .particles of sand lie close together and one 

 is wetter than the other. The dryer one will attract some 

 of the water from the other until both are equally wet. 



Experiment. — This capillary movement of water may 

 be seen very plainly by following this plan as suggested: 

 Fill a glass half full of sand and pour in enough water to 

 thoroughly wet the sand, being careful not to wet the sides 

 of the glass. Now fill the glass with dry fine sand and 

 watch the moisture creep upward. The water is moving 

 by capillary attraction. Moisture will move by capillary 

 force in any direction, but always from moist to drier soil. 



Surface Mulch. — If you will go out in a field, on a bright 

 day, where cultivation is being done, you will notice that 

 very soon after the cultivator has gone over the ground 

 the surface soil begins to look dry, while the surface soil 

 where it has not been cultivated appears more moist. Moist- 

 ure is being evaporated from both surfaces, but where the 

 soil is firm moisture moves up from below to replace that 

 evaporated; and this process will continue if not checked, 

 until the soil is robbed of all available moisture. The 

 cultivated portion is so loose that the moisture cannot 

 readily pass up through it, as the particles of soil are not 

 close together, hence evaporation is checked. 



Too much attention can 'lardly be given to maintain- 

 ing this surface mulch, or loose soil on top. A shower of 

 rain just sufficient to pack the surface may be more injurious 

 than beneficial to a crop, by ci using a great loss of moisture,' 

 unless the soil is cultivated S( on after the shower. 



Destruction of Weeds. — / Mother reason for cultivating 



