1902 Encyclopedia > Irrigation

Irrigation




IRRIGATION is the systematic application of water to land in order to promote present or prospective vegetation. Water, thus used for the general purpose of growing or increasing the crops on which animals and man have to subsist, is employed in special ways and at special times according to the particular end in view, the individual plant to be grown, and the very divergent conditions of soil and climate which have to be studied in different countries. Sometimes the art of irrigation is practised for the simplest of all reasons, to make up for the absence or irregular seasonal distribution of rain or for a local deficiency of rainfall; sometimes a particular crop is irrigated, because the plant is of an aquatic or semi-aquatic nature; sometimes lands are irrigated for the sake of the encouragement to early growth afforded by the warmth of the water, or for the sake of the dissolved plant-food which it furnishes ; and sometimes the object is that the land may be enriched and its level raised by means of the deposit from the water used.

In considering the vast importance of water to plant growth, it must be remembered that seeds must absorb a very large quantity of water before germination can begin; that the growth of the young plant, while still dependent upon the seed, involves the employment of a constant supply of water in order that the transference of nutrients from the stores in the seed to the newly developed parts may proceed without interruption; that soils which do not contain more than 5 to 9 per cent, of moisture will yield none of it to the plant, and that when such low per-centages of moisture are approached there is a constant struggle —often fatal to the plant—between the soil and the plant for water; that during the period of the plant's active growth, the absorption of all mineral matter and all nitrogen compounds from the soil takes place through the medium of an exceedingly weak aqueous solution of these substances, which solution is indeed absorbed in such quanti-ties that a single plant of barley needs the passage through it during the five months in which it occupies the ground of more than an imperial gallon of water. It should be also remembered that all vegetable produce when in a growing state contains an immense proportion of water, often 70 to 80 per cent, and sometimes as much as 92 to 96 per cent., the latter figures representing the percentage of water in turnips and watercress respectively.

From all this it will be readily understood that artificial supplies of water are needed for vegetation in many dry countries. An illustration of this need presents itself in the district which comprises parts of the south of Spain, Portugal, and Italy, including Sicily and Greece. Along this zone, which includes the Mediterranean coasts north of the rainless region of Africa, with its currents of hot dry air from the Sahara, the annual rainfall may be as high as 30 inches, but the amount during the summer quarter is but 4 per cent, of the whole. All the district suffers from droughts, which are often most severe. Again, in many parts of central and eastern Europe there are table-lands, as in Moravia, Poland, and parts of Russia, where the yearly rainfall is insufficient—from 10 to 15 inches only. There are about twice as many rainy days in western as in eastern Europe. In very many of these rainless or arid countries and districts there are remains (mostly in ruins) of important ancient irrigation works; Spain, Sicily, and Syria furnish abundant examples of aqueducts and canals for agricultural irrigation. In Egypt, and in some parts of Persia, India, and China, artificial watering is employed for the reasons given above; while in Peru and many other parts of America the same scarcity or irregular distribution of rain occurs. Special reference will be made further on to the very important irrigation works of India.

The next point to which reference has been made is the peculiar aquatic or semi-aquatic nature of some of the plants which are grown by means of artificial watering. Rice is the chief example of a plant of this kind; a rice swamp is proverbial, and wherever rice is grown in China, in India, in Japan, in Egypt, or in Italy, the land is under water till the crop is just ready for harvesting.

The third reason for irrigating mentioned above is the determining cause of nearly all the artificial watering of land in temperate climates. It is not performed because the soil is dry and hot, for it is carried out mainly in the wettest and coldest months of the year. It is not performed because the crop to be raised is of an essentially aquatic nature, for ordinary grasses and meadow herbage only are watered. But it is performed that growth may be stimu-lated and fed, through certain agencies which the water brings to bear upon the vegetation in question. The water-meadows of England afford examples of this kind of irri-gation. These are, in some instances, of immemorial origin, and may, like those of the Avon in Wiltshire and the Churn in Gloucestershire, be traceable back to Boman times. In the early part of the present century the system received further developments, but at present there is some tendency to depreciate the value of this kind of irrigation.

A fourth reason for irrigation is found where the solid matter suspended in the water is valuable and valued for its richness as manure, and for the actual increase which its deposition on the land makes to the height or level of the country. In England this kind of irrigation is practised mainly in the estuary of the Humber. But wherever a decided deposition of fertilizing silt, clay, or mud from water allowed to rest on the land takes place, there " warping," the name given to this kind of irrigation, may be said to be practised. The waters of the overflowing Nile in Egypt act, partly at least, in this manner, for their dissolved constituents (about 10 grains per gallon) are perfectly insignificant when compared with those which are suspended.

In addition to these various kinds of irrigation with ordinary water, there are several systems in which town sewage is employed. These involve the introduction of many new and complex conditions, and maj^ be more conveniently considered under the heading SEWAGE (in article SEWERAGE).

It is the irrigation determined by the third of the fore-going reasons—water-meadow irrigation'—that calls for more particular notice here. The subject may be con-veniently treated in the following order:—quantity of water; quality of water; influence of mining refuse on water - meadows; grasses suitable for water - meadows ; changes in irrigated herbage; methods of irrigation, in-cluding (1) bedwork irrigation, (2) catchwork irrigation, (3) upward irrigation, and (4) warping; management and advantages of water-meadows; theory of irrigation of water-meadows. The article will close with some account of irrigation in India, and in Italy, France, and Belgium, and of the history of irrigation.

Before the systematic conversion of a tract into water-meadows can be safely determined on, care must be taken to have good drainage, natural or artificial, a sufficient supply of water, and water of good quality. It might indeed have been thought that thorough drainage would be unnecessary, but it must be noted that porous subsoils or efficient drains do not act merely by carrying away stagnant water which would otherwise cool the earth, incrust the surface, and retard plant growth. They cause the soil to perform the office of a filter. Thus the earth and the roots of grasses absorb the useful matters not only from the water that passes over it, but from that which passes through it. These fertilizing materials are found stored up in the soil ready for the use of the roots of the plants. Stagnation of water is inimical to the action of the roots, and does away with the advantageous processes of flowing and percolating currents. Some of the best water-meadows in England have but a thin soil resting on gravel and flints, this constituting a most effectual system of natural drainage. The fall of the water supply must suffice for a fairly rapid current, say 10 inches or 1 foot in from 100 to 200 yards. If possible the water should be taken so far above the meadows as to have sufficient fall without damming up the river. If a dam be abso-lutely necessary, care must be taken so to build it as to secure the fields on both sides from possible inundation; and it should be constructed substantially, for the cost of repairing accidents to a weak dam is very serious.

Quantity of Water.—Even were the objects of irrigation always identical, the conditions under which it is carried on are so variable as to preclude calculations of quantity. Mere making up of necessary water in droughty seasons is one thing, protection against frost is another, while the addition of soil material is a third. Amongst causes of variation in the quantity of water needed will be its quality and temperature and rate of flow, the climate, the season, the soil, the subsoil, the artificial drainage, the slope, the aspect, and the crop. In actual practice the amount of water varies from 300 gallons per acre in the hour to no less than 28,000 gallons. Where water is used, as in dry and hot countries, simply as water, less is generally needed than in cold, damp, and northerly climates, where the higher temperature and the action of the water as manure are of more consequence. But it is necessary to be thoroughly assured of a good supply of water before laying out a water-meadow. Except in a few places where unusual dryness of soil and climate indicate the employment of water, even in small quantity, merely to avoid the consequences of drought, irrigation works are not to be commenced upon a large area, if only a part can ever be efficiently watered. The engineer must not decide upon the plan till he has gauged at different seasons the stream which has to supply the water, and has ascertained the rain-collecting area available, and the rainfall of the district, as well as the proportion of storable to percolating and evaporating water. Reservoirs for storage, or for equaliz-ing the flow, are rarely resorted to in England; but they are of absolute necessity in those countries in which it is just when there is least water that it is most wanted. It is by no means an injudicious plan before laying out a system of water-meadows, which is intended to be at all extensive, to prepare a small trial plot, to aid in determin-ing a number of questions relating to the nature and quantity of the water, the porosity of the soil, &c.

