ALKALI CONDITIONS AT FOUGALA. 79 



addition to these native wells the Companie de 1'Oucd Rirh has put down several arte- 

 sian wells which are some 80 meters deep and yield from 50 to 75 gallons of flowing 

 water per minute, which is conducted directly into the irrigation ditches. This water 

 is remarkably pure, containing very much less salts in solution than the artesian water 

 of the Oued Rirh country or that of Biskra. A rough test of its electrical conductivity 

 indicated the presence of about 0.085 per cent of dissolved salts. 



The effect of irrigation with this water is marvelous. Old date palms which had 

 made a slow and stunted growth and which had fruited but little, at once grew 

 luxuriantly when irrigated and began to bear heavy crops of fruit. Inasmuch as 

 these trees had their roots in constantly moist layers of earth, the effect of irrigation 

 was in all probability due not so much to the increased supply of water as to other 

 actions brought about by irrigation. In the first place, the structure of the soil and 

 the manner in which the date palms are planted in pits which penetrate the hard- 

 pan, below which standing water occurs, hinder the aeration of the subsoil and at 

 the same time favor the accumulation at the surface of the alkali dissolved by the 

 capillary currents of water in ascending through the strongly alkaline soil. On the 

 other hand, irrigation with the remarkably pure water furnished by the deep arte- 

 sian wells would tend to have exactly the opposite effect, namely, the subsoil would 

 be aerated by means of the water which had been flowing in surface ditches, and 

 secondly, the watering of the date palms with an abundant supply of pure water, 

 coupled with a perfect system of drainage by means of the holes through the imper- 

 vious subsoil & over which the trees are planted, would bring about the washing out 

 of the alkali from the soil, especially where the trees were irrigated frequently and 

 with large amounts of water. The hardpan would tend to confine the alkali and 

 prevent its rise between the trees after it was once washed out of the soil. 



Although the date palm can grow, as will be shown further on, in soils containing 

 as high as 3 per cent of alkali, even when irrigated with strongly brackish water con- 

 taining over 0.6 per cent of salts in solution it being in fact able to endure more 

 alkali than any other plant cultivated in the Sahara Desert there can nevertheless 

 be no doubt that its growth is retarded and its fruitfulness lessened by the presence 

 of large amounts of alkali in the soil or in the irrigation water. It was noticeable at 

 Fougala that the trees which were grown in the most alkaline parts of the oasis, and 

 especially where surface irrigation with pure water had not been practiced, were 

 stunted and show r ed a pronounced yellowish color of the leaf and especially of the 

 leafstalk. This was later seen in the oases in the Oued Kirh country, and it would 

 seem to be an indication of an excess of alkali beyond the amount which the trees can 

 endure without noticeable injury. 



An effect of pure water similar to that observed at Fougala has been noticed at 

 Koseir, in the Egypto-Arabian desert, on the shores of the Red Sea, w r here Klunzinger 

 reports c that dwarfed date palms 30 to 40 feet high grow on the very alkaline soil 

 and were nourished by very brackish water, but yield crops of small but very sweet 

 dates only in good years after heavy rains. The action of these heavy rains probably 

 would be much like that of the irrigation with the pure artesian water at Fougala. 



The natural springs in the Western Zab, according to Rolland (Hydrologie du 

 Sahara) , are supplied from the same source that feed, 1 the artesian wells, viz, the 

 water carried in the cretaceous strata which are upturned in the Aures Mountains 

 limiting the Sahara on the north and which underlie the whole northern belt of the 

 Sahara. The water of these springs soaking into the soil feeds the superficial layer 

 of water which directly underlies the hardpan at Fougala. Very probably this 

 hardpan has been formed by the action of this standing water. 



& Professor Hilgard has noted the drainage through holes in the hardpan in the 

 San Joaquin Valley in California. Bui. No. 83, California Experiment Station. 



c Klunzinger, C. B. Die Vegetation der egyptisch-arabischen Wiiste bei Koseir, 

 in Zeitschrift d, Gesellschaft f. Erdkunde, Berlin, vol. 13 (1878), pp. 432-462. 



