474 IRRIGATION PRACTICE 



ships among soils, waters and plants are the same over all 

 the earth. Under irrigation, the great water factor may 

 be controlled, and thereby greater power for good or for 

 evil is possessed by the farmer under the ditch. 



Yet there are some who, while admitting the great 

 present value of irrigation, fear that in it is an element of 

 weakness which will make the practice temporary. 



272. History assures permanence of irrigation. A 

 sufficient answer may be the history of the past. As shown 

 in the preceding chapter, great tracts of lands are known 

 that have been farmed successfully, under irrigation, dur- 

 ing the last 2,000 to 4,000 years and are today as pro- 

 ductive as ever. In fact, the human race was cradled and 

 grew to maturity in irrigated countries. That some of 

 the great nations of antiquity crumbled to dust was not 

 because they dwelt on irrigated lands; their fall was 

 rather delayed because of the bounteous yields of their 

 irrigated fields; and, in truth, the fallen nations of the 

 past practised irrigation for so long often for thousands 

 of years that the permanent nature of this branch of 

 agriculture was well demonstrated before the shifting 

 scenes of history brought new lands and other peoples 

 into emphatic view. 



273. The question of plant-food. The fertility of the 

 soils must be carefully guarded under irrigation as under 

 rainfall. When moderate quantities of water are used no 

 more plant-foods are washed away than under an equiva- 

 lent rainfall. Instead, the deep, rich soils of the arid re- 

 gions, because of the possible water storage in them, can 

 better retain the essential elements of plant-food. During 

 the course of modern American irrigation, extending over 

 two-thirds of a century, the average productive power of 

 the irrigated lands has steadily increased. Against the 



