63 



made in various states gived uties ranging from 1.00 acre foot per acre in 

 the San Joaquin valley of California, to 7.8 acre feet in Nevada. 



The duty of water measurements give above show the usual conditions 

 obtained on an ordinary irrigation system. The large losses in conveyance 

 which occur from the head of the main canal to the point of delivery on the 

 farm, are shown by the large difference between the gross duty and net 

 duty. The values of net duty of water show the variations in the quan- 

 tities of water applied not only on different crops but also for the same crop 

 under similar conditions. These variations are due not only to local con- 

 ditions but largely to the skill used by the irrigator in preventing losses of 

 water and to the value of the water. The decrease of the losses or increase 

 in duty as the water becomes more valuable and the irrigators more skill- 

 ful, is well shown by the measurements obtained on the Sunnyside project 

 in eastern Washington. 



FACTORS INFLUENCING "THE CORRECT USE OF WATER 

 IN IRRIGATION. 



The net duty of water represents the best use of water only when suffi- 

 cient water is applied to give the best crop production and when the losses 

 of percolation and evaporation are eliminated as much as practicable by 

 skillful application of water and proper cultivation. An intelligent use 

 of water in irrigation requires a careful consideration of the following 

 principles: 



1st. Disposal of water applied to the soil. 



2nd. Relation of soil water to soil texture. 



3rd. Evaporation of soil water and methods of checking it. 



4th. Percolation of water applied to the soil and percolation losses. 

 1. Disposal of Water Applied to the Soil. 



The water applied to the soil is disposed of in four ways: 



1st. Plant transpiration. A useful part is used to produce plant 

 growth. It passes from the soil into the root hairs, from the root hairs 

 into the stem and is carried to the leaves from where it evaporates. This 

 process is called plant transpiration. 



2nd. Soil moisture evaporation. A part is lost by evaporation from the 

 soil. This loss will depend on the texture of the soil, the porcentage of 

 moisture in the soil, the method of irrigation, the time and frequency of 

 cultivation, the temperature, the humidity in the air, the amount of wind 

 movement. 



3rd. Soil percolation. A part is lost by percolation into the soil beyond 

 the reach of plant roots. This loss depends on the character and quality of 

 soil and subsoil, the depth to the water level, the topography of the land, 

 the skill of the irrigator, the efficiency of the distributing system, the 

 length of the furrows. 



4th. Surface waste. A part is lost by the waste of water at the ends 

 of fields or furrows. This water passes to the lower neighbor or on the 

 roads where it may do considerable damage. This loss can be prevented 

 by using care. 

 2. Relation of Soil Moisture to Soil Texture. 



Water may exist in the soil in three conditions: (1) hygroscopic water, 

 (2) capillary water, and (3) gravity water. 



Hygroscopic water is that which occurs in all soils not dried by artificial 

 heating. It is the moisture which a soil dried by artificial heat will absorb 

 from moist air. It exists as a very thin film surrounding each particle but 



