66 THE ESSENTIALS OF AGRICULTURE 



This is the water which forms the water table. The wet, seepy 

 places on hillsides are usually caused by gravitational water flow- 

 ing along the top of a heavy layer of clay beneath the ground 

 until it reaches the surface on a hillside. 



At all times, except when the soil is saturated, there is more 

 or less movement of the film, or capillary, water of the soil. If 

 the subsoil contains less moisture than the surface soil, the capil- 

 lary movement is downward. If the subsoil contains more water 

 than the surface soil, the movement of capillary water is upward. 

 During the warm summer months the loss of water by evapora- 

 tion from the surface of the soil is considerable, especially 

 where the surface is not covered with a crop and where no care 

 is taken to check evaporation by proper tillage. 



72. How to save the soil water. Where the surface of a soil 

 is compacted, the capillary water can move directly to the surface 

 and evaporate into the air. If, however, the soil is stirred or 

 cultivated to a depth of two or three inches, the capillary rise 

 of water will be checked at the point where the cultivated and the 

 uncultivated layers of soil touch, and the loose layer of surface 

 soil will serve as a blanket to retard the evaporation of the water 

 from the surface. This is known as a soil mulch. The principle 

 of soil mulching is employed in the preparation of land for grain 

 crops in all parts of the country, as well as in the cultivation of 

 intertilled crops. 



73. Preserving a soil mulch. A soil mulch is destroyed by 

 a rain which packs the surface soil. The mulch should, if pos- 

 sible, be renewed by stirring as soon as the soil is dry enough 

 to pulverize. In time a mulch settles together without rainfall, 

 and it should be stirred occasionally, even though no rain falls. 



There are times when the surface layer of the soil is porous and 

 dry and it becomes desirable to increase the rise of capillary water. 

 This may be done by rolling, which compacts the soil and brings 

 more particles into contact, thus drawing moisture nearer the sur- 

 face by capillary action. This treatment may be of importance in 

 hastening the germination of grain. It is usually wise to follow 

 a roller with a harrow within a few days to form the soil mulch again. 



