IRRIGATION PRACTICES

New Zealand Journal of Agriculture, Volume 71, Issue 1, 16 July 1945, Page 23

IRRIGATION PRACTICES

'HE irrigation of land is as 1 old as history, and was practised by the ancient civilisations of the world in Asia Minor and China. There were well-defined irrigation systems in South America in the lands of the Aztecs and Incas when their country was invaded by the Spaniards, and apparently they had been in operation for many years before that.

By

G. G. CALDER,

Instructor in Agriculture, Ashburton.

★ 4 ’ODAY there are few countries of TODAY there are few countries the world where irrigation is not

practised in some form or other. The most extensive irrigation areas are in tropical and sub-tropical districts, usually situated inland from the coast, where there are definite periods of low rainfall, as in most of the riceproducing areas of the world, where large amounts of water are required to bring the crop to maturity. Also, hot desert areas where water has been made available have become veritable gardens, such as in Mexico, Southern California, and parts of Australia, where orchards, pastures, and truck crops are irrigated. Although the main purpose of irrigation is to supply moisture to the land, this is not always so, and in a number of cases the value of irrigation is not due to the water but to the silt or plant foods carried in the irrigation water and deposited on the land. This is the case with irrigated areas in Scotland, England, and Europe. Indeed, on one of the Italian irrigation schemes the land has been built up many feet by the deposits of silt left after irrigation. In the case of the Egyptian Nile and the Chinese Yellow River, the combination of both moisture and silt derived from the irrigation water of these rivers has maintained the. fertility of these irrigated lands for cen-

turies without the use of chemical fertilisers. Start in Central Otago Irrigation in New Zealand commenced in Central Otago in the goldmining days. With a rainfall varying from 9.5 to 15in. a year and hot summer temperatures, the miner found it necessary to use some of his mining water to produce a garden. He then extended it to provide grazing and hay paddocks to keep a cow, until today there are 70,000 acres of established irrigated landmainly pasture land with lucerne and red clover for haying, and a small area in drill crops of potatoes, mangolds, or carrots. In sheltered areas there are highproducing irrigated orchards. During the years of development of irrigation in Central Otago the irrigator, to make a living on the relatively small holdings of the irrigation farmer, has had to learn by experience the best methods of management of pastures and crops under irrigation, and then the best methods of utilisation of the crops produced. Before irrigation the land was arid and sparsely covered with native grasses, with a carrying capacity of one sheep to many acres. Today this land is carrying the best pastures in Otago, if not in New Zealand, and

in some cases grazes up to 8 ewes and their lambs per acre, or a milking cow and a dry beast to 2 acres, as well as providing sufficient hay for winter feeding for 5 months of the year. Farmers’ Scope Limited The present position of Mid-Canter-bury farmers, especially on the lighter land, is that a certain type of farming is “forced” on them by weather conditions and periodic droughts requiring them to cash in on their fertility. This'• is a costly system, involving renewing of expensive pasture and heavy wear and tear on implements. Under irrigation, with security against droughts, these farmers could determine their own system of farming. Irrigation opens up new and profitable avenues for fanning, not only from the individual but also from a national point of view, in that farms which today, without irrigation, are little more than or barely economical holdings, will, under irrigation, be capable of subdivision into two or three farms, each capable of , returning a reasonable and decent standard • of living to the occupier. Under normal climatic conditions in Mid-Canterbury the drying out of the

land and the burning up of the grass by the nor’-west winds during December, January, and February, limit the activities of the' farmer on the light plains land to sheep-farming and grain growing. The stock-carrying capacity of the farm is restricted to the carrying capacity of the dried-up pastures during these three months. Bottleneck Eliminated This bottleneck to stock-carrying capacity during December, January, and February, will be eliminated under irrigation by the production of vigorous-growing pasture. ■■ The growing of large areas of rape, which itself can be a doubtful crop, may also be avoided, as the lambs will probably fatten on the irrigated grass paddocks. By the, saving of hay and ensilage supplementary crops of turnips and greenfeed can be considerably reduced or cut out. The growing of grain on the light land is not done so much from choice as from necessity. With worn-out pastures requiring renewal every few years a grain crop is taken to pay the costs of cultivation and regrassing of the area, and, incidentally, to cash in on what fertility the pasture has built up. Under grassland irrigation, with the consequent heavy stocking required to utilise the feed produced, the fertility of the land will be built up to the extent that a good grain crop can be taken without having an exhaustive effect on the land. Without irrigation, paddocks ploughed up for wheat are those carrying inferior turf and on which the pasture has practically run outin other words, land in which there is a poor supply of humus. On an irrigated farm wheat will' be grown on lea paddocks on which a solid turf has been established. The incorporation

