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IRRIGATION. 



IRRIGATION. 



water having deposited the fertilising substances which it held in 

 solution, or which were diffused through it, but to its having taken 

 up some substances which are detrimental to vegetation, and being 

 saturated with them : at least this is the most probable opinion when 

 all circumstances are taken into the account. 



The general principle of irrigation may be described as the supplying 

 every portion of the surface with an abundance of water, and taking it 

 off again rapidly. In many situations the great difficulty in irrigation 

 arises from the want of a supply of water ; but even then a partial 

 irrigation may be effected, which, although not perfect, will have ite 

 advantages. A small rill which is often quite dry in summer may 

 still, by judicious management, be made to improve a considerable 

 portion of land : its waters may be collected and allowed to accumu- 

 late in a pond or reservoir, and let out occasionally, so that none be 

 lost or rim to waste. If there is but a small quantity it must be 

 husbanded and made to flow over as great a surface as possible. If 

 there is water only at particular seasons of the year, and at a time 

 when it would not be of much use to the land, it may be kept in ponds, 

 and it will lose none of its qualities by being exposed to the air. If 

 animal or vegetable matter in a partial state of decomposition is added 

 to this water, it will much improve its quality, and by a judicious 

 distribution of it over the land a great benefit may be obtained. 



If there is not a want of water, there may be a want of declivity to 

 enable it to flow off, which, it should always be remembered, is an 

 essential part of irrigation. Art may in this case assist nature by 

 forming a passage for the water, either in its course towards the land 

 to be irrigated, or from it after it has effected its purpose. Where 

 there is no natural exit, and it might lead to too great an expense to 

 make an artificial one, the water may sometimes be led into shallow 

 ponds, where a great part is evaporated ; or porous strata may be found 

 by boring, into which it can be made to run and be dispersed. Along 

 rivers where the fall is very imperceptible a channel brought from a 

 considerable distance may give such a command as to throw the water 

 over a great extent of surface ; and to carry it off another channel may 

 be cut, emptying itself at some distance below : so that lands which 

 lie along the banks of a river may be irrigated, although they .ire 

 actually below the level of the river, and require banks to protect them 

 from inundation. 



When the surface to be irrigated ig very flat and nearly level, it is 

 necessary to form artificial slopes for the water to run over. The 

 whole of the ground is laid in broad beds, undulating like the waves of 

 the sea. The upper part of these beds is quite level from end to end, 

 and here the channel which brings the water is cut. From the edge of 

 this channel the ground is made to slope a foot or two on both sides, 

 and a ditch is cut at the bottom parallel to the float. The whole of 

 the ground is laid out in these beds. All the supply furrows are fed 

 by a main channel at right angles to the beds and somewhat above 

 them, and all the ditches or drains run into a main ditch parallel to 

 the main float, and below the lowest drain. The course of the water 

 is very regular. As soon as the flood-gates are opened it flows into all 

 the upper channels, which it fills till they overflow in their whole 

 length. The sloping sides are covered with a thin sheet of running 

 water, which the lower drains collect and carry into the main ditch. 



Experience has shown that there are particular seasons when the 

 water has the best effect; a perfect command of it is therefore 

 indixpensable, and also a regular supply. During frost, when all dry 

 meadow.-* are in a state of torpor, and the vegetation is suspended, the 

 water-meadows, having a current of water continually flowing over 

 them, are protected from the effect of frost, and the grass will continue 

 to grow aa long as the water flows over it. Too much moisture 

 however would be injurious, and the meadows are therefore laid dry 

 by shutting the flood-gates, whenever the temperature of the air is 

 above freezing. By this management the grass grows rapidly at the 

 first sign of spring. Before the dry upland meadows have recovered 

 the efteets of frost and begun to vegetate, the herbage of the water- 

 meadows is already luxuriant. As soon as they are fed off or cut for 

 the first crop of hay, the water is immediately put on again, but for a 

 shorter time ; for the warmer the air, the less time will the grass bear 

 to be covered with water. A renewed growth soon appears, and the 

 grass is ready to be cut a second time when the dry meadows only give 

 their first crop. Thus, by judicious management, three or four crops 

 of grass are obtained in each season, or only one abundant crop is 

 made into hay, and the sheep and cattle feed off the others. The 

 usual way in which the grass of water-meadows is made profitable is by 

 feeding ewes which have early lambs till the middle of April. A short 

 flooding soon reproduces a crop, which is mown for hay in June ; 

 another flooding gives an abundant aftermath, which is either mown 

 for hay, or fed ofl by cows, bullocks, and horses ; for at this time the 

 sheep, if pastured in water-meadows, are very subject to the rot. The 

 value of good water-meadows could scarcely be believed by those who 

 are not familiar with them. Where the water is suited to irrigation 

 they never require manuring. Their fertility is kept up continually, 

 and the only attention required is to weed out coarse aquatic plants, 

 i are neither nutritious nor wholesome in hay or pasture. 



The best noil for a water meadow is a good gravel. The finest water- 

 meadows on the Avon in Wiltshire, where the richest herbage is found, 

 have scarcely any soil at all, but are on little more than a bed of shingle 

 matted together by the roots of the grass, which proves that the waters 



ARTS AXD HCI. DIV. VOL, IV. 



of the Avon contain all the principles essential to rapid vegetation. 

