IRRIGATION AND ITS PRACTICE.

New Zealand Journal of Agriculture, Volume XXVIII, Issue 6, 20 June 1924, Page 357

IRRIGATION AND ITS PRACTICE.

( Continued.) 111. METHODS OF APPLYING WATER AND PREPARATION OF . ' THE LAND. - ■ .

R. B. TENNENT,

N.D.D.,

Instructor in Agriculture, Dunedin, and J. R.

MARKS, A.M.Inst.C.E., M.N.Z.Soc.C.E., Resident Engineer, Public Works Department, Alexandra.

< | AHERE are three main principles under which the natural moisture . . content of soil may be artificially supplemented natural improvecontent of soil may be artificially supplemented for the improve- ■ ment of plant -growth. 7.-These are (1) sub-irrigation; (2) standing water ; ' (3) surface irrigation. ■ (Fig. 19.) . '• ■ - •’ 7 The .'first. principle is likely to have so little bearing on the purpose of these articles that it will be dismissed with a few brief remarks. The second, though- not at all.likely to be purposely attempted in Central Otago, . has already come about in some measure as the unavoidable result of surface -irrigation, and no doubt it will continue to be the inevitable complement of the latter principle. It comes in between the questions. of surface irrigation and drainage (with which the writers will deal at a later date), and must therefore be given something more than a ...transitory place in these discussions. The third principle embodies the vital subject-matter of this series of articles, and will be dealt with by the writers in considerable detail. '

" . SUB-IRRIGATION. K This principle of irrigation consists in adding water to the soil by injecting it at intervals into the subsoil through buried pipes under low pressure. The pipes are either porous or have a series of holes bored in their upper side. Instead of relieving the. soil of some of its moisture, as is done by the well-known system of field-tile drains, extra water is introduced into the soil.- . It has been proved to be fairly efficient, but careful experiments have shown that no other artificial method is as highly productive per unit of water used as surface irrigation. Sub-irrigation would generally prove prohibitive in initial cost, and might only be used in very small plots where the object is the propagation of rare and valuable plants or seed, in connection with which the introduction of foreign, plants or weeds, through the medium of water applied to the surface, might render the desired object futile. The principle is sometimes applied to bowling-greens where it is desired to add moisture without even temporarily saturating the surface. . tk, * . ■ STANDING WATER. Under every unirrigated piece of land there is a certain depth below which the subsoil is in a state of permanent and complete saturation. In other words, free water lies at this depth in all the interstices, and if a well were sunk into it the water would rest at this level, known as the ground-water level. This level is fixed by the balance which is struck between natural inflow of water to the subsoil from rainfall and the outflow through natural drainage facilities to' rivers and lakes. In low river-flats the ground-water level is likely to be sufficiently near the surface to keep the soil and subsoil, within range of the plant-roots, sufficiently moist for vigorous plant-growth. In such cases irrigation would not be required.

In higher terraces the ground-water level is generally too deep under to be of use to plants. It would in some circumstances be possible, but probably not economical, to permanently raise the. ground.water the desired amount, by constructing weirs in the river or stream which controls the ground-water level. However, the same effect is frequently brought about quite unintentionally on low areas with inferior subdrainage by the surplus irrigation water which has been ■applied to higher adjacent areas. This surplus water percolates through the subsoils* to the . lower areas, giving a greater inflow than their natural drainage facilities can cope with. These lower areas may have been too dry to be of much use in their previous natural condition ; but the result may be that the ground-water level is raised permanently (in some parts probably even too high, causing swamps and necessitating expensive drainage), and always in such cases there will be a certain strip of land, between the surface-irrigated area and the area requiring draining, in which the ground-water level has been raised about the necessary height to bring the moisture content in such, strip to something approaching ideal requirements. This strip of land is thus benefited under the principle of “ standing-water irrigation.”

