^84 IRRIGATION FARMING. 



if the soil is sufficiently porous, it may be possible to 

 give the crop all the moisture needed without surface 

 application. 



If a field has a steep sidehill slope, it is best to bring 

 the water upon it by a supply ditch on the highest part, 

 as shown at a in Figure 93, and conduct it by a series of 

 dams or drops, b b b, to the lowest part of the field. 

 Then run laterals, c c, from above each drop nearly 

 along a contour or equal level line of the field, diking 

 these laterals up to keep the water above accidental high 

 places. These laterals should be permanent and should 



. 



FIG. 93. DIAGKAM OF SUIMKKHJATKI) FIELD. 



be near together at the top of the field, the intervals 

 widening as they near the lower edge, as the seepage 

 from the upper laterals will necessarily make tbe ground 

 more and more moist toward the lower edge of the field. 

 The field should be made as long as possible and the 

 laterals should be made as near parallel as the ground 

 will permit, so as to obtain as large and regular an area 

 between the furrows as possible. Whenever it is neces- 

 sary to flood growing crops, an opening can be made in 

 these permanent ditches at points where the grade line 

 intersects a slight knoll. From these openings the water 