 Great attention is required, and some experience, to irrigate meadows, 

 so as to give the greatest profit. 



In hot weather, when we should' imagine that the land must be 

 thirsty, and that too much water cannot be poured over it, much mis- 

 chief may be done by injudicious flooding. In winter, on the contrary, 

 the laud may be covered with water for weeks without injury ; and if 

 an earthy deposit takes place, the subsequent fertility is greatly 

 increased. But this is not properly irrigation : it is inundation, and 

 the effects depend on entirely different causes. When low meadows 

 are inundated in winter and spring, it is the muddiness of the water 

 which enriches the laud : a fine layer of extremely divided matter 

 is deposited, and when the water subsides this acts as a coat of 

 manure. 



Water may be carried in small channels through meadows without 

 being allowed to overflow, and in this case the effect is similar to that 

 caused by rivers or brooks which wind slowly through valleys, and 

 produce a rich verdure along their course. This is watering, but not 

 properly irrigating. When this is done judiciously, the effect is very 

 nearly the same as when the land is irrigated ; and in hot climates it 

 may be preferable, by giving a constant supply of moisture to the 

 roots, while the plants are growing. The great advantage of water- 

 meadows in England is not so much the superior quantity of grass or 

 hay which is obtained when they are mown, as the early feed in spring, 

 when all kinds of nutritive fodder are scarce. When the turnips are 

 consumed before the natural grass or the rye sown for that purpose is 

 fit to be fed off, the water-meadows afford abundant pasture to ewes 

 and lambs, which by this means are brought to an early market. The 

 farmer who has water-meadows can put his ewes earlier to the ram, 

 without fear of wanting food for them and their lambs in March, 

 which is the most trying season of the year for those who have sheep. 

 At that time an acre of good grass may be worth as much for a month 

 as a later crop would for the remainder of the year. 



When it is intended to form a water-meadow on a nearly level surface, 

 or where a fall of only two or three feet can be obtained in a con- 

 siderable length, the whole of the land must be laid in beds about 

 20 or 30 feet wide, the middle or crown of these beds being on a level 

 with the main feeders, and the bottoms or drains on a level with the 

 lower exit of the water, or a little above it. To form these beds most 

 expeditiously, if the ground is already in grass, the sod may be paired 

 off and relaid after the beds are formed, by which means the grass will 

 be sooner re-established ; but except in very heavy soils, where the 

 grass is some time in taking root, the easiest and cheapest way is to 

 plough the land two or three times towards the centre, and dig out. 

 the drain with the spade : the earth out of the drains, and that which 

 is taken out of the upper trench or feeder, may be spread over the bed 

 to give it the proper slope. A roller passed over the bed in the 

 direction of its length will lay it even, and the seeds of grass being 

 sown over it, the water may be let on for a very short time to make 

 them spring. As soon as the grass is two or three inches above ground a 

 regular flooding may be given, and in a short time the sward w'll be 

 complete. Instead of sowing seed, tufts of grass cut from old sward 

 may be spread over the newly formed beds, and they will soon cover 

 the ground. The Italian rye-grass, for instance, grows so rapidly, 

 that if it be sown in February, or as soon as the snow and frost are 

 gone, it will afford a good crop to feed off in April, or to mow for 

 hay by the beginning of May ; and after that it may be cut repeatedly 

 during the summer. But where the soil is good and the water abun- 

 dant, good natural grasses will spring up without much sowing, and 

 soon equal the old water meadows. 



It seems essential to the formation of a good water-meadow that 

 the bottom be porous and free from stagnant water ; hence under- 

 draining is often indispensable before a water-meadow can be esta- 

 blished : and a peat-bog, if drained and consolidated, may have water 

 carried over its surface, and produce very good herbage. If the soil 

 is a very stiff clay, draining is almost indispensable where a water- 

 meadow is to be made. The more porous the soil the less depth 

 of water is required, which is not obvious at first sight; but the 

 clay lets the water run over the surface without soaking into the 

 roots, whereas the porous soil is soon soaked to a considerable depth. 

 The water must therefore be longer on the clay than on the sand or 

 gravel to produce the same effect. If the water is properly applied all 

 kinds of soils may be converted into fertile water-meadows. On very 

 stiff clays a coat of sand or gravel, where it can be easily put on, will 

 greatly improve the herbage. It should not be ploughed in, but laid 

 on the surface two or three inches thick : chalk will also improve the 

 herbage. 



The usual time of letting on the water on water-meadows is just 

 before Christmas, and it may continue to flow over the land as 

 long as the frost lasts, unless the frost be very severe and the land 

 be frozen : in mild weather it may be turned off during the day 

 and put on again at night until the frost is gone. The grass will soon 

 begin to grow, ond be ready to be fed off. When this is done the water 

 is immediately let on for a short time, and turned off again to allow the 

 ground to dry after a few days' flooding, and the water is let on again 

 at short intervals. The warmer the air is, the shorter time must the 

 water be allowed to cover the meadows. As soon as the grass is five 

 or six inches long it must be left dry entirely till it is mown or fed off. 



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