52 



THE IRRIGATION AGE. 



Irrigation of Alfalfa 



By SAMUEL FORTIER, 



Chief of Irrigation Investigations, Office of Experiment Stations, 

 U.S. Department of Agriculture. 



Seeding Alfalfa. 



In the Yakima valley, March and" April are preferred 

 for seeding alfalfa, both on account of the climate and 

 the abundant water supply of that period. The ground is 

 plowed deep, graded, smoothed, and harrowed. From 10 

 to 20 pounds of seed are then put in with a broadcast 

 seeder and harrowed lightly. The furrows are then 

 marked off and irrigation begins. The ground is kept 

 moist constantly until the young plants are fairly well 

 established. The use of so much water at the start is 

 due largely to the tendency of the soil to bake if allowed 

 to become dry. 



The alfalfa growers of Montana are about equally 

 divided in opinion as to the advantages of using a nurse 

 crop. Those who seed grain with alfalfa claim that they- 

 get more out of the land the first season, while those 

 who are opposed to this practice believe that the injury 

 done to the alfalfa plants by the grain crop extends 

 through several years and that the small gain of the first 

 year is more than offset by the lessened yields of alfalfa 

 in subsequent years. 



In northern Colorado, rotation of crops is practiced 

 and alfalfa seed is sown with a nurse crop, usually wheat 

 or barley. The seed is drilled early in the spring with 

 a common force-feed press drill equipped with an auxili- 

 ary seed box for alfalfa seed, which is scattered broad- 

 cast between the grain rows and covered by the disk 

 wheels of the press drill. From 12 to 20 pounds of alfalfa 

 seed are sown. Irrigation before seeding is not prac- 

 ticed. There is, as a rule, sufficient rainfall to furnish 

 both crops with moisture until the grain is ready to 

 head out and the alfalfa is 4 to G inches high, when the 

 field is irrigated. 



At Wheatland, Wyo., various methods of seeding 

 iilfalfa are in use, but the cue which gives the best results 

 may be described as follows: Drill in 1 bushel of barley 

 to the acre; then in a week or ten days cross drill the 

 field, sowing 12 to 15 pounds of alfalfa, setting the press 

 drill so that the seed will be covered 0.75 inch to 1.5' 

 inches deep. 



In Yuma and other valleys of Arizona, October plant- 

 ing is preferred. Frequently in this dry climate the land is 

 irrigated before being seeded. It is cultivated, then 

 seeded and harrowed. In the dry-planting method the 

 seed is sown broadcast on the dry soil, harrowed lightly 

 with a brush drag, and then irrigated. A second irrigation 

 is necessary in about eight days to break the surface 

 crust. 



In California the treatment given to alfalfa in the 

 first stage of its growth varies somewhat with the locality; 

 in Kern county the seed is sown from December to April, 

 inclusive, with a preference for February and March seed- 

 ing. If the soil is dry it is first irrigated. In the Modesto 

 and Turlock districts more or less seeding is done 

 throughout the winter months, but the greater part is 

 seeded in March and April, just before the dry season 

 begins. From 30 to 40 acres can be seeded in a day with a 

 hand-broadcasting machine if the operator sits iin the 

 back of a wagon which is driven over the field. Eighteen 

 pounds of seed to the acre is the average amount sown. 



Rise of Ground Water and Its Effects on Alfalfa. 



In their natural state the typical soils of the 

 arid region are characterized by the depth to water and 

 their looseness and dryness. The diversion and use of 

 large quantities of water in irrigation soon change some 

 of these natural conditions. A part of the flow in earthen 

 channels escapes by seepage and still larger quantities 

 percolate into the subsoil from heavy surface irrigations. 

 The waste water from these and other sources collects in 

 time at the lower levels and raises the ground-water level. 

 This rise is usually noticed first in wells, a permanent 

 rise of 5 feet in a vear being not uncommon. 



