IRRIGATION 



263 



which will better retain water received from rains or 

 ditches. They become droughty in a moister climate 

 earlier in the spring and sooner after rain. They must be 

 irrigated more frequently than the lands better prepared 

 to conserve moisture. It is difficult on such lands to dis- 

 tribute the water because of the great amount of waste 

 by rapid percolation down 

 below the area reached by 

 the roots of plants and by 

 seepage, and in many cases 

 it is not practicable to use 

 the water on this land, 

 when the same water might 



be Of greater USe On lands Figure 161. Grade level of light planed 

 boards, made accurately as shown. To estab- 



?%& 



better adapted to irrigation. 

 Canals made of this kind of 



c-ati/Kr 11-1 A m-nrall-ir ,-no-fa distance one-fiftieth of the length of"" the 



sandy and gravelly mate- base line, A c. The piumb ime wm cross 



i 1 i_ i ITT the board D E, in some line away from the 



rial are liable tO leak large center, a b. Mark this crossing, as x y. The 



r . same grade can then be found at any point in 



aniOUntS OI Water and this the drain by leveling till plumb line crosses at 



a b, and then raising the updrain end till the 



is also true of laterals and gJaSca^thus 8 ^ established y ' A uniform 

 farm ditches. In some 



cases it is practicable to place clay in the bottom and 

 along the sides of ditches made of open soil, or to allow 

 them to become coated with sediment from muddy waters 

 that the denser walls thus formed may 

 enable the canal better to retain its 

 water. With some such materials, 

 puddling, i. e., working the clay layer 

 in the ditch when wet, will make it 

 much more retentive. But the greater 

 difficulty in sandy lands lies in getting 

 the water to flow over the field and 

 moisten the surface rather than to sink 

 Figure 162. Listing away immediately and do little good. 



plow, useful in making TT , . , ., - - . 



shallow ditches on level Heavy clay soils, on the other hand, 



land, as it throws the J \ 



furrow-siice out on both serv e nicely to carry the water forward \ 