of this turf in the soil by ploughing and subsequent workings will produce an excellent tilth with a good humus content, humus being a valuable soil constituent for crops, especially under the dry conditions . of MidCanterbury. Irrigation will increase grassland farming by producing truly permanent pastures; it will in- , crease the sheep and lamb population, reduce or eliminate costs of producing rape, turnip, and greenfeed crops, and will not only halt the depletion of fertility of light land by wheat-growing, but will actually build it up to produce heavier wheat yields. Methods of Irrigation There are a number of methods of irrigating land, of which the following are the principal:— 1. Border Dike. 2. Border Ditch. 3. Contour. 4. Wild Flooding. 5. Furrow. 6. Basin-check.

7. Overhead. 8. -irrigation. Modifications and combinations of the above methods are also used. 1. The Border Dike method is the most efficient in utilisation of water and saving of labour. It is used where the land is comparatively flat and the fall does not exceed about Ift. per chain. “Dikes” or “ridges” are built up on the field more or less along the fall of the land and the land levelled between them. The dikes are approximately half a chain apart and from 5 to 10 chains in length, and are used to confine the flow of water between each pair of dikes or levees (a term used freely in America). The actual length and width of the borders depend on the volume of water available for irrigation. In Central Otago the borders are half a chain or less in width and usually about 1 5 chains in length. The volume of water used is 4 cusecs or less. In the Ashburton district, with 8 cusecs available, borders are 40ft. in width and ' 10 chains in length. The outlet gates are constructed at the top of each

border on the bank of the farmer’s head-race. By damming this headrace, usually with a canvas sheet, the water-level is raised and water flows out of the outlet gates on to the borders. "If desired, a number of borders can be irrigated simultaneously. This, of course, means dividing up the available water. Some Central Otago orchards are irrigated by this method, the trees growing on the line of the border. Preparing land for the border dike system requires experience. Central Otago farmers have improvised their own machinery and have become expert in its use. The land is ploughed and worked, and then the high spots are levelled and the hollows are filled in with the scoop. The dikes or levees are set up by using a levelling implement which is driven across the line of the borders, levelling' the land as it goes. When it comes into line with a dike it dumps the load of soil it has ed and travels on to the line of the next dike, where another load of soil is dumped, and so on, backwards and forwards across the area, until all the dikes, are built up. A ridger is then run along each dike to straighten it up. The leveller is made in the form of the capital letter “H,” suitably

stayed. The cross-piece is of iron plate and projects about Jin. below the level of the parallel runners. The iron cross-piece forces soil ahead of it, dropping it in hollows, and when on the line of a dike the iron piece is raised by means of the long lever and the soil is dropped. The crosspiece is then dropped, and raised again on reaching the next dike. In Mid-Canterbury the Works Department is making a good job of bordering for farmers at about £3 to £4 per acre, using powerful road graders. One machine makes the borders . while the other levels the land between the borders. The machines, also make the head-races, this work being included in the above charge. 2. The Border Ditch method is used where the fall of the land is over Ift. per chain, and can be constructed direct on to pasture land without previously working and levelling it. Instead of dikes being constructed as in the border dike method, races or ditches are made down the fall of the land from the head-race. From these races the water is distributed on to the land. 3. The Contour method is carried out on land with fair to considerable

