IRRIGATION AND ITS PRACTICE.

New Zealand Journal of Agriculture, Volume XXIX, Issue 6, 20 December 1924, Page 381

IRRIGATION AND ITS PRACTICE.

( Continued.)

VI. LUCERNE-GROWING UNDER IRRIGATION.

R. B. TENNENT, N.D.D.,

Instructor' in Agriculture, Dunedin, and J. R.

MARKS, A.M.Inst.G.E., M.N.Z.Soc.C.E., District Engineer, Public Works Department, Dunedin. , ■ CENTRAL OTAGO AND LUCERNE. On account of its adaptability to the mica-schist, soils' of Central Otago lucerne has become the main irrigated crop in that district. Under irrigation, yields of 5 tons ' of hay per acre for the season are regularly obtained, and no great difficulty is experienced in establishing the crop. When its permanency is taken into consideration —- some stands even now growing luxuriantly and yielding heavily after fifteen years' occupation of the same piece of ground — the cost of establishment must be considered quite moderate. A satisfactory feature of lucerne-growing in that semi-arid region is the fact that haymaking operations can be carried out expeditiously and with great certainty of favourable weather conditions being maintained during the process. ■ The importance of lucerne to the Central Otago irrigation well warrants a short account of the procedure most suited to growing the crop in that region. No attempt at a detailed description of the history of the .crop and the numerous modifications of the general method here described will be attempted. Each farmer must realize that certain modifications will be required to suit his particular conditions,'' for even in such a comparatively limited area as is embraced by this series of articles there exist considerable ’ variations in regard to soil and climatic factors. SOILS ADAPTED FOR LUCERNE. ■ . As has already been indicated, the bulk of Central Otago soils are well adapted for growing lucerne. Particularly is this so in the case of the deep alluvial deposits of mica-schist, which, overlying gravelly subsoils, make soil conditions ideal for this crop. The lighter admixtures of gravel and schist soils which exist in fairly large areas are also well adapted for the growth of lucerne, provided more frequent irrigations are given during the growing-period, and care taken to obtain- suitably moist conditions for fits establishment. To the uninitiated these lighter types of gravelly soils would appear to be hungry and unproductive, yet, given cultivation, moisture, and seed, striking results will in almost every case be obtained, the land previously covered with weed (Raoulia) being quickly transformed into luxuriant fields of lucerne. ' .

Certain soils in Central Otago have a subsoil of a heavy clay nature, where free natural drainage does not exist to the degree required by lucerne. Such soils, unless ’ drained, cannot be expected to grow good lucerne crops, the common experience of farmers being the failure of the crop after a short period. It is a recognized fact

that lucerne requires much more complete drainage of the soil than do other field-crops. Fortunately, only a comparatively small acreage of such soil exists in Central Otago, and where such is the case farmers will be well advised to establish permanent pasture in preference to lucerne. It is perhaps opportune to here mention that waterlogging of the soil through deficient under-drainage or over-irrigation rapidly leads to the destruction of lucerne. Seepage from water-races should therefore be looked to and prevented, particularly during the winter months.

