EVAPORATION OF SOIL WATER 



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creases the porosity of the soil will decrease the seepage and 

 thus help to retain the plant food. This may be done by 

 adding humus, and sometimes, where the soil is very porous, 

 by rolling. At the time rain is likely to fall, however, the 

 soil must be kept loose and mellow so that the water can 

 sink into it. 



Evaporation is, however, the cause of soil's losing the 

 greatest amount of water. Soil water is constantly mov- 



AN ARTESIAN SPRING 

 A deep water layer has been pierced and the water diverted to the surface. 



ing toward the surface on account of capillary action, and 

 is being evaporated. This loss by evaporation must be 

 counteracted, if in arid countries or during dry spells agricul- 

 tural plants are to be provided with sufficient moisture. 



Experiment 99. Fill full of soil four tin cans having small holes 

 punched in the sides and bottom. Water each with the same 

 amount of water. Cover the first with about an inch of grass and 

 the second with about an inch of sawdust, and weigh carefully. 

 Weigh the third and fourth. Record the weight of each. 

 Thoroughly stir the surface of the third, as soon as it is dry enough, 

 about an inch deep. Keep this stirred. Let the fourth stand 

 undisturbed. Weigh all four every school day for two weeks. 



