IRRIGATION

Press, Volume LXX, Issue 21355, 24 December 1934, Page 15

IRRIGATION

<&. CONSIDERATION OF DETAILS CHAMBER OF COMMERCE BULLETIN The monthly bulletin prepared by Canterbury Agricultural College, Lincoln, for the Canterbury Chamber of Commerce, discusses preliminary considerations in irrigation. It states: — On many Canterbury farms irrigation would increase carrying capacity, reduce costs of production, and remove the danger of drought. But to reap these advantages, changes in farm practice are required, and great care must be given to details. The object of this bulletin is first to show the importance of these details,, and second to emphasise the heed for balanced investigation in which farm management, economics, and the technique of irrigation may each receive due attention. The first lands to be irrigated should be those that have shown their capacity for high production in seasons of good rainfall. Soils of low fertility that do not produce heavy crops in the wet seasons will present special problems. Very shallow light soils or heavy clays should bo avoided. The suitability of the soil and sub-soil for the various irrigation projects in Canterbury is being determined by soil scientists and engineers and at present need not be further discussed.

Of the many methods of applying water, five are of special importance. 1. Border Dyke Flooding: For this the smoothest part of a farm is selected and surveyed. A head race about four feet wide is raised on ground level and is so placed as to have a fall of about half an inch to the chain. Rough wooden gates are placed on one side of this water race at about forty feet intervals, each gate opening on to a strip of land 40 feet wide and from live to 1U chains long. Between the strips are wide ridges of earth about seven to nine inches high. The strips themselves are smoothed with a grader so as to give continuous fall from the gates to a waste furrow at the bottom. This method varies widely in cost, with a usual range of £3 to £7 according to the unevenness of the ground and the perfection of the work. With this method less water js used and less labour is required for irrigating than for other methods. 2. The border ditch method costs about 10s per acre to install and is most efficient where the fall is suitable —that is, about one foot to the chain. There is a head race as before, but instead of ridges there are ditches one to three feet wide running at about one chain intervals down the fall of the land. When several of these ditches are blocked by boards or sods the water overflows and runs over the land bordered by ditches. This method is wasteful o£ water and very laborious to operate unless a large quantity of water is available.

3. Contour flooding is the easiest method on down country. A ditch falling about one inch a chain follows around the spurs of a hill, and when the ditch is blocked the water spreads down the slope. 4. The furrow method is suited to many row crops, including root crops grown in ridges. Orchards are irrigated most easily by running the water in three, four, or five furrows between the rows of trees.

5. Overhead spraying is practised to some extent, but because of the expense is confined to high-priced products (raspberries, etc.). For the irrigation of pasture on the Canterbury Plains smooth areas should be watered where possible by the border dyke system and more uneven ' land by the border ditch. Fairly uneven fields may be watered by furrows running along the high ridges unci some high mounds may be left as "camping grounds" for stock. These methods are subject to modification according to the depth and texture of the soil, the amount of water available, the slope and unevenness of 'ho surface, and the funds available for the work'. Water Utilisation There are many details of water utilisation on the farm such as quantity per flooding, frequency of flooding, spacing of furrows and ridges, etc., which must be studied under varying conditions in Canterbury. It is hoped that it will be possible later to issue a bulletin dealing with some of these matters. Pasture should be the first crop to be irrigated, because of its great importance as well ns permanence. Under the heading of pasture, may be 1 included first-class permanent mixed pasture for grazing and hay, red clover for hay and perhaps seed, white clover for pasture hay and seed, and lucerne for hay. It is probable that roots will occupy only a small area of the irrigated portion of the farm, particularly on medium and light land where good irrigated pasture hay as a winter feed should receive first consideration. Roots on ridges lend themselves to irrigation. Irrigation of grain crops is not likely to receive much attention at this stage of development, and in fact irrigation of cultivated areas requires a much higher skill and knowledge than that necessary for irrigating permanently growing non-cultivated crops. Good permanent pastures and good hay crops are most important.

