38 BULLETIN" 339, U. S. DEPARTMENT OF AGRICULTURE. 



show that light but rather frequent applications would give good 

 results with these soils and that the application of water in this 

 manner would result in a great saving of water, an experiment was 

 carried on that it is believed has determined these factors in a satis- 

 factory maimer. 



A water-tight galvanized-iron tank, 2 feet in diameter and 6 feet 

 deep, with an outlet at the bottom terminating in a three-fourths inch 

 galvanized-iron pipe 10 feet long, was installed in the soil flush with 

 the surface of the ground. This tank was filled with 6 feet of soil in 

 as near its original position as possible, three bands of hot asphaltum 

 1 foot wide were painted around the inside of the tank at 1-foot inter- 

 vals to prevent percolation between the soil and the inside of the tank, 

 after which the tank was irrigated each time an adjoining experi- 

 mental plot was irrigated b} r applying the same amounts to the tank 

 that were applied to the plot. Whatever water percolated through 

 the 6 feet of soil in the tank drained out of the outlet pipe and was 

 caught in a tub in a curbed pit 10 feet away. A total of 6.6 feet in 

 depth in seven irrigations was applied to the experimental tract 

 handled by the owner of the land and to the' tank, and a quantity 

 representing an equivalent of 5.5 feet per acre, or 83.5 per cent of the 

 amount applied, percolated from the tank and was caught in the tub 

 in the curbed pit, yet alfalfa which was planted on the tank when 

 the experiment was started grew luxuriantly, demonstrating that the 

 supply retained in the tank was adequate for the proper growth of the 

 alfalfa. It was found that the tank during the season retained an 

 average in its 6 feet of soil of 0.15 foot of water per acre for each 

 application, and the experiment was continued during the following 

 year, that of 1912, by irrigating the alfalfa in the tank whenever it 

 appeared to require irrigation with 0.15 foot in depth at each appli- 

 cation, no limit having been placed on the number of irrigations that 

 were to be applied to the tank. It was found that the alfalfa in the 

 tank required 10 irrigations during the season, and that there was 

 but a trace of percolation from the tank. The alfalfa grown on the 

 tank was cut, cured, and carefully weighed, and produced at the rate 

 of 7.147 tons per acre, with an equivalent of 1.5 feet of water per acre 

 plus a precipitation during the growing season of 8.51 inches. While 

 this experiment was not conducted upon a scale broad enough to 

 demonstrate the feasibility of this small amount of irrigation on large 

 tracts or that this volume would produce the same comparative yield 

 on them, it is believed, after taking into consideration the other 

 observations, that it has been demonstrated that porous soils actually 

 require but a very small supply at each application. 



The securing of similar results from a practical application of the 

 experiment just described requires a careful adaptation of methods 

 of applying water to the types of soil to be irrigated. If an irrigation 