Lucerne thrives best in a non-acid soil, and in its establishment lime is frequently applied to bring about such a condition. Generally speaking, the necessity for liming does not exist at present in Central Otago, and unless a farmer knows that his soil has a high limerequirement there will in all probability be little need to carry out this, operation. The application of lime, however, may be regarded as highly beneficial in general, and, where economic conditions permit of it, a dressing of approximately i ton per acre of carbonate of lime (raw. ground limestone) is advised. PREPARATION OF THE LAND. On account of the smallness of lucerne-seed and the tender nature of the young plant a fine firm seed-bed is advocated. It is generally advisable to select, if possible, a piece of land which is comparatively free from weeds, or land which has grown a cleaningcrop during the preceding season. Such land is best put under the plough during the.autumn, so that it will be open to the beneficial effects of the winter frosts. If ploughing is, delayed later the ground may become too hard to plough satisfactorily. Deep ploughing is advised, provided too much gravel is not brought to the surface. Where only a thin, layer of schist soil exists skim-ploughing, should be. resorted to. The land should be well worked up in the spring with a view to obtaining a fine seed-bed and preventing weed-growth: This may necessitate cross - ploughing, a double cut with disk cultivators, and double harrowing. Too great emphasis cannot be laid on the desirability of carrying out the proper levelling of the surface of the land prior to sowing. How this is accomplished has already been, described in a previous article, and it will be to the farmer’s interest to put this recommendation into practice. The permanency of the lucerne crop well merits careful preparation of the land, and of all the operations which go to constitute this none will prove more economical than that of levelling. High dry spots and low oversaturated ones will thus be eliminated, and the field will be more evenly and more expeditiously irrigated. It is of importance that the preparation should be uniformly good, as poorly prepared portions are subject to failure. Such bare places form centres from which weeds may spread, . particularly grasses, and these may ultimately destroy the whole stand. TIME OF SOWING. The months of November, December, or January are probably the most suitable for sowing lucerne. When it is sown early in the spring weeds prove extremely troublesome, particularly fat-hen

(Chenopodium album) and sorrel. It is of decided advantage to delay sowing until the first crop of spring weeds has germinated and has eventually been killed by cultivation. Fat-hen is not to be regarded as a very serious weed in lucerne stands in Central Otago, provided it is not too thick while the crop is in its young stage ; it disappears with the cutting of the lucerne. By delaying the sowing until at least November, and keeping the ground well cultivated periodically, this trouble will be greatly diminished. When lucerne is sown in the autumn the young plants are liable to be badly damaged by the ground “ lifting ” during the frosty winter months; consequently autumn sowing is not recommended. SELECTION OF SEED. Under no circumstances should cheap seed ■ be sown. Such seed is likely to contain a high percentage of harmful weed impurities, and is in addition liable to be' of poor germinating-power. The best seed possible should be obtained, and fresh season’s seed asked for. There are many varieties of. lucerne-seed on the market, but for Central Otago conditions the writers are satisfied that New-Zealand-grown Marlborough seed is very satisfactory, and consequently this variety is recommended. Much has been heard lately of the Grimm variety, but there appears to be no sound reason why this should be sown in preference to Marlborough, particularly when its price is more than double that of the latter. The main characteristic which has made Grimm’s lucerne largely grown in certain parts of the United States is its capability of living through' severe winters; but winter killing of lucerne does not concern us in this country. One looks forward to the production of lucerne-seed in Central Otago itself in the course of the next few years, and when such takes place locally grown seed should undoubtedly be used for the establishment of new crops. METHODS OF SOWING. The manner of sowing the . seed will vary according to the implements at the disposal of the farmer. *1 One thing, however, is of great importance. • If the soil has not sufficient moisture to germinate the seed and allow the young plant to grow to about 4 in. in height a preliminary irrigation should be, given before . sowing. Irrigating after sowing is bad practice and results in the caking of the soil, with consequent poor germination. The best- method of sowing is by the ordinary grain-drill with a lucerne-seed attachment. Failing this, the seed may be sown through the manure-spout of the ordinary drill, by setting the drill to sow, say, 1 cwt. of manure, mixing the seed with 1 cwt. of basic superphosphate, and so conveying the correct mixture of manure and seed to the soil. By this method successful stands of lucerne were obtained at the Galloway Irrigation Farm. Where the drill is used great care should be taken not to sow the seed too deeply. The depth will depend somewhat on the character of the soil. * [Covering to | in. on the heavier types of soil is usually ample, but on the lighter types, which are likely to dry out quickly, up to 1 in. is desirable. The seed should be sown at the rate of not more than 15 lb. per acre. Many quite thick stands have been obtained from sowings of as low as

io lb., but to be on the safe side from 12 lb. to 15 lb. is advocated. The average farmer is inclined to sow lucerne-seed too deeply, which means that much of the seed sown 1 is. lost, and unless special care is taken it is ,well to look upon a 15 lb. seeding as the standard. The practice at Galloway is 12 lb. per acre.

