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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. 



Amount of Water Required. 



Alfalfa requires more water than most crops. This is 

 readily accounted for by the character of the plant, the 

 rapidity with which it grows, the number of crops pro- 

 duced in one season, and the heavy tonnage obtained. 



As a result of careless practice there is a lack of uni- 

 formity in the quantity of water used, the volumes applied 

 frequently being far in excess of the needs of the crop. 

 The majority of the records collected and published by 

 this office show a yearly duty of water for alfalfa ranging 

 from 2.5 to 4.5 feet in depth over the surface, while in 

 quite a large number of cases the volumes applied would 

 have covered the area irrigated to depths of 6 to 15 feet. 



From the large number of measurements made on the 

 duty of water it is possible to select some that possess 

 great value, since they indicate what can be accomplished 

 with a given quantity of water. 



During the season of 1904 careful measurements were 

 made by C. E. Tait, of this office, of the amount of water 

 used on alfalfa fields in the vicinity of Pomona, Cal. The 

 rainfall at Pomona for the winter of 1903-4 was much 

 below the normal and amounted to about 9.1 inches.* The 

 quantity of irrigation water applied by pumping averaged 

 2.3 feet in depth and the yield of cured hay averaged from 

 1 to 1.5 tons per acre per crop, five or six crops being 

 common. These figures are corroborated by many others 

 collected in sotUhern California. Perhaps in no other 

 locality of the arid region is a greater tonnage of alfalfa 

 obtained, yet in a climate of scanty rainfall having a long, 

 dry, hot summer only a comparatively small amount of 

 water is used. About a third of the 9,000 acres irrigated 

 by the Riverside Water Company is in alfalfa and for the 

 past seven years the average depth applied has been 2.31 

 feet, while the depth of rainfall and irrigation water com- 

 bined has averaged 3.18 feet. 



In 1903 the writer, when director of the Montana Ex- 

 periment Station, applied different depths of water to 

 seven plats of alfalfa with the results given in the follow- 

 ing table. It will be seen that a high tonnage for so short 

 a season as prevails in Montana was obtained from plat 5 

 with the use of 2 feet of water. By irrigating plat 6 seven 

 times, and plat 7 eight times, it was possible to increase 

 the yield to the amounts stated. The results of this experi- 

 ment seem to confirm the best practice of southern Cali* 

 fprnia, which may be summed up by stating that in locali- 

 ties having an annual rainfall of about 12 inches remark- 

 ably heavy yields of alfalfa may be obtained from the use 

 of 24 to 30 inches of irrigtion water, providing it is prop- 

 erly applied. 



Quantities of Water Applied to Alfalfa and Yields Secured, 

 Montana Experimental Station. 



Yield per 



Depth of Depth of Total acre of 



Plat irrigation. rainfall. depth. cured, 

 number. alfalfa. 



Feet. Feet. Feet. Tons. 



1 0.5 0.70 1.20 4.61 



2 None .70 .70 1.95 



3 1.0 .70 1.70 4.42 



4 1.5 .70 2.20 3.75 



5 20 . .70 2.70 6.35 



6 2.5 .70 3.20 7.20 



7 . 3.0 .70 3.70 7.68 



The Proper Time to Irrigate Alfalfa. 



The general appearance, and more particularly the 

 color of the plant, are the best guides, perhaps, as to when 

 water is needed. When healthy and vigorous, alfalfa is 

 of a light-green color; but when the supply of moisture is 

 insufficient the leaves take on a darker and duller shade of 

 green and begin to droop, and unless water is provided 

 both stems and leaves wither and die. Another test is to 

 remove a handful of soil 6 inches or so beneath the sur- 

 face and compress it in the hand. If it retains its ball-like 

 shape after the pressure has been removed and shows the 

 imprints of the fingers, the soil is sufficiently moist, but 



*U. S. Dept Agr., Weather Bureau, Climate and Crop Ser- 

 vice, California, Ann. Sums.. 1903 and 1904. 373. 



if it falls apart readily it is too dry. In connection with 

 such tests it is well to bear in mind that they are more 

 or less influenced by both soil and climate. It is therefore 

 necessary to observe the growth of the plant closely on all 

 new alfalf^ fields to determine if possible how far such 

 tests may be relied upon, the chief object being to main- 

 tain at all times as nearly as practicable the proper amount 

 of moisture in the soil surrounding the roots of the plants 

 to prevent a checking of their growth. 



