SOIL MOISTURE 59 



wsitev is present, proper drainage may help; if too little, by- 

 adding water or by adding vegetable matter and barn manure, 

 to aid the soil in retaining water, the crops will be improved. 

 Soils with good texture are seldom too wet or too dry. The 

 average rainfall of a certain region may be enough, but the 

 best growth is impossible if the rain is not well distributed 

 through the growing season. 



Exercise. — Three Conditions of Water in Soils, — Fill 

 a glass jar or drinking glass with some fine sand or other 

 loose soil and pour in water until half full of free water. 

 Above the free water the soil wi 11 become wet with capillary 

 water. By stirring the top soil it will become dust like or 

 some dust may be spread on to p. The dust, though perfectly 

 dry in appearance, is supplied with fine film water. 



Just after heavy rainfalls the free water is close to the 

 surface, and falls lower at drier times. 



Capillary Moisture. — Capillary water clings to the sur- 

 faces of the soil particles and cannot be seen as free water can. 

 When a soil has all the capillary water it will hold, its presence 

 can be felt with the fingers. The color is darker than the 

 same soil when dried in the air. 



Take a pound of soil fresh from the garden and spread it 

 out on a paper to dry. The next day weigh it and determine 

 how much capillary moisture it has lost. 



Fine Film or Hygroscopic Moisture. — Dry dust from a 

 road contains a very fine film of moisture on each soil grain. 

 This is too fine to be seen. Put some road dust in the bottom 

 of a glass tube or vial and heat it gently. Moisture will be 

 seen collecting in the top of the tube. This was held in the 

 form of fine films on the soil grains before they were heated. 



Capillary Moisture Most Useful. — The roots of plants 

 take up capillary moisture. This in turn is supplied from 

 the bed of free water deeper in the soil. Farm crops cannot 

 make direct use of free water. Plants need air in the soil 

 about the roots. Free water would exclude the soil-air, and 