fall, and is probably the most common system in use in Central Otago on pastures, lucerne, etc. The irrigation race follows the contour of the land. It is given a fall of 3 to 4in. per chain, and when dammed with a canvas sheet is allowed to spill over in small volumes from a number of points and trickle down some chains to the next contour race. 4. Wild Flooding is not as haphazard as its name suggests. The water is discharged from the headrace at a high spot, and the irrigator directs it with a shovel to different parts of the area through small channels and stop-banks until the whole area - is covered. With subsequent irrigations the water travels along the line into which it was previously directed, although it is usually necessary for the irrigator to keep his eye on it and do' a little more re-directing. All the above methods are used for pastures and permanent hay crops. Annual . crops such as wheat, oats, barley, and peas do not generally lend themselves to irrigation under New Zealand conditions. This is due principally to the fact that with springsown crops the land is not sufficiently consolidated to carry irrigation water on the surface. It seeps through the field to the depth of the plough fur-

row, resulting in a heavy application of water and a consequent bogging of the land. With autumn-sown crops the land consolidates sufficiently during the winter and early spring, but with the earlier harvesting of autumnsown crops irrigation water as a rule is not required. If it is given, it frequently induces second growth in barley, oats, and peas. Field crops have been, and are, successfully irrigated in Central Otago from contour races where land has a fairly good fall, but this is the exception more than the rule. 5. Furrow method. Annual crops are, however, grown well under the furrow system of irrigation. They are grown in drills and the water is run down between them. Potatoes, mangolds, swedes, carrots, and maize for greenfeed are regularly grown in this way in Central Otago, and this method will undoubtedly have a place in Mid-Canterbury. In the preceding irrigation methods irrigation water flows over the land and soaks down through it. In furrow irrigation the water flows along between the drills and travels sideways and upwards as well as downwards in the soil. In the actual furrow one quickly gets the fourth stage of wetness described later to at least the depth of the ploughed soil. Then, by capillary action, the water moves sideways into the drill. Small volumes of water are used on 'a number of drills simultaneously. In a dry spring the land frequently dries out during the working and erection of the drills. The seed is sown and the area is irrigated to provide moisture to germinate it. As soon as possible after irrigation, when the furrows will carry a horse, they are scuffled with a horse hoe to mulch the surface, thus checking evaporation. Furrow irrigation can be used on land with a gentle fall of a few inches per chain when the furrows are made directly up and down the fall of the land, or can be used on relatively steep land with a fall of some feet per chain by continuing the drills or furrows, not up and down the fall of the land, but at a gentle slope across the fall of the land. 6. Basin-check method. This method is apparently used more extensively overseas in orchards and in rice production. The writer has seen this method used on only one orchard in Central Otago, where it was quite satisfactory. A check is formed round a tree or a number of trees and the basin thus formed is filled with water. 7. Overhead. This is a system of overhead sprays, and an excellent one for irrigation. The writer is aware of only three systems of this type in operation in Central Otago. The limiting factors to its use are the cost of piping the area to be irrigated and

the need of a good pressure to force the water through the pipes and spray nozzles. This method is apparently extensively used overseas on orchards and for truck crops. . , 8. Sub-irrigation. By this method the water-table is raised to a little below the roots of the plants, or water is • forced from a series of openings in a system of pipes placed . under-' ground; the water then rises to the surface by capillary attraction. IRRIGATION AND SOIL MOISTURE. The amounts of irrigation water to use and the frequency of application vary with each soil type and also with the subsoil underlying it. Some of the first questions an irrigator asks himself are, “How often will I irrigate, what volume of water will I use, and how long will I let it run?” These questions are ’ naturally bound up with the type of soil and the fall of the land. The type of land to be irrigated is a major factor in the amount of water the land will absorb and hold. Drainage goes hand in hand with irrigation. Without drainage irrigation would be 1 rather a difficult business. An open, gravelly subsoil is probably the ideal type to allow the escape of surplus water, although over-irrigation must be guarded against, or many of the valuable soil constituents may be leached out and lost in the drainage. A subsoil of a hard-pan nature is the most difficult type of land to irrigate, as great care is required to apply only the correct amount of water that the soil will hold; otherwise water-logging of < the land will occur. Between these two types there is a wide range of subsoils, and once a farmer has had practical experience of any one type he then has an idea of what to expect when he encounters another type. A coarse sandy soil has a poor water-holding capacity and requires frequent irrigations of small amounts of water, say 2 to 3in. of water every 10 days or fortnight, as compared with a good clay or silt loam soil that will take 4 to 6in. every 3 to 4 weeks. The incorporation of humus

