THE RELATION OF THE PLANT TO WATER 159 



cent, of the water is unavailable for most of our crop plants, but 

 in the coarse sandy soils it may be reduced to 1 per cent. The 

 amount of unavailable water varies greatly in different types of 

 soil, as shown in the table : 



Hygroscopic Unavailable 



Water Water 



Coarse sand 0.42 1.5 



Ordinary garden soil 1.68 4.6 



Sandy loam 2.40 7.8 



Peat soil 20.60 49.7 



The amount of unavailable water also varies with the type 

 of plant, when grown in the same soil, as shown in the follow- 

 ing table: 



Plant Unavailable 



Water 



Morning-glory 3.0 



Cabbage 5.8 



Corn 5.9 



Sugar beet 5.9 



Oats 6.2 



Asparagus 7.0 



Lettuce 8.5 



Cucumber 10.8 



Water Movements in the Soil. The amount of water in our 

 agricultural soil varies from season to season and from day to 

 day. Immediately following a heavy rain the ordinary agri- 

 cultiiral soil is saturated and contains more water than is neces- 

 sary or can be used by the growing plant. In fact, the amount of 

 water may be so great as to be injurious to the growth of the 

 plants which ordinarily grow in that soil. This excess of water 

 sinks into the deeper layers of the earth or evaporates into the 

 air. During a period of reduced rainfall the evaporation of 

 water from the soil and the absorption of water by the plant 

 may reduce the water to a point below that necessary for the 



