FURROW IRRIGATION 



129 



times, and under other systems, they are given small streams for 

 longer periods. 



1. Flooding. — Flooding is a method of surface irrigation. The 

 water applied covers the whole surface of a field either as a thin 

 sheet of running water, continued until sufficient water has soaked 

 into the ground, or as a sheet of standing water which is allowed 

 to remain until the soil has absorbed enough. Flooding is usually 

 practiced when the land is not too sloping and when irrigation 



Fig. 64. — Roosevelt Dam, Salt River, Arizona. One of the big dams of the world. 

 Date of construction, 1905-11. Approximate cost, $10,000,000. Used to irrigate 219,000 

 acres, j ^U. S. Reclamation Service.) 



water is abundant. It is commonly done on fields cropped to 

 small grains, alfalfa, and grasses. 



2. Furrow Irrigation. — Furrow irrigation is a second method of 

 surface watering. By this method the water is guided over the 

 land in furrows, or channels, which traverse the whole field — 

 the water covering only a part of the soil surface. Furrow irriga- 

 tion is one of the most common methods, and is one of the best for 

 all conditions. When crops like potatoes, corn sorghum and 

 sugar beets are grown, it is usually best to irrigate by the furrow 

 method after the crop is on the ground. This is also the commonly 

 adopted method of all orchard irrigation (Fig. 63). 



9 