in sandy soils will build up the waterholding capacity of this type of soil considerably. This is seen in most of the Central Otago irrigated pasture areas, which are mainly ( of a sandy nature. When first sown down they require frequent irrigations, but now, with the heavy stocking, a good humus content and a thick turf have been built up. The humus and turf act partly as a sponge to hold the moisture and partly as a mulch to check evaporation. Water Content of Soil Capillary water is the film of water surrounding each particle of soil and actually combines soil particles together to form crumbs of soil. These crumbs are held' together by the surface tension of the water. Capillary water moves slowly to right and left or to the surface to even up the supply as it is drawn off by the root hairs of plants. Probably the greatest movement is towards the surface to replace the moisture lost by evaporation. Consequently, anything that can be done to form a mulch on the soil surface to check evaporation will conserve moisture. As the capillary moisture of the topsoil is used, more is drawn from . the subsoil. The water-holding capacity of the subsoil as well as the topsoil determines the length of time before another irrigation is necessary. Excess gravitational water saturates and percolates down through the soil between the soil crumbs and is usually lost in drainage or assists in forming the water-table found at varying depths below the soil surface. i When the water-table is deep down there is no ■ return of water by capillarity. If the water-table is near the surface, but below the limit of plant roots, there is a return of water by capillarity. If the water-table is very near or at the surface, it will seriously affect any crop through water-logging of the soil. The amounts of water to use vary with the type of soil. A light or gravelly soil requires small and frequent irrigations to avoid too great

a loss through drainage; a : loamy soil will hold larger amounts of water for longer periods; a heavy clay type of soil has the best water-holding capa city. Frequently these clay soils have not a free drainage and care must be exercised not to , over-irrigate them. Apart from drainage and evaporation, there is a steady loss of water through transpiration of plants. Moisture is always travelling up from the roots through the stems and passing out through the leaves. For every lib. of dry matter produced some hundreds of pounds of water are used by the plant. Thus a steady supply of water from the soil through the plants is required to produce maximum yields. Any check- in the water supply or a shortage of water will

produce wilting or a check to plant growth, which will be reflected in a lowering of its production. An excess of water for any length of time will be equally detrimental to the plant in excluding air from the soil, air being necessary for root development. Apart from the actual soil itself, bacterial content of the soil is a very important feature in the growth of healthy plants. A healthy bacterial growth plays a big part in soil fertility, its main function being the breaking down of humus into nitrogenous compounds. These bacteria live and thrive best under moist conditions in the presence of air. Consequently, if the land is too dry or too wet, the activity of the bacteria is slowed down or stopped, and under water-logged conditions undesirable bacteria begin to become active. Therefore, the irrigator must aim at keeping the land moist or wet, but not to the extent of excluding air from the soil for any prolonged period. There are four distinct stages of wetness of the soil, with, of course, all the intermediate stages — 1. Dry soil. This stage is below wilting point of plants; the land is too dry and hard to plough, or, if the plough can be held in the ground, the furrow turned consists of hard lumps of soil which require rain before they can be worked down. 2. The second stage is when the land is in ideal condition for ploughing and is above the wilting point of plants. The soil is moist and the mouldboard breaks up the furrow into a nice crumbly condition. That pleasant smell of Mother Earth is present, and the land requires very little working down to be ready for sowing. , . ■ 3. The third stage is when the land is just too wet for ploughing. The suction of the water makes the ploughing hard pulling and the mouldboard puts a shine or polish on the furrow, but the crumb condition of the soil is still intact. 4. The fourth stage is the . waterlogged or bogged condition of the land through over-irrigating or flooding. The soil crumbs break down into their finest particles, resulting in mud,

which, on drying out, becomes very hard and cracks. Actually, the crumbly physical condition of the land is destroyed, and air is excluded from the soil.

