304 



THE IKRIGATION AGE. 



thereby preventing evaporation from its surface, was 

 the cause. On dry, dusty soils, where there is none, or 

 very little rainfall, the accumulation of dew during the 

 night is generally sufficient to "trickle" along the leaves 

 and carry down the dust and other accumulations on 

 the leaves which interfere with evaporation. Some- 

 times the plant, as if aware that there is a stoppage 

 in its circulation, will throw out fresh, new leaves to 

 cure the defect, but this is done at the expense of the 

 root, tuber, or fruit. 



The amount of loss due to natural and mechanical 

 evaporation from plants, of course, differs very greatly 

 in the various species of plants depending, in a great 

 measure, on the special structure of the leaf, whether 

 fine or coarse meshed, large or small, lean or fleshy, 

 the natural perspiration, however, always exceeding the 

 mechanical. Both processes, moreover, are more rapid 



31,000 pounds. During ninety-two twelve-hour days, 

 the life of the maple leaf, the evaporation would amount 

 to 2,852,000 pounds. During that period the rainfall 

 was 8.333 inches or 43.8 pounds to every square foot 

 of surface, equal, per acre of 43,560 square feet, to 

 1,890,504 pounds. The evaporation from the leaves 

 of the trees, therefore, exceeded that of the actual fall 

 of rain by nearly one million pounds. Whence did the 

 surplus come? Evidently from the water stored in 

 the water table and drawn up by the action of the roots 

 of the trees. Where there is no water table or ground 

 water and the soil is dry "all the way down," it is 

 necessary to create one by irrigation and this is not so 

 difficult as might be imagined, for we must consider 

 that in the case of maple trees the roots may reach 

 down into the subsoil for fifty feet, and in the case of 

 ordinary fruits, vegetables, and cereals, a water table 



SOME BUSINESS BLOCKS, OGDEN. UTAH. 



35. First National Bank Building. 

 38. Eccles Building. 



37. Union Depot. 



38. John Scowcroft & Sons Co. 



39. Z. C. M. I. 



under the influence of a warm, dry atmosphere aided 

 by the direct rays of the sun. 



As showing the quantity of evaporation an experi- 

 ment was tried with an acre of maple trees containing 

 640 trees. The calculation is not positively exact, but 

 it is worth accepting as a basis for other experiments 

 on crops of all kinds and may come somewhere near 

 enabling the irrigator to determine the quantity of 

 water to be applied to the soil, whether there is a water 

 table within the reach of the surface or none at all. 



The evaporation was assumed to take place only 

 during a day of twelve hours and each of the 640 trees 

 were estimated as carrying 21,192 leaves. From an esti- 

 mate based on the quantity of evaporation from one tree 

 containing the number of leaves above specified, which 

 were carefully counted, the 640 trees evaporated from 

 their leaves in twelve hours 3,875 gallons of water, or 



at that depth would be wholly unnecessary even if gen- 

 erally impracticable. Soil saturation at any depth 

 beyond four feet with unlimited surface cultivation is 

 sufficient, although in the case of vines and trees it 

 should be much deeper. 



The above experiment with the maple trees al- 

 though, perhaps, of no practical value on account of 

 its uncertainty, being more or less guess, demonstrates 

 two things, when there is also taken into consideration 

 the quantity of sap in plants and the amount of salts 

 held in solution in it. 



First How easily a soil may be exhausted by cut- 

 ting and removing plants and crops therefrom. 



Second As a direct corollary, through its diametric 

 opposite, it shows how easily alkaline salts may be re- 

 moved from the soil by cutting and removing the plants 

 and crops. These alkali-consuming plants hold large 