The drainage-works, which have' to be carried out in respect to the overwetted areas, if scientifically designed and controlled, will lower the ground-water level again by just the correct amount to enable these swamped areas also to be benefited' —or, • rather, irrigated the

standing-water principle. In this manner a condition of affairs arising out of surface irrigation on the higher lands, which may at first sight appear to be a decided offset- to the benefits derived from the irrigation of such higher lands, can, if properly dealt with, be converted into a twofold benefit. Just as it devolves, upon the engineer to turn this threatened defect into a blessing with respect to a whole valleybottom, so, in a smaller measure, can the irrigation farmer benefit by the study and application of the principle of standing-water irrigation, allied with his problems of drainage where such may exist.

Generally in Central Otago the subdrainage is so free that not much benefit can be derived from the principle of standing-water irrigation, but in Ida Valley it is already apparent to a marked degree, and in that locality it is quite obvious that several thousands of acres along the valley-bottom may be reclaimed into first-class land by a system of controlled drainage and regulation of the ground-water level.

Before passing on from this principle of irrigation it should be remembered that, once properly established, it has an advantage over the principle of surface irrigation, by being free from the cost of making and maintaining irrigation-ditches and levelling -the land, and from the fact that practically no labour is required in its application. . j , SURFACE IRRIGATION. This principle, which is the one more generally practised throughout most irrigation districts of the world, consists of adding moisture to the soil by intermittently spreading or running water over its surface. From centuries of practice it has developed into a distinct branch of agricultural science. It has many variations of application, but before dealing with these it would perhaps be interesting to touch upon the problems which faced mankind, and have to a large degree been solved, in arriving at the present period of advanced knowledge.

In the history of irrigation development the problems of applying water to the land seem to have been fairly satisfactorily solved in respect to the two extremes of conformationnamely, : hillsides and almost dead flatslong before any satisfactory methods of dealing with the intermediate gradients were evolved. A reasonable explanation of this can be found in a consideration of the natural association of both these extreme classes of country. In hilly land the frequent divisions of the watersheds by ridges prevents the accumulation of rainfall into anything but very small streams, or, if larger ones exist, they are usually in deep inaccessible gorges. The small streams were easily led round the hillsides in small contour ditches, and, being caused to overflow, trickled readily down the steeper slopes, and watered considerable areas before being entirely absorbed by the soil. This method still remains in use under the name of “ flooding from contour ditches ” (Fig. 20), and is still highly recommended ; it is, in fact, the only practical way for irrigating steep slopes.

Where the land below the foothills merges into gently falling plains, as is usually the case, the small streams of water, if discharged from contour ditches as described, would travel too slowly over the surface, and would undoubtedly be found to percolate into and through the subsoil before benefiting large enough areas to warrant the trouble involved. The development of .irrigation on these moderate slopes

was therefore delayed until time and the necessities of increasing populations caused industry and intelligence to be brought to bear on the subject, and, as a result, some of the. modern and now most universally adopted methods of application were evolved.

On the other hand, prior to the irrigation of the moderate slopes, and possibly before the irrigation of hillsides, very flat plains were irrigated. Here again is evidence of nature being easily adapted. Very flat plains are generally associated with large sluggish rivers, often requiring very little obstruction to raise them so that waters might readily be diverted on to the flat lands. In such cases vast quantities of water were usually available, and, from their very vastness, would readily spread over huge flat areas without further effort on the part of man. This uncontrolled method is practically what is now known as “ wild flooding ” (Fig. 21). ...

But here again any plain with even a very moderate slope was found to give difficulties, in that the large flow of water, if not checked by levees or borders of raised earth and subdivided and spread by specially designed ditches and furrows, would peruse a mad course back to the river, watering only a comparatively narrow strip of land, and as likely as not washing away the soil. Until economical solutions were found for the design and construction of methods of control, the irrigation of these moderate slopes was again delayed, as in the case of irrigation by small streams from contour ditches.

. Irrigation practice in Central Otago, with a few exceptions, is not yet very far advanced'from the primitive methods referred to. There are very few places where dead-flat plains exist (most of the plains having quite considerable gradients), and most of the larger streams or rivers are cut too deeply into the plains to permit of large quantities of water being easily diverted. Consequently it is not surprising that wild flooding was .practically non-existent among the. many small irrigation projects of the pioneer irrigators. The numerous small streams with which. the foothills abound attracted their attention, with the result that almost all the older irrigated lands of Central Otago are on hillsides, and are irrigated ■by the contour-ditch method. There are, however, one or two instances of wild flooding, the most noticeable being on Mr. J. Lethbridge’s property at Ardgour.

