i8 



FUNDAMENTALS OF AGRICULTURE. 



DEVICE TO ILLUS- 

 TRATE ACTION 

 OF CAPILLARY 

 WATER. 



remain in such a condition is said to be water-logged. 

 If now the stopper be removed a portion of the water 

 will be drawn off by the force of gravi- 

 tation, and it is often spoken of as the 

 gravitational water or drained water. 

 If the funnel is again stoppered and 

 allowed to stand with the surface ex- 

 posed a large part of the moisture re- 

 tained by the grains in clusters will 

 move up through the soil to replace 

 the loss by evaporation from the sur- 

 face. This upward movement of 

 water is produced by the surface ten- 

 sion of the moisture films which be- 

 comes greater as some of the water 

 is lost by evaporation. This move- 

 ment is of a capillary nature, and the 

 water held and moved by surface ten- 

 sion is therefore spoken of as the 

 capillary moisture of the soil. If this funnel of soil 

 be allowed to stand exposed in this way for several 

 days or weeks, protected from rain, the soil will ap- 

 parently become dry. It is air dry. However, if the 

 soil be now weighed and placed in an oven and kept 

 above the boiling point of water for a few hours and 

 again weighed it will be found to have lost more mois- 

 ture. Again if this oven-dry soil is exposed to the air 

 of the room for a few hours and re-weighed, it will be 

 found to have taken up some moisture. This moisture 

 taken up in this way is spoken of as hygroscopic mois- 

 ture. 



Drainage. The removal of gravitational water by 

 natural or artificial underdrainage is necessary since 

 if it remains in the soil the latter becomes water-logged. 

 The oxygen is absorbed by chemical combination of 

 substances in the soil and roots of crops are unable 

 to develop in it. Fresh water falling as rain absorbs 

 considerable oxygen from the air so that if there is a 

 more or less constant movement downward of rain 



