ALKALI CONDITIONS AT CHEGGA. 



87 



The amount of alkali is enormous, the largest found in a date plantation in the 

 Sahara, and is probably more than young offshoots just rooting can stand, as is 

 evidenced by the death of one planted not long before the sample was taken. Older 

 palms can doubtless endure this amount of alkali, for several were growing near by 

 in soil apparently identical with the sample analyzed. It should be noted that the 

 bulk of the alkali (some 70 per cent of all the alkali present and 2.35 per cent of 

 the total weight of the soil), is sodium sulphate (Glauber's salt), and only 23 per 

 cent of the alkali, or 0.82 per cent of the total weight of the soil, is composed of 

 chloride, whereas at Fougala, Station 1, where the alkali was also almost strong 

 enough to prevent the growth of the date palm, the total alkali content of the soil 

 was much less, being some 2.46 per cent instead of 3.53 per cent, but consisted of 

 1.98 per cent of chlorids, more than twice as much as at Chegga. The chlorids 

 are, however, without doubt more injurious than sodium sulphate, and both of these 

 stations are to be considered as representing very nearly the limit of endurance of 

 the date palm Fougala for chlorids; Chegga for sulphates. 



The surface accumulation of sodium sulphate, as suggested by Mr. Seidell, may 

 wejl have some connection with the composition of the very alkaline waters used for 

 irrigation in which the sulphates predominate and in which sodium sulphate is pres- 

 ent to the extent of 121.5 parts per 100,000, constituting 18.98 per cent of the dissolved 

 salts (see p. 95). 



Station No. 2, at Chegga (PI. XVI, fig. 2), is very unlike the first, as it represents 

 reclaimed land where Saharan alfalfa** was growing. It is to be noted that deep 

 drainage ditches ran through the orchard at 50 to 60 feet intervals and provided escape 

 for the superabundant alkali, and that this sample was secured near one of these 

 ditches as may be seen in Plate XVI, figure 2. The analysis is given herewith. 



TABLE 21. Per cent of alkali in washed-out surface soil of date plantation, station No. 2, 



Chegga, Algeria. l 



1 Mr. SeidelFs original analysis of the samples from this station is as follows: 



This soil shows a very low per cent of alkali, considering that the date plantation 

 is on a very alkaline area and that the water used for irrigating is very brackish. 

 This is almost the same amount of alkali as was found in the valley of the Colorado 

 River near Yuma, where alfalfa grew in soil containing 0.498 per cent of alkali in the 

 4 upper feet (Loughridge, Bull. 133, California Agricultural Experiment Station, p. 

 27) . However, at Yuma the irrigation water was of good quality, containing less than 

 0.1 per cent of dissolved salts, whereas at Chegga the water was very bad, containing 

 over 0.64 per cent of alkali. 



See footnote a, p. 23. 