In more recent years Government irrigation schemes have provided for the supply of water upon a much larger scale, and largely to the intermediate plains of moderate slope. Many of the settlers are, unfortunately, endeavouring to irrigate by one or other of these primitive methods lands which are neither flat and even enough for wild flooding nor steep enough for contour ditches. They are using more water than is economical or good for the land, and involving themselves in an extreme amount of unnecessary labour. In making this statement it is not intended to belittle the intelligence of these settlers, who are mostly inexperienced in irrigation,’ and until recently had only the examples of the older irrigation to be guided by. Some of them have, in fact, brought considerable intelligence to bear upon the situation, and have unconsciously adopted methods closely approaching some of the more modern systems ; - but too frequently they have not adopted the most efficient method for their particular areas. They should

realize, that, in attempting to evolve methods of their own they are wasting time, trouble, and expense. They are going over old problems which have been solved in older countries by previous generations of men whose knowledge, gained by trials, failures, and successes, is available to any one who will spare a .few hours to read and study the many excellent works on irrigation now obtainable. Instead of delving in the dark, new irrigation settlers should carry on from the point reached by others and devote their’energies to further improvements in methods.

It is admitted that the new settler placed upon a bare plot of land, without fencing or building, has his side of the question. He has to put labour and money into his section for some time before he can get a return. Meantime he has to live, and it is quite understandable that his first inclination is to irrigate his land, in order to produce something, by any method, or lack of method, so long as it will make something grow quickly and without much initial cost in preparing the land. In some circumstances he may be justified in ’ starting by roughly irrigating most of his farm by any crude method, with the final object of going back over it later to redevelop upon more efficient lines. However, he should avoid laying down fields in permanent crops on any but the most efficient lines. I . .-METHODS OF SURFACE IRRIGATION. ■’ There is some diversity in the nomenclature of some of the’ recognized methods, but the writers propose to enumerate' the principal ones, and . later describe and comment upon them, under certain designations, which will be adhered to throughout these articles. • ■ For general field irrigation, the- following list enumerates six of the principal methods, arranged in their order, with relation to the steepness or gradient of the lands upon which they are, in the . opinion of the writers, generally most suited for adoption (commencing with the steepest lands).: (j.) Flooding , from contour ditches ; (2) .flooding from field laterals.; (3). the border-ditch system ; (4) the border-dyke system ; (5) the basin-check method ; (6) wild flooding.

-The first and last of the foregoing are the primitive methods which, as already explained, appear to have first suggested themselves to man, while the intermediate ones are the outcome of centuries of practice. While no one of them is entirely condemned under its most favourable conditions, it is intended to suggest the circumstances under which each might most economically and efficiently be employed. In these suggestions it will be found that the degree of gradient of the land is generally taken as the’ principal factor in deciding which method should be adopted. There is no doubt that the texture of the soil, its power to resist erosion, and its degree of porosity must have some bearing upon the matter. Also, the volume of flow of water which the irrigator may have at his command should influence the selection of a method or a modification of the same, as would also the class of crop to be grown. But these, are minor considerations as compared with, the general one of gradient, and the writers therefore believe that the intelligent irrigator will, from the remarks about.to be made, be able to modify the general, recommendations to conform with the particular; characteristics of his own fields. It should be added that the writers-

have in view mainly the irrigation of pastures and permanent fodder and hay crops, and to some extent cereal crops.

■ Time and further experience may eventually cause the writers to modify or alter their views in some degree, but it is here perhaps appropriate to state that the recommendations about to be made are based upon their personal observations, much study of the subject, and a very intimate knowledge of conditions in Central Otago, for which district their recommendations are essentially designed.