Quality of Water.—The quality of the water employed for any of the purposes of irrigation is of much importance. Its dissolved and its suspended matters must both be taken into account. Clear water is usually preferable for grass land, thick for arable land. If it is to be used for warping, or in any way for adding to the solid material of the irrigated land, then the nature and amount of the suspended material are necessarily of more importance than the character of the dissolved substances, provided the latter are not positively injurious. For use on ordinary water-meadows or on rice-fields, however, not only is very clear water often found to be perfectly efficient, but water having no more than a few grains of dissolved matter per gallon answers the purposes in view satisfactorily. Water from moors and peat-bogs or from gravel or ferru-ginous sandstone is generally of small utility so far as plant food is concerned. River water, especially that which has received town sewage, or the drainage of highly manured land, would naturally be considered most suitable for irrigation, but excellent results are obtained also with waters which are uncontaminated with manurial matters, and which contain but 8 or 10 grains per gallon of the usual dissolved constituents of spring water. Experienced English irrigators generally commend as suitable for water-meadows those streams in which fish and waterweeds abound. But the particular plants present in or near the water-supply afford further indications of quality. Water-cress, sweetflag, flowering rush, several potamogetons, water milfoil, water ranunculus, and the reedy sweet watergrass (Glyceria aquatica) rank amongst the criteria of excellence. Less favourable signs are furnished by such plants as Arundo Donax (in Germany), Cicuta virosa, and TypJia latifolia, which are found in stagnant and torpid waters. Water when it has been used for irrigation generally be-comes of less value for the same purpose. This occurs with clear water as well as with turbid, and obviously arises mainly from the loss of plant food which occurs when water filters through or trickles over poor soil. By passing over or through rich soil the water may, however, actually b& enriched, just as clear water passed through a charcoal filter which has been long used becomes impure. It has been contended that irrigation water suffers no change in composition by use, since by evaporation of a part of the pure water the dissolved matters in the remainder would be so increased as to make up for any matters removed. But it is forgotten that both the plant and the soil enjoy special powers of selective absorption, which remove and fix the better constituents of the water, and leave the less valuable.

The Influence of Mining and other Refuse.—In some of the districts of Devonshire and of Wales, in which the sloping sides of narrow valleys have been converted into small catchwork irrigated meadows, the injurious effects of water from mines have been most marked. A stranger visiting the district in early spring would notice, along the sides of a valley, a number of small irrigated fields. Some of these, watered directly from little streams behind and above them, would show grass of great luxuriance, especially close to the main and secondary carriers. But where the river-water, contaminated by mining refuse, had been used, the grass bordering the water-courses would show a sickly yellow tint, and be generally less developed than the herbage of the rest of the field. This difference between the fields irrigated by small local brooks and those watered by the river cannot be explained by any inferiority in the river water as river water; for above the entrance of the refuse from the first mine it was every-thing that could be wished. But just below the place of entrance of the mine water the grass on the banks looked as if it had been burnt up with vitriol, while in the stream itself not a vestige of a living waterweed could be detected.

The injurious effects thus caused by the mine water have led to its partial disuse for the purposes of irrigation. Some of the most profitable water-meadows are no longer irrigated : the herbage in these is now of inferior character, and mosses and weeds, suppressed by total immersion, have reappeared, to the detriment of the more valuable grasses. Besides, there is now no early feed. Manure, not before wanted, has now to be applied, and the yield of grass is reduced in annual value by 30s. to 60s. per acre. To get a fair growth of grass the plant-food which the water formerly brought at little expense has to be furnished by costly farmyard manure; and even with this the crop is late and light.

It is clear in the particular instance to which reference has been made that water pumped from copper mines or used in dressing the ores is the origin of the mischief. Several changes in the composition of the water have been found to occur in its passage through the mine. The original water lost much of its free carbonic acid gas; its carbonates were converted into sulphates; and it con-tained now the metals iron, manganese, cobalt, and alum-inium, all as sulphates,—hardly a trace of any of these metals being present in the uninjured water. And matters in suspension were found to be both more abundant and more injurious than matters in solution. They consisted chiefly of copper pyrites and iron pyrites, in a very fine state of division. According to their degree of fineness the pyritic particles which escape from the settling pits at the mines travel varying distances down the stream, and may even be detected several miles below, both in the mud of the bed of the stream and on the leaves of grass and other occasionally immersed plants. Oxidation of the pyrites into the sulphates of copper and iron was proved to occur all through the course of the stream,—these salts, with their concomitant free sulphuric acid, producing a most injurious effect on vegetable growth. The presence of this acid in the free state has been detected in the waste water from a Welsh lead mine, in sufficient abundance to kill instantly, on several occasions, many salmon in the river into which it was discharged. The evil done by some of the most deleterious materials in mine-waters can be arrested by the interposition of conduits filled with chalk or limestone, which act as chemical filters. The carbonate of lime neutralizes the free sulphuric acid and stops the heavy metals by converting them from soluble sulphates into insoluble carbonates.

Among the most injurious sorts of refuse which can find their way into streams used for irrigating meadows are the chemical wastes from mills and factories in which the processes of dyeing, paper making, metal working, &c, are carried on. In the majority of such cases the fatal effects on vegetation are obvious, and the rivers polluted in this way, even if their volume of pure water be very large, cannot be used at all for irrigation.

The Seeds for Water-Meadows.—Of the few leguminous plants which are in any degree suitable for water-meadows, Lotus corniculatus major, Trifolium hybridum, and T. pratense are those which generally flourish best: T. repens is less successful. Amongst grasses the highest place must be assigned to ryegrass, especially to the Italian variety, commonly called Lolium italicum. The mixture of seeds for sowing a water-meadow demands much consideration, and must be modified according to local circumstances of soil, aspect, climate, and drainage. From the peculiar use which is made of the produce of an irrigated meadow, nnd from the conditions to which it is subjected, it is necessary to include in our mixture of seeds some that produce an early crop, some that give an abundant growth, and some that impart sweetness and good flavour, while all the kinds sown must be capable of flourishing on irrigated soil.
I. II.
Festuca pratensis 0 2
Festuca loliacca 3 2
Anthoxanthumodoratum 0 1
Phleum pratense 4 2
Phalaris arundinacea... 3 2
Lotus corniculatus major 3 2
Trifolium hybridum. ... 0 1
Trifolium pratense 0 1

The following mixtures of seeds (stated in pounds per acre) have been recommended for sowing on water-meadows, Messrs Sutton of Reading, after considerable experience, regarding No. I. as the more suitable :—
i. ii.
Lolium perenne 8 12
Lolium italicum 0 8
Poa trivialis 6 3
Glycerin fluitans 6 2
Glyceria aquatica 4 1
Agrostisalba 0 1
Agrostis stolonifera 6 2
Alopccurus pratensis 0 2
Festuca elatior 3 2

Changes in Irrigated Herbage.—In irrigated meadows, though in a less degree than on sewaged land, the reduc-tion of the amount or even the actual suppression of certain species of plants is occasionally well-marked. Sometimes this action is exerted upon the finer grasses, but happily also upon some of the less profitable constituents of the miscellaneous herbage. Thus Ranunculus bidbosus has been observed to become quite rare after a few years watering of a meadow in which it had been most abundant, R. acris rather increasing by the same treatment; Plantago media was extinguished and P. lanceolata reduced 70 per cent. Amongst the grasses which may be spared, Aira ctespitosa, Briza media, and Cynosurus cristatus are gene-rally much reduced by irrigation. Useful grasses which are increased are Lolium perenne and Alopecurus pratensis, and among those of less value Avena favescens, Dactylis glomerata, and Poa pratensis.
Methods of Irrigation.—There are four ways of irrigating land with water practised in England :—(1) bedwork irri-gation, which is the most efficient although it is also the most costly method by which currents of water can be applied to level land; (2) catchwork irrigation, in which the same water is caught and used repeatedly; (3) subter-raneous or rather upward irrigation, in which the water in the drains is sent upwards through the soil towards the surface; and (4) warping, in which the water is allowed to stand over a level field until it has deposited the mud suspended in it.

