PHYSICAL PROPERTIES OF SOILS 19 



This water furnishes a means for the carrying on of the Hfe 

 processes of the plant. 5. Some water is actually built into 

 the tissues of the plant. Even though a piece of vegetable 

 matter seems quite dry, there is still moisture in it. This 

 may be easily noticed in the burning of a match. 



Kinds of Water in the Soil. — Even though the soil be as 

 dry as the dust im the road, it has moisture in it. If some 

 of this dry soil were heated at a boiling temperature for 

 two hours it would be found that the soil had lost weight. 

 The moisture contained in such dry soil is called hygroscopic 

 moisture. It exists there as a very thin film around each soil 

 grain. If you can think of a marble inside of a soap bubble 

 and the bubble shrinking down upon the marble you will 

 have a good idea of how the hygroscopic moisture exists in 

 the soil. Plants growing in the soil cannot make any direct 

 use of hygroscopic moisture. 



When the soil is in good condition to cultivate it contains 

 considerable moisture. The films around the soil grains are 

 thicker and some of the small pores between the grains are 

 filled with water. Such water is called capillary water and is 

 useful to plants. When all the little spaces are filled with 

 water and the soil is so wet that water is almo3t ready to drip 

 from it, the soil is said to be saturated. In this condition it is 

 too wet for farm crops to grow well. It must never be stirred 

 when it is so wet. Soil is in the best condition to farm when 

 it contains about one-half of the amount of moisture which 

 it contains when saturated. 



The water which oozes out of the soil and runs away in the 

 tile drains is called free water or hydrostatic water. The water 

 which runs down the slopes of the field without soaking into 

 the ground is also free water and is generally called surface 



