I2 4 



THE ESSENTIALS OF AGRICULTURE 



will pass through them to the tile very slowly. On such lands 

 it is necessary to lay a larger number of lines of tile to a given 

 area than on more porous lands. Tile are sometimes laid on 

 rolling lands to aid in preventing surface washing and erosion. 



They are also often laid 

 across hillsides which are 

 wet because of water seep- 

 ing out on the surface 

 in draining from higher 

 levels. Lands on which 

 tile pay best are usually 

 those which are porous 

 enough to drain well, but 

 which are wet because they 

 are level. 



, The cost of tiling varies 



B from $5 to $40 an acre, 



according to the size of tile 

 used, the distance the lines 

 are apart, and the depth at 

 which the tile are laid. 



II. IRRIGATION 



A 



151. The object of irri- 

 gation. In regions of little 

 rainfall it is necessary to 

 supply water artificially if 

 crops are to be grown 



FIG. 51. Section of a tile drain, and tools 

 for laying drains 



A, ditch ready for laying tile, one tile in place; 



the grading line and upright measuring stick 



make it possible to secure the desired evenness 



in fall of the ditch ; , a tile hook for laying the economically. The prOCCSS 



tile ;C, a grading scoop for finishing the bottom Qf brmging water tQ the 



land from ponds, rivers, 



or wells is known as irrigation. Irrigation is ordinarily most 

 profitable where the rainfall is less than sixteen inches. Con- 

 siderable areas in the western part of the United States 

 particularly in the Rocky Mountain region and the high plains 

 have been brought under systems of irrigation (Fig. 52). 



