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THE IRRIGATION AGE. 



Irrigation of Alfalfa 



By SAMUEL FORTIER, 



Chief of Irrigation Investigations, Office of Experiment btations. 

 U. S. Department of Agriculture. 



THE FURROW METHOD. 



Alfalfa, native meadows, and grain are most com- 

 monly irrigated by one of the methods previously described 



T 



Fig. 14. Plat Showing laterals and headgates. 



rather than by the furrow method, which is the usual 

 method of irrigating orchards, gardens, root crops and 

 vegetables. The irrigating of alfalfa from furrows is at 

 present confined to the Yakima Valley, 

 Washington, to portions of the Snake 

 River Valley in Southern Idaho, and to 

 comparatively small areas in other 

 states. In the localities named the soil 

 is .a fine clay loam which runs together, 

 puddles when wet, and bakes and cracks 

 when dry. Flooding the surfaces by 

 any of the customary methods tends to 

 puddle the top layer of soil, which be- 

 comes quite hard when the moisture is 

 evaporated. The puddling and baking 

 processes injure alfalfa, and it was with 

 the object of keeping as much as pos- 

 sible of the surface dry that furrows 

 were introduced. When a small stream 

 is permitted to run in the bottom of a furrow for several 

 hours the soil beneath and for some distance on each side 



in one of the orange orchards of Southern California. 

 The alfalfa grown in the Yakima Valley in Washing- 

 ton is practically all irrigated by means of furrows. The 

 grading is usually done by buck scrapers, while a long, 

 rectangular drag similar to the one shown in a previous issue 

 removes most of the surface inequalities that remain after 

 the surface has been leveled roughly by the scraper. The 

 float is made of two 2 by 6-inch timbers about 20 feet 

 long, held in position by crosspieces of the same size, 

 6 feet long. 



The common practice is to run the furrows across 

 the entire width or length of a field, 

 and in consequence their length varies 

 from 20 rods or less in small fields to 

 80 rods in large fields. As a rule, the 

 furrows are too long. Farmers object 

 to cutting up a field by head ditches, 

 but in a climate like that of the Yakima 

 Valley in midsummer, by far the most 

 essential element in plant production is 

 water, and all other considerations 

 should give place to it. It has been 

 shown* that water is rarely distributed 

 evenly in furrow irrigation and that 

 much is lost by deep percolation. To 

 increase the length of a furrow beyond 

 660 feet, or one-eighth mile, not only 

 increases the loss, but renders a uni- 

 form distribution more difficult to 

 secure. Except in rare cases, this dis- 

 tance should be regarded as to the limit 

 for the length of furrows. In light, 

 sandy soils, having a porous gravel 

 stratum beneath, the length may well 

 be reduced to 250 feet. 



Figure 17 shows the manner of divid- 

 ing an alfalfa field for furrow irrigation 

 at Kennewick, Wash. Lumber head 

 flumes, either 8 by 8 inches or 6 by 6 

 inches, are placed along the upper 

 boundary of each strip and the direction of the flow in 

 both flumes and furrows is indicated by arrows. Auger 

 holes are bored through one side of the flume flush with 



Fig. 15. Outlines of percolation from furrow 5 inches deep, in seven 



hours. 



becomes wet. while the surface may remain nearly dry. 

 This is shown in Fig. 15, which gives the area wetted 

 from a furrow 5 inches deep in seven hours as determined 



Fig. 16. Buck scraper. 



the bottom at points where water is to be delivered to 

 the heads of furrows. A short piece of lath revolving on 

 a nail controls the flow from each opening. On steep 

 grades a cleat on the bottom of the inside of the flume 

 nailed on crosswise just below each opening will dam back 

 the water and increase the discharge. 



When flumes are considered too costly the water is 

 distributed among the furrows through wooden spouts set 

 in the bank of an ordinary earthen dtich (Fig. 18). These 

 head ditches when in operation are divided into a series 

 of level spaces by means of drop boxes which hold the 

 surface of the water at the desired elevation. The spac- 

 ing of these drop boxes depends on the grade of the head 

 ditch and their cost averages about $2.50 each. Spouts are 

 made usually by nailing together four lath. There is a 

 special lath on the market somewhat heavier than the 

 ordinary one used for plastering buildings, being 0.5 inch 

 thick, 2 inches wide, and 3 feet long. Four of these when 

 nailed together cost about 3.5 cents and each spout in 

 place costs about 6.5 cents. Assuming that they are 

 spaced 4 feet apart, the spouts for a square tract of 10 

 acres would cost $10.73, or slightly more than $1 per acre. 



*U. S. Dept. Agr., Office Expt. Stas. Bui. 203. 



