108 THE DATE PALM. 



About three-quarters of the area occupied by this type of soil con- 

 tains less than 0.6 per cent of alkali, which amount is absolutely with- 

 out harmful effect on the date palm. It will probably grow nearly as 

 well on an additional 10 per cent of the land even without drainage, 

 and could struggle along on 10 per cent more of the area, while if 

 drainage were provided doubtless the whole area of sandy loam could 

 be planted to date palms. 



The Imperial loam soil has a smooth surface as level as a floor and 

 almost devoid of vegetation. 



It has the peculiar slick, shiny appearance often seen in localities where water has 

 recently stood. It is the direct sediment of the Colorado River, which was deposited 

 in strata when the area was under water. These strata are from 0.01 inch to 2 or 3 

 inches thick, very much resembling shale; in fact, to all external appearances being 

 exactly similar. When water is applied, however, the soil softens up and is a red- 

 dish, sticky loam, a little heavier than a silt loam. It is from 4 to 6 feet deep, under- 

 lain by a clay or clay loam, and contains considerable organic matter, including an 

 abundance of nitrogen and potash. When free from alkali it is well adapted to the 

 growing of wheat, barley, and alfalfa. a 



The Imperial loam is much like the heavj 7 soils in the oases at the 

 northern edge of the Sahara, in Algeria, and is well adapted to the 

 date palm if properly irrigated to prevent its becoming too dry and 

 if kept in a proper state of tilth to prevent packing. This soil is very 

 alkaline in the region surveyed in the Salton Basin, but about 60 per 

 cent of the area covered by this soil has less than 0.6 per cent of alkali, 

 and an additional 10 per cent will support the date palm nearly as well, 

 making TO per cent of the land where this plant will be unhampered 

 by alkali. The date can grow, though less vigorously, on an addi- 

 tional 15 per cent of the area, though it may not fruit Well unless 

 drainage be provided and some of the alkali washed out. 



The Imperial clay soil (PI. XVIII, fig. 1) is found as a surface soil 

 or as subsoil at greater or less depth throughout the surveyed area. 



It is usually comparatively level, although in some places small hummocks have 

 been blown up on its surface. It is this soil that surrounds both the towns of Calexico 

 and Imperial, the only difference in the soils of the two districts being in the alkali 

 content. The soil has been formed by the deposition of the finest sediment of "the 

 Colorado River, and is stratified in the same way as the loam. It is a heavy, sticky, 

 plastic soil, very much resembling the clay subsoil found in the Mississippi River 

 Delta. When dry and in its natural state, it exists in hard cakes and lumps, which 

 may be cut with a knife and are susceptible of taking a high polish. When wet, the 

 lumps are very plastic and sticky, making a soil which is very refractory and difficult 

 to cultivate, Upon drying, the soil becomes very hard and cracked. Sorghum and 

 millet were grown this year on several hundred acres of this land in the vicinity of 

 Calexico, and produced good crops. The sorghum, however, was the best, the yield 

 being 6 or 8 tons to the acre. 



Cultivation of this clay soil will be very difficult. A similar soil is found in the 

 Salt River Valley as a phase of the Glendale loess, and is locally known as "slick- 

 's Means and Holmes. Field Operations of the Bureau of Soils, U. S. Department 

 of Agriculture, 1901, p. 595. 



