RUN-OFF IN OLIVE CULTURE. 



37 



ures being taken to conserve the soil moisture. The olive is also an 

 important tree in some of the oases of southern Tunis, where the 

 scantiness of the rainfall a is compensated for by the abundant supply 

 of water from springs that is available for irrigation. 



But in one of the most important olive-producing regions in 

 Tunis, i. e., that surrounding Susa h on the eastern coast, the normal 

 annual rainfall of 16.6 inches, although greatly exceeding that at 

 Sfax, is yet so small as to make it worth while to employ a special 

 method for utilizing it to the fullest possible extent. This method 

 is very different from that used at Sfax, and in its way is almost 

 equally interesting. The country around Susa is very hilly, being 

 divided by limestone ridges into small valleys and ravines. The 

 bottoms of these valleys and the lower slopes, which are made suf- 

 ficiently level for the purpose by a system of terracing, are occupied 

 by small basins, separated one from another by low banks of earth. 

 Each basin contains a few olive trees, usually only from two to eight. 

 The stony upper slopes and summits of the ridges, which produce a 

 scanty natural growth of shrubs and grasses, are not cultivated. At 

 intervals along these slopes, or " meskas," as they are termed by the 

 Arabs, are shallow trenches running obliquely toward the bottom. 

 These are so arranged as to catch and conduct to the basins as much 

 as possible of the rain water that falls upon the slope. The owner 

 of each orchard has a recognized right to all water that falls upon 

 the slopes adjacent to his property. The basins are said often to 

 remain filled with water during the month of January. 



The heavier texture of the soil around Susa as compared with that 

 at Sfax is favorable to this method of irrigation by rainfall, as it 

 permits the water to flow from basin to basin, instead of being all 

 quickly absorbed in the first one. It is generally observed in this 

 region that olive orchards that are watered by the rain that falls on 

 the " meskas " give larger and especially more regular yields than 

 those receiving only direct rainfall. 



From the nature of the case, accurate alignment and widely dis- 

 tant planting of the trees as practiced at Sfax are out of the question 

 at Susa. The trees stand comparatively close together, so that there 

 are often forty to the acre instead of only seven to ten, as at Sfax. 

 Much less care is taken to cultivate the soil, and this also is more or 



a The normal annual rainfall in the oasis of Gafsa is S.5 inches ; in that of 

 Gabes, 7.6 inches ; in that of Tozer, 5.1 inches. In the oasis of El Oudiane, 9 

 miles distant from Tozer (see Bulletin 02, Bureau of Plant Industry, p. 16), 

 there are 25,000 olive trees, with an average yearly production of 132,000 gallons 

 of oil. 



6 Susa, better known by its French name of Sousse, is about 70 miles south- 

 east of Tunis and about an equal distance north of Sfax. 

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