Present Types of Pasture
There is a variety of pasture types in New Zealand, ranging from the high-producing dairy pasture on the plains and easy rolling country to the low-producing, lightly stocked tussock grasslands of the South Island mountains. Because moisture is the main factor limiting pasture production and improvement, the types of pasture which have been developed are determined very largely by this consideration.
1. High Fertility Pastures with Optimum Moisture for Most of the Year
These pastures are confined mainly to well-drained areas with an adequate and well distributed rainfall. Irrigated pastures are included in this group.
In the northern part of the North Island these pastures, which are left down for many years, frequently contain paspalum as a dominant plant. This grass is high producing in summer and dormant in winter but, if neglected, it rapidly becomes sod bound and low in production. To maintain paspalum pastures in high production, the turf mat has to be destroyed either by ploughing or by deep-surface cultivation. This is followed by the sowing of ryegrass and white clover, usually with phosphatic fertiliser. Such a mixed pasture of ryegrass, paspalum, and white clover is capable of a higher production over a longer period than that of ryegrass and white clover, or paspalum and white clover alone. The value of the paspalum pasture is limited to the warmer areas where it is able to make a major contribution to the total annual production.
In other parts of both islands, reliance is placed mainly on ryegrass and white clover, a combination which is capable of high production and of recovery from the heavy trampling that accompanies the intensive grazing of high-producing pastures. Although these are the two main plants used, cocksfoot, timothy, and red clover are often included for summer production. Crested dogstail is frequently included in sheep pastures, particularly in the South Island. In the warmer dairying districts, such as Taranaki, prairie grass is used to a limited extent because of its ability to grow in the winter. Although it is seldom sown deliberately, Yorkshire fog is one of the most abundant pasture grasses in the higher rainfall dairying districts. Its increase over the last 20 years has been unwittingly encouraged by the common practice of autumn and winter spelling of pastures. Commonly regarded as a weed grass, it makes a very substantial contribution to production, particularly in the winter when it is more readily eaten than in the summer. When it is growing vigorously, Yorkshire fog is fairly palatable but its palatability falls off rapidly when it matures, and particularly in the warmer months. It is this lack of summer palatability that has made Yorkshire fog unpopular, but it is undoubtedly of more value than is generally believed.
2. Pastures of High Fertility but Liable to Suffer from Lack of Moisture in the Summer
Pastures of this type are of necessity usually reserved for sheep rather than for dairy cows, and are present mainly on the eastern side of both islands. Although cocksfoot and red clover are often included to maintain summer production, ryegrass is usually the main grass in this type of pasture. White clover is liable to dry out in summer, and its permanence as a major constituent in these pastures cannot be assured. For this reason the annual subterranean clover is also used extensively because of its useful winter, spring, and early summer production. Further, it has the ability to maintain its plant population through reseeding.
The clover content of these pastures tends to vary appreciably from year to year according to the extent of summer droughts. Dry summers are usually followed by a dominance of subterranean clover; wet summers are followed by a dominance of white clover. The general tendency has been for subterranean clover to be a pioneer fertility-building legume in the drier areas. As the fertility rises, it tends to be gradually, but not entirely, replaced by white clover.
3. Surface-sown Hill Country
A very large proportion of the North Island's grassland consists of surface-sown hill country, most of which was developed long before the use of fertilisers for this type of country was seriously considered. Most of the sowing was on the ash, after the burning of the fern, scrub, and felled bush, with mixtures based mainly on ryegrass. The seed mixtures used were often fairly complex – in the hope that at least some of the species sown would survive under the often variable and difficult conditions. After the burning, the initial high fertility disappeared in about three years, with the result that many of the sown species did not thrive. These were replaced by lower-producing grasses and sometimes unpalatable native plants. Over the years, two main types of grassland have developed. The first was in the higher-rainfall areas and consisted mainly of low-fertility grasses such as browntop and Yorkshire fog, with unthrifty white clover. In some areas considerable improvement resulted from the surface sowing of Lotus major (Lotus pedunculatus), which was able to grow well and produce useful feed under conditions of low soil fertility but with ample moisture. The second type was developed in the lower rainfall areas where Danthonia pilosa was a common constituent. The danthonia was frequently burnt to keep it in a palatable condition, and, as it was better able to withstand fire than most other species, it continued to thrive. Other associated plants, particularly the useful clovers, were virtually eliminated or reduced to an unimportant level.
