Liquid Manure. 



151 



Almost every farmer lias a mode of accounting for the highly 

 fertilizing effects of irrigation. Davy added another to the list of 

 explanations. He thought that a winter-flooding protected the 

 grass from the injurious effects of frost; he examined with a ther- 

 mometer, and with his usual address, the water-meadows near 

 Hungerford in Berkshire, and ascertained that the temperature 

 of the soil was ten degrees higher than the surface of the w ater, 

 and that too on a frosty Alarch morning. He remarked, also, a 

 fact that most farmers will confirm, that those waters w^hich breed 

 the best fish are ever the best fitted for watering meadows.'^ 



Such were the opinions of Davy as to the fertilizing properties 

 of water. It is to be lamented that the agricultural opportunities 

 for observation of this great chemist were so few, for his valuable 

 remarks were always cautiously made. He appears, however, never 

 to have steadily investigated the chemical composition of river- 

 water, with regard to its uses in irrigation, and in consequence he 

 knew little of the value of some of its impurities to vegetation. 

 Thus, if the river-water contains gypsum (sulphate of lime), which 

 it certainly does if the water is hard, it must, under ordinary cir- 

 cumstances, on this account alone, be highly fertilizing to mea- 

 dows, since the grasses contain this salt in very sensible propor- 

 tions. Calculating that one part of sulphate of lime is contained 

 in every two thousand parts of the river-water, and that every 

 square yard of dry meadow-soil absorbs only eight gallons of 

 w^ater, then it will be found that by every flooding more than one 

 hundred- weight and a half of gjnpsum per acre is diffused through 

 the soil in the water, a quantity equal to that generally adopted 

 by those who spread gypsum on their clover, lucern, and sainfoin 

 crops as a manure, either in a state of powder, or as it exists in 

 peat-ashes. 



And if we apply the same calculation to the organic substances 

 ever more or less contained in flood w^aters, and if we allow only 

 twenty-five parts of animal and vegetable remains to be present 

 in a thousand parts of river -w^ater, 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 application of ten tons of organic 

 matter. The quantity of foreign substances present in river- 

 w^ater, although commonly less, yet very often exceeds what I 

 have calculated to exist. 



T have found it impossible to give from analysis the amount of 

 the foreign substances, under ordinary circumstances, present in 

 river-waters, with any tolerable accuracy, since the proportion not 



* Agricultural Chem. p. 352. 



