FERTILITY OF SOILS. 35 



In well-cultivated gardens the upper few inches of the soil contain 

 a considerable amount of humus and are quite black in color, as 

 would be expected from the fact that not only date palms and other 

 fruit trees, but garden vegetables, forage crops, and cereals have 

 been grown in the oases, probably without intermission, for many 

 hundreds of years. 



FERTILITY. 



As to the composition of the soils of this oasis, so far as the impor- 

 tant elements of plant food are concerned, the following table of a 

 chemical analysis by acid digestion will furnish an indication: 



TABLE 10. Plant food constituents of soils of Tozer oasis. 



Per cent. 



Nitrogen (total) 0.03 



Lime (CaO) 13.08 



Potash (K 2 O) 1.10 



Phosphoric acid (P 2 O 5 ) .14 



The sample (No. 2 of Tables 9 and 11) was taken to a depth of 

 36 inches in a well-cultivated garden of young Deglet Noor palms, 

 amid a thin, newly planted stand of alfalfa, and contained only a 

 moderate amount of readily soluble " alkali " salts, as will be seen 

 by reference to column 4 of Table 11. 



If it be permissible to generalize upon the scanty data given above, 

 it can be said that the soils of Tozer are decidedly low in nitrogen. 

 When we consider that these soils are continually and lavishly irri- 

 gated with water that contains very little organic matter, that 

 manure is scarce, and that leguminous crops occupy at no time more 

 than a small fraction of the total area of the oasis, the poverty of the 

 soil in nitrogen is not remarkable. If the analysis had been based 

 only upon the surface 6 inches, a much better showing in this respect 

 would doubtless have been made. Lime is present in much larger 

 quantity than is usually considered necessary in the average cul- 

 tivated soil. Potash, likewise, is present in far more than the usual 

 proportions. Finally, the phosphoric-acid content is such as would 

 generally be considered satisfactory. 



According to the conventional standards the soils of Tozer would 

 therefore be in all respects first-class, so far as plant- food constitu- 

 ents are concerned, were it not for their low nitrogen content. It 

 would seem that to remedy this deficiency the growing of berseem 

 (Egyptian clover) should be undertaken, as this crop ought to thrive 

 in the Jerid region, with its mild winter climate and abundance of 

 irrigating water. 



92 