For orchard - work, market-gardening, and certain field crops a further method known as “ furrow irrigation ” is frequently used ; and for . several classes .of production one or two other methods, involving the reticulation of the water through pipes, will be referred to under the general heading of pipe irrigation.” These will be dealt with in a later article. Flooding from Contour. Ditches. The general principles of this method have already been referred to.. Fig. 22 shows a field laid out for irrigation on these lines. The distributory ditches or furrows follow very . nearly the contours of the land. It is the only method which can be recommended for very steep land, and is quite efficient for any slopes of 3 ft. per chain or steeper. Slopes as steep as 30° are frequently in evidence in Central Otago growing clover and grasses well under this method. It can be used for flatter slopes than 3 ft. per chain, but becomes uneconomical, in duty of water and labour costs, as against other methods. It has the inconvenience of many furrows or contour ditches placed irregularly about the land, but, as the steep lands upon which it is recommended are usually only capable of being used for grazing purposes, this does not matter much. These steep lands usually grow very sweet grasses, and, no matter how steep or rough-looking, every part of them should be utilized by the irrigation farmer.

The chief point for caution is to make ditches small, so that it is impossible for a large flow of water to concentrate and cause damage. . One good plough-furrow should usually suffice, and the flow of water used should be between g- cusec for very, steep land and | cusec on the easier slopes. The gradient of the contour ditches should be kept fairly, low (say, about 6 in. of fall per chain), so that the water may easily be made to overflow from them in many places at once. The distance between contour ditches should be in the vicinity of 2 chains, and the distance which water is run along any contour ditch should not exceed about 5 chains ; that is to say, the supply-ditches should be about 10 chains apart and contour ditches run each way from them. Using contour ditches .of too great length will involve unnecessary loss of water on the way. . The supplyditches, which are directed straight, down the: steep hill, must be stone-pitched or constructed 'of wooden or. iron fluming to prevent erosion. However, being very steep, ‘ these supply-ditches need only be of small dimensions. Sheets of ordinary corrugated galvanized iron placed end for end with a short overlap, and bent sideways into, semicircles," form good protection in supply-ditches. Sometimes a natural flat-bottomed gully is used as a supply,-ditchj the water being

allowed to run down unrestricted. This is not recommended, as the gully either erodes or becomes choked with swamp-grasses, which retard the water too much, thus permitting the gully-bottom to absorb too much water, which is likely to come out lower down and cause damage to lower lands by overwetting.

The operation of irrigating is usually worked downward from the top contour ditches, which are shut off as soon as their portions of land are watered. Meantime, any water which escapes from the upper levels will be collected by the lower ditches, and will go towards the fulfilment of their duties. In the initial laying-out of the field the supply-ditches should .first be constructed, and the top contour ditch should be made and set in operation. Then the irrigator may decide the exact position of each succeeding contour ditch, as he observes the distance which the water from the one above reasonably irrigates. The initial cost of this method of irrigation is about £2 10s. per acre for iron for the supply-ditches, plus the small labour of making contour furrows. The latter may be done by the irrigator, but for purposes of comparison it is estimated at 10s. 6d. per acre, making a total initial cost per acre of £3 os. 6d.' As only a small flow of water can be utilized under this method with: safety it is rather slow in- operating, and may take sixty hours to irrigate a 10-acre field. This may have to be repeated eight times during the irrigation season. After grass is established to hold the soil the irrigator need not be in constant attendance, but will have to leave his other duties several times a day to redirect the flow ; or the work, being very light, may be done by a youth. Flooding from Field Laterals. As the slope of the land becomes easier, though still of a decided degree, the thin film of water from contour ditches travels too slowly, resulting in over-irrigation near the ditches and complete disappearance -of the water before irrigating reasonably wide strips of land. Some method becomes necessary of assisting the flow of water downwards, concentrating it upon a small area for a brief period, and then quickly transferring it to another.