Since the introduction of aerial topdressing a few years ago, a change has taken place in the surface-sown grassland. In the wetter areas the topdressing is usually associated with the sowing of a good type of white clover. Not only has this increased production from the pasture, but it has also enabled weed plants, such as manuka, tauhinu, and hard fern, to be controlled by grazing much more successfully than they have been in the past. As the fertility rises, and as the white clover increases, the existing grasses grow more satisfactorily. Associated with this is the stimulation and increase of the surviving useful plants such as ryegrass, cocksfoot, and dogstail.
In the drier areas the same pattern of change is taking place. The oversowing and topdressing of the danthonia-dominant country with subterranean and white clovers have resulted in the establishment of an essentially annual legume content in a sward of a low-fertility perennial grass. The effect is the gradual replacement of the danthonia by higher-fertility-demanding grasses such as ryegrass and cocksfoot. Associated with this is a logical increase of other high-fertility-demanding species, some of which are very undesirable — for example, barley grass and thistles. This major change from a low-fertility perennial grass dominant sward to a sward of annuals, including undesirables, is one that needs close attention. From a short-term viewpoint, such a change is desirable as it increases both the quality and quantity of the feed. From the long-term point of view, however, such a complete change may be undesirable because of the greatly increased risk of soil movement after summer rains when the plant cover, mainly annual, is dead. The ideal could quite well be a carefully managed association of a danthonia-dominant sward with some fairly vigorous annual legume which would not be allowed to become dominant. The best combination would include a drought-resistant perennial legume, but unfortunately such a plant is not available.
4. Tussock Grassland
Most of the eastern side of the South Island was covered with tussock grassland of various kinds which can be considered under the following major groups:
A. Red Tussock:
Although present in the higher hill country, this tall unpalatable tussock was the dominant plant in large areas of poorly drained plains and rolling country of South Otago and Southland, and in consequence these areas provided very little grazing. Most of this tussock grassland has now been drained, ploughed, cropped, and sown down to pasture. For many years much of it reverted rapidly to cloverless, unthrifty pastures dominated by browntop. This was due partly to the low fertility of the soils and partly to the lack of persistent high-producing strains of grasses and clovers. During the last few years, however, a major change has taken place in the former red tussock country. The main factors have been the increase in clover vigour as the result of the application of adequate phosphatic fertiliser, the use of molybdenum, and the sowing of persistent, high-producing strains of grasses and clovers.
B. Snow Tussock:
Snow tussock was the dominant plant on much of the higher-altitude tussock country. When left alone, it forms an almost pure association and not only provides little or no grazing but also hinders the movement of stock. For these reasons the practice for many years was to burn this country periodically. This had several worth-while effects — first, the young growth was palatable to sheep; secondly, it eliminated the tophamper of leaves, thus allowing the free movement of sheep; and, thirdly, it allowed more palatable grasses and herbs to establish themselves between the tussocks. Burning, however, had some undesirable effects, the worst being the killing of the tussock itself, which often happened after a burn when the base of the tussock was dry. Such burning, when repeated, had the effect of so reducing the amount of tussock and litter that the action of frost, rain, and wind caused erosion which ranged from minor soil movement to large areas of shingle screes on the steep, unstable hill country. Since the establishment of catchment boards and catchment commissions, the burning of this country has been governed by permit which stipulates the time of year (usually early spring) and the frequency with which specific areas may be burnt.
One of the important problems confronting those who are investigating tussock grassland improvement is that of deciding upon the most suitable treatment for this type of country, not only to save it from further deterioration but also to control the “run-off” which effects the low country by floods and the building up of rivers with shingle. Revegetation with trees, grasses, and legumes, as well as natural regeneration, are also being studied. The problem is a difficult and complex one, and it is unlikely that a simple and economical solution will be found in the near future. Present efforts are in the direction of halting the deterioration by the control of burning and the reduction of grazing by all animals. Indeed, some of this country has been freed from grazing.
