DRAINAGE. 145 



of the canals to prevent loss of water. It may be that 

 the cheapest plan would be to make the bottom and lower 

 side of the canal of boards. In this case, a board of 14 

 inches in with would form the bottom of the canal, and 

 one of 8 inches the lower side. A canal of this capacity 

 would convey water enough for several acres, and would 

 not be more costly than to puddle or cement the bottom, 

 when clay is not readily at hand. 



CHAPTEK XI V . 



DRAINAGE OF IRRIGATED FIELDS. 



The absolute necessity of water to vegetable growth 

 must not be accepted in an unqualified sense. Water is 

 a good and necessary thing, but there may be too much 

 of it, and too much is as fatal to the profitable culture of 

 land as too little. As the circulation of air brings life 

 and vigor to the lungs of an animal, so the circulation of 

 water brings vitality to the roots of a plant. Stagnant 

 water is as fatal to plant growth as stagnant air is to the 

 health and well-being of animals. Therefore irrigation 

 cannot be successfully used without adequate drainage. 

 Sometimes this is naturally provided. Light soils, with 

 gravelly subsoils, may permit the passage of water through 

 them with facility, acting as filters to retain all its fer 

 tilizing qualities. Such lands are the most readily adapt 

 ed to irrigation, and any artificial provision for carrying 

 off the wafcer from them is unnecessary. But there are 

 many lands with retentive surface or subsoil, and others 

 with subsoil practically impermeable to water, that if 

 brought under irrigation must be. thoroughly drained, or 

 they will be injured instead of improved, and the charac- 

 7 



