324 SCIENCE OF AGRICULTURE. Part II. 



plants. Hence the origin of surface-draining, that is, laying land in ridges or beds, or 

 intersecting it with small open gutters. 



2143. Sjrrings. Where the upper stratum is porous in some places, and retentive in 

 others, and on a retentive base, the water, in its progress along the porous bed or layer, 

 will be interrupted by the retentive places in a great variety of ways, and there accumu- 

 lating will burst through the upper surface in the form of springs, which are more in- 

 jurious than surface-water, as being colder, and generally permanent in their operation. 

 Hence the origin of under-draining in all its varieties of collecting, extracting, and con- 

 veying water. 



2144. The water of rivers may become injurious to lands on their banks, by too fre- 

 quently overflowing their surface. In this case the stream may be included by mounds 

 of earth or other materials impervious to water : and thus aquatic soils rendered dry 

 and fit for useful herbage and aration. The same may be said of lands occasionally 

 overflown by the sea. Hence the origin of embanking, an art carried to a great extent 

 in Holland and Italy. (See Smeaton's Posthumous Works; Sigismondi, Agr. Tosc. ; and 

 our article Embankment, in Sujrp. Encyc. Brit. 1819.) 



2145. Irrigation. Plants cannot live without water, any more than they can prosper 

 in soils where it is superabundant ; and it is therefore supplied by art on a large scale, 

 either by surface or subterraneous irrigation. In both practices the important points are to 

 imitate nature in producing motion, and in applying the water in the mornings or even- 

 ings, or under a clouded sky, and also at moderate intervals, The effects of water con- 

 stantly employed, would, in most cases, be such as attend stagnated water, aquatic soils, 

 or land-springs; and employed in hot sunshine, or after violent heats, it may check 

 evaporation and destroy life, exactly as happens to those who may have bathed in cold 

 spring water after long and violent exercise in a hot day. {Phytologia, xv. 3. 5. ) 



2146. In surface irrigation the water is conveyed in a system of open channels, which 

 require to be most numerous in such grounds as are under drilled annual crops, and 

 least so in such as are sown in breadths, beds, or ridges, under perennial crops. This 

 mode of watering has existed from time immemorial. The children of Israel are repre- 

 sented as sowing their seed and " watering it with their foot ;" that is, as Calmet 

 explains it, raising the water from the Nile by a machine worked by the feet, from 

 which it was conducted in such channels as we have been describing. It is general in 

 the south of France and Italy ; but less required in Britain. 



2147. Subterraneous irrigation may be effected by a system of drains or covered 

 gutters in the subsoil, which, proceeding from a main Conduit, or other supply, can be 

 charged with water at pleasure. For grounds under the culture of annual plants, this 

 mode would be more convenient, and for all others more economical as to the use of 

 water, than surface irrigation. Where the under-stratum is gravelly, and rests on a 

 retentive stratum, this mode of watering may take place without drains, as it may also 

 on perfectly flat lands, by filling to the brim, and keeping full for several days, surround- 

 ing trenches ; but the beds or fields between the trenches must not be of great extent. 

 This practice is used in Lombardy on the alluvial lands near the embouchures of the 

 Po. In Lincolnshire the same mode is practised by shutting up the flood gates of the 

 mouths of the great drains in the dry seasons, and thus damming up the water through 

 all the ramifications of the drainage from the sea to their source. This was first sug- 

 gested by G. Rennie and Sir Joseph Banks, after the drainage round Boston, com- 

 pleted about 1810. A similar plan, on a smaller scale, had been practised in Scotland, 

 where deep mosses had been drained and cultivated on the surface, but where, in 

 summer, vegetation failed from deficiency of moisture. It was first adopted by J. 

 Smith, (See Essay on the Improvement of Peat-Mass, 1795,) on a farm in Ayrshire, and 

 has subsequently been brought into notice by J. Johnston, the first deUneator and pro- 

 fessor of Elkinson's system of draining. 



2148. Manuring by irrigation. Irrigation with a view to conveying additions to the 

 soil has long been practised, and is an evident imitation of the overflowing of alluvial 

 lands, whether in meadow or aration. In the former case it is called irrigation or 

 flooding, and in the latter, warping. Warping is used chiefly as a mode of enriching 

 the soil by an increase of the alluvial depositions, or warp of rivers, during winter, 

 where the surface is not under crop, and is common on the banks of the Ouse. 



2149. The rationale of irrigation is thus given by Sir H. Davy. " In general in 

 nature the operation of water is to bring earthy substances into an extreme state of 

 division. But in the artificial watering of meadows, the beneficial effects depend upon 

 many different causes, some chemical, some mechanical. Water is absolutely essential 

 to vegetation ; and when land has been covered by water in the winter, or in the begin- 

 ning of spring, the moisture that has penetrated deep into the soil, and even the subsoil, 

 becomes a source of nourishment to the roots of the plants in the summer, and prevents 

 those bad effects that often happen in lands in their natural state, from a long con- 

 tinuance of dry weather. When the water used in irrigation has flowed over a calcareous 