While the slope of the land is still between -3 ft. and i|ft. .per chain this can be effected by the method of flooding from field laterals (Figs. 23 and 24). The head ditch, instead of being directed straight downhill, is taken somewhat diagonally across the slope, preferably (but not necessarily) at the greatest gradient the soil will stand without protection against scouring. Most ■ soils in Central Otago will stand a grade of 1 ft. 6 in. per chain in fairly small ditches not used constantly and thus protected on the sides by the natural growth of grass. Lateral ditches, on the steepest gradient permissible with safety, are then run off from the head ditch, in an opposite diagonal direction with respect to the general slope of the land. This will make their direction somewhat square to the head ditch. From |to cusecs may be used in this system, the water being concentrated to one or two points in one of the laterals at a time, and let out at these points on to the land by means of canvas dams, which may also be used for diverting it from the head ditch into any lateral (Fig. 25).

The canvas dam (Fig. 26) is used by resting the rod across the top of the ditch, preferably before the water reaches it, hauling the slack end up-stream, letting it sag into the shape of the ditch, and anchoring it down with 'sods. It will thus form a fairly watertight dam capable of being moved easily. It is preferable to have a few of these canvases, so that they may be . set in advance.

In Fig. 23 the field is assumed to have its main fall running diagonally across it, and in such a case the ditches will run about parallel to the sides of the field. If the fall were directly down the field the system of ditches would be arranged as in Fig. 24.

The, whole of the preparation work for this system can be done by the irrigator at a cost estimated at £1 ss. per acre, which is the total cost of preparation. When operating, a man must be in constant attendance. He should, however, be able to irrigate 10 acres in thirty-six hours. The method is a good one, but should be confined to land with about 2 ft. of fall per chain. Border-ditch Method. I. ■■■ . . • . . As soon as the slope of .the field becomes easy enough to permit water to be run directly down it in ditches without damage the two methods previously described should be abandoned and the borderditch method used (or one of the methods described later). Fig. 27 shows the use of this method. The head ditch is taken across the top side of the field on a fairly flat grade, so that if dammed in one place it will back up the water to discharge into two or more of the branch ditches at one time. The head ditch will have to be fairly large, on account of its low gradient, in order to carry a flow of water of, say, 3or 4 cusecs. The branch ditches are taken off from the head ditch, at intervals of about 70 ft., straight down the .fall-of the field. They need not be so large, as they will have a considerable gradient. Two furrows thrown in opposite directions and trimmed up a little will form one of these branches. The canvas dam is used for diverting water into the branch ditches (Fig. 28), and also for diverting it out of the latter .on to the land (Fig. 29) in a very similar manner to that employed in the field-lateral method. One difference from and decided advantage over the latter is that the border-ditch method waters on both sides of the ditch, and the raised edges of each ditch form borders, confining the flow of the water directly down definite strips of land. Hence the name “ border.”

The film of water on the land being thus confined very materially reduces the amount of attendance required. One man should be able to irrigate a 10-acre field in fifteen hours.

In the previously described methods, recommended for steeper lands, slight inequalities of the land-surface do not matter much, but in this system it is desirable that the surface be made fairly regular by a little grading, if necessary (though a very high degree of evenness is not absolutely essential). Allowing for a moderate amount of surfacelevelling and the construction of the ditches, all of which may be done by the settler himself, the cost of preparation is estimated at £2 12s. 6d. per acre. This method can be used on land with a slope of lift. per chain or considerably less. It is fairly - efficient, and probably the best method to use on lands with slopes between 1 ft. and i|ft. per chain. However, on lands having less than .1 ft. of fall per chain there should be no hesitation in discarding it for the border-dyke method.

Border-dyke Method.

For flat land this method (Fig. 30) is undoubtedly the most efficient,' and, though expensive in first cost, is in the long-run the most economical from every point of view.

The head ditches should be formed almost on a dead flat, • across the upper end of a field and at further intervals of 10 chains, and, being flat in gradient, must be fairly large, as the method involves the rapid use of a comparatively large, flow of water. Instead of leading the water down the field and distributing it in smaller ditches, as with the border-ditch method, it is put on to the; land direct from the head ditches. The border ditches are replaced by small levees, ridges, or “ borders ” running down the direct slope of the land and dividing it into strips. If the land is level across the field, as in the lower half of Fig. 30, the strips will be regular and parallel to the sides of the field. On the other hand, if there is slight irregularity in the contour the strips may be curved to. run always at right angles to the contour. In other words, the direction of the borders will follow the steepest direction of fall at each point in their progress from the head ditch. This is to ensure that each strip will be perfectly level in cross-sections at every point. For operating, a large flow is let into the top end of a land. It spreads into an even film a few inches deep confined between the borders, and travels right down the full length of the strip (Fig. 31), watering the land in that strip evenly and thoroughly.