There are two things to be attended to most carefully in the construction of a water-meadow on the first or second of these plans. First, no portion of them what-ever should be on a dead level, but every part should belong to one or other of a series of true inclined planes. The second point of primary importance is the size and slope of the main conductor, which brings the water from the river to the meadow. The size of this depends upon the quantity of water required, but whatever its size its bottom at its origin should be as low as the bed of the river, in order that it may carry down as much as possible of the river mud. Its course should be as straight and as near a true inclined plane as possible. The stuff taken out of the conductor should be employed in making up its banks or correcting inequalities in the meadow.

Bedwork Irrigation.—In this species of irrigation, which is eminently applicable to level ground, the ground is thrown into beds or ridges. Here the conductor should be led along the highest end or side of the meadow in an inclined plane ; should it terminate in the meadow, its end should be made to taper when there are no feeders, or to terminate in a feeder. The tapered end will retard the motion of the water ; and, as this contains, of course, less water, the water will overflow the banks of the conductor. The main drain to carry off the water from the meadow should next be formed. It should be cut in the lowest part of the ground at the lower end or side of the meadow. Its dimensions should be capable of carry-ing off the whole water used so quickly as to prevent the least stag-nation, and discharge it into the river. The stuff taken out of it should be used to fill up irregularities in the meadow. In case the river takes a turn along the lower end or side of the meadow, the turn should be utilized to carry off the water. It might be imagined that, as a portion of the water will be absorbed by the soil, the main drain need not be made so large as the conductor, merely to carry off the water that has been used ; but in practice it will be found that, when the water is muddy, very little of it comparatively will enter the ground, the sediment acting as an impervious cover-ing. The next process is the forming of the ground intended for a water-meadow into beds or ridges. That portion of the ground which is to be watered by one conductor should be made into beds to suit the circumstances of that conductor ; that is, instead of the beds over the meadow being all reduced to one common level, they should be formed to suit the different swells in the ground, and, should any of these swells be considerable, it will be necessary to give each side of them its respective conductor. The beds should run at or nearly at right angles to the line of the conductor. The breadth of the beds is regulated by the nature of the soil and the supply of water. Tenacious soils and subsoils, with a small supply of water, require beds as narrow as 30 feet. Porous soils and a large supply of water may have beds of 40 feet. The length of the beds is regulated by the supply of water and the fall from the con-ductor to the main drain. If the beds fall only in one direction longitudinally, their crowns should be made in the middle; but, should they fall laterally as well as longitudinally, as is usually the case, then the crowns should he made towards the upper sides, more or less according to the lateral slope of the ground. The crowns should rise a foot above the adjoining furrows. The beds thus formed should slope in an inclined plane from the conductor to the main drain, that the water may flow equably over them.

The beds are watered by "feeders," that is, channels gradually tapering to the lower extremities, and their crowns cut down, wherever these are placed. The depth of the feeders depends on their width, and the width on their length. A bed 200 yards in length requires a feeder of 20 inches in width at its junction with the conductor, and it should taper gradually to the extremity, which should be 1 foot in width. The taper retards the motion of the water, which constantly decreases by overflow as it proceeds, whilst it continues to fill the feeder to the brim. The stuff which comes out of the feeders should be carefully and evenly laid along the sides of the beds. The water overflowing from the feeders down the sides of the beds is received into small drains formed in the furrows between the beds. These small drains discharge themselves into the main drain, and are in every respect the reverse of the feeders ; that is, their tapering extremities lie up the slope, and their wide ends open into the main drain, to accelerate the motion of the departing water. The depth of the small drain at the junction is made about as great as that of the main drain, and it gradually lessens towards the taper to 6 inches in tenacious and to less in porous soils. The depth of the feeders is the same in relation to the conductor. The stuff obtained from the small drains is employed to fill up inequalities in the meadow. For the more equal distribution of the water over the surface of the beds from the con-ductor and feeders, small masses, such as stones, or solid portions of earth or turf fastened with pins, are placed in them, in order to retard the momentum which the water may have acquired. These "stops," as they are termed, are generally placed at regular intervals, or rather they should be left where any inequality of the current is observed. Heaps of stones answer very well for stops in the con-ductor, particularly immediately below the points of junction with the feeders. When tough pieces of turf are used, care must be taken to keep the tops of the pins below the reach of weeds floating on the surface of the water. These stops, however, are nothing but expedients to rectify work imperfectly executed. It must be obvious that a perfectly formed water-meadow should require few or no stops. The small or main drains require no stops. The descent of the water in the feeders will no doubt necessarily increase in rapidity, but the inclination of the beds and the tapering of the feeders should be so adjusted as to counteract the increasing rapidity. At all events notches cut into the sides of the feeders to retard the velocity of the water are much more objectionable than stops, although some recommend them. The distribution of the water over the whole meadow is regulated by the sluices, which should be placed at the origin of every conductor. By means of these sluices any portion of the meadow that is desired can be watered, whilst the rest remains dry; and alternate watering must be adopted when there is a scarcity of water. All the sluices should be substantially built at first with stones and mortar, to prevent the leakage of water ; for, should water from a leak be permitted to find its way into the meadow, that portion of it will stagnate and produce coarse grasses. In a well-formed water-meadow it is as necessary to keep it perfectly dry at one time as it is to place it under water at another. A small sluice placed in the side of the conductor opposite to the meadow, and at the upper end of it, will drain away the leakage that may have escaped from the head sluice.





To obtain a complete water-meadow, the ground will often require to be broken up and remodelled. This will no doubt be attended with cost; but it should be considered that the first cost is the least, and remodelling the only way of having a complete water-meadow which will continue for years to give satisfaction. To effect a remodelling when the ground is in stubble, let it be ploughed up, harrowed, and cleaned as in a summer fallow, the levelling-box employed when required, the stuff from the conductors and main drains spread abroad, and the beds ploughed into shape,—all operations that can be performed at little expense. The meadow should be ready by August for sowing with one of the mixtures of grass-seeds already given. But though this plan is ultimately better, it is attended with the one great; disadvantage that the soft ground cannot be irrigated for two or three years after it is sown with grass-seeds. This can only be avoided where the ground is covered with old turf which will bear to be lifted. On ground in that state a water-meadow may be most perfectly formed. Let the turf be taken off with the spade, and laid carefully aside for relay-ing. Let the stript ground then be neatly formed with the spade and barrow, into beds varying in breadth and shape according to the nature of the soil and the dip of the ground,—the feeders from the conductor and the small drains to the main drain being formed at the same time. Then let the turf be laid down again and beaten firm, when the meadow will be complete at once, and ready for irrigation. This is the most beautiful and most expeditious method of making a complete water-meadow where the ground is Eot naturally sufficiently level to begin with.

