•600 Thirty-second Annual Report 



Wells were dug in the midst of two forests, one of mesquite 

 and the other of cottonwood. The wells were equipped with 

 autographic water level recorders, the record sheets of which 

 are changed weekly. For several weeks the slight fluctuations 

 were found to correlate quite closely with barometric pressures 

 but after the growth of leaves the fluctuations became much 

 more pronounced, and the effects of transpiration produced a 

 daily cycle consisting of the transpiration drop by day and 

 the recharge curve at night. After the beginning of the sum- 

 mer rainy season, additional correlations were obtained, notably 

 those of light, temperature, and humidity. 



SOIL SURVEYS 

 The soil surveys in the San Simon and San Pedro valleys, 

 begun in October, 1920, have been completed. The surveys were 

 conducted by the United States Bureau of Soils and the Irri- 

 gation Department jointly, each party furnishing one field man 

 and the field expenses being divided equally. 



METHODS OF IRRIGATION IN CASA GRANDE VALLEY 

 Owing to the difficulty experienced by many farmers in 

 the Casa Grande Valley in the irrigation of alfalfa, considerable 

 time has been given to the problem of the best method of irri- 

 gation. On some farms the alfalfa lands have been laid out 

 along the contours, and are, therefore, terraces, usually of irreg- 

 ular shape. The borders are high and meander along the con- 

 tours, and the land is difficult to work with farm implements. 

 There does not seem to be any merit in this method of laying 

 out the lands for irrigation. 



Tests of absorption were made on two ranches. The soil 

 moisture to depths of four to six feet was determined both 

 before and after irrigation, and the quantity of water applied 

 was measured. The distribution of the water over the land 

 was found to be quite uniform, much more so than was found 

 in similar tests in the Santa Cruz Valley described in 1913.* 

 It was demonstrated that on the McClellan loam it is prac- 

 ticable to run the water down the slope of the land in long 

 lands, and this method has important advantages over all 

 other methods. Adjustment of the velocity of the flow and of 

 the duration of the period of wetting can be made by varying 

 the length and width of lands and the head of water turned into 

 €ach land. 



•Arizona Agricultural Experiment Station, Twenty-Fourth Annual Report, page 283. 



