46 



of the field, so that but little loss occurs between the pump and the 

 irrigated land. In lower Egypt it has been found that a depth of 

 water of 2.55 feet is sufficient for the irrigation of cotton. A depth of 

 4.3 feet is required for rice. The winter crops, which have already 

 been enumerated, demand from 1.6 to 2 feet. Although the growing 

 season of sugar cane, the most valuable crop in upper Egypt, covers a 

 period of nine months, a depth of water of 2.5 feet suffices for its 

 needs. 



The following discussion of the duty of water under some of the 

 pumping plants of the Societe du Behera. in Lower Egypt, has been 

 furnished V)y Mr. Thorwald L. Smith: 



* * * The loss throujih evaporation and absorption varies greatly according to 

 the following conditions: 



(1) Quality of soil: (a) Sandy; (b) medium; (c) heavy. 



(2) Time of year: (a) Hot; (b) cold. 



(3) Number of days elapsed since last watering. 



(4) Distance of field from pump: (a) Water carried in old permanent channel; (b) 

 carried in temporary channel for that particular crop. 



As to the first, we find that in (a) sandy soil (pure alluvial deposits) the quantity 

 of water reciuired for each watering is aV)out double that wanted for heavy (c). On 

 the other hand, such soil cracks less, and, consequently, there is not so much loss, 

 should the time between Uvo waterings be prolonged, as there is in heavy soil where, 

 after a long drought in summer, the cracks (unless the land be frequently hoed) 

 will continue to absorl) all the water for some minutes and will conduct it to the sub- 

 soil, which is salt, where it can be of little use to the surface-feeding crops. 



Second. Time of year makes a difference in two ways: First, 1)ecau8e in summer a 

 lot of water is lost by evaporation so soon as it is spread in a thin layer over the 

 baked land, and second, because in the cooler months the canals are all generally 

 running full and consequently all low lands can be irrigated by gravitation and are 

 more or less water-logged, especially where drainage is bad. In fact, for winter crops 

 the only time when pumps are used for such lands is when the upper reaches of the 

 canals have been closed for clearance and the water in the lower reaches falls below 

 the ground level. 



Third. The number of days between each watering for cotton should be an aver- 

 age of fifteen, but through want of water this is frequently prolonged to thirty or even 

 more. Naturally from causes mentioned above, i. e., cracking, and from the fact 

 that evaporation directly and through the plants has been going on continually, the 

 land takes more water to show any sign on the surface. For the rice crop these last 

 conditions can not obtain, for water must be changed in rice fields while the crop is 

 young at least every four days, and when stronger at a maximum of eight days on 

 good soil. (Where the land is very salt the crop would suffer very much, if not die, 

 in an eight-day interval.) On the other hand, as the rice land is continually wet 

 the absorption at the time of watering is much less, and of course there are no cracks. 

 However, as the water is on the surface there is great"evaporation from sun and wind, 

 especially so long as the plant is small and does not shade its own roots. 



In calculating (theoretically) the amount of water necessary for each watering, 

 about 3.(U inches in depth would appear to be sufficient. Indeed, in the case of 

 cotton which is sown on ridges, one might think that the area of the furrows only, 

 into which the water runs, i. e., about half the total area, would be the figure on 

 which to liase the quantity necessary. But the ridges, being made up entirely of 

 loose soil, soak up water at once, especially the first watering or after a hoeing, and 