The water should be let on, and trial made of the work, whenever it is finished, and the motion of the water regulated by the introduction of a stop in the conductors and feeders where a change in the motion of the current is observed, beginning at the upper end of the meadow. Should the work be finished as directed by August, a good crop of hay may be reaped in the succeeding summer. There are few pieces of land where the natural descent of the ground will not admit of the water being collected a second time, and applied to the irrigation of a second and lower meadow. In such a case the main drain of a watered meadow may form the conductor of the one to be watered, or a new conductor may be formed by a prolongation of the main drain ; but either expedient is only advisable where water is scarce. Where it is plentiful, it is better to supply the second meadow directly from the river, or by a continuation of the first main conductor. In some instances it may be necessary to carry a conductor over a hollow piece of ground along an aqueduct made for the purpose, called a "carry-bridge. " Such an aqueduct may be made either of wood, cast-iron, or stone and mortar ; or inverted siphons may be used.

Catchwork Irrigation.—In the ordinary catch work water-meadow, the water is used over and over again. On the steep sides of valleys the plan is easily and cheaply carried out, and where the whole course of the water is not long the peculiar properties which give it value, though lessened, are not exhausted when it reaches that part of the meadow which it irrigates last. The design of any piece of catchwork will vary with local conditions, but generally it may be stated that it consists in putting each conduit save the first to the double use of a feeder or distributor and of a drain or collector. The following description of one of the best ways in which a catch-work meadow plan may be constructed is condensed from Mr Bickford's account in the Journal of the E. Agrie. Soc., 1852. This comparatively cheap system, though at first chiefly used on the sloping sides of Devonshire and Somersetshire valleys, has been successfully applied to level meadows. In one case the fall was but 1 in 528.

'' This system has the advantage over the common system of obviating the necessity for large and frequent level gutters ; it has the effect of continuing (and even causing) a smooth and uniform surface to the meadow, allowing of the operations of mowing and carting without any sensible perception of the existence of the gutters ; and also that of accelerating the speed of the water over the land when ' turned on,' and the speedily draining the water from the surface when ' turned off.' It becomes a ready instrument in the hands of the irrigator, and obviates that waste of land occasioned by the usually large gutters. It is every way better than the old system : it can be done in half the time, and for less than half the expense. The chief features of the system consist in causing the ground intended to be irrigated to be covered with a network of small gutters, intersecting each other as nearly at right angles as circumstances will permit. These gutters are about i inches wide and 1 inch deep ; they are cut with a ' die,' fixed in a sort of plough of simple construction, drawn generally by one horse. This network of gutters is fed at the highest level possible, or thought desirable, by a carriage gutter of sufficient size.

" Let fig. 1 be a piece of meadow; look first where the water enters the meadow, or where it can best be made to enter. Let this be ascertained to be at A 1. Then estimate roughly where it may be supposed the water will run,—say, along the dotted line 1 .... 2. Next proceed, using a simple level adjusted by means of a plumb-line, to lay down a level line made across the meadow, such as BC. The arrows marked on the line show the way the B water is to be made to run on in the D gutter line, —to obtain which it is necessary to deviate from precise levelling, and allow the plumb-line to drop a little before the level mark when inclining down, and a little behind it when inclining up the meadow. This will have the effect of running the water out of the low places, and upon the high places. Care must be taken in levelling to follow out the indications of the level, however crooked and curved the line may appear, going down around every elevation, and avoid-ing every disposition to cut the line straighter.
" Having completed that line, return to the side first begun, say to D, about 10 paces down from B ; and by proceeding as in BC the line DE will very likely be produced. Should C and E be too far asunder, begin again at F, and produce the line FG. The middle of the meadow is supposed to be lowest, and the meadow itself to be flat, rising on each side of the middle by two gentleundulations, so that the lines of gutter curve very considerably. From the nature of the ground it may next be necessary to begin at H, and to produce HI. It will now be perceived that D and I are too far asunder, making it necessary to introduce KL, beginning at K. The higher side must be finished in like manner

" Let now fig. 2 represent a meadow, with all the lines of fig. 1 marked with the level and ploughed, but not ' turned out.' It will be perceived that the curves of the lines form a series of loops, and that the undulations of the meadow are prettily mapped out by the curves going down round the hills and up round the valleys. It will be at once seen where the water is principally wanted, viz.,
just above where the , / a s :i * s

curves form the greatest downward bend, as at A, fig. 2. Next draw the lines which, upon an aver-age, will be ,at right angles to the level, but in each particular line will deviate from the right angle, more or less, according as the ground is more or less irregular. This may be done by walk-ing in advance of a plough, and leaving foot-prints to mark where the plough must follow. Care must be taken to go as nearly through the centre of the downward loops as possible. In order to do this, first cut the lines 1, 2, 3, 4, 5, and then fill up the intervals by cutting a, b, c. The best distance for these seems to be from ten to fifteen paces apart.
"The next business is to bring in the water, after just lifting the turf out of the gutters already cut. A spirit-level may be used, the gutter being allowed to drop or 2 inches every 2 poles, if the nature of the ground will allow of it; not less than J inch will do at all well. A much larger gutter is required at J-inch drop than at 2 inches; and, besides, it will not run itself dry so well when the water is turned off. The 2-inch drop gutters will run the water off directly; the £-inch will scarcely do it at all. Regard must be had to the supply of water required at the further end. In the case supposed in fig. 2, it is wanted on the rising ground, at the further end A ; therefore the gutter should drop that way, and be of a good size. If the water is wanted chiefly at the beginning of the gutter, the drop need not be so much, and the gutter should taper away so as to end nearly in a point.

" The size of the stream is the next consideration. If it can water the whole piece at all times, one gutter, of sufficient size, should be made. Stops in a gutter should be avoided. Where the stream is small, make a leading gutter, and take out from it taper gutters, each of a size suited to the stream when at its smallest, so that when the stream increases (from rain or any other cause), as many taper-gutters may be used as will disperse the whole stream. The leading gutter should continually decrease in size from the place where the first taper-gutter is taken out of it, and finish in a taper-ing water-gutter itself at last. In fig. 3, AB is a carriage-gutter as

Fig. 3.

far as c, and a watering-gutter from c to B ; a and b are watering-gutters taken out of it. When the stream is small, a stop at 1 will cause it to work in a; a stop at 2 will work in b ; without any stop it will work in cB. If the stream is too much for cB, it will work b at the same time ; and, should there be water enough, it will also fill a without any stop at all. Care should be taken not to make AB larger than just to carry the full stream wanted; and in every case when the gutter becomes too large by frequent clean-ing out, cut it anew on one side or the other.

"The hedge-trough may be made a carriage-gutter wherever it can be done conveniently, care being always taken to keep the water running in it. Covered gutters made with large tiles could also be substituted for the deep open carriage-gutter, where it is necessary to cross the middle of meadows ; this obviates the danger of the open gutter to sheep and lambs, and the tiled gutter does not require the annual ' cleaning out.' •

" When a small stream insufficient for the whole meadow is used, the water must be confined to ground determined on by stops in the gutters which run on the two sides of it, thus :—

"Fig. 4 is a section of the net-work of gutters; AB is the carriage-gutter ; a is a taper watering-gutter, to the extent of which the water is supposed to be determined to be confined ; b, c, d, e, are the feeding gutters (perpendicular to the levels); the cross-gutters are the ' level' ones ; b and e serve as the two side gutters of the section to be watered. The water is confined to the ground between them by stops at the crossings, arranged thus :—b and e (fig. 5) are crossings on the feeders ; 1, 2, 3, 4 are stops, the purpose of which is obvious enough. The arrows show the direction the water is made to run. The stops are pieces of the turf taken out of the gutters, which, being cut with a ' die,' fit -the gutters with exactness, and can be put in opera-tion instantly, without trouble or 2 loss of time.

" The gutters are not to be cut in the same places 3 two successive years, but on one side, as near as can be conveniently done, say about a foot and a half from the former ones ; and the turf of the new gutter is to be used to fill in the old one, the latter not being crammed too full. By this means the gutters are always new, and always the proper size. If cut on the right-hand side and above one year, the next year they should be cut the left-hand side and be-low.

