69 



<end of the furrows percolated to depths as great as 30 feet. Where irriga- 

 tion is practiced less carefully the waste is no doubt still greater. Mr. D. 

 H. Bark, in charge of Irrigation Investigations in Idaho, states that some- 

 times on porous soils where the water is run long distances, as high as 

 95 per cent, of the water percolates so deep on the upper one-third of the 

 field that it passes beyond the zone of the roots and is lost. The waste can 

 be minimized by using short furrows 



Sandy soil underlaid with gravel is the most difficult to handle to pre- 

 vent percolation losses but they may be made small by using frequent 

 irrigation applied in light quantities instead of heavy irrigations, a part of 

 which is wasted, and by laying out the distribution system so that the water 

 does not have to travel long distances in the furrows or over the fields. 



Percolation of water applied in furroivs. 



It is important that the irrigator should know how the water applied to 

 orchards in furrows distributes Jtself within the soil, in order that he may 

 know how far apart the furrows should be, how long they should be and 

 the length of time water should be run in the furrows. The correct prac- 

 tice will vary with the different types of soils and each irrigator should be- 

 come acquainted with his soil by observing the motion of the water in the 

 oil by means of borings made with a soil auger and trenches dug across 

 -the furrows. 



Very interesting experiments were made in southern California citrus 

 orchards by Professor Loughridge for the Irrigation Investigations Office 

 of the U. S. Department of Agriculture (Bulletin 203, Office of Experiment 

 -Stations). Cress trenches were dug across several furrows to a depth of 

 5 or 6 feet, the furrows were extended over the trench by ishcrt wooden 

 troughs. At regular periods during irrigation a thin slice of soil was cut 

 from the face of the trench exposing a fresh surface of the wet area. The 

 outlines were measured and recorded during and after the period of irri- 

 gation. The accompanying diagrams give the percentage cf free moisture 

 in the soil and show by irregular curves the depth of percolation at 

 different times. 



Fig. 49. Outlines of percolation under sixteen furrows in sandy loam. 



(O. E. S. Bulletin 103, U. S. Department of Agriculture.) 



