156 IRRIGATION. 



placing a few stout poles from each bank to the bottom 

 of the canal upon the opposite sides, crossing them and 

 placing upon them in a line with the canal a few rails or 

 poles to make a level passage. This leaves a passage for 

 the water in the canal, and by laying two or three poles 

 or rails on the ground at each side of the canal, the edges 

 will be preserved from injury. 



Generally, the season of irrigation in our Northern 

 States will be from April to October. As the climate be- 

 comes warmer, and as the Southern States are ap- 

 proached, the season -will be lengthened at each end, com- 

 mencing earlier in the Spring and closing later in Autumn. 

 In some localities the season will continue through the 

 "Winter. But when the water is warmer than the soil, 

 danger of unseasonably exciting vegetation is to be ap- 

 prehended where severe late frosts occasionally occur, and 

 must be carefully guarded against, either by suspending 

 the irrigation, or by refraining from drawing off the water 

 from meadows that arc entirely submerged, leaving the 

 covering of water as a temporary protection until the dan- 

 ger has passed. The best times for flowing meadows are 

 at night, or on cloudy, calm days when there is little 

 wind, or when it is raining ; windy, clear days or times 

 when the sun is bright, should be avoided. The reason 

 for this is, that the rapid evaporation which would occur 

 on bright sunny or windy days would greatly depress the 

 temperature of the wet soil and retard the growth of the 

 grass. A calm evening is the most favorable time for any 

 irrigation, and nocturnal watering tends to restrain the 

 radiation of heat from the surface, which is active upon 

 calm, clear nights. Intelligent judgment is to be exer- 

 cised in this regard. When water is applied to a meadow, 

 it is better to give it abundantly rather than sparingly. 

 Generally the temperature of the water is, or should be, 

 higher than that of the subsoil in which the roots exist. 

 A copious irrigation will be sufficient to overcome this 



