94 



General Principles and Directions for Irrigation. Vol. XI. 



General Principles and Directions for 

 Irrigation. 



Some points respecting irrigation may be 

 considered as well established, to which it 

 is proper that I should refer. It is settled 

 that simple water, without any admixture, 

 is in itself a great enricher of the soil, or 

 perhaps, more properly, a great promoter of 

 vegetation. If the water of irrigation is 

 charged with enriching matters in a state 

 of solution, its beneficial effects are of course 

 increased. Waters charged with mineral 

 substances, such as water strongly impreg- 

 nated with iron from peat bogs, or water 

 from copper mines, is pernicious to vegeta- 

 tion, as any one may see, who will visit the 

 outlets of the copper mines of Cornwall. 

 It is established, likewise, that water in irri- 

 gation, in order to produce its best effects, 

 must not be suffered to stagnate upon the 

 land, but must pass in a steady progress 

 over it; and that this progress should be 

 comparatively gentle, and not sudden and 

 rapid. It is equally well established, that 

 lands which it is proposed to irrigate, should 

 be thoroughly drained, so that the water 

 poured upon the land should not be suffered 

 to stand in the land, nor upon it. The effect 

 of stagnant water upon the surface, or the 

 complete saturation of the soil, is to change 

 the nature of the herbage, and to produce 

 those grasses, which are coarse or innutri- 

 tions, in place of the finer, sweeter, and 

 more healthful. Yet it is not the mere 

 transition of the water over the surface 

 that is to be sought. It is desirable to have 

 it soak into the ground, but not to remain 

 there. Its speedy transition over the sur- 

 face is to be effected by the inclination of 

 the land from where it is received to the 

 trench, furrow, or ditch, by which it is to be 

 carried off. Its passing into the ground, 

 and finding a speedy passage off, is to be 

 effected by a system of thorough draining 

 and subsoiling; for if the subsoil is impervi- 

 ous, the irrigated field becomes converted 

 into a marsh. One of the most eminent 

 farmers in Scotland, whose hospitality I had 

 the pleasure of enjoying, but whose death 

 since that time is deeply to be lamented, — 

 Mr. Oliver, of Lochend, near Edinburgh, — 

 who had a large extent of meadow, irrigated 

 by the sewerage water from the city, found 

 that, after his fields were thorough drained, 

 the benefit of the irrigation was greatly in- 

 creased ; for by the descent of the sewerage 

 water into the soil, as well as over it, the 

 enriching portions of the manure in a state 

 of solution were carried to the roots of the 

 plants. In the irrigated meadows of the 

 Duke of Portland, — ^for its extent one of the 



most beautiful and finished agricultural im- 

 provements which can be found — he showed 

 me, that portions of his irrigated lands, which 

 had even been drained, continued to affect 

 his sheep with the rot ; and this evil was 

 not remedied until the draining was carried 

 to the depth of eight feet or more. Before 

 that, without doubt, the stagnant water at 

 the bottom prevented the water of irrigation 

 from passing off, and may be said to have 

 poisoned the whole ground. 



In irrigation skilfully managed, the in- 

 crease of product is often very great — two- 

 fold, fourfold, in many cases even fivefold. 

 Even sands which were barren, have, by ir- 

 rigation, been made productive. Plants, in 

 such cases, having once found a footing, by 

 the spread and decay of their own roots, 

 have at length formed a soil, and created 

 around themselves the elements of fertility. 

 The effect of pure water, I have already 

 said, is considerable; but when this water 

 brings with it the refuse of the streets and 

 habitations of a town in a state of solution, 

 the effects, as we shall presently see, are 

 most remarkable. I have seen it stated, 

 that water issuing from a limestone soil, and 

 strongly impregnated with lime in the form 

 of a sulphate or other combination, has been 

 employed with great success in irrigation. 

 Such instances have not come under my ob* 

 servation; but I cannot doubt the effect, 

 where the soil was of a nature to require 

 that element. In respect to manures, or 

 any of the constituents of plants, it is evi- 

 dent they can be taken up only in a state of 

 the finest solution. Here homoepathy tri- 

 umphs, and no human sense is acute enough 

 to discern, no human scales are fine enough 

 to measure, those infinitesimal atoms out of 

 which the rough substance of the gnarled 

 oak is formed. 



It would be idle, in a work of this nature, 

 to attempt to lay down any thing more than 

 the general principles of irrigation. In the 

 accomplishment of any particular work, all 

 the localities are to be considered, and the 

 effecting of it upon any large scale would re- 

 quire considerable engineering skill. 



Irrigation of land and inundation are not 

 the same. The inundation of land resem- 

 bles what I have already described under 

 the process of warping, where, the land 

 being enclosed by embankments, the water 

 is admitted to flood the land, and is held fast 

 until its floating riches are deposited. This 

 can seldom be done without disadvantage 

 upon a growing crop, unless when in its 

 earliest stages of growth. Irrigation is the 

 gradual filtering and spreading of the water 

 over the soil, and, where not too rapidly ap- 

 plied, may be done with safety at any period 