The aim of every irrigator should be to keep the moisture content of his land between stages 2 and 3. A few hours after irrigating the land should be at stage 3, and when it returns to stage 2 one should prepare, to irrigate again, always avoiding stages 1 and 4. In this way the moisture and air content of the soil is maintained in the best condition for the activity of the beneficial bacteria, a steady supply of soil t moisture is maintained for transpiration through the plant, the physical condition of the land is held at its best while under irrigation, and over-irrigation with its attendant troubles is avoided. Estimating Applications As the irrigator is supplied with a definite volume of water measured in terms, of “cusecs” (1 cubic foot of water flowing every second) he should estimate the amount of water to be applied to his land in inches per acre, and at each irrigation give the land say, 2, 3, 4, or 6 inches of water per acre, whichever actual experience has shown that the land can absorb. “Acre inches” is the term used for inches per acre. The following table will be of use in indicating the amounts of acre inches of water obtained when using different volumes for different times: —

Acre. TIME REQUIRED TO IRRIGATE AN ACRE USING:— | .1 2 3 4 5 6 7 8 Inches. i cusec. cusecs. cusecs. cusecs. cusecs. cusecs. cusecs. cusecs. < hrs. hrs. mins. mins. mins. mins. mins. mins. 1 | 1 1 20 15 12 10 81 71 2 | 2 1 40 -30 24 20 17 15 3 | 3 11 60 45 36 30 251 221 4 | 4 2 80 60 48 40 34 30 5 I 5 21 100 . 75 66 50 421 371 6 | 6 3 120 90 72 60 51 45 7 | 7 31 140 105 84 70 . 591 521 8 ' 8 4 160 120 96 80 68 , 60 i 1 day cusec

Coarse Medium Fine Sandy Fine Silt Silty sand sand sand loam sandy loam clay Jin. fin. lin. lfin. loam Ijin. loam per per per per l|in. per 2in. foot foot foot foot per foot • per > foot foot Useable water capacity of different types of soil.

lhe above table nas been worked out assuming that 1 day cusec = 24 acre inches, which for practical purposes is quite satisfactory, and reduces the above equation to the simple unit value of 1 cusec for 1 hour 1 acre inch. Thus, if one wants 4 acre inches of water, it can be obtained by using 1 cusec for 4 hours. 2 cusecs for 2 hours, 4 cusecs for 1 hour, or 8 cusecs for 30 minutes, and so on. What volume of water to use will depend on the porosity of the soil, the fall of the land, and the length of the border. After experience of irrigation one will arrive at a satisfactory time or volume with

which to work. This sounds rather a complicated business, but actually it is not. At each irrigation some allowance should be made for loss by evaporation, especially when applying the smaller amounts of acre inches. When using larger amounts loss by drainage of gravitational water should be watched for. Loss by surface drainage when using large volumes is probable where there is a good fall to the land. A proportion of the water may run

[After “Highway Magazine.” off the area before soaking in. This is more likely to happen when the land is dry. In this case a smaller volume of water is used per border and run for a longer period.

Duty of water is the term used in defining the total amount of irrigation water used on the land to produce successfully any given crop. The duty of water is said to be high or low, depending on the amount - of ’ water used. On a given soil type and' crop a high duty of water is obtained! under careful and efficient management, or a low duty of water under careless and wasteful management where the consumption of water has, increased. Since so many factors come intoplay when determining duty of water, it is impossible to lay down any hard-and-fast rules regarding it. Apart from the different requirements of different crops, there are large varia-

tions in the water-holding capacity of the soils and subsoils themselves. It has been stated earlier that soils composed of fine particles, i.e., clays and silts, can absorb and hold a definitely greater volume of water than soils composed of coarser particles such as fine . gravels and sand. Consequently, the latter type ' requires more frequent but smaller irrigations than the former. Further, the depth of soil, the presence of a clay subsoil, or an open gravel subsoil, all necessitate using different amounts of water when irrigating to obtain a high duty of water. With a good depth of soil a larger volume of water can be used and the surface soil saturated; there is a downward movement of water which, however, rises again by capillarity after the moisture near the surface has been used up. Where a pan or hard clay subsoil is present smaller quantities of water must be used so as not to bring about > water-logged conditions. Where a gravel subsoil, is present, with free drainage, there is no return of excess moisture by capillarity. Consequently, to get a high duty of water here only sufficient irrigation water should be used to meet the current requirements of the crop or the water-holding capacity of the soil, without penetrating into the shingly subsoil. Evaporation from a wet soil surface is much faster than from a free water surface. The average loss from a free water surface at Alexandra for the three-yearly period 1933-35 was 31.7 in. per annum. Since a loss such as this is often as much as and sometimes more than the irrigation water applied to the land, some measure must be taken to conserve the irrigation water. A grass, clover, or lucerne crop supplies a natural cover to stop excessive evaporation, but when a crop such as potatoes, mangolds, carrots, or maize is grown in drills the soil requires mulching. This mulching or loosening up of the surface can be done with a cultivator or horse hoe; it retards the capillary movement of the moisture to the surface and to a large extent checks evaporation. It was found by Tennent and Marks, working at Galloway, that where land had not received cultivation till eight days after irrigating the water lost by evaporation was in the vicinity of 2in. On adjacent land where surface cultivation had been carried out after irrigation the loss amounted in eight days to half an inch. IRRIGATION PRACTICE IN MID-CANTERBURY. For the first year or two the Canterbury irrigator may have difficulty in irrigating frequently enough without overdoing it to produce a steady growth of grass. The efficient util-

