94 SOILS AND FERTILIZERS 



rooting system is developed. By this method water 

 reaches the surface of the ground only by capillarity, 

 hence the soil does not become so packed as to exclude 

 the air and hinder root penetration. The furrows 

 should usually be run three to eight feet apart, de- 

 pending, as stated above, on the texture of the soil 

 and the consequent readiness with which the water 

 penetrates it. This point may easily be determined 

 by experiment before the furrows are laid out. 



After the water has been shut off from the furrows and 

 the surface has become dry enough, the furrows should 

 be filled again to prevent rapid evaporation. Losses 

 due to this cause often amount to as much as 50 per 

 cent of the water applied. 



Suggestive Experiment. To illustrate how irrigating furrows 

 moisten the soil laterally, bore a hole in the. middle of one side of a box 

 near the bottom and plug it up. Fill the box nearly full of dry, finely 

 crumbled soil. Make a shallow groove, or trench, across the middle 

 of the soil. Slowly pour water into it until the soil at the bottom 

 of the box is damp. This can be ascertained by removing the plug and 

 thrusting a small stick into the hole. Remove a layer of two or three 

 inches of soil near the trench and notice how far from the trench the 

 water has extended by capillary action. Continue removing layers of 

 two or three inches, and notice the difference in lateral extent of mois- 

 ture at different depths. 



Tiling or Subirrigation. What is considered by some 

 experts to be the climax of scientific irrigation and at 

 the same time the most economical method, is the laying 

 of porous tile pipe under the ground. Some writer* 

 call this subirrigation. The principle is the opposite 

 of that applied in drainage in that the pores and joints 

 of the pipes give out sufficient water to supply the plant 

 life above them. This plan is considered practicable 



