44 SOIL MOISTURE} 



ground water. It is also called the water table. In many parts of 

 Florida the water table is within a foot of the surface. In other 

 places it varies from a few feet to several hundred. When the 

 ground water is near the surface it fills all the spaces of the soil; 

 and as the air cannot enter the roots of the plants, they cannot grow 

 and soon die. In many cases this can be remedied by proper drain- 

 age. Ground water serves its purpose better when it sinks below 

 the surface of the soil about three or four feet. 



Capillary Water. We have frequently noticed that the oil 

 passes upward through a lamp wick as fast as it burns in a lamp. 

 When we examine the wick, we find that it contains a number of 

 small spaces or pores connecting with one another. The oil 

 passes from one space to another, and the force which causes it to 

 rise is called capillary attraction or capillarity. Water will rise 

 in the same way through the small spaces between the soil par- 

 ticles. In dry weather water rises from the moist soil below to 

 supply the plants. If we leave a plank on the ground until the 

 next day and pick it up again, we find that the lower surface is cov- 

 ered with moisture brought from the ground by capillarity. A 

 loose blanket of plowed soil acts in the same way and serves as a 

 trap to hold the moisture. From this we learn that frequent 

 shallow plowing in dry weather is one of the best possible ways of 

 saving soil moisture. This is a principle in " dry farming." 

 Capillarity is feeble in sandy soils because its particles are so far 

 apart. Many clay soils, on the other hand, are glutinous and the 

 grains enlarge upon becoming wet and greatly retard the capillary 

 movement. Capillarity w r orks best in soils of medium texture. 



Hygroscopic Water. Every particle of dust, no matter how 

 dry it appears, contains some moisture. Its presence can be de- 

 tected by heating a small quantity of dry dust in a test tube to a 

 temperature of 212 F. On allowing it to cool, drops of moisture 

 will collect on the sides of the tube. The soil will suffer a loss in 

 weight from 1 per cent to 10 per cent or more. Again, in some 

 brick-making plants where hard pressed brick are manufactured, 

 the dry clay is put in molds, and after being subjected to heavy 

 pressure the clay comes out looking as damp as if it had been mixed 

 with water, although not a drop of water is added to it at any time. 



Uses of Soil Moisture. We may mention four important pur- 



