1917] KURAL ENGINEERING. 85 



native meadows on central Oregon marshes was obtained with from 10 to 12 

 in., and the maximum yield with an average of about 18 in, depth an acre. 

 These meadows can be greatly improved in productiveness and a higher effi- 

 ciency from irrigation water secured by seeding in tame grasses and clovers. 

 On sandy upland at Paisley, the most economical yield was received with from 

 11.16 to 18 in., and the maximum yield with from 32 to 34 in. The best yield 

 on black sage land in Harney Valley was secured from 6 in. on grain, 8 in. on 

 peas, and 18 in. on alfalfa. In Goose Lake Valley the depth giving maximum 

 yield was 7.5 in. for potatoes, 9 to 16 in. for grain, and 18 in. for alfalfa. 

 In Rogue River Valley 10 in. depth gave the maximum yield of sugar beets, and 

 6 in. the maximum yield of corn." Results secured in the Willamette Valley 

 from several crops with different amounts of water and the effect of crop 

 rotation and manure in lowering the amount of water required are also 

 reported. "A close relation was found between irrigation, fluctuations in the 

 water table, the substrata, and concentration of alkali on different flat areas." 



With reference to the effect of soil texture on the economical use of irriga- 

 tion water, it was found that " the coarser soils generally have a low water re- 

 quirement and a comparatively low amount of surface area, pore space, organic 

 matter, and are apt to be medium in fertility. The light, frequent irrigations 

 required on these soils necessitate more waste and it is Impracticable to use as 

 small an amount of water on these soils as on the soils of finer texture. 



" The kind of crop affects the amount of water required. Alfalfa and other 

 meadow crops are requiring relatively large amounts of water, grain and field 

 peas but medium amounts, and cultivated crops, such as potatoes, still less. 



" The altitude and accompanying climatic conditions affect the irrigation 

 requirements. ... In general for the same soils and crops where 3 ft. depth is 

 needed per season up to 2,000 ft. elevation, 2 ft. is a reasonable amount at 3,000 

 ft. elevation, and 1.5 ft. for each season is a reasonable amount for elevation 

 of 4,000 ft. or more. Drying or other effects of the weather are intensified at 

 the lower altitudes. 



" Soil fertility is one of the most important factors affecting irrigation re- 

 quirements. . . . Frequently, applying the simple fertilizer needed has saved 

 from a quarter to one-half the total irrigation or doubled the returns for each 

 unit of water where fertilizer was applied. This is especally true on the lighter 

 types of soil. 



" The time of irrigation affects greatly the efficiency of the water applied, 

 since irrigation ... is worth more when applied just at the right time. . . . 

 The amount applied at each irrigation will affect the economical use of water 

 or irrigation requirement. . . . Coarse-textured soils or those with gravelly 

 substrata should have a distribution system that will permit or supply com- 

 paratively light and frequent applications which can be retained in the soil 

 without percolation loss. The frequency of irrigation is related to the time and 

 amount for each irrigation. Irrigation should only be applied when the 

 moisture content drops to near the wilting point for the particular soil and 

 crop, and in sufficient amount to fill it up to the excess point in all cases except 

 where flood irrigation in the early spring is necessary to retain as much water 

 as possible in the soil reservoir. This would be true in the absence of artificial 

 storage for summer irrigation. . . . 



"The head and length of run should be such that the plat irrigated can be 

 covered by the time the irrigation has wet up the root zone of the crops. A 

 high head forces over the land rapidly and is necessary in flood irrigation 

 or in irrigating loose soils. The longer length of run gives more time for 

 soaking during irrigation on the heavier textured soils. Longer runs can be 

 used on more sloping land and shorter runs with a higher head should be used 