Experiments and experience have shown that the strips should not be more than 10 chains long (the writers are ’ inclined to recommend about 7 chains) and 50 ft. wide. The levees or borders should be about 7 in. high at the start, where the film of water will be deepest, reducing to a couple of inches at the bottom end, where the water should have been reduced in depth to practically nothing by absorption en route.. These borders are formed, by ploughs assisted by a special ridger (Fig. 32). They should be a few feet wide at the base, so that when they have settled and rounded off they resemble gentle waves rather than sharp ridges. If so formed they will present no obstacle to a reaper or other farm implement.

The volume of flow of water used will be decided by the slope of the land, other things (such as the porosity or rate of absorption of the land) being equal. On average porous Central Otago land, for giving a watering equal to about 3 in. of rainfall the film of water should only be on the surface of the land at each point for about thirty minutes. Enough water to irrigate a whole strip must therefore be allowed to run into the head of it .in thirty minutes. By this time the travelling end of the film of water will (if the volume of flow has been large enough) have reached roughly four-fifths of the way towards the end. The supply is then cut off at the" head ditch and transferred to another strip (or “ check,” as they are commonly called). The film in the first check will continue to move forward by the accumulated water in the upper end passing on, and if everything has been gauged rightly should just peter out at the bottom end.

It might appear at first sight that this, method would over-irrigate the top end and leave the lower end underwatered. : However, this is not so. The amount of water which soaks in at any point is not dependent upon the depth which may be passing over the surface at that point, but rather upon : the length of time during which free water of any depth has been resting on the surface. Almost immediately the supply is cut off, the film at the upper end, being a few inches deep and thus having more velocity, runs forward, leaving the surface there uncovered. But its progress at points lower down -is slower and slower. It therefore takes longer to run off these dower points, and this happens to compensate in a remarkably correct

manner for its not having reached these lower points so soon when the supply was coming on. The volume of water.used should be adjusted by trial to give the proper effect. Roughly, for land with a gradient of i ft. per chain a flow of about 3 cusecs should be used, increasing to 6 cusecs when the gradient reduces to 3 in. per chain. Not often will land be found to have a lesser fall than 3 in. per chain, but this method can be used for very much flatter land by increasing the size of flow. As the whole essence of this system is speed and precision, canvas or sod dams are not recommended ; but a simple wooden gate should be set in the side of the head ditch leading to each check. Also, one of these' gates will be necessary in the branch ditch leading from one head ditch to the next, so as to hold back the water in the upper head ditch while it is in use. These gates should be about 6 ft. wide but only one board deep : that is to say, the movable part consists of one board, with handle to lift it by, set in a simple frame (Fig. 33). It will readily be seen that the land must be smoothed perfectly and "made quite level in cross-section, or the film of water would run all to the low side. The main levelling, such as cutting off decided hummocks and filling into hollows, is done in the first place with horse scoops or scrapers, and the finer levelling by special implements (which can be home-made). Even the slight hollows made by the removal, of the soil for the borders must be refilled by scraping a little soil into them from the middle portion of the lands, and the ordinary road-grading machine comes in very useful for this work. The matter of irrigation implements will, however, be dealt with more fully in a later article.

The initial cost of preparation for the border-dyke method is much higher than for any of the others yet described, being as follows per acre • £ s . a. Labour making head ditches . . . . ..200 Making borders .. . . . . .. ..0180 Levelling field (varies) . . . . . . ..100 Making head-gates . . . . .. ..076 Total labour (including horse-hire).. ..456 Materials for head-gates ..." .. . . ..0146 Total initial cost per acre . . • • 0 0

It will be seen that only a very small portion is for material, and that all the rest can be done by the farmer and his teams. Though the initial cost is much higher than for other methods, it should be remembered that it is non-recurring, and it is amply justified by economy in labour for all time thereafter, in the amount of water used (which has to be paid for), and, still more important, in evenness of irrigation, ensuring the best crops. The work when done is an added and visible improvement to the capital value of the land. .