Where a drill is not available, sowing; can be carried out in several ways, the chief among which are the use of the “ hurdygurdy,” the fiddle,” the wheelbarrow seeder, or the hand method. Where any of these methods are adopted it is usually advisable to ■ sow half the. seed one way across the field and the other half at right angles to the line of the first sowing. The seed should. then be covered with a light harrow. Probably the best harrow for this purpose is a home-made one constructed by lacing together a few long strips of wire netting .side by side, attaching them to a light drawbar, and fastening a few bolts to the end of the strips. A brush harrow made of. manuka or wild-irishman is also quite suitable. If the soil , is inclined to be too loose it may be rolled with a light roller, although this, is not generally desirable. Before sowing seed broadcast it is usually good practice to roll the field with a Cambridge roller. . This firms the soil, leaves the surface rough, . and . makes it possible to cover , the seed well by cross-harrowing. / . ■' Under irrigation conditions the sowing of lucerne in wide drills of 21 in. or 14 in. apart, as is sometimes advocated, is not recommended ; it allows too much room for the intrusion of grass and other weeds, and exposes too much soil-surface to the sun and wind, causing great loss by evaporation. The intertillage of lucerne sown in this manner is an expensive and ever-recurring operation, and in view of the excellent results obtained by sowing through every coulter of the drill or broadcast there appears to be no advantage in doing otherwise with regard to irrigated lucerne. / INOCULATION. In Central. Otago, with few exceptions, artificial inoculation of the soil is unnecessary for the successful growth of lucerne. In certain localities where difficulty has been experienced in establishing; a stand it is probably advisable to inoculate . before . sowing, but the general experience where lucerne has been growing for a number of years with every success is that inoculation is a useless, expense. There are two general methods of inoculating soil. The first and cheapest consists of spreading soil from an old and well-established field at the rate of 2 cwt. per acre. Provided the soil is not exposed to the sunlight for a length of time, nor allowed to dry, good results will probably be obtained by this method. A cloudy day is most suitable, and the soil should be harrowed in immediately after it is spread. The second method is that of using cultures for inoculating the seed. The culture is usually contained in a special bottle, and when used according to the directions the seed is inoculated with the organisms. In certain parts of the Dominion soil-inoculation appears to be quite necessary to ensure the successful establishment of 'a. lucerne stand. Probably, then, where inoculation does not mean much labour or expense it would be advantageous to take this precaution prior to

sowing, and thus eliminate at least one potential cause of failure when establishing stands in localities where lucerne has not been tried previously. IRRIGATION OF LUCERNE. ' ■ The secret of successful lucerne-growing is to so regulate the number of irrigations given to the crop that at no time will- the plants growth be checked through loss of moisture. The chief considerations affecting the time of irrigation are appearance of the crop, weather conditions and evaporation, soil moisture-content, and -water-supply. When the lighter portions of the field show the least sign of wilting or yellowing of the leaf it is at once an indication that irrigation is required. The moisture content of the field should be maintained. in such a condition that this wilting-point will not be reached. Generally speaking, in Central Otago a spring crop of lucerne does not require irrigation. The subsequent crops will require quite a number of irrigations, depending upon the rainfall experienced. Of all crops few respond to such a degree in direct ratio to the water supplied as does lucerne. This may be appreciated when one bears in mind the rapidity with which the plantigrows, the number of ■=cuttings produced in the one season, and the heavy green weight obtained. It must not be assumed that incessant pouring on of water is a desirable way in which to supply the plant with moisture. In Central Otago to-day one too often sees water being applied far in excess of the needs of the crop. It is quite a common practice there to use anything from five to seven acre-feet of water during the - irrigation period. Such quantities are quite unnecessary, and, in point of fact, may prove in some circumstances injurious. Until definite waterrequirements for lucerne in Central .Otago have been ascertained it can be assumed as a working basis, from the results of experiments elsewhere, that the maximum amount of water which should be applied during the season is in the vicinity of 30 in., although no doubt excellent results will be obtained with a lesser quantity. Experiments conducted at the Werribee State Research Farm, Victoria, indicated that up to a limit of 48 m. of water, in addition to 16 in. of rainfall, : the yield of lucerne varied directly but not proportionately to the water applied. Results obtained by the Montana Experiment Station showed that in localities having an annual rainfall of about 12 in. remarkably heavy yields could be obtained from the use of from 24 m. to 30 in. of irrigation-water, provided it was applied properly. From information collected by the Oregon -Experiment Station it was ascertained that in the chief irrigated valleys of that State, where the average rainfall was 11.15 m. and the irrigation-water applied was 33-3 in., the yield, of lucerne hay amounted to 5-63 tons per acre. On quite a large area of .Central Otago soils, on account of the free under-drainage, it is practically impossible to irrigate lucerne to the point where decrease in yield occurs ,' still, once a reasonable amount of water has been reached, - the proportion of increase is very slight. The use of water, like the .use of fertilizers, is subject to the law of diminishing returns. The frequency of applications to the crop will largely be regulated by the water-holding capacity of the soil. On the light soils six to eight applications of 4 in. in depth throughout