isation of the feed produced may also be a problem, as he will not be dependent on the irrigated area alone for a living. As the border dike method of irrigation is the most efficient system where the land is suitable, and, incidentally, the most costly system to lay out, it behoves the farmer to take some care in the sowing down, management, and utilisation of the area. It can be a truly permanent pasture, and should build up the fertility of the field over the years. After a farmer has decided on the area to be bordered it should be ploughed and worked up. If twitch is present, extra workings of the paddock will be well repaid to clean it up. After bordering it should occasionally be worked up to keep down weeds, at the same time consolidating the land to produce the firm seed-bed so desirable for grass and clover seed. The dikes may appear rather high on completion of the layout of the field, but they should not be worked down too low, as they will subside naturally and also wear down with sheep over the course of a few years. It is most probable that the land between the dikes will build up over the years, and the dikes that are high enough today may be too low in five years time. Some dikes have been rolled or consolidated by running the big, wheel of the tractor down the dike, at the same time harrowing with a tine-harrow leaf on each side of the dike to smooth it down, thus facilitating the crossing of the dikes by implements. Another method is

to roll the paddock across the dikes and then harrow along them. Whatever method is adopted, a final rolling across the dikes after sowing will put a good finish on them, bury any stones that may be present, and level off the land for mowing at any future date. The dikes should be left as high as possible, but not high enough to prevent implements such as haymaking machinery passing over them. Time to Sow The time to sow is about the end of February or, at the latest, early March. The main objection to sowing in the spring, apart from weed competition, is that although good germination is obtained, once the hot dry weather commences the seedling plants must suffer to some extent. Under steady north-west wind conditions many seedling plants will die, as it is not good practice to irrigate before the plants are fully developed if it can be s avoided. If irrigation is carried out a month or two after sowing, the land, not being sufficiently consolidated to carry water, may bog to the depth of the ploughing, lose its physical condition, dry out hard, exclude air, and crack. Under these conditions it would be hard going for seedling plants. Even if the land has consolidated reasonably well, root development will not be as good when irrigation is done early and the plants obtain their moisture requirements easily, as when they are allowed to develop without irrigation. If the young sward is given say 8 months or more to develop, as is the case with autumn sowing, before irrigating, the ground has had time to

consolidate and carry irrigation water, Also, the plants have had time to produce a well-developed rooting systern, which not only helps to hold the physical condition of the soil, but is better able to utilise the irrigation water than are plants with a lessdeveloped rooting system. L Pasture Mixture Where the pasture is intended for grazing or haying purposes only the following mixture is recommended as a guide for sowing on irrigated land: — Certified Permanent Pasture ' Certified Permanent Pasture 201 b. rvnoracQ 201 b Timothv " \ : 4 51b rSSS doestail " 21b u-resiea uogsiaii .. .. Certified white clover .. 2-31 b. Certified Perm Past Mont cerunea rerm. vast. ivionu red clover . . .. l-21b. Timothy has been included in the above mixture, as experience has shown that it is an excellent grass under irrigation. It is very palatable, produces a large bulk of feed for both grazing and haying, and, apart from being specially suited for damp conditions, has probably the highest feeding value of any of the grasses. It is a true perennial. ' One or perhaps two pounds of dogstail is quite useful in the mixture. It keeps the sward' dense by filling up weak spots in it. It is particularly