" It will be proper now to call attention to the manner in which the water is carried, with its sus-pended matter, to the extreme end of the meadow, by the plan we are pursuing. It will be observed that the ground is covered by a sort of network of little gutters, one set being, in a sort, parallel to each other, intersected by another set at right angles to them and also parallel to each other. This would be strictly true were the surface strictly a plane surface; but, this being very rarely the case, both sets deviate from a strictly parallel condition in order to meet the undulations of the ground,— the deviations compensating each other on the aggregate. Now, instead of carrying the water down to the lower end by means of one large gutter, and then dispersing it by another large gutter (a level one), we do it by twenty or so little gutters which feed the dispensing gutter about every ten or fifteen paces; being so small, these never fret away, and, being newly cut every year, they never increase in size.

"These small gutters are sufficient when the little stops are taken out of the perpendicular gutters, and the level gutters are stopped so as to confine the water to the perpendiculars, to carry down the requisite water. The level gutter of a lower section (if a lateral section is to be watered), instead of being fed by a large stream at the end, is supplied every ten or fifteen paces by one of those little gutters, thus giving a uniform supply throughout the length of the level gutter. A larger supply than this will afford is ' an evil. When the water is shut out from the ' leading-in' guttel it is not necessary to move any of the little stops ; the same per-pendicular gutters that are effectual to run the water on are as effectual to run it off, leaving the surface of the meadow dry and solid. The water is evenly distributed over the surface by these minute gutters, which are made to follow all the undulations of the land (which can never be done by the large gutters); and also, from the draining effect of the perpendicular gutters, the water is never suffered to accumulate in ponds. The water on the meadow is therefore never 'over-shoe' anywhere. These gutters are no way dangerous to sheep or lambs, are never in the way of mowing, have an elegant rather than an unsightly appearance, are not perceived either in raking or carting, and suit the horse-rake or hay-making machine admirably. It may be added that the leading-in gutters can be so arranged as to tend themselves in cases of flood."

Upward or Subterranean Irrigation.—In this kind of irrigation the water used rises upward through the soil, and is that which under ordinary circumstances would be carried off by the drains. The system has received considerable development in Germany, where the elaborate method invented by Petersen is recommended by many agricultural authorities. In this system the well-fitting earthenware drain-pipes are furnished at intervals with vertical shafts terminating at the surface of the ground in movable caps. Beneath each cap, and near the upper end of the shaft, are a number of vertical slits through which the drainage water which rises passes out into the conduit or trench from which the irrigating streams originate. In the vertical shaft there is first of all a grat-ing which intercepts solid matters, and then, lower down, a central valve which can be opened and closed at pleasure from the top of the shaft. In the ordinary English system of upward or drainage irrigation, ditches are dug all round the field. They act the part of conductors when the land is to be flooded, and of main drains when it is to be laid dry. The water flows from the ditches as conductors into built conduits formed at right angles to them in parallel lines through the fields ; it rises upwards in them as high as the surface of the ground, and again subsides through the soil and the conduits into the ditches as main drains, and thence it passes at a lower level either into a stream or other suitable outfall. The ditches may be filled in one or other of several different ways. The water may be drainage-water from lands at a higher level ; or it may be water from a neighbouring river ; or it may be drainage-water accumulated from a farm and pumped up to the necessary level. But it may also be the drainage-water of the field itself. In this case the mouths of the underground main pipe-drains are stopped up, and the water in them and the secondary drains thus caused to stand back until it has risen sufficiently near the surface. Of course it is necessary to build the mouths of such main drains of very solid masonry, and to construct efficient sluices for the retention of the water in the drains. Irrigation of the kind now t:nder discussion may bi practised wherever a command of water can be secured, but the ground must be level. It has been success-fully employed in recently drained morasses, which are apt to become too dry in summer. It is suitable for stiffish soils where the subsoil is fairly open, but is less successful in sand. The water used may be turbid or clear, and it acts, not only for moisten-ing the soil, but as manure. For if, as is commonly the case, the water employed be drainage-water from cultivated lands, it is sure to contain a considerable quantity of nitrates, which, not being subject to retention by the soil, would otherwise escape. These coming into contact with the roots of plants during their season of active growth, are utilized as direct nourishment for the vegetation. It is necessary in upward or subterranean irrigation to send the water on and to take it off very gently, in order to avoid the displacement and loss of the finer particles of the soil which a forcible current would cause.

Warping.—In this variety of irrigation the suspended solid matters are of importance, not merely for any value they may have as manure, but also as a material addition to the ground to be irrigated. The waters of the Nile and the Ganges afford con-spicuous examples of rivers rich in suspended matter, which occasionally amounts to one hundredth of their volume, and fre-quently to more than one part in two hundred parts of water. The warping which is practised in England is almost exclusively con-fined to the overflowing of level ground within tide mark, and is conducted mostly within the districts commanded by estuaries or tidal rivers. The best notion of the process of warping may be gained by sailing up the Trent from the Humber to Gainsborough. Here the banks of the river were constructed centuries ago to pro-tect the land within them from the encroachments of the tide. A great tract of country was thus laid comparatively dry. But, while the wisdom of one age thus succeeded in restricting within bounds the tidal water of the river, it was left to the greater wisdom of a suc-ceeding age to improve upon this arrangement, by admitting these muddy waters to lay a fresh coat of rich silt on the exhausted soils. The process began more than a century ago, but has become a system in recent times. Large sluices of stone, with strong doors, to be shut when it is wished to exclude the tide, may be seen on both banks of the river, and from these great conduits are carried miles inward through the flat country, to the point previously prepared by embankment, over which the muddy waters are allowed to spread. These main conduits, being very costly, are constructed for the warp-ing of large adjoining districts, and openings are made at such points as are then undergoing the operation. The mud is deposited, and the waters return with the falling tide to the bed of the river. Spring-tides are preferred, and so great is the quantity of mud in these livers that from 10 to 15 acres have been known to be covered with silt from 1 to 3 feet in thickness during one spring of ten or twelve tides. Peat-moss of the most sterile character has been by this process covered with soil of the greatest fertility, and swamps which used to be resorted to for leeches are now, by the effects of warping, converted into firm and fertile fields. The art is now so well understood that, by careful attention to the currents, the expert warp farmer can temper his soil as he pleases. When the tide is first admitted, the heavier particles, which are pure sand, are first deposited ; the second deposit is a mixture of sand and fine mud, which, from its friable texture, forms the most valuable soil; while lastly the pure mud subsides, containing the finest particles of all, and forms a rich but very tenacious soil. The great effort, there-fore, of the warp farmer is to get the second or mixed deposit as equally over the whole surface as he can, and to prevent the deposit of the last. This he does by keeping the water in constant motion, as the last deposit can only take place when the water is suffered to be still. Three years may be said to be spent in the process, one year warping, one year drying and consolidating, and one year growing the first crop, which is generally seed hoed in by hand, as the mud at this time is too soft to admit of horse labour.





