AMOUNT OF WATER NECESSARY. 47 



access to moist earth throughout the entire year, since, as has hern 

 stated above, the date palm is not at all a desert plant, in the sense of 

 being able to exist on very dry soil, and would die in many <>f the situ- 

 tions in the Southwest where cacti and yuccas thrive. 



Where the supply of irrigation water is limited, as at IViskra. where 

 there is only 0.12 liter per minute available for each palm and where 

 the soil is very heavy and consequently difficult to saturate, irrigation 



is commonly practiced by filling up with water a cavity "dahir" 



excavated at the base of the tree (PL XVII, fig. 2, and Yearbook, 1000, 

 PI. LV, fig. 3). Where water is more abundant and especially where 

 crops are grown under the palms it is customary to flood the whole 

 surface of the ground, the land being divided into small beds from 10 

 to 30 feet in diameter, which are surrounded by a slightly raised rim 

 (PI. XVII, fig. 1). When irrigated the whole bed is flooded, the water 

 being retained by the surrounding ridge. A larger amount of water 

 is required when applied in this manner than would be necessary if 

 poured into a trench at the side of the palm, but the alkali is washed 

 into the subsoil by surface flooding, whereas it is brought to the sur- 

 face by the trench system, which should never be followed in danger- 

 ously alkaline soils. In the Salton Basin in particular, where the 

 subsoil is often heavily charged with alkali, the land should always be 

 watered by flooding or else by deep furrows, even where the surface 

 soil does not contain harmful quantities of alkali." 



Where there is water at a short distance from the surface within 

 reach of the roots, as is the case in the area about the Cooperative Date 

 Garden at Tempe, Ariz, (see Pis. XXI and XXII), at Farfar, Algeria, 

 in the western Zab, between Fougala and Biskra, Algeria (PI. XIV, 

 fig. 1, and Yearbook, 1900, PL LIX, fig. 7), and in the Souf country 

 in the Sahara (fig. 8, p. 69) the amount of water required for irriga- 

 tion is less when once the palms have become established. They can 

 even exist without any irrigation whatever from the surface, although 

 in this event they do not grow as well and bear very much less fruit, 

 probably because of imperfect aeration of the soil about the roots and 

 because of the continual rise of alkali from the subsoil, as will be 

 explained in the chapter on drainage. 



Well aerated running water is desirable for date palms and water- 

 logging of the soil must be prevented. If these conditions are fulfilled 

 this plant can live and thrive when irrigated with water so salty a> to 

 kill all ordinary plants, as will be shown later in treating of the alkali 

 resistance of the date palm. 



Snow, Hilgard, and Shaw (in Bui. 140, Cal. Exp. Sta., pp. 36-39) recommend 

 for the Salton Basin first washing the alkali down by surface flooding and then pre- 

 venting its subsequent rise by deep-furrow irrigation. However, the date palm is 

 not sensitive to surface accumulation of alkali when once established, as will l>c 

 shown farther on (see p. 117). 



