IRRIGATION 273 



well as ineffective ways of applying water. It is distributed under 

 pressure through pipes, the water escaping by means of nozzles or 

 by small openings. It is used principally to supplement the rain- 

 fall (Fig. 124) in humid regions where crops of high value, such 

 as vegetables and small fruits, are grown. Usually the application 

 is sufficient to penetrate only to a slight depth, hence it soon evapo- 

 rates. It has a tendency to produce shallow rooting of the plants. 

 The method has the advantage of easy control, little' waste land, 

 and may be used on very uneven land. 



Cultivation After Irrigation. Where possible the irrigated 

 land should be cultivated as soon as the soil is in proper condition. 

 The loss by evaporation following irrigation is enormous, especially 

 where no crop is on the land large enough to shade it. The Utah 

 Station found that where land was not cultivated till seven days 

 after irrigation the loss of water by evaporation was 1.45 inches or 

 1G4 tons per acre, while 14 days gave a loss of. l.!K> indies or 21!) 

 tons per acre, and 21 days gave a loss of 2.7 inches or :><>T tons. The 

 cultivation should be as deep as possible under the circumstances. 

 As the result of an experiment a loss of 1.75 inches occurred in 

 28 days where there was no mulch. When a layer of dry granular 

 soil three inches thick was placed upon the surface the evaporation 

 was reduced to 0.78 of an inch or 57.7 per cent, while a ten-inch 

 mulch practically stopped evaporation. 



Crops for Irrigated Lands. Practically all crops adapted to 

 the climate will grow under irrigation. Some require more water 

 than others, but this is easilv adjusted by the applications of water. 

 (Fig. 125.) 



Cereals. Wheat. The best cereal under irrigation is wheat. 

 While it is primarily a crop for dry-land agriculture, yet it yields 

 well when irrigated and is a good crop to fit in with rotations used 

 on irrigated lands, and is grown quite extensively. The amount of 

 water required by wheat depends upon the perviousness of the soil, 

 but in a deep, fertile 1 , well-tilled soil 12 inches will be sullicient. 

 The Utah Station found that an application of 7.5 inches of water 

 gave 11.5 bushels, 10 inches gave i:?.5 bushels, and 15 inches gave 

 45.7 bushels per acre. 



Oafs. The growing of oats on irrigated land probably will 

 never become very extensive, although it will be used t<> some extent 

 to give variety in rotations. It produces well and requires about the 

 same amount of water as wheat. 



Ttarlcii. The barley crop is a valuable one under irrigation. 

 18 



