flCIENTIFIC AGRICULTURE. 179 



IRRIGATION. 



Irrigation has been practiced by the Chinese and Egyptians 

 from the remotest antiquity. In countries where rains seldom 

 fall, and the ground becomes dry and parched, irrigation is of 

 immense value. It consists in taking water from lakes, sewers, 

 running streams or reservoirs, and causing it to flow over the 

 land by means of small canals or furrows, then by proper out- 

 lets to carry it off again. It is confined, according to Colman 

 and Johnston, almost exclusively to meadow lands. 



The benefits of irrigation in a country where rain falls fre- 

 quently and abundantly, are the same as those of manuring. 

 When the water used holds in suspension any organic matters, 

 they subside while the water remains on the fields, and leave 

 a visible layer of manure on the surface, after the water is 

 drained off. An example of the fertilizing effects of irrigation 

 is seen in the lands along the banks of the Nile and Ganges. 

 But the effects of irrigation with water that contains no organic 

 sediments, must be considered the same as that of rains. Run- 

 ning water furnishes to plants some gasses, which are absorb- 

 ed, and in this way are beneficial. Crops of young and ten- 

 der plants should be irrigated by pure water : it may be re- 

 peated every two or three weeks when there is any want of 

 rain, and the water be allowed to lie on the field only three or 

 four days. It is thought by English Agriculturists to be inju- 

 rious to meadows to flood them immediately after mowing. 



Warping is a process similar to irrigation: the object of 

 this, however, is more especially to obtain the sediments of 

 muddy streams, &c. ; the water should never be allowed in 

 either process to remain on the field until stagnated. Irriga- 

 tion is most beneficial on land which is well drained beneath, 

 so as to allow the water to penetrate the subsoil, and not stand 

 too long on the surface. Meadow lands are sometimes water" 

 ed in the winter to prevent the injurious effects of frost upon 

 the roots of the grass. Irrigation is not practiced to much ex- 



