IRRIGATION. 



IRRIGATION. 



effects produced by it in irrigation, adding a 

 few remarks upon the practice of the best and 

 most skilful cultivators of the water meadows 

 of the south of England. 



1. With regard to the composition of river 

 water, there have been several chemical ex- 

 aminations ; that of the Thames was analysed 

 by Dr. Bostock, who found, in 10,000 parts, 

 after most of its mechanically-suspended mat- 

 ters had subsided, about If parts of foreign 

 substances, viz. : 



Parts. 



Organic matters - 0'07 



Carbonate of lime - - - 1-53 



Sulphate oflime .... 015 



Muriate of soda .... 002 



In an equal quantity of the waters of the 

 Clyde, Dr. Thompson found l part of solid 

 substances, namely : 



Parts. 



Common salt .... 369 

 Muriate of magneaia ... 0-305 

 Sulphate of soda ... 0-114 

 Carbonate of lime - 0'394 



Silica 0-118 



The water of the Itchen, in Hampshire, is 

 one of the most celebrated of all the southern 

 streams, for the use of the irrigator. I found, 

 in 10,000 parts of water, about 2 parts of 

 solid matter, viz.: 



Parts. 



Organic matter .... 02 



Carbonate of lime - - - I 89 



Sulphate of lime .... 0-72 



Muriate of soda .... 01 



From an examination of the substances 

 found in these streams (and they afford a 

 pretty correct view of the contents of most 

 others), the farmer will see that they all yield 

 ingredients which are the food or natural con- 

 stituents of the grasses. Thus, sulphate and 

 carbonate of lime are found in most of them, 

 and there is no river-water which does not 

 contain, in some proportion or other, organic 

 matter. To ascertain, therefore, whether pure 

 water was alone able to effect all the magic 

 I'fK-cis of irrigation, it was necessary to em- 

 ploy other water than that of rivers, lakes, or 

 even springs. Pure water, as obtained by dis- 

 tillation, therefore, has been tried as a sup- 

 porter of vegetation, but it was found totally 

 inadequate to the support of plants ; they 

 merely vegetated for a time, but they could 

 not, by any means, be made to perfect their 

 srrds. In this conclusion the experiments of 

 Dr. Thomson, and of MM. Saussure and Has- 

 senfratz, entirely agree. Pure water, there- 

 fore, notwithstanding the dreams of the Greek 

 philosophers, and the celebrated deceptive ex- 

 periments of Van Helmont with his willow 

 tree, is not able to support the growth of the 

 grasses. Van Helmont's tree, when he planted 

 it in an earthen pot, weighed 5 pounds; the 

 earth, previously dried in an oven, weighed 

 200 pounds ; after 5 years it weighed 164 Ibs., 

 although it had been watered during that time 

 with only rain and distilled water, and the 

 earth had lost only two ounces of weight. 

 Hence, said Van Helmont and his disciples, 

 water is the sole food of plants. Bergman, in 

 1773, first pointed out the source of error. He 

 showed, from the experiments of Margraff, that 

 the rain-water contained a sufficient quantity 

 of earth to account for the increased weight in 



the willow, every pint of rain-water containing 

 one grain of earth. Then, again, the earthen 

 vessel (which was sunk in the earth) would, 

 in this experiment, transmit its moisture im- 

 pregnated with all kinds of soluble substances. 

 And yet it has been shown that impure water, 

 such as that from a sewer, or from a dunghill, 

 is alone sufficient to sustain vegetation. This 

 was clearly evidenced in the experiments of 

 M. Lampadius ; for he found that plants placed 

 in a pure earth, such as silica or alumina, 

 although they would not grow when watered 

 with pure water only, yet, when watered 

 with the liquid drainage of a dunghill, they 

 flourished very luxuriantly, and this fact has 

 been also proved in another way. It has been 

 shown, by chemical analysis, that the quantity 

 of solid or earthy matters absorbed by plants 

 is in exact proportion to the impurity of the 

 water with which they are nourished. Thus, 

 equal quantities of some plants of beans, fed 

 by distilled water, yielded 



Parts. 



Of solid matter or ashes - - 3-9 



Those fed by rain-water - - - 7'5 

 Those grown in garden inoiil I - - 12'0 



These facts strongly confirm the conclusions 

 of some of the most sagacious cultivators, that 

 the chief advantages of irrigation are attributa- 

 ble to the foreign substances with which the 

 water is charged; although, as I have else- 

 where observed, almost every farmer has a 

 mode of accounting for the highly fertilizing 

 effects of irrigation ; one thinks it cools the land, 

 another, that it keeps the grass warm in winter. 

 And this was Davy's opinion. He thought that 

 a winter flooding protected the grass from the 

 injurious effects of frost. He says, "Water is 

 of greater specific gravity at 4.2 than at 32, 

 the freezing point; and hence, in a meadow 

 irrigated in winter, the water immediately in 

 contact with the grass is rarely below 40, a 

 degree of temperature not at all prejudicial to 

 the living organs of plants. In 1804, in the 

 month of March, I examined the temperature 

 in a water-meadow near Hungerford in Berk- 

 shire, by a very delicate thermometer. The 

 temperature of the air at 7 in the morning was 

 43. In general, those waters which breed the 

 best fish are the best fitted for watering mea- 

 dows ; but most of the benefits of irrigation 

 may be derived from any kind of water." 



Such were the opinions of Davy as to the 

 fertilizing properties of water. It is to be re- 

 gretted that the opportunities for agricultural 

 observations of this great chemical philosopher 

 were so few, for his valuable remarks wen* 

 always cautiously made. He appears, how- 

 ever, as I have remarked elsewhere, never to 

 have steadily investigated the chemical com- 

 position of river-water, with regard to its uses 

 in irrigation, and, in consequence, knew little 

 of the value of some of its impurities to vege- 

 tation. Thus, if the river-water contains gyp- 

 sum (sulphate of lime), which it certainly does 

 if the water is hard, it must, under ordinary 

 ircumstances, on this account alone be highly 

 fertilizing to meadows, since all grasses con- 

 tain this salt in very sensible proportions; fcr, 

 calculating that one part of sulphate of lime is 

 contained in every two thousand parts of river- 



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