This rise of the ground water is an advantage, pro- 

 vided the water table does not rise too high. It lessens 



greatly the cost of sinking wells, less water is needed in 

 irrigation, and it furnishes a reservoir from which water 

 can be pumped to supply other lands. 



It is not until the water level encroaches upon the 

 feeding zone of valuable plants that its injurious effects 

 are felt by the farmer. Its near approach to the surface 

 may prove so disastrous that its upward trend should be 

 noted with the greatest care. Perhaps the best means of 

 providing for such observations is the use of test wells. 



There is some difference of opinion as to what depth 

 below the surface marks the danger line for alfalfa. It 

 has been shown by Doctor Loughridge, of the University 

 of California, and by other soil physicists that water may 

 be withdrawn by capillarity from soils to depths varying 

 from 4 to nearly 5 feet, depending on the character of the 

 soil. This fact has an important bearing on the subject, 

 because when the ground water is brought to the surface 

 and evaporated the salts held in solution are deposited at 

 or near the surface. If these salts contain much sodium 

 sulphate, or even sodium chlorid, all of which are usually 

 grouped under the common term alkali, the crust formed 

 by them will in time destroy the alfalfa. It may be stated, 

 therefore, that when alkali is present in harmful quantities 

 in the ground water it should not be allowed to rise nearer 

 than 4 feet below the surface. 



The percentage 'of harmful salts in the ground water 

 is usually determined by the chemist of the nearest agri- 

 cultural experiment station, but when an accurate test 

 cannot be made in the laboratory the farmer may make a 

 practical test in the following manner, in accordance with 

 .1 suggestion made by A. T. Sweet, of the Bureau of 

 Soils of this department: 



Take three pots containing equal amounts of soil and 

 plant the same number of grains of wheat in each. Water 

 each pot with equal quantities of water. In Xo. 1 apply 

 fresh water, in No. 3 ground water, and in Xo. 2 an equal 

 amount of each kind. The injury, if any, caused by the 

 ground water will be indicated by the longer time required 

 lor the plants to appear above the surface, the smaller 

 number of plants to germinate, and their general appear- 

 ance. 



In soils free from alkali but saturated with water 

 there is not the same necessity for holding the ground 

 water continuously below a so-called danger line. In parts 

 of Kern county, Cal., the ground water sinks to 8 feet 

 below the surface of alfalfa fields in summer, but rises 

 to within 1.5 feet of the surface in winter. There is no 

 indication of root rot and the plants have retained their 

 full vigor. Xumerous cases might be cited to show that 

 the rise of water to within a foot or two of the surface 

 for comparatively short periods of time does little injury 

 to the plants. On the other hand, wherever water stands 

 continuously during the irrigation season within a few 

 feet of the surface it is pretty certain to kill alfalfa in three 

 years or less. 



The Injurious Effect of Silt on Alfalfa and the Benefits 

 to be Derived From Disking. 



The silt-laden waters of the rivers of the Southwest 

 during periods of high water in time form a crust over the 

 surface of irrigated alfalfa fields. The soil formed by 

 such rivers is naturally impervious, and when a coating of 

 fine sediment is deposited around the plants the effect is 

 injurious, particularly to young plants, which may be 

 killed as a result, notwithstanding the fertilizing value of 

 the silt. In irrigating with water carrying much silt the 

 larger and heavier particles are deposited in the channels 

 which convey the water from the streams, while the finer 

 and lighter particles are carried to the fields. These fine 

 particles cement together and form so hard a crust when 

 dry as to exclude both air and moisture from the soil. 



Engineers may in time devise a practical remedy for 

 this evil by building settling basins and storage reservoirs, 

 but at present the tendency of many officers of canal com- 

 panies is to increase the grade of the channels so .as to 

 carry the greater part of the silt to the fields. This does 

 not solve the problem; it merely shifts the burden to the 

 water users. To such, disking the surface at the proper 

 time has proved the most efficient remedy. An effort is 

 made to secure well water or clear ditch water while the 

 alfalfa is young and later to counteract the bad effects of 

 muddy water by the free use of the disk. 



