THE IKRIGATION AGE. 



209 



Irrigation of Alfalfa 



By SAMUEL FORTIER, 



Chief of Irrigation Investigations, Office of Experiment btatioos. 

 U. S. Department of Agriculture. 



Methods of Irrigating Alfalfa. 



The methods of applying water to alfalfa differ widely 

 because of diversity in soils and subsoils, in climate and 

 topography, in the nature of the water supply, the size 

 of the farm, the amount of money available for preparing 

 the land for water, the prevailing crops grown, and the 

 early training and environment of the irrigator. The 

 standard methods have been grouped under the following 

 heads, namely, the border method, the check method, 

 flooding from field laterals, furrow ir- 

 rigation, and other less common meth- 

 ods, with various modifications of 

 each. 



In passing it may be said that 

 the usual order is to locate and build 

 the farm ditches first and prepare the 

 land afterwards. In this bulletin it 

 has been deemed best to describe the 

 methods in use and them to consider 

 the location and construction of farm 

 ditches. After one has a general 

 knowledge of the various ways of ap- 

 plying water and of the size and char- 

 acter of the ditches required for 

 each method he is in a better posi- 

 tion to understand the proper meth- 

 ods to adopt in building farm ditches. 

 This subject will therefore be 

 treated separately under its own head- 

 ing. 



The Border Mfethod. 



Essentially the border method 

 consists of the division of a field or 

 tract into long, narrow strips or lands 



by low flat levees which usually extend in the direction of 

 the steepest slope and confine the water to a single strip. 

 The bed of each strip is carefully graded to a uniform 

 slope, although the slope may change to conform to the 

 contour of the natural surface. The water to irrigate each 

 strip is taken from the head ditch extending across the 

 upper edge of the field, and is controlled by an outlet box 

 or border gate, although the gates are sometimes omitted 

 to save in first cost of preparing for irrigation. Check 

 ates, canvas dams, or metal tappoons are used to hold 

 up the water in the head ditch to cause it to flow into the 

 borders. 



This method is confined chiefly to the irrigation of 

 alfalfa and grain, and in its various modifications is used 

 extensively in Arizona, California, and, to a less extent, in 

 Idaho, Montana, and other Rocky Mountain States. It 

 can be used best under canals which deliver water to 

 users in large streams, since the smallest head that can be 

 applied successfully is seldom less than 2 or 3 cubic feet 

 per second, but heads of 5 to 10 cubic feet per second are 

 the rule. It is adapted especially to light, open soils, into 

 vhich water percolates rapidly, as the use of a large 

 stream confined between borders makes it possible to 

 force water over the surface without great loss by percola- 

 tion. 



On the university farm at Davis, Cal., the borders or 

 lands average about 50 feet wide by 900 feet long. Each 

 levee has a base 7 feet wide and is 12 inches high, when 

 newly made, but settles to about 10 inches before the first 

 crop is harvested. The bed of each strip is leveled cross- 

 wise and slopes regularly from top to bottom. In prepar- 

 ing the surface of this field, the barley stubble was burned, 

 then the soil was disked and roughly graded. The location 

 of each border was marked out either by a drag or by 

 making a farrow. Sufficient earth to form the border was 

 obtained by skimming the surface with scrapers. The 

 scraper teams began next to the head ditch and worked 



down. They crossed and recrossed the field at right 

 angles to the borders, and as a scraper passed a border 

 marking it was dumped. Each scraper width of the bor- 

 ders was made up of two loads, but the last load over- 

 lapped the first by half the width of the scraper. The sur- 

 face of each border was then leveled to within 0.1 or 0.2 

 foot of accuracy. The levees when first built were rough, 

 irregular, and steep. They were cut down to a uniform 

 grade by a homemade device called a planer, shown in 

 figure 3. 



In Imperial Valley, California, a 40-acre tract is 

 divided in 22 lands each 60 feet wide and 0.2S mile long. 

 When the slope is too steep the lands run diagonally 

 across the tract. In order to lessen the first cost the 

 material for the borders, instead of being scraped from 

 the high portions of the lands, is taken from the sides of 

 the borders. This creates hollows in which water may 

 collect, makes the mowing and raking more difficult, and 

 frequently lessens the yield. Such borders may be made 



Fig. 3. Levee Smoother Made by H. I. Moore. 



by the use of the plow and ridger (fig. 4). In this method 

 a narrow strip is first plowed and then the ridger, drawn 

 by a number of horses, forms the loose earth into a ridge. 

 The cost per acre for preparing the land by the border 

 method in this valley varies all the way from $5 to $20, 

 depending on the character of the native vegetation and 

 the size and number of the hummocks. When creosote 



Fig. 4. Adjustable Ridger. 



bushes and mesquite trees are surrounded by wind-driven 

 sands, the cost may run as high as $40 per acre. 



In Salt River Valley, Arizona, the customary method 

 of preparing the land for alfalfa is to remove the brush, 

 plow the high places, and roughly level the surface with 

 suitable scrapers. Then the borders are marked off from 

 30 to SO feet apart. The spacing depends on the porosity 

 of the soil, the configuration of the land, and the head 