The immediate effect, which is highly beneficial, is the deposition of silt from the tide. To ensure this deposition, it is necessary to surround the field to be warped with a strong embankment, in order to retain the water as the tide recedes. The water is admitted by valved sluices, which open as the tide flows into the field, and shut by the pressure of the confined water when the tide recedes. These sluices are placed on as low a level as possible, to permit the most turbid water at the bottom of the tide to pass through a channel in the base of the embankment. The silt deposited after warping is exceedingly rich, and capable of carrying any species of crop. It may be admitted in so small a quantity as only to act as a manure to arable soil, or in such a large quantity as to form a new soil. This latter acquisition is the principal object of warping, and it excites astonishment to witness how soon anew soil may be formed. From June to September a soil of 3 feet in depth may be formed under the favourable circumstances of a very dry season and long drought. In winter and in floods warping ceases to be beneficial. In ordinary circumstances, on the Trent and Humber, a soil from 6 to 16 inches in depth may be obtained, and inequalities of 3 feet filled up. But every tide generally leaves only J inch of silt, and the field which has only one sluice can only be warped every other tide. The silt, as deposited in each tide, does not mix into a uniform mass, but remains in distinct layers. The water should be made to run completely off, and the ditches should be-come dry, before the influx of the next tide, otherwise the silt will not incrust, and the tide not have the same effect. Warp soil is of surpassing fertility. The expense of forming canals, embank-ments, and sluices for warping land is from £10 to £20 an acre. A sluice of 6 feet in height and 8 feet wide will warp from 60 to 80 acres, according to the distance of the field from the river. The embankments may be from 3 to 7 feet in height, as the field may stand in regard to the level of the highest tides. After the new land has been left for a year or two in seeds and clover, it produces great crops of wheat and potatoes.

Warping is practised only in Lincolnshire and Yorkshire, on the estuary of the Humber, and in the neighbourhood of the rivers which flow into it—the Trent, the Ouse, and the Don. The silt and mud brought down by these rivers is rich in clay and organic matter, and sometimes when dry contains as much as one per cent, of nitrogen.

The Management and Advantages of Water-Meadows.— Constant care is required if a water-meadow is to yield quite satisfactory results. The earliness of the feed, its quantity, and its quality will all depend in very great measure upon the proper management of the irriga-tion. The points which require constant attention are —the perfect freedom of all carriers, feeders, and drains from every kind of obstruction, however minute ; the state and amount of water in the river or stream, whether it be sufficient to irrigate the whole area properly or only a part of it; the length of time the water should be allowed" to remain on the meadow at different periods of the season; the regulation of the depth of the water, its quantity, and its rate of flow, in accordance with the temperature and the condition of the herbage ; the proper times for the commencing and ending of pasturing and of shutting up for hay; the mechanical condition of the surface of the ground ; the cutting out of any very large and coarse plants, as docks ; and the improvement of the physical and chemical conditions of the soil by additions to it of sand, silt, loam, chalk, &c.

Whatever may be the command of water, it is unwise to attempt to irrigate too large a surface at once. Even with a river supply fairly constant in level and always abundant, no attempt should be made to force on a larger volume of water than the feeders can properly distribute and the drains adequately remove, or one part of the meadow will be deluged and another stinted. When this inequality of irrigation once occurs, it is likely to increase, from the consequent derangement of the feeders and drains. And one result on the herbage will be an irregularity of composition and growth, seriously detrimental to its food-value. The adjustment of the water by means of the sluices is a delicate operation when there is little water, and also when there is much ; in the latter case the fine earth may be washed away from some parts of the meadow; in the former case, by attempting too much with a limited water current, one may permit the languid streams to deposit their valuable suspended matters instead of carrying them forward to enrich the soil. The water is not to be allowed to remain too long on the ground at a time. The soil must get dry at stated intervals in order that the atmospheric air may come in contact with it and penetrate it. In this way as the water sinks down through the porous subsoil, or into the subterranean drains, oxygen enters, and supplies an element which is needed, not only for the oxidation of organic matters in the earth, but also for the direct and indirect nutrition of the roots. Without this occasional drying of the soil the finer grasses and the leguminous plants will infallibly be lost; while a scum of confervae and other algae will collect upon the surface, and choke the higher forms of vegetation. The water should be run off thoroughly, for a little stagnant water lying in places upon the surface does much injury. The practice of irrigating differs in different places with differences in the quality of the water, the soil, the drainage, &c. As a general rule, when the irrigating season begins in November, the water may flow for a fortnight con-tinuously, but subsequent waterings, especially after December, should be shortened gradually in duration till the first week in April, when irrigation should cease. It is necessary to be very careful in irrigating during frosty weather. For, though grass will grow even under ice, yet jf ice be formed under and around the roots of the grasses the plants may be thrown out by the expansion of the water at the moment of its conversion into ice. The water should be let off on the morning of a dry day, and thus the land will be dry enough at night not to suffer from the frost; or the water may be taken off in the morning and let on again at night. In spring the newly grown and tender grass will be easily destroyed by frost if it be not protected by water, or if the ground be not made thoroughly dry.

Several other important matters in the management of water-meadows have to he noticed. Among these the times for depas-turing with sheep and other stock are of considerable moment, not only because one of the main services rendered by a water-meadow is the early and valuable feed which it ought to afford, but for securing the health of the animals, particularly their immunity from sheep-rot. A water-meadow cannot be trusted late in the season, especially in view of what is now known concerning the liver-fluke of sheep. It seems to be judicious to depasture the early grass on water-meadows with ewes and lambs at the end of March and in April, and to have it eaten down, bare before May with a heavy stock. On good land and in good seasons a second and even a third crop of feed may be got before the 1st of May, the water being let on after each feed. After that the grass is allowed to stand for hay, but it should be irrigated for a few days to clean the pasture. Further particulars as to the management of irrigated meadows may be gathered from the two accounts which follow, which embody, though in a very condensed form, the system pur-sued in the district which is perhaps the most noted for its water-meadows, namely, that of the Christchurch Avon. Some of these afford characteristic examples of the usual English system of irri-gation. They consist in the main of alluvial soil, often very shallow, lying upon gravel. Professor "Wrightson, of the College of Agriculture at Downton, near Salisbury, gives the following particulars concerning the water-meadows in his own neighbour-hood. They are very valuable as they assist to keep sheep from Lady Day until the end of April, a time when green food is scarce ; at that season they never rot sheep. After sheep have been pas-tured on the water-meadows, these are shut up for hay, of which they yield in fair seasons about 2 tons per acre. The hay is cleared off in July, and the meadows are then fed off by cows until about the first week in October. At this time the work of clearing out the water-carriers and ditches is proceeded with ; banks, stops, sluices, &c, are repaired ; and holes and deep hoofprints filled up or laboriously stamped out. As soon as possible the water is let on, the irrigation being continued throughout November, December, January, and February. On the Downton College farm the water, during the above four months, is shared, on alternate weeks, with the neighbours. The water is caused to flow regularly over all the meadows, and the "meadman"is almost constantly employed in " watering" and "drowning." In March the water is shut off, and the meadows are ready for sheep during the first week in April. In about four weeks' time the sheep are taken off, and the meadows are again watered on alternate weeks up to mid-June. At this time the ground is allowed to become dry and firm so as to permit of grass-cutting (with scythes) and of hay-making. The hay is good and of agreeable flavour, but not equal to upland hay. The Avon meadows begin at Britford, just below Salisbury ; and here the results of irrigation are as good if not better than anywhere else in England. They continue from Britford to Fordingbridge, but below the latter place down to Eingwood and Christchurch they degenerate into mere flooded meadows and marshes abounding in wild duck, and yielding a very coarse and innutritious herbage. The Avon valley waters are derived from the Chalk, the Upper Greensand, and the Upper Oolite.

The late Mr J. Combes gave, in a paper read before the Royal Agricultural Society, some remarkable instances of the value of the grass produced on some of these Avon water-meadows. He mentioned the fact that £7 or £8 per acre had been given for the spring feed when there had been a failure of the turnip crop ; once under such circumstances the spring feed of 6J acres fetched no less than £80. He cited an instance of a meadow of 20 acres, depastured by sheep in spring, as keeping eight hundred sheep twenty-five days, and as yielding after this, in the first and second cuttings, no less than 40 tons of hay.
The following directions for the management of water-meadows given by the late J. Combes of Tisbury (whose observation as a practical irrigator was exact, and whose experience was very exten-sive), though in the first instance applicable to the Wiltshire Avon meadows, are of general value.