Alfalfa commonly receives careless treatment at the 

 hands of western irrigators. When water is available and 

 is not needed for other crops it is usually turned on the 

 alfalfa fields or meadows whether these need it or not. 

 There is no question that yields of alfalfa might be consid- 

 erably increased if more care was used in finding out when 

 to apply water. In each kind of soil and under any 

 given set of climatic conditions there is a certain per- 

 centage of soil moisture which will give the best results. 

 Under the present unskilled practice it is impossible to 

 maintain uniform soil-moisture conditions for any length 

 of time. The soil is apt to receive too much or too little 

 water, or else it is deluged with cold water at a time when 

 it needs only heat and air. The number of irrigations 

 required depends upon the depth and nature of the soil, 

 the depth to ground water, the number of cuttings, and 

 the rainfall, temperature, and wind movement. Other 

 things being equal, more frequent waterings are required 

 in the warm sections of the South than in the cooler 

 portions of the North. The number of irrigations per year 

 for alfalfa ranges from 4 in Montana and Wyoming to as 

 many as 12 in parts of California and Arizona. In locali- 

 ties where water is scarce during part of the season the 

 number of waterings as well as the amount used each time 

 depends on the available supply. It is a common prac- 

 tice to apply frequent and heavy irrigations in spring when 

 water is abundant and to water less often and more spar- 

 ingly when the supply is low. 



Winter Irrigation of Alfalfa. 



When water is applied either to bare soil or to crops 

 outside of the regular irrigation season it is termed winter 

 irrigation. The practice thus far has been confined largely 

 to the warmer parts of the arid region. It has become 

 well established in Arizona and California and is being 

 quite rapidly extended to parts of Oregon, Kansas, and 

 the Rocky mountain states. 



Experience has shown that a deep retentive soil is 

 capable of storing a large quantity of water. On account 

 of the fluctuation of western streams of all kinds, from the 

 small creek to the large river, the greatest flow of water 

 often comes at a season when there is least demand for it. 

 In a few localities adequate storage facilities have been 

 provided to retain the surplus, but as a rule it is allowed to 

 go to waste. The passage of so much waste water led to 

 the introduction of winter irrigation and in nearly every 

 case the results have been satisfactory. The chief clit- 

 ferences between winter and ordinary irrigations are the 

 larger volumes used, the crude manner of conveying and 

 applying the water, and the dormant or partially dormant 

 condition of the plants at the time of irrigation. 



In Fresno county, Cal., water is turned into the canals 

 in January and February. The larj e canals of the Modesto 

 and Turlock districts run more than half a head during the 

 latter half of February. This is the rainy period in both 

 these localities and the soil is usually too wet for plant 

 growth, but water is applied to alfalfa fields to fill up the 

 subsoil so as to provide a surplus for the rainless summer 

 when water is scarce. 



Besides furnishing a supply of much-needed moisture, 

 winter irrigation, when conditions are favorable, prevents 

 winterkilling and improves the mechanical condition of the 

 soil. 



Winter Killing of Alfalfa. 



The winter killing of alfalfa is confined chiefly to the 

 colder and more elevated portions of the Rocky mountain 

 region and to the northern belt of humid states. Damage 

 from cold is rare in Arizona and in California it is con- 

 fined to young plants. In both the Sacramento and San 

 Joaquin valleys of the latter state the seed is frequently 

 sown in midwinter and the slight frosts which occur occa- 

 sionally in December and January in both these valleys 

 are severe enough to kill very young plants. The belief 