Good Pasture is Essential for Irrigation The limiting factor on all lands in the dry areas in Canterbury is moisture, but on the lighter plains lands soil fertility is also a limiting factor. When one or both these factors are operating particular pasture plants found growing on these areas are such as can accommodate themselves to the limited food or water supply. This is why we find in many Canterbury pastures grasses, such as dry land brown top, danthonia, and many weeds —capable of surviving where good grasses or clovers have died out. Plants surviving under such conditions are known as low-production types; these types are probably useful when it is impossible to remove the limiting factors, as they produce some feed and give some grazing on lands which, but for their persistence, would be unproductive. On the other hand, when it is possible to fertilise or water pastures composed of low-production types, very little response is obtained, as these low-production plants are incapable of being stimulated to higher production, which can only be obtained when the right type of plant is growing on the land. A further consideration, therefore, in preparing for irrigation, is the clearing of the land to be irrigated of low-production plants and replacing them with plants of the right tyne. The cost of eradicating low-production plants will have to be calculated when preparing an estimate of the cost. The nnnortance of irrigating a really good rjr.stura rather than a poor one cnnno+ ho over-stressed. It may mean the difference between success and failure of an irrigation scheme. Trumble and ' Davis (Bulletin RO, Commonwealth Council for Scientific nnd_ Industrial Research) give tTie following records of herbage production over a two-year period from various

At Seafield. near Ashburton, irrigated brown top carried one dry sheep an acre, while irrigated pasture of perennial ryegrass, cocksfoot, wild white clover, and red clover carried just under five dry sheep an acre for the year. Withtout good pasture irrigation at Seafield would bave been a failure. Under irrigation a good pasture in Canterbury should provide lambing green feed, feed for fattening lambs on the mothers, for fattening lambs after weaning, for fattening surplus owes, for fattening wethers, and for flushing ewes in the autumn and before lambing.

Preparation of Land The establishment of good permanent pasture is necessary, and need not be a costly matter since most of the cultivation and twitch cleaning would occur normally in the annual programme of growing rape, turnips, or temporary grass. Land cropped with roots for two years in succession 'can be made reasonably free from twitches and weeds, the crops paying in large part for the cultivation. The main cost of preparation for pasture irrigation is then the cost of building the head races and grading lands for border dyke flooding or of building head races and ploughing ditches for border ditch flooding. For border ditching the ditches may be ploughed on good established pasture. For border dyking the land must be levelled and prepared before sowing. As soon as moisture ceases to be the limiting factor in plant growth, other factors become dominant. For Canterbury soils under irrigation, fertility is a limiting factor and can be raised to, or maintained at, a standard which is most economical only by the application of fertilisers. Observations at the Seafield irrigation farm indicate that superphosphate and carbonate of lime should be applied annually. The amounts to be applied will depend upon circumstances. Without suitable fertilisers irrigation there would be a very mediocre success and perhaps a failure.

Conclusion It has been shown that the intending irrigator must be certain that the sou is suitable, the ditches properly arranged, the pastures well established, and the proper manures applied. Even then there are many opportunities for failure. . There is the importance of applying water at the best times and in the best quantities, according to the varying conditions of weather, soil, and crop. How much water is being applied? How should the races be operated to give the least waste of water and the least labour cost? What is the best manner of utilising both pastures and hay? How will the irrigated section fit in with the rest of the farm or must the rest of the farm be altered to fit in with the irrigated section? Is there any change of policy required in respect to the type of sheep stocked, or in respect of the growing of clovers for seed, or in the avoidance of growing root crops? Much of this information has yet to be obtained. If farmers starting irrigation have to learn all these things for themselves there will be many failures and disappointments, and there will be much loss of time in the successful development of irrigation.

Demonstration and experimental farms are necessary on the main soil types in various parts of Canterbury, so that information may be obtained quickly and thoroughly on these aspects of farm management and irrigating technique. At this stage it is highly desirable to test on these farms whether or not irrigation will pay before large sums are spent introducing schemes in Canterbury. It is appropriate to quote from a paper delivered in Christchurch to the second grassland conference in August, 1933, by Mr R. B. Tennent, director of the Fields Division (then fields superintendent for Otago) of the New Zealand Department of Agriculture. The statement reads: "One of the most regrettable features of our irrigation schemes in the Dominion is the fact that although hundreds of thousands of pounds have been and are still being spent in the erection of magnificent irrigation works, practically nothing is being done to determine the best manner of utilising the water when it is made available to the land."

Copies of tins bulletin may be obtained from the secretary, Canterbury Chamber of Commerce, P.O. Box 137, Christchurch.

irrigated pastures grown on claimed swamp land. Yield acre Typo of Sown Over two pasture. An acre. years. • Brownlop . . liGlb 126 rich reof hay an (cwt.) Annually. 03 (Vrt. perennial 113 ; 72 Cert, perennial ryegrass . . 201b Akaroa coeksCert. while clover . . 21b Red clover . . 21b 212 121 Mil)