WHAT WATER DOES IN SOILS 51 



Why we irrigate. We irrigate to make up for lack of 

 rain, so that crops may get all the water they need at 

 the right time. Irrigation on a large scale is most 

 commonly done in the arid region, where there are few 

 or no ^summer rains. Lawns, flowers, and vegetable 

 gardens are watered more or less everywhere, so as to 

 push their growth as much as possible. 



How to irrigate. It seems most natural that we 

 should imitate the rain when we want to make up for 

 the lack of it, by sprinkling with a watering pot or hose 

 sprinkler. But that can only be done on a small scale, 

 and it is a very troublesome and wasteful way of using 

 water. It is wasteful because, as a rule, nearly half of 

 the water we sprinkle (particularly in the morning) 

 evaporates into the air, and so is of no use to the 

 plants. 



Flooding. A common way to irrigate is to flood the 

 fields or gardens from ditches. This is less troublesome 

 at the moment, but cannot be done well unless the 

 ground is nearly level. When the ground is uneven, 

 as it mostly is, we have to level it first, and throw up 

 little dams or dikes to hold the water long enough to 

 soak the ground. We call this " check irrigation " 

 (figure 25). 



Furrow irrigation. But when we flood land, we still 

 lose a great deal of water by evaporation. Therefore 

 where water is scarce, we mostly irrigate in furrows 

 (figure 26). That is, we draw furrows three to eight 