valuable in being an out-of-season grass, as it commences growth in the. autumn and supplies some greenfeed in winter, while in late winter and early spring it is at its best before the other species have really commenced to come away. White clover is shown as 2-31 b. per acre. If the land to, be sown contains a fair proportion of white clover,. 21b. of the certified type will probably be sufficient. Although alsike clover is not included in the mixture, it is another clover that can be sown with advantage under irrigation, and, if advantage under lib. per acre is well obtainable pure, 11b. per acre is well worth including. Some lines of white clover seed frequently have alsike in +hprn „ n • n ritv o b „ pan them as an impurity buck lines can tie sown with confidence under irnnation m. ‘ . 011 j The 1 to 21b. of Montgomery red clover is also added to the mixture partly for hay purposes, and as a palatable high-producing clover it adds variety to the mixture. When sowing down a permanent pasture it should be given every chance to establish quickly with the least amount of • competition from other plants. It is therefore a mistake to sow a few ounces of turnip seed per acre or a light seeding of rape. This appears to be a common practice, and under non-irrigated con-

ditions in Canterbury this may be a sound idea to obtain a catch crop when the permanent pasture is going to open up a little in any case next summer. With an irrigated pasture a catch crop should not be necessary, and, in fact, can be harmful if the catch crop is a reasonably good one. The cac crop will probably be grazed irrespective of the condition of the young grass. If the autumn is wet ’ some , Ppaching of the land mayoccur, apart from the smothering effect that a healthy rape or turnip plant must have On the pasture plants m immediate vicinity. Since the y iniuieuiam vicinity. °nice me turnip shells cannot be eaten, it takes ™ ai W months for them to rot and for the space occupied by them to be m con d it i O n for anything to grow on a condition lor anytning to grow on. Eventually there is left a number of small bare spaces for weeds, particujariy Scotch thistle, to start in. Harrowing Irrigated Pastures Harrowing irrigated 1 astures With the heavy concentration of stock on irrigated pasture it is desirable, in fact necessary, to harrow the area periodically with light tine or chain harrows to spread animal droppings evenly over the field. This is best carried out after the stock have been shifted and before an irrigation is due. If this spreading is not carried out, it will result in tufts

of rank, unpalatable growth. Not only is the growth itself wasted, but also the manurial value of the droppings producing it. v After some years, when a solid turf has been built up, the paddock may tend to become sod-bound, when the use of a heavier or more drastic type of harrow will be required to penetrate and tear open the turf. This has an invigorating and rejuvenating effect. Pasture Management To obtain the maximum production and feeding value from the field growth should always be kept reasonably short. The growth can usually be kept , down by stocking until the seed heads begin to make their appearance, when it may be necessary to top the paddock with a mower. For hygienic purposes a short pasture into which the sunlight penetrates is of considerable value in controlling internal parasites of sheep and also foot-rot; it also has a higher feeding value and productive capacity than long or rank growth. For the production of grass growth frequent irrigation with maximum amounts of water is required to produce the maximum bulk of feed, but for seed production a minimum amount of water is required—no mere than is necessary to keep the plants healthy. Under these conditions a quick and abundant flowering of the clovers is obtained, with a good seed yield. If more water is given, a profuse growth of stems and foliage is produced, while flowering is sparse and continues throughout the season. A large bulk of material is produced, and the seed crop is disappointing. In growing for seed the sparing amount of water required even in a dry season and the fact that, practically no water at all is needed in a number of seasons would indicate the advisability of using non-irrigated land for seed production, while pasture production can be concentrated on the bordered paddocks, with fre-

