THE ART OF IRRIGATION. 



SEVENTH PAPER: CHOICE OF METHODS. SMALL STREAMS. 



BY T. S. VAN DYKE. 



YOUR choice of methods in irrigation is not only 

 limited by the quantity and heads of water at 

 your disposal, as explained in the last chapter, but by 

 the texture of your soil, its slope, drainage and sev- 

 eral minor points. 



All these things you should determine before lay- 

 ing out your ground for any system, for whatever 

 system you adopt you will not be likely to change. 

 As important as any of these is the texture of the 

 soil. If it is very open you will have to use a differ- 

 ent system from the one you could probably use if 

 it were of closer texture. 



FORMATION OF SOIL. 



All soil is formed from disintegrated rock, some- 

 times disintegrated in place from the bed rock 

 beneath, in other places washed in from a distance. 

 Where this wash has been by the flow of some 

 stream it forms what is called bottom land. Where 

 it has been carried only by occasional heavy rains, 

 aided by the drift of winds, it is called slope or plain. 

 This is a truism, but you want to keep in mind the 

 distinction. 



Part of this disintegration of the rock is chemical 

 and part mechanical, resulting from the incomplete 

 work of the chemical operation. By the chemical 

 part the rock decays into a fine powder or paste, 

 according to the amount of water present. This in 

 all its forms is called clay, and the name is suffi- 

 ciently accurate for our purpose. The part that has 

 not yet decayed is in hard pieces, and called sand or 

 gravel according to its size. Sedimentary clay is 

 where this fine part has been washed out and depos- 

 ited in beds. It rarely makes good soil to work. 



THE BEST SOIL. 



The best all-around soil, and the best to irrigate as 

 well as cultivate, is that which contains clay, sand 

 and gravel in about equal proportions. If it has too 

 much clay it will be tough and hard for the water to 

 penetrate, and when it does once penetrate it may 

 stay too long and in too great quantity and keep the 

 soil cold. When it dries it is quite apt to harden 

 quickly at a certain point, leaving you little time to 

 work it fine ; and when it does harden it is quite dif- 

 ficult to make fine without wetting again. Though 

 this soil may be very rich, like some of the adobes, 

 it may be very troublesome to work with water. It 

 has, however, one advantage. It can under all cir- 

 cumstances be irrigated with small streams, and it is 

 never necessary to flood it unless it should be very 



much cracked from excessive dryness, which is quite 

 apt to be the case if clay is much in excess. 



Where soil contains an excess of gravel it will not 

 crack when dry. Nor will it hold any excess of 

 water or bake so that it cannot be easily broken up. 

 It is also warm and often far more fertile than it 

 appears. While it will rarely produce good grain 

 or heavy corn, it is generally the best fruit land, 

 owing to its warmth and perfect drainage. But it 

 will let water through like a sieve, and is called by 

 some " leachy." It is so named because the water is 

 supposed to leach out and carry away the fertilizers 

 it contains. From the irrigator's point of view it is 

 objectionable because it will not hold up streams of 

 moderate size, but must be flooded. And as a rule it 

 takes water in large heads and quickly handled to 

 flood it properly. 



Soil containing an excess of sand is a medium be- 

 tween these two, and is generally so open that it must 

 be flooded. It may not require such large heads or 

 need them so quickly handled as the gravelly soil, 

 but it is too open to hold up small, slow streams. 

 Some of it may be irrigated by side soaking from 

 large streams, but often it is too open for that and 

 water drops through it too directly downward and 

 too fast. It is also deficient often in capillary attrac- 

 tion of the kind you want, and will not bring up 

 moisture from any distance below, while it will let it 

 off from the few inches at the top so fast that shallow 

 rooted stuff will need irrigating every few days in 

 spite of all the cultivating you can do. Some of this 

 soil you cannot keep moist by any amount of culti- 

 vation. Other ground, that to the eye may be of the 

 same texture, may contain so much more clay that it 

 will retain moisture perfectly with cultivation. 



BOTTOM LAND. 



Much river bottom land is so open that it must be 

 flooded, and where it is a wash of particles quite uni- 

 form in size it is not likely to retain moisture well. Nor 

 as a rule will water soak sideways in it at any dis- 

 tance from furrows. You must, therefore, prepare 

 to flood such land, and for shallow-rooted vegetation 

 must be prepared to flood it often. If you cannot get 

 water in large heads, and at nearly the right times, 

 put deep-rooted stuff in the ground. 



UPLAND. 



As a rule upland, or drift by rains and wind from 

 the hills, contains enough clay to hold up very small 

 streams to allow the water to soak some distance on 



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