2 BULLETIN 835, U. S. DEPARTMENT OF AGRICULTURE. 



first aim is to obtain a uniform distribution of moisture within reach 

 of the plant roots and to maintain such distribution. The economical 

 application of water to prevent waste from deep percolation or sur- 

 face run-off and to maintain an optimum percentage of moisture 

 within the soil is the vital problem. For instance, under specified 

 soil and topographic conditions, how long should the furrows be 

 and how far apart? With turns of irrigation coming at specified 

 intervals, how much water should be applied and how long should 

 an irrigation be continued at each turn? To approximate an accurate 

 answer to questions of this kind it is necessary to know more accu- 

 rately than we now know the rate and extent of movement of the 

 soil moisture by capillarity during the several periods of an irriga- 

 tion season. 



The drainage engineer in the arid region has frequently been per- 

 plexed by a condition of water-logging under conditions which seem 

 to preclude the possibility of the movement of free water as such 

 from any known source to the wet area. He has often felt a want of 

 specific information which would indicate the development of free 

 water from capillary moisture and the importance of this form of 

 moisture in farm drainage. 



OBJECT. 



As a basis for answering some of the above questions investiga- 

 tions were undertaken in 1915, and the data given below are in the 

 form of a progress report. 



The object of these experiments is to furnish specific data as to the 

 capillary movement of moisture in the soils of the arid region. It 

 is felt that these will be of prime importance to the irrigation en- 

 gineer in the proper construction and operation of conveying chan- 

 nels and impounding reservoirs, and that they will enable him to 

 point out the most economical methods of applying water to fields. 

 These data were obtained for different soils and under different con- 

 ditions. 



PLAN OF EXPERIMENTS, 



Because it was realized that the rate and extent of movement of 

 moisture in soils by capillarity differs materially where the source 

 of moisture is a body of free water from where it is a body of wet 

 soil, the experiments have been divided into two parts : 



1. Where the source of the moisture is a body of free water into 

 which the soil column extends. 



2. Where the source of moisture is a body of soil containing a per- 

 centage of moisture greater than the wilting percentage, and not 

 connected with a body of free water. 