quent irrigations. As the returns from grass and clover seed are rather attractive, a number of bordered areas could be sown down for this purpose and irrigation used only as a premium to guard against dry weather conditions burning up the crop. A seeding 'of 251 b. perennial ryegrass, 31b. white clover, and 21b. dogstail will give a ryegrass crop the first season, with some white clover, and a white clover crop with some ryegrass during subsequent seasons. The addition of 21b. dogstail will be of value for grazing purposes during the period that the area is not closed for seed. For Montgomery red . clover seed production a seeding of 10 to 201 b. certified perennial ryegrass and 41b. Montgomery red clover should be satisfactory. The area can be grazed till towards the end of November, when it is closed. up. If patches of rank growth are present after grazing, they should be removed with a mower to allow an even growth to come away over the whole area. If the area is not grazed, a light crop of hay can be taken towards the end of November, and the paddock then closed up. At the time of closing up the area a quick flush of water will give the clover a good start. Probably no more irrigation water. will be required, unless the season is a particularly dry one, as the deep-rooting habit of the Montgomery red clover will carry the crop on to a successful seed-setting stage. Montgomery red clover in particular, under good growing conditions as supplied by irrigation, produces a large bulk of material which is slow in flowering, and is inclined to lodge and kill itself out if lodged for any length of time. Lucerne Under Irrigation The increased stock-carrying capacity obtained from the utilisation of an irrigated area on the farm necessitates the provision of increased winter feed, which can probably be best met by devoting part of the irri-

gated area to hay production. For this purpose lucerne probably takes pride of place. It will do well on practically all irrigated land; that is, land that has at least fair drainage. Where there is a water-table near the surface it must be . some feet lower for lucerne than would be necessary for pasture. The preparation of the seed-bed is similar to that required for grass or clover. Sow seed in the autumn towards the end of February on a firm seed-bed, which, unless it has been recently limed, should have at least i to 1 ton of lime per acre applied to it. About 141 b. of inoculated seed per acre is a reasonable seeding, although up to 181 b. per acre is sown by some farmers. If the seed-bed has been well prepared and no seed buried deeper than jin. or so, less than 141 b. will give a good stand. The seed can be either drilled in 7in. rows or broadcast. With broadcasting there is not' the danger of burying the seed too deeply and the seed is distributed over the field more evenly. However, there are some excellent stands of drilled lucerne, and under dry conditions a better strike will probably be obtained by drilling the seed. The Marlborough strain or any seed produced in New Zealand is preferred to imported seed, although most of the lines from South Africa and Australia, particularly the Hunter River strain, have proved quite satisfactory. Some of the Canadian lines are later than the above in coming away in the spring. The first irrigation will probably be in the early summer following sowing. The first cut will be taken when either 5 to 10 per cent, of the crop is in flower, when the bottom leaves of the crop are commencing to turn yellow in colour, or at the first sign of new growth commencing to come away from the crowns of the plants. If the land is getting dry towards the time of cutting, irrigate the area and harvest the crop as soon as the

land is sufficiently firm to carry harvesting implements. This ensures a quick new growth immediately the crop has been removed. If the land is reasonably moist, the irrigation is better delayed until the crop is removed. Under good drying conditions the crop can be cut one day, teddered the next, and baled the following day, although this is not always possible with the first cut. Many Central Otago farmers make their first cut into ensilage. The ensilage is valuable for feeding in the late winter or early spring just before lambing or calving commences. Probably three good cuts and a fourth lighter one can be expected under Mid-Canterbury conditions. Montgomery red clover is coming into favour with some farmers for hay production, mainly due to the fact that it is a more versatile crop than lucerne. The time of cutting can be more varied than with lucerne without deterioration of the crop, and the clover can be utilised for grazing or for seed production purposes much more easily than can lucerne. However, with an area of lucerne one will always have hay, which is the main purpose in growing it, while with Montgomery red clover, apart from the point that it takes more drying out than lucerne and may kill

itself out by lodging, one can become short of hay by using the crop for some other purpose. The above has been written in the hope that it will be of use to those Mid-Canterbury farmers who are this year commencing irrigation farming for the first time, and thus save them from mistakes which are possible through lack of knowledge or experience. This statement is not considered to be anything like a complete work on irrigation, nor are the: principles outlined expected to be consistently exact when applied to Mid-Canterbury conditions, as these have yet to be learned by experience and study. However, in conjunction with , the farmer’s local knowledge of his own farm' and his own conditions, it is expected that the foregoing will aid him for the first season or two by explaining some of the basic principles of irrigation practice. Ultimately his own. experience and ready adaptability will give him confidence to go ahead and exploit to the full the possibilities of irrigation. Officers of the Fields Division of the Department of Agriculture at Ashburton may be consulted on irrigation problems.