40 Effective Farming 



scopic water is present. However, it is of some use in hold- 

 ing plant-food in solution. 



Capillary water. As soon as the film of hygroscopic water 

 is satisfied, a film of capillary water begins to form around the 

 hygroscopic film and, as the moisture-content increases, capil- 

 lary water moves from place to place in the soil in the same way 

 that oil is carried through a lamp-wick. It occupies much of 

 the pore space in the soil and moves in every direction, up, 

 down, sidewise, from a wet portion to a dryer portion. When 

 moisture is used by roots or is evaporated from the surface, 

 capillary water moves to take the place of that removed. Capil- 

 lary water may be defined as that water in the soil that moves 

 from place to place by capillary force. It is the form of water 

 taken up by roots ; consequently in productive soils it is neces- 

 sary that abundant capillary water be present and that the 

 soil be kept in a favorable condition for its transference. 



Gravitational water. If the moisture-content of a soil is 

 increased beyond a certain amount, a point is reached where 

 the force of gravity on the soil-water is stronger than is the 

 capillary force and, as a result, drops of water move downward. 

 This movement is known as percolation and the water when it 

 fills all the spaces is known as gravitational. Below a certain 

 level, the soil is saturated with water. The distance of this 

 water-level below the surface is determined by the rainfall, 

 the condition of drainage, and the kind of soil. The top of 

 the water in surface wells is the top of the gravitational water. 

 Whenever capillary water becomes deficient, water from the 

 water-level, unless this is too far below the surface of the soil, 

 passes by capillary force to the dry portion. 



Water in percolating to the water-level carries much soluble 

 plant-food out of reach of the roots. This is known as leach- 

 ing and it is responsible for the loss of much plant-food annually. 

 If the water-level is very near the surface, there is too limited 

 a zone left for capillary water and growth cannot continue. 

 The remedy for such a condition is drainage. 



