THE IREIGATION AGE. 



259 



A few practical ideas may be gathered from the foregoing 

 which are worth considering : 



First It is evident that deep plowing will enable the 

 rainfall or the irrigation water to penetrate deeper into the 

 soil, in which case it will remain longer and the effects of a 

 small quantity of rain may extend over a period long enough 

 to mature a crop where half as much again would show 

 nothing. 



Second To be effective and beneficial to vegetation the 

 water in the subsoil must be in constant motion. When water 

 eases to flow in the subsoil streams, or when capillary action 

 > entirely suspended, the water becomes stagnant, ceases to 

 imbibe oxygen, nitrogen and carbonic acid, and practically 

 rots, causing vegetation within its influence also to decay. Run- 

 ning water coming from the clouds or irrigating ditch enters 

 the soil charged with gaseous matters above specified, mixed 

 in their proper proportions, and carries along with it various 

 dissolved inorganic substances which are not permitted to be 

 deposited out of it while it is in motion. Hence, to derive the 

 full benefit of the water, the land must be drained even where 

 irrigation is practiced, so that the surplus water, after irri- 

 gation is stopped, may find a ready outlet. If 'there should be 

 no surplus, no harm is done by drainage facilities ; on the con- 

 trary, the tendency of all drainage is to open the soil below 

 and "draw" the moisture from above as well as to carry off 

 the surplus water in a soaked subsoil if there be one. Drain- 

 age does not carry off moisture, but only the surplus water ; 

 capillary attraction will always hold the moisture. 



Third Whenever sufficient water is added to the soil to 

 ompensate for loss by evaporation from soil and plant, the 

 business of the irrigator is accomplished. To keep on add- 

 to soak the soil continually, would be to injure vegeta- 

 tion as much as by furnishing too little water, as it is only by 

 keeping the surface soil loose and finely pulverized the deeper 

 the better that evaporation from the soil may be retarded. 



As to the quality of the water the more impure it is, par- 

 ticularly in organic matter, the better it is for vegetation. 

 There is no more impure water in the world than that of the 

 river Nile, yet it gives fertility and produces luxuriant vege- 

 tation where there would be barrenness and sterility were it 

 pure. The exception in the case of irrigating alkali lands 

 would be water heavily charged with alkali salts, this kind of 

 water being one of the causes of deleterious alkali deposits. 



The oxygen of the atmosphere is essential to the germi- 

 nation of the seed and to the growth of the plant. The whole 

 plant must have air, the roots as well as the leaves, therefore 

 it is of consequence that this oxygen should have access to 

 every part of the soil and thus to all the roots. This can 

 only be effected by working the land and rendering it suffi- 

 ciently porous. 



Some soils absorb oxygen faster and in greater quanti- 

 ties than others. Clays absorb more than sandy soils, and 

 vegetable molds or peats more than clay. It depends, how- 

 ever, upon their condition as to porosity, and also upon their 

 chemical constitution. If the clay contains iron or manganese 

 in the state of oxides these latter will naturally absorb oxygen 

 in large qualities for the purpose of combining with it, having 

 . great affinity therefor, while a soil containing much decay- 

 ng vegetable matter will also drink in large quantities of 

 oxygen to aid the natural decomposition constantly going on. 



In addition to absorbing oxygen and nitrogen, of which 

 the air principally consists, the soil also absorbs carbonic acid 

 and portions of other vapors floating in it whether ammonia 

 or nitric acid. This absorption of atmospheric elements and 

 gases of every kind occurs most easily and in greater abun- 

 dance when the soil is in a moist state. Hence it is that the 

 fall of rains and the descent of dew, or the application of ir- 

 rigation water, favors this absorption in dry seasons and in 

 dry climates ; it will also be greatest in those soils which have 

 the power of most readily extracting watery vapor from the 

 air during the absence of the sun. It must be clear from this 

 that the influence of dews and gentle showers reaches much 

 "arther than the surface of the soil, watery vapor following 

 lie atmosphere down deep into the soil, penetrating as deep 

 the porous nature of the soil will permit it. Some say 

 bat, under proper conditions as to cultivation, the soil will 

 ain in dew at night nearly as much as it loses by evaporation 

 uring the day. It appears reasonable enough to suppose that 

 the atmosphere, under a pressure of fifteen pounds to the 

 iqaare inch, will penetrate to any depth and carry with it 

 vhatever of moisture and gases it contains. 



Irrigation of Alfalfa 



By SAMUEL FORTIER, 



Chief of Irrigation Investigations, Office of Experiment Stations. 

 U. S. Department of Agriculture, 



The Check Method 



The -essential features of the check method of irriga- 

 tion consist in surrounding nearly level plats of ground 



with low levees, 



ui and in making 



provision to 

 flood each by 

 means of a ditch 

 and check box or 

 gate. T h e in- 

 closed spaces 

 may be laid out 

 in straight lines 

 in both directions, 

 thus forming with 

 their levee bor- 

 ders a series of 

 rectangles, or the 

 levees may follow 

 more or less 

 closely the con- 

 tour lines of the 

 natural surface of 

 the ground, thus 

 forming contour 

 checks. The most 

 favorable condi- 

 tions are a light, 

 sandy soil on a 

 c omparatively 

 even slope of 3 to 

 IS feet to the 

 mile, abundantly 

 supplied with 

 water. This meth- 

 od is also used 

 on heavy soils, 

 where it is neces- 

 sary to hold the 

 water on the soil 

 to secure its per- 

 colation to the 

 desired depth. 



I n California 

 not only does 

 the form of the 



checks vary, but their size as well, some of the smaller 

 being less than one-half acres in area, while some of the 

 larger contain more than 10 acres. 



Fig. 6. Laying Out Rectangular Checks on 

 Farm of T. K. Beard, Modesto, Cal. 



Fig. 7. Grader. 



In the Modesto and Turlock irrigation districts the 

 surface of the land under ditch slopes about 5 feet to the 

 mile, and is too uneven to be irrigated without being 

 leveled first. The unevenness consists in swales, hog 

 wallows, and mounds. The land is surveyed first either 

 by an engineer or by the owner. In the latter case use 

 is made of a carpenter's level, with peep sights, mounted 

 on a tripod (fig. 5). The long side of each check should 