the season might be necessary. On the more retentive soils four to five applications of 6 in. at each application would probably suffice. Generally speaking, it will be necessary to irrigate from every fourteen to twenty-one days. The period of time between irrigations will be entirely dependent upon the appearance of the crop or the condition of the soil. The chief object is to maintain at all times as nearly as practicable the proper amount of moisture in the soil surrounding the roots of the plants, so as to prevent checking of growth.

The question naturally arises as to the advisability of irrigating before cutting or after cutting. Experiments in this connection show little difference ; both cutting and irrigating check the growth of lucerne temporarily. If an irrigation can be given when the plant shades the ground and begins to bloom it will produce the second crop earlier. If it is decided to irrigate before cutting, this operation must be conducted several days before, in order to . allow of harvesting operations. It is often asserted that irrigation prior to cutting leaves the ground in a damp condition and thus detrimentally, affects the hay, in addition to lengthening the haymaking-period. That the latter drawback to this practice is quite feasible is recognized, and, quite apart from other considerations, the increasing difficulty of obtaining labour for harvesting makes it essential when once the crop is cut to have, it in the stack with as little delay as possible. It must, however, be taken into consideration that if irrigation is to take place after cutting the crop must be cut on the early side, so that no loss of leaf may occur. When the crop is in the flowering stage the rate of 'transpiration is high. This, coupled with the low moisture content of the soil which usually prevails at that time, soon accounts for the dying-off of a large number of leaves and consequent lessening of the value of the crop. By leaving the irrigation until after cutting the danger of allowing the plant to' reach wilting-point will be increased, and before the irrigation can be given a serious check will result to the following crop. The farmer will probably be guided more by practical considerations than hypothetical reasons in regard to whether he will irrigate before or after cutting. CUTTING AND CURING. Generally speaking, lucerne should be cut for hay when the young shoots at the base of the plants are about i in. in length. If these shoots are allowed to grow too long they are liable to be damaged by the mower. The flowers usually appear with the second growth, but in the spring crop cannot be regarded as a reliable guide to time of cutting. The earlier the crop is cut after coming into flower the better will be the quality of the hay for cattle and sheep. From a haymaking point of view the general weather conditions of Central Otago are ideal. .Most farmers are inclined, to leave the cutting of their crop too long, and in making their hay they allow it to become too dry in the field. This results in a poor, harsh hay which does not retain the leaves, and breaks like brittle sticks in the hand. Good hay should have a nice green appearance, smell sweet, bend readily without breaking in the hand, and have an abundance of fine adhering leaves. The leaves contain about 50 per cent, of the feeding-value of lucerne hay, and are to be regarded as very valuable from a feeding point of

