252 AGRICULTURE 



This is to say that they can not grow in a soaked soil. "Wa- 

 ter-logged" soil excludes air from the roots, and the plants 

 soon suffer for want of oxygen. Standing water also keeps 

 the roots of most plants too cold for good growth. Hence 

 the necessity of conditions that will allow the soil to drain 

 readily after rains, so that the free water may escape. 



Capillary water. Soils will not drain entirely dry. 

 After your funnel of earth has lost all the water that will 

 run from it, it is still wet. This wetness is caused by what 

 is called capillary water. 



Capillary water exists in the form of thin films around 

 the soil particles and in the spaces between them, as de- 

 scribed in an earlier chapter. Each separate particle is sur- 

 rounded by its own film, while larger films bind the separate 

 particles together in granules. Since the particles of a given 

 weight of soil of fine texture present a larger surface area 

 than the particles of a soil of coarse texture, it is evident 

 that the finer the soil the greater the amount of capillary 

 water required to make up the films. 



Plant growth and capillary water. It is the capillary 

 water of the soil that plants use in their growth. Their 

 root tips come in contact with the water films surrounding 

 the soil particles and drink this water in. One of the first 

 requisites of a good crop soil, therefore, is its ability to act 

 as a reservoir for a large amount of capillary water. 



2. Capacity of Soils of Capillary Water 



Soils differ greatly in their capacity for capillary water. 

 This can easily be shown by a simple experiment. Bake a 

 pint of sand and a pint of clay until all the water is dried 

 out; then place the samples in separate funnels over the 

 lower end of which is tied a piece of cheese cloth. Now 

 slowly pour water from a graduate over each soil until the 