Let the meadows be ready to receive the water in the first week in November, that the manurial matters present in the first freshet of the river after the autumnal rains have commenced may be caught and utilized. Water as much as possible during November and December. In January let the water on six days out of seven, in February three out of four, in March two out of four, in May and June two out of seven, in July and August one out of six ; and shut off the water entirely during September and October. The young grass coming up where sheep have just fed off a portion should not be immersed ; but generally thin watering is bad, and, if there is not enough water for the whole meadow, let one portion be generously treated at a time. Such sections, in Wiltshire called steins, may be watered for five days at a time in winter and two days at a time in summer. It is better to water by night than by day, and in shady rather than in sunny weather.

Assuming that the sluices are in working order, and the conductors or carriers, the feeders, and the drains sound and clear of all obstructions, then actual irrigation begins thus. The sluice is drawn up, and if the water be abundant the conductor and feeders will be filled in about half an hour. The motion of the water should first be adjusted in all the conductors, then in the feeders nearest the upper part of the meadow, and then successively in those which are lower. The sluices regulate the water in the conductors, and the position of the " stops regulates the water in the feeders. The stops should be so placed as to cause the water to overflow the sides of the feeders, by so adjusting the stops as to make the openings or waterways at either side of them wider or narrower as required. The first general inundation will show any irregularities in the levels and meadow surfaces ; these should be noted for rectification in the ensuing summer. It will in general need three trial adjustments of the sluices and stops before an experienced irrigator can satisfy himself that the meadow is properly irrigated with the requisite depth of 1 inch of water. During each period of irrigation the meadow should be visited and inspected at regular intervals to see that obstructions are removed and accidents repaired. In Scotland irrigation is generally continued all April, though in reduced amount towards the end of the month.

The average annual repairs of a water-meadow have been estimated at 5s to 6s. an acre ; the greatest expense will be incurred for levelling, &c, in the second year after laying out the ground.

Mention has been made already not only of the general advantages resulting from that variety of irrigation practised in water-meadows, but also of particular examples of profitable results. It would not be difficult to accumulate many further examples of the latter sort, but they must always be received as applying to the particular circumstances of the case, and very often to seasons and commercial and agricultural conditions different from those which have ruled. An example or two of favourable results obtained by irrigation of water-meadows may be cited here. The late Mr Pusey, aftei having converted a field of 2 acres on his Berkshire home farm into a water-meadow, was able to obtain from it five months' keep for seventy-three sheep. The grass of the meadow had previously become hardly worth cutting, from the land having got out of' condition ; but by irrigation 2 acres of it had become equal to 5 acres of superior grazing land unwatered. The late Mr Stephens quoted in his Practical Irrigator a case of the conversion of 5 acres (valued at 8s. per acre) of a peat bog into a bedwork water-meadow. The expense was £6 per acre, and the crop of hay was 4 tons 114 cwts. per acre, with an aftermath valued at 18s. per acre.

Theory of Irrigation.—Although in many cases it is easy to explain the reasons why water artificially applied to land brings crops or increases their yield, the theory of our ordinary water-meadow irrigation is rather obscure. For we are not dealing in these grass lands with a semi-aquatic plant like rice, nor are we supplying any lack of water in the soil, nor are we restoring the moisture which the earth cannot retain under a burning sun. We irrigate chiefly in the colder and wetter half of the year, and we " saturate " with water the soil in which are growing such plants as are perfectly content with earth not containing more than one-fifth of its weight of moisture. We must look in fact to a number of small advantages, and not to any one striking beneficial process, in explaining the aggre-gate utility of water-meadow irrigation. We attribute the usefulness of water-meadow irrigation, then, to the follow-ing causes :—(1) the temperature of the water being rarely less than 10° Fahr. above freezing, the severity of frosts in winter is thus obviated, and the growth, especially of the roots of grasses, is encouraged; (2) nourishment or plant food is actually brought on to the soil, by which it is absorbed and retained, both for the immediate and for the future use of the vegetation, which also itself ob-tains some nutrient material directly; (3) solution and redistribution of the plant food already present in the soil occur mainly through the solvent action of the carbonic acid gas present in a dissolved state in the irrigation-water ; (4) oxidation of any excess of organic matter in the soil, with consequent production of useful carbonic acid and nitrogen compounds, takes place through the dissolved oxygen in the water sent on and through the soil where the drainage is good ; and (5) improvement of the grasses, and especially of the miscellaneous herbage, of the meadow is promoted through the encouragement of some at least of the better species and the extinction or reduction of mosses and of the innutritious weeds.

To the united agency of the above-named causes may safely be attributed the benefits arising from the special form of water-irrigation which is practised in England. Should it be thought that the traces of the more valuable sorts of plant food (such as compounds of nitrogen, phos-phates, and potash salts) existing in ordinary brook or river water can never bring an appreciable amount of manurial matter to the soil, or exert an appreciable effect upon the vegetation, yet the quantity of water used during the season must be taken into account. If but 3000 gallons hourly trickle over and through an acre, and if we assume each gallon to contain no more than one-tenth of a grain of plant food of the three sorts just named taken together, still the total, during a season including ninety days of actual irrigation, will not be less than 9 S> per acre. It appears, however, that a very large share of the benefits of water-irrigation is attributable to the mere contact of abundance of moving water, of an even temperature, with the roots of the grass. The growth is less checked by early, frosts; and whatever advantages to the vegetation may accrue by occasional excessive warmth in the atmo-sphere in the early months of the year are experienced more by the irrigated than by the ordinary meadow grasses by reason of the abundant development of roots which the water has encouraged.

Irrigation in India.—The irrigation works of India may be grouped under five descriptions or classes, as follows :—(1) perennial canals,—works fed by rivers of which the discharge at all times of the year suffices, without storage, to supply the canals; (2) intermittent canals,—works fed by rivers having an uncertain and very variable discharge, which is stored and rendered constantly available for the canals by means of reservoirs formed in the river-6asins themselves ; (3) periodical canals,—works fed by rivers having a supply available during the rainy season only ; (4) inun-dation canals,—works fed by rivers having a constant discharge of s >me magnitude, but fed only when the rivers are in flood ; (5) tanks,—works which either impound a supply from rivers or small catchment areas, or collect a supply by means of embank-ments thrown across valleys or gorges.

The rainfall of India is not only very irregular in its yearly distribution, but the annual amount varies much from year to year, while the annual average differs in the twenty-two " meteorological tracts " into which the empire has been divided. The following table of average annual rainfall, stated in inches, is from the Report for 1879 of the Select Committee on Indian Public Works :—

1. Sind and Cutch 9
2. Punjab plains 22
3. Hyderabad and South Deccan 25
4. North Deccan plateau 28
5. Khandeish and Berar 29
6. Rajputana and Gujerat 32
7. Carnatic 34
8. Northern Circars 36
9. Upper Ganges plains, North-
west Provinces 38
10. Central India and Nerbudda 44
11. Central Provinces (South) 49
12. Western Bengal 56
13. Western Himalaya 65
14. Lower Ganges plains , 68
15. Pegu 76
16. As6amand East Bengal 96
17. Bay Islands 108
18. Malabar and Ghats, 112
19. Eastern Himalaya 144
20. Concan and Ghats 145
21. Tenasserim 173
22. Arakan 193

The following statistics of the irrigated acreage in different Indian presidencies and provinces belong generally to the years 1877-8, but are in several directions imperfect. Averages are in many cases not yet available. Of course the figures here given must be received with due reserve, since the areas irrigated vary much, from year to year, according to the season ; while, as new works are brought into action, great additions to the irrigable acreage are suddenly made.

