IRRIGATION AND ITS PRACTICE.

New Zealand Journal of Agriculture, Volume XXX, Issue 2, 20 February 1925, Unnumbered Page

IRRIGATION AND ITS PRACTICE.

(Concluded.) VII. THE ESTABLISHMENT AND MANAGEMENT OF IRRIGATED GRASS PASTURES.

R. B. TENNENT,

N.D.D., Instructor in . Agriculture, Dunedin, and I. R.

MARKS, A.M.Inst.C.E., M.N.Z.Soc.C.E., District Engineer, Public Works Department, Dunedin.

AS has been stated, lucerne is one of the most. important forage crops in Central Otago, and for the production of a high-class cured hay it cannot be excelled. On account, however, of its tendency to bloat stock it must be regarded as unsatisfactory in general as a pasture crop. Very little cured hay is used for feeding cattle or sheep during the summer months, as the farmer looks for grass pastures to supply the bulk of the summer feed. The average irrigator usually keeps, in addition to his dairy cows and horses, a small flock of sheep, and where such is the case good irrigated pastures undoubtedly are a. most valuable asset. Central Otago is ideally adapted to the growing of pasture grasses and clovers. There, with an abundance of water coupled with soil low in lime requirement, and the presence of almost continuous sunshine, conditions are. ideal for the establishment of first-class pastures. For fattening purposes or the production of milk a well-designed pasture containing a proper proportion of clover and grasses in its composition is unsurpassable. Such pastures fit excellently into any

system of crop-rotation, and are very effective in building up and maintaining the fertility of the soil. As has already been mentioned, some of the soils in Central Otago are low in organic matter or humus, and in such cases by growing grass for several years and depasturing stock thereon the ground will be considerably benefited, thus paving the way for further crops. demanding a higher state of fertility. Sufficient has been stated to show that the pasture is to be recognized as the most valuable asset that can be grown by the irrigator, and every effort should be expended in - having more than half his farm laid down in this crop. . As a crop, pasture is probably the least understood and most maltreated. Insufficient attention is given to the adaptability or otherwise of certain grasses and clover to soil and climatic conditions. The writers have examined many irrigated pastures, and have interrogated the owners in regard to their method of establishment, mixtures used, and . subsequent treatment ; and sufficient indication has been obtained showing clearly the need for a brief account being given of the lines along which pastures should be laid down in Central Otago. LAND SUITABLE 'FOR PASTURE. The best pastures will be obtained from the richest ground. It is quite wrong to assume that only the poorer pieces of land unsuitable for general cropping should be utilized for growing pastures. In many cases, however, oh account of the steepness of land or its undulating nature, it may be regarded as the most economical proposition to use such types of ground for growing grass. . Every farm has its piece of land which might be regarded as waste on account either of its. low-lying, underdrained condition or stony nature. Such pieces of. land if. sown with suitable grasses can readily be brought to a comparatively high state of production. Many cases have been noted where farmers have devoted the bulk of their best land to the production of hay and commercial crops, and have relegated to their pastures the small remaining portion of poorer ground. In such cases it invariably follows that there is a lack of summer feed and a surplus of winter hay, this pointing to bad regulation of their cropping system. Indications have already been given of the opinion of the writers that as little hay should be grown as possible, sufficient only being conserved for the winter feeding of the farm stock. In view of the fact that, the life, of permanent-grass pastures will be extended over many years, it is advisable to have them conveniently located. Again, the fact that they require frequent irrigations should be borne in mind, and on this account they should be located where irrigation can be readily and easily carried out. SUITABLE MIXTURES. In laying down grass pastures the aim should be to obtain a judicious mixture of grass and clovers in such a proportion as to produce a palatable sole of grass with a high feeding- It is to be recognized that there is no single variety of grass having all the characteristics that are looked for in an irrigated pasture. A mixture of several varieties of grasses and clovers is usually desirable, and gives better results than any single variety sown alone. The different grasses

■have varying, times of maximum growth, and since with the aid of irrigation the pasture can be maintained in good' growing-condition through the entire irrigation season it is quite necessary that a mixture should be ' sown containing some early-, medium-, and late-growing varieties. In Central Otago perennial rye-grass, Poa pratensis, alsike clover, and white clover grow exceptionally well, and every permanent pasture should certainly contain a proportion of these plants. For ordinary conditions such as exist generally in Central Otago the following mixture is likely to prove highly satisfactory: Perennial rye-grass, 14 lb. ; cocksfoot, 6 lb. ; timothy, 4lb ; Poa pratensis, 2 lb. ; alsike clover, 2 lb. ; white clover, 1 lb. : total, 29 lb. per acre.

