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iime. If the pipe is on a grade and open at bottom and top so that 

 .air passes thi-ough it, there will never be trouble from orange roots. 

 Valves, once thought necessary, are not now used. The high cost of 

 the present sub-irrigation systems places them beyond the reach of 

 most orange-growers. 



Spread of Water from Deep lurrows. — The diagrams show the ex- 

 tent to which water from fairly deep furrows penetrates the sandy soil 

 and the heavy loam of the substation. A moment's study of them 

 will convince any one that the only way in which to lessen waste in 

 surface irrigation is to let the water flow slowly through as deep and 

 narrow furrows as practicable, thus making a larger cross-section of 

 wet soil, even narrower at the surface than in the chart, and checking 

 the evaporation by filling the furrow with dry earth and by cultiva- 

 tion at the earliest moment. 



Examining these suggestive diagrams of soil saturation, let us first 

 call attention to the three showing the spread and descent of water 

 on the heavier soil. Here it has spread much more slowly and to a 

 less extent than in the case of the adjacent sandy land. Even after 

 two days run of water (of twelve hours each) and seventy-two hours 

 turther delay, the total sectional area of saturation is hardly more 

 than half as great, covering about sixteen square feet, as against about 

 thirty square feet on the lighter, more porous soil. A still deeper and 

 narrower water channel is highly desirable on this heavier soil. In- 

 stead of eight inches, it might well be sixteen or eighteen, which 

 would make the cross-section No. 3 nearly a foot deeper, and narrower 

 on the surface. 



The cross-section on the sandy soil show that the eight-inch furrow 

 is practically sufficient to carry the water well down into the soil. A 

 deeper, narrower channel even here will result in economy in the use 

 of water, a smaller flow producing as large an area of saturation with 

 less surface. These two sets of illustrations of the results of irrigation 

 in furrows on different soils, under conditions otherwise practically 

 identical, explain and enforce the entire argument respecting deep irri- 

 gation set forth in this bulletin, and long and earnestly recommended 

 by Professor Hilgard. 



[Issued 1st July, 1903.] 



