360 



THE IRRIGATION AGE. 



stream, or other source of supply, until it is absorbed 

 by the fibrous roots of living plants, has led us into a 

 new field of inquiry. We have found, particularly in 

 the warmer portions of California, that the greatest 

 loss of irrigation water is from moist soil into dry air. 

 There would seem to be no end of tolls on water 'on 

 its way 'to the plant. To such an extent is this true 

 that the amounts actually utilized by vegetation fre- 

 quently bear but a small percentage to the volumes 

 diverted. For every 100 miners' inches which pass 

 through the headgate, thirty are liable to be lost in 

 percolation before the field is reached. Then in apply- 

 ing the remaining seventy inches, if the surface is 

 uneven the greater part will flow into low places 

 and be partially wasted while the high places may re- 

 main dry. In this way probably not more than fifty 

 out of the seventy inches reach the land it is intended 



During past years, observations have likewise been 

 taken and records made of the rate of evaporation from 

 the surface of soils 9f different character, but unfor- 

 tunately for arid America these experiments have been 

 carried on for the most part in the humid regions of 

 Kurope and America and can not be considered as safe 

 guides in western practice. It may be said, therefore, 

 that the investigation of the loss of water by evapo- 

 ration from the standpoint of the irrigator is a new 

 field concerning which little is definitely known. This 

 being true, the question naturally arises as to its rela- 

 tive importance compared with other questions which 

 demand consideration. Whether it is entitled to rank 

 among the first is for you to determine. In mv hum- 

 ble opinion the interests of western agriculture demand 

 that it be given considerable prominence. 



The loss of water by evaporation injuriously af- 



View of Santa Clara Valley, California. [A Famous Irrigation District.] 



to water. Now having nioistened the soil with these 

 fifty inches, the chances are that 40 per cent will pass 

 off into the air without benefiting in the least degree 

 the plans which it was intended to nourish. Thus of 

 the 100 inches diverted only thirty may fulfill a useful 

 purpose. 



I have referred to this subject of losses by evap- 

 oration as a new field of inquiry. This is true only as 

 regards irrigated agriculture. For at least fifty years 

 men have observed and recorded the evaporation' of 

 water from water surfaces, but with the purpose of 

 ascertaining the probable losses from reservoirs. Res- 

 ervoirs, as a rule, impound large quantities of cool water 

 on more or less elevated sites which may be surrounded 

 by forests, while irrigated fields, on the other hand, 

 are usually covered by thin sheets of warm water, and 

 the rate of evaporation from them is far different. . 



fects both the Western farmer who irrigates and 

 the one who cultivates the dry bench. All other 

 taxes paid by the farmer are small in comparison 

 to the one levied by the atmosphere in robbing 

 the soil of its much needed moisture. The mag- 

 nitude of this loss, which is borne by the irrigators, 

 is enormous. Between seed time and harvest of 

 each year there is sufficient water spread over the West 

 to cover all of New England a foot deep. In some sec- 

 tions this water is still reasonably cheap; m others it 

 is very dear. The annual cost to the farmers in apply- 

 ing so much water probably exceeds $25,000,000. Now 

 if we assume that 40 per cent of this water which costs 

 so large a sum each year is lost by evaporation it is 

 equivalent to an annual tax of $1 per acre on every 

 acre that is irrigated. 



The loss to the drv farmer is caused bv diminished 