Where a more simple mixture is required for sowing on rough sidelings the following can be used with satisfactory results : Perennial rye-grass, 16 lb. ; . cocksfoot, 6 lb. ; alsike, 2 lb. : . total, 24 lb. per acre. Where it is intended only to sow down a temporary pasture under irrigation, with the idea of breaking it up at the expiry of the season following sowing, the following mixture is quite suitable : Italian ryegrass, 18 lb. ; alsike, 4 lb. : total, 22 lb. per acre. It is to be remembered that in these suggested mixtures the weights of seed given are not intended to be adhered to in every circumstance, but should act as a guide in regard to the proportions of different grasses and clovers to be used. Preference is given to the use of alsike rather than red clover in the mixtures on account of there being less likelihood of its causing bloat than the latter, and the fact that when -autumn-sown it grows much better than red clover. Under Central

Otago conditions white clover . appears to grow without seeding in many localities whenever water is applied to the soil. Where such is the case there is little need to use white-clover seed in the mixture. SOWING. As with lucerne, a good seed-bed will give the most satisfactory results, ' and neglect of this has often resulted in many unsatisfactory soles of grass being obtained. The aim should be to obtain a seed-bed with the soil fine, firm, and moist, as against one that is open and lumpy with a tendency to dry out, thus causing the death of the seedlings. Generally • speaking, the ground should be ploughed in the autumn and allowed to lie exposed to the winter frosts. . In the spring it should be double disked and harrowed, after which the leveller should be used to eliminate small surface inequalities. . Sowing may be carried out from the beginning of November to the middle of February. If sown too early or too late, damage by lifting of the soil as a result of frosts is likely to occur. Broadcasting the seed with a hand-seeder of a good type is quite satisfactory. Where a grass-seed- attachment is used in conjunction with the ordinary grain-drill, care must be taken to sow the seed as shallow as possible. If it can be sown on the surface and then harrowed in by either a brush or wire-netting harrow (described elsewhere), so much the better. The use of a nurse-crop in sowing down grass, although often adopted for economical purposes, is not recommended. Care must be taken to see that the ground is sufficiently moist at the time of sowing to ensure a good germination. In actual practice it will usually be necessary to irrigate the ground prior to sowing, following the irrigation by a good harrowing. The importance of using good seed of high germination and freedom from weed-seeds cannot be overstressed. Where grass is being laid down on a steep sideling it is rarely advisable to plough the ground, on account of the liability of serious erosion taking place when water is applied. The practice to be adopted in such a case would be to give the ground a good double disking and follow this by harrowing. Sowing can then be carried out in the usual manner, and although such conditions cannot be regarded as ideal a good strike will usually be obtained. IRRIGATION OF GRASS. A grass pasture, on account of the great growth made throughout the season, requires frequent irrigations to maintain a fresh luxuriant flush of grass. The principles outlined for the irrigation of lucerne apply equally to the irrigation of grass. The system of irrigation adopted will .to a great extent be regulated by the grade of land upon which the grass is being grown. For moderately flat lands either the border method or the close-furrow method can be adopted'. * On steeper land contour irrigation will be practised. From, the time of sowing until the grass is well established is the most critical time in the management of a grass pasture. The length of time between irrigations will depend upon the type, of soil and weather conditions. The applications of water need not be heavy, but should be given : at frequent intervals to keep the surface of the ground moist. It is to be remembered that, as the roots of grasses are comparatively shallow, light

frequent irrigations will give better and more economic results than heavy irrigations extended over .long intervals.. - If a pasture is to produce maximum returns it is necessary to keep it growing continuously throughout the season. It is sometimes stated that growing grass under irrigation is an unprofitable undertaking on account of the large supply of moisture required by the pastures. The water requirement of grass is no higher than that of lucerne; but it is waste of water to apply by means of irrigation as much to grass as would be done in the case of lucerne. Where grass is sown in spring there will probably be a fair amount of feed at the end of the first summer. Under such circumstances light grazing should be carried out, thus allowing sorrel and other weeds to be eaten oft and encouraging the grasses to stool out before coming, into seed. The young pasture must not be eaten too closely or overconsolidated by the trampling of stock. SUBDIVISION OF FIELDS, AND PROVISION OF SHELTER. It is generally advisable to divide a large field into sections, the number of divisions being dependent on the size of the field, the method of irrigation employed, and -the number of stock being grazed. The value of changing' stock from one section to another, and thus allowing each section • spells in rotation, cannot be emphasized. This practice is extremely important when dealing with irrigated grass. Nothing will more quickly ruin an irrigated pasture ■ than continuous grazing, and the only way in which this can be avoided is to subdivide the grazing-field. In the case, say, of a 30-acre field it is desirable to subdivide it into three 10-acre fields.. This will allow for the animals being changed from one field to another while irrigation is being carried out. It should never be necessary to irrigate a pasture while the animals are grazing upon it, since they would considerably damage it by cutting up the turf with their feet. For these and other, reasons the practice of alternating from one pasture to another ensures fresher, better, and far more abundant feed.

Provision of shelter-trees for the stock depasturing oh. the grass is highly important. As the animals spend the bulk of their time in the fields, provision should be made, by the planting of adequate belts or clumps of trees, to shelter them from the hot sun or cold biting winds;