view. The crop should be cut in the morning of a good day for curing. In the late afternoon' it should be quite ready to rake into windrows with the ordinary rake, or preferably a side-delivery rake. During the following forenoon it will most probably be fit to bunch together into rough cocks with the ordinary rake, and in the afternoon of that day it may be stacked. The hay should not be allowed to cure too long in the windrow, otherwise too many leaves will be lost in raking and handling the crop. , When lucerne is raked before the leaves are entirely cured they continue, to draw moisture from the stem, thereby ensuring a more uniform curing. Occasionally the baling of lucerne hay direct from the field has been attempted in Central Otago, but this operation has rarely been satisfactory, heating taking place in the bales. It is much better practice to stack the lucerne first, and bale from the stack when it is from six to eight weeks or more in age. If heating is to be avoided in baling direct from the field the hay requires to be thoroughly cured. The result is a hard hay with loss of leaf, and rarely warrants the saving of the double handling. One of the big drawbacks to growing lucerne in extensive areas in Central Otago is the difficulty of obtaining labour to carry, out harvesting operations. The average farmer has not the capital. necessary to pay the high ruling rate of harvesters' wages, nor can he. reasonably be expected to have a full equipment of up-to-date labour-saving devices. By . co-operative . endeavour much can be done to reduce the cost of harvesting, but it is to the farmer’s' own benefit, particularly on the smaller farms where dairying 'is being conducted, to sow only sufficient lucerne. to provide winter hay for the cows and horses, putting the bulk of the land under irrigated pasture. The use of hay-sweeps and derricks certainly reduces the amount of labour in harvesting and permits the building of large stacks. These are to be preferred to small stacks, as a smaller proportion of the hay is exposed to the elements. LUCERNE AS A PASTURE. < Irrigated lucerne is essentially a -hay crop, but occasionally it is used as a pasture. The practice of depasturing an irrigated stand of lucerne, on account of the liability of cattle and sheep to become blown,” presents considerable difficulties, and great care has to be exercised to prevent hungry stock from gorging themselves rapidly. In general the grazing of irrigated lucerne is not recommended, and should be confined to either the grazing of very early spring growth or the last crop of the season. The common practice of grazing the last crop or roughage of lucerne in the autumn may be regarded as quite sound practice, provided care is taken not to graze too closely. The plants should be allowed to go into winter with, some growth upon the crowns, thus enabling them to stand the winter better, and also to store up reserve food material for a vigorous growth in the following spring. ’ Where grazing is carried out the ground should be frequently cultivated with a spring-tooth harrow to loosen up the overconsolidated soil resulting from the trampling of stock. ; .

CULTIVATION. Under irrigation frequent cultivation of. lucerne is of great necessity. One of the commonest causes of a lucerne stand rapidly going out is the intrusion of weed plants. Of these probably the grasses are most aggressive, and it is only by repeated cultivation that their invasion can be arrested. By cultivating during the winter months at least twice with a strong spring-tooth cultivator the bulk of the weeds can be kept under control. Where it is possible a cultivation after each cutting is desirable. Not only will cultivation of this.description check the growth of weeds, but its secondary effect of breaking up the consolidated soil, thus separating it and lessening the rate of evaporation, will be of great advantage in maintaining the vitality of the crop. Any damage likely to accrue from this practice may be considered as negligible in contrast with the benefits conferred on the crop.

WINTER IRRIGATION. So far the winter irrigation of lucerne has not been practised in Central Otago. In the near future, as the land becomes more closely settled and large areas of the lighter soils are brought under cultivation, it will probably be of advantage to give the land a good irrigation during the months of July or August. Winter irrigation will probably be of greater advantage on permanent pastures than on lucerne. The chief advantages of winter irrigation, apart from supplying the soil with a store of moisture, would appear to lie in the fact that lucerne is not likely to be damaged by frost, and that the mechanical condition of the soil is improved.

(To be continued.)