IRRIGATION. 



IRRIGATION. 



water, and that every square yard of dry mea- ' 

 dow soil absorbs only eight gallons of water 

 (and this is a very moderate allowance, for 

 many soils will absorb three or four times that 

 quantity), then it will be found that, by every , 

 flooding, more than one hundred weight and a 

 half of gypsum per acre is diffused through the 

 soil in the water, a quantity equal to that gene- 

 rally adopted by those who spread gypsum on 

 their clover crops, lucern, and sainfoin, as a 

 manure, either in the state of powder, or as it 

 exists in ashes. And if we apply the same 

 calculation to the organic substances ever more 

 or less contained in flood-waters, and allow 

 only twenty parts of animal and vegetable re- 

 mains to be present in a thousand parts of 

 river-water, then we shall find, taking the 

 same data, that every soaking with such water 

 will add to the meadow nearly two tons per 

 acre of animal and vegetable matters, which, 

 allowing, in the case of water-meadows, five 

 floodings per annum, is equal to a yearly appli- 

 cation of ten tons of organic matter. 



The quantity of foreign substances present 

 in river-water, although commonly less, yet 

 very often exceeds what I have thus calculated 

 to exist in it. I have found it impossible, how- 

 ever, to give, from analysis, the amount which, 

 under ordinary circumstances, is present in 

 river-waters, with any tolerable accuracy, since 

 the proportion not only varies at different sea- 

 sons of the year, but a considerable proportion 

 of the merely mechanically suspended matters 

 subside, when the specimen water is suffered 

 to rest. In my conclusions with regard to the 

 theory of irrigation, I have found many excel- 

 lent practical farmers concur. Thus, Mr. Sim- 

 mons, of St. Croix, near Winchester, considers 

 that the great benefit of winter flooding for 

 meadows is derived, in the first place, from the 

 deposits made by the muddy waters on the grass ; 

 and, secondly, from the winter covering with 

 water preventing the ill effects to the grass of 

 sudden transitions in the temperature of the 

 atmosphere. This gentleman is perfectly aware 

 of the value of the addition of the city drainage 

 of Winchester to the fertilizing qualities of the 

 Itchen river-water, and of its superiority for 

 irrigation after it has flowed past the city, hav- 

 ing water-meadows both above and below the 

 town ; and he finds that, if the water has been 

 once used for irrigation, that then its fertilizing 

 properties are so materially reduced, that it is 

 of little value for again passing over the mea- 

 dows ; and so convinced is he of this fact by 

 long experience, that, having in this way long 

 enjoyed the exclusive and valuable use of a 

 branch of the waters of the Itchen for some 

 grass land, a neighbour higher up the stream 

 followed his example, constructing some water- 

 meadows, and using the water before it arrived 

 at those of my informant, who, in consequence, 

 found the water so deteriorated in quality 

 (though not sensibly diminished in quantity), 

 that he had once thought of disputing the right 

 with his more upland neighbour. The expe- 

 rience of other irrigators tends to the same 

 conclusion. In the best-managed water-mea- 

 dows of Hampshire, the farmer does not pro- 

 cure annually more than three crops of grass ; 

 yet in situations where a richer water is em- 

 672 



ployed, as near Edinburgh, four or five are rea- 

 dily obtained. It is evident, therefore, that the 

 chemical properties of water have a much 

 greater influence in irrigation than is common- 

 ly believed. The quality of the water, there- 

 fore, employed for the purposes of irrigation, 

 is of the first importance to be well understood 

 by the farmer ; and although many more mo- 

 dern discussions have taken place upon the 

 subject, yet the definition which the great Lord 

 Bacon gave, in his Natural History, of the ad- 

 vantages of "Meadow Watering," has never 

 been excelled, "that it acts not only by sup- 

 plying useful moisture to the grass, but like- 

 wise by carrying nourishment dissolved in tht 

 water." This nourishment is, generally speak- 

 ing, composed almost entirely of the animal 

 and vegetable matters mechanically suspended 

 or chemically dissolved in the water; the 

 fouler the water, the more fertilizing are its 

 effects. The objection which has been some- 

 times urged to this explanation, by instancing 

 the prejudicial effects of some very thick mud- 

 dy waters (as those of the Humber) on meadow 

 lands, is very erroneous ; for, in those cases, 

 the mud deposited on the grass did not consist 

 of animal or vegetable matters, but of fine 

 earthy particles, such as clay or chalk, sub- 

 stances of which the alluvial soil, on which 

 the same flood waters had for ages occasion- 

 ally deposited their earths, was in fact en- 

 tirely composed, and to which, in consequence, 

 any further supply was almost useless, the 

 earthy slime merely covering the grass with 

 mud, without adding a single fertilizing ingre- 

 dient not already abounding in the soil. If, 

 however, the soil is naturally deficient in any 

 of the earthy ingredients contained in the wa- 

 ter, then even such flood waters are ever found 

 most fertilizing. 



" The agency of water in the process of ve- 

 getation," says Mr. Stephens, " has not till of 

 late been distinctly perceived. Dr. Hales has 

 shown that, in the summer months, a sunflower, 

 weighing three pounds avoirdupois, and regu- 

 larly watered every day, passed through it or 

 perspired 22 ounces each day, that is, half its 

 weight. Dr. Woodward found that, in the space 

 of 77 days, a plant of common spearmint i'i- 

 creased 17 grains in weight, and yet had no 

 other food than pure rain water ; but then he 

 found that it increased more in weight when 

 it lived in spring water, and still more when 

 its food was Thames water." (Practical Irri- 

 gator, p. 2'.) And when speaking of the fact, 

 that some irrigators think clear spring water 

 equal to any, he adds (p. 24), "I would recom- 

 mend to those who are of the same opinion, 

 to inspect the irrigated meadows which are 

 watered by the washings of the city of Edin- 

 burgh, where, I trust, they will find the supe- 

 riority of muddy water to that of clear spring 

 water most strikingly manifested." 



Edinburgh has many advantages over the 

 most of her sister cities ; the large supply of 

 excellent spring water is one of the greatest 

 blessings to her numerous inhabitants, both in 

 respect to household purposes and keeping the 

 streets clean, as well as irrigating the extensive 

 meadows situated below the town, by the rich 

 stuff which it carries along in a state of semi- 