Acres Irrigated. Annual Rainfall.
5.265,320 20.786 1,267,054 360,304 1,461,429 1,320,124 35 inches. 24 „ 9 „ 50 „ 40 „ 18 „
Bombay

Sind

North-West Provinces and Oudh....

The annual average rainfall refers only to that of the irrigable areas, and is a very rough approximation.

Emilia 96,000 hectares.
Other provinces 214,000 „

Irrigation in Italy, France, and Belgium.—In Italy the practice of irrigating meadows and crops has been long followed, and is carried out in some parts by means of a complex and costly system of canals. The extent of lands irrigated was in 1878 :—

Lombardy... 678,000 hectares.
Piedmont 443,000 „
Venetia 74,000 „

Rice is extensively grown in artificially irrigated lands in the basin of the Po. The produce in rough grain oscillates between 30 and 50 times the weight of seed sown ; if official reports may be trusted, a hectolitre and a half of seed rice will yield from 45 to 75 hectolitres. During the four years in which a field is in rice the annual crop, beginning at 70 hectolitres, sinks successively to 65, 50, and 40. About 42 hectolitres of cleaned rice is the general average yield.

In some parts of Italy the system of winter irrigation, with which we are familiar in England, is carried out upon meadows in which the Lolium italicum abounds. This is the case in many of the valleys of Lombardy and in the neighbourhood of Padua. The cuttings of grass are about six in the year, but where certain sewage waters from towns are mingled with the natural water supply eight or even nine cuttings are not unusual. The average yield of hay in these meadows when irrigated with clean river water is abou t 14,000 kilograms annually, or twice the amount obtained from per-manent pasture in the same district. The cuttings begin as early as the end of February, the heaviest amount being obtained in the May cutting, and the lightest in that of October.

In France irrigation has met with increasing favour of late years. Since 1875 there have been Government competitions for prizes for the best examples of irrigated farms. In 1879 there were competitors from eight departments of France, two departments, those of ;he Basses Alpes and Hantes Alpes, in which the areas irrigated amount respectively to 8500 and 20,000 hectares, furnishing no less than seventy-two. There are many canals in these departments. Other important irrigation works are to be found in Provence, Dauphiné, and Languedoc. The valley of the Isère near Grenoble affords a good illustration of how a devastating torrent may be turned into a source of continual fertility, 3000 hectares of useful land having now been conquered from floods and reclaimed. In the Roussillon district the irrigated area has been doubled between 1820 and 1880, and exceeds 25,000 hectares. One farmer, M. François Coste, whose grandfather was ruined by having^ to pay 2 francs per hectare for a rugged mountain farm, now obtains rfrom 18 hectares of the same land no less than 125,000 kilos of hay, or 6000 to 7000 kilos per hectare, a fair yield even for the average meadows of the north of France. In the Pyrenees Orientales there are canals which have been constructed since 1850, and which now water over 6000 hectares. It is scarcely necessary to say that in some lands irriga-tion without any application of manure has been unremunerative, but that with manure the natural produce has been raised from 7000 to 16,000 kilos of hay per hectare.

There appear to have been some instances where that terrible vine scourge, the Phylloxera, has been entirely eradicated by autumnal submersion of the roots of the affected plants. Irrigation has also been employed in the cultivation of lucerne, of green maize fodder, and of asparagus and other market-garden produce.

The notion that irrigated rice fields are unhealthy has led to the abandonment of rice-growing in France and Portugal. But it is only when the layer of water is exceptionally shallow or discontinu-ous as well as stagnant that bad effects on the health of the district have followed. It is at the close of the growing season, when during very hot weather the water no longer covers the soil, and also in the ease of badly-planned and badly-managed rice fields, that there is danger from the rapid decomposition of organic matters in the earth.
In Belgium irrigation is extensively practised in the district La Campine, where the whole process is carried out in the most methodical way, and under strict Government supervision. The following figures, given by Mr E. Laveleye, afford some notion of the results of Belgian irrigation. An area of 2281 hectares of barren soil (sand dunes, in fact), yielding absolutely nothing, now produces an average of about 3000 kilos, of hay per hectare, 100 kilos, being worth 10 francs. The value of the aftermath is further estimated at 100 francs per hectare, so that the total yield from one hectare becomes 400 francs, or £16. Full particulars concerning irrigation in Belgium may be learned from the treatise by J. Keelhoff, entitled Traite Pratique de I'Irrigation des Prairies (Brussels, 1856). M. Keelhoff recommends the following mixture of seeds (stated in kilos, per hectare) for sowing on the Belgian sandy fields which are to be irrigated :—

Loliurn perenne 16 Poa pratensis 5
Phteum pratense 6 Anthoxanthuui odoratum 10
Alopecurus pratensis 25 Medicago ttipulina 4
Ifofcus lanatits 25 Trifotium pratense 4
Cynosurus cristalus 5

History of Irrigation.—This part of the subject is very exten-sive, not merely because it deals with a very ancient art, and one very widely practised, but because the materials are very varied, and in many cases very difficult of interpretation. Still we pos-sess not merely a considerable number of allusions to irrigation in ancient Egyptian, Hebrew, and Oriental records, and in Latin and Greek authors, but we have very tangible remains, still extant, of aneient irrigation works in many countries of Europe and Asia, and in some parts of northern Africa. In Egypt the art can- be traced back to a very early period. In that comparatively level country an extensive system of artificial ponding reservoirs or lakes, with a network of distributing canals, was in existence at least as early as the time of Sesostris. If the art of irrigation was taught to the ancient Egyptians by the natural overflowing of the Nile, it is probable that Egypt in her turn afforded an example to Assyria and Babylon, to Carthage and Phoenicia, and also to Greece and Italy. The early history of irrigation in Persia and China has received some little elucidation in recent years, but even in the case of India our exact knowledge of the development of this art remains imperfect. What has been done during the present century in India may, however, be studied in a compact form, though rather from the financial than from the agricultural side, in Mr R. B. Buckley's Irrigation IVorks of India (1880), a book which has been laid under contribution in preparing the present article. Amongst Latin authors Cato, and more particularly Colu-mella, speak of the formation and management of irrigated meadows as well as of watered gardens. The Lombard kings, following the Roman practice, encouraged and extended irrigation in Italy. From Lonibardy the art extended to France ; while the Moors encouraged it in Spain, Sicily, and Algeria. In Great Britain irrigation was not extensively practised until the close of the 18th and beginning of the present century, although one Pallavicino, an Italian of the time of Mary and Elizabeth, introduced the irrigation of fields on a large scale on his estate of Babraham in Cambridgeshire. It has been thought that some of the existing English water-meadows originated in Roman engineering skill. And the extensive tracts of irrigated land in the vicinity of ancient Roman stations, as in the neighbourhood of Cirencester, lend some support to this view.

The irrigation of grass land, laid out in accordance with one or other of the plans to which reference has been made, is in England a localized custom almost confined to a few southern counties :— Berkshire (watered by the Kennet) ; Derbyshire (valley of the Dove) ; Dorset (the Stour in the vale of Blackmore) ; Devonshire (catchmeadows in the valleys of many rivers and brooks); Gloucestershire (valleys of the Churn, Severn, Avon, Lidden, &c ); Hampshire (the Avon, Test, and Itchen); Wiltshire (valley of the Avon) ; Worcestershire (certain canals). In Scotland systematic irrigation is practised to a very limited extent, and was not introduced until the early part of the present century. It is, however, peculiarly adapted to many lands lying near rivers, which could be made most serviceable in fertilizing poor soils and bringing on an early feed of grass for sheep, while at the same time an ampler supply of hay for the winter feeding of stock could thus be secured. (A. H. C.)



The above article was written by Prof. A. H. Church, F.R.S., Royal Academy of Arts, London.




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