By this method one man can irrigate 10 acres in eight hours, and, what is more, knows that every inch of it has been done thoroughly. It is the only really scientific method known, and settlers should be prepared to undertake very 'considerable grading and levelling work to adapt even very uneven land to its use.

Basin- check Method. ’• This, is a method (Fig. 34) which, though, very old and adapted for very flat land,; has been largely replaced for field irrigation by the more speedy and labour-saving border-dyke method. ‘ It consists essentially in forming basins or ponds on the land by throwing up slight mounds or checks and flooding each consecutively. For marketgardening and orchard irrigation (Fig. 35) it is still recommended in the right circumstances. Where the land is practically dead-flat and even, the basins will be ' rectangular and regular, but if on a slight slope they will conform in shape to the contours of the land.

The size of each pond will depend upon the flow of water available. The method would not be practicable to use on . fields with a slope greater than about 6 in. in 2 chains (unless the irrigator were prepared to terrace the land). In Fig. 34 the field has about the maximum slope as mentioned. The hatched markings represent slight levees which could be formed with a plough. Those running across the field would be 6 in. high throughout, to pond up the water that height and make it back up to the upper edge of each enclosure. The ridges running up and' down the field would have practically no height at the upper edge of each pond and increase to 6 in. at the lower edge. -

For a lay-out as shown in Fig. 34 a flow of about 5 cusecs would have to be applied to each basin for about fifteen minutes. It would then be turned into the next lower basin, and the embankment between the two immediately cut to allow the surplus water impounded in the upper basin to also run into the next. It would cost fully £6 per acre to prepare properly with gates, and, though just about as speedy as the border-dyke method, would take two men to operate over the same area. This means that it would be about twice as costly to manipulate. . It is recommended only for odd corners of a field not large , enough to set out in borders.

Wild Flooding. This method cannot be recommended under any Government irrigation scheme. - In very exceptional circumstances, where plenty of water is available without extra cost and good drainage exists, it might be employed. ' Summary of Costs and Expenses of Surface-irrigation Methods. The following is a summary of the per-acre costs and operatingexpenses of each system described, assuming eight irrigations in a season :

The Influence on Agriculture' on International Relations was a subject considered by the Paris International Congress of Agriculture last year. It was held that an association of the leading agricultural and pastoral societies of the world would lead to the development of sound international good-fellowship, and the elaboration of a common programme for the benefit of world agriculture.

Noxious Weeds. — The Tomahawk Road Board has declared Californian thistle not to be a noxious weed within its district. The Foxton Borough Council has declared the whole of the plants enumerated in the Third Schedule of the Act to be noxious weeds within that borough. Matakaoa County has declared Bathurst burr, foxglove, gorse, milk thistle, and Japanese wineberry to be noxious weeds.

Hotes.Labour is allowed for at 13s. 4d. per eight-hour day. Horse-hire is included with labour at 7s. per eight-hour day for each horse. Ordinary cultivation has not been included in cost of preparation of 'the land. The cost of the wild-flooding method is extremely small, but not possible to estimate.

! • Initial Cost. Annual Cost Method. of Initial Cost. Annual Cost of Operating. Method. Labour. Material: Total. £ s. d. £ s. d. £ s. d. £ s. d. Flooding from contour ditches (man o io 6 2 IO O 3 0 6 2 IO O i two-thirds time) o io 6 2 IO O 3 0 6 2 IO O Flooding from field laterals i 5 o i 5 0 280 Border ditch . . 2126 212 6 IOC Border dyke .. 4 5 6. 0146 5°o 0 10 8 Basin check . . ■ _ . . 3 16 6 236 600 1 1 4 Wild flooding . . . . 3 16 6 236 6 0 0 i i 4

Table 9.