C. Silver Tussock:
Silver tussock is confined mainly to the more fertile country, and occurs in comparatively small areas. The farming of this country has resulted in very little damage. Much of it has been ploughed and sown down to permanent pasture. A considerable part of the remainder has been advantageously modified by the gradual, but not deliberate, replacement of the tussock by plants such as browntop, sweet vernal, white clover, and flatweeds, with some cocksfoot and ryegrass in the more favourable and moist situations.
D. Fescue Tussock:
A great deal of the fescue tussock grassland on the easier country such as the Canterbury Plains and downlands has disappeared as the result of many years of rotation farming. Most of this country is now capable of carrying fattening pastures and producing good crops. On the moist areas white clover is the dominant legume, while subterranean clover has played an important part in fertility building on the drier parts of the plains. There is, however, a large area of fescue tussock grassland on the hills and inland plains. For many years this country has been farmed intensively and stocked mainly with Merino and half-bred sheep. All of this fescue tussock grassland has been modified (to a greater or lesser extent) as a result of farming. On the more fertile sites there has been a tendency for the tussock to be slowly and partly replaced by other plants such as browntop and flat-weeds. This country is fairly stable and presents no major problems of restoration. In the higher-rainfall areas, there have been marked changes on country that has been fairly heavily grazed and occasionally burnt. The greatest change has been the almost complete replacement of the tussock with manuka and also gorse. Some of this country is now being improved by burning, ploughing, and sowing down to pasture, with an associated rise in fertility, by the application of suitable fertilisers and trace elements such as phosphorus, sulphur, and molybdenum.
In some of the areas of moderate rainfall, where manuka does not invade the pastures, there has been a gradual replacement of the tussock with unthrifty browntop which, although providing ground cover, produces very little feed, and then for only a short time each year. In the areas of low rainfall, the effects of grazing by sheep and large numbers of rabbits were very considerable. The tussock disappeared over large areas, particularly in Central Otago, and was replaced by the unpalatable xerophytic scabweed. The only feed available to sheep was a scant supply of annual grasses and some herbs.
During the last decade great changes have taken place in the fescue tussock grassland. In the depleted country the rabbits have been reduced to insignificant numbers, with a resultant rapid recovery of annuals followed by some of the tussock grasses. Some white clover and cocksfoot have been oversown, but this has been successful mainly on the more favoured shady faces.
The main change on the fescue tussock grassland is the result of oversowing and topdressing areas which still carried a reasonable amount of tussock, often with some browntop. The success of this has been spectacular, but two problems remain. The first is how and when to introduce better grasses such as cocksfoot. It seems that this is successful only after the introduction of legumes and before volunteer grasses such as Yorkshire fog and sweet vernal are stimulated to the extent that they form too dense a sward for the cocksfoot to establish itself in. The second problem is the utilisation of the feed that is produced after the improvement.
If the feed is not grazed, the change brought about by the topdressing and oversowing merely becomes an expensive demonstration of what can be achieved. To make use of this new feed involves a change to farming methods approximating to those used by the down-country farmer. This includes the very expensive item of subdivisional fencing, possibly the use of a breed of sheep which will provide a better financial return in relation to costs than does the Merino, and the introduction of supplementary feeding during the winter. On some properties this is already taking place. There are, unfortunately, many properties where the wholesale improvement of fescue tussock grassland and its utilisation will not be profitable. Where, however, this improvement is feasible, it is likely to have the desirable effect of reducing the grazing pressure on the higher, critical, snow-tussock country.
Where improvement by oversowing and topdressing is not warranted, there is every indication that minor adjustments in present management practices will allow such country to be spelled at periods which have a bearing on the seed production and the consequent strengthening of the sward by the shed seed.
5. Soil Fertility
Apart from certain alluvial types, the soils of New Zealand are of too low a fertility to enable pasture plants to produce to their maximum. The chief deficiency which limits pasture production is nitrogen. In some countries where the climatic conditions are suitable, this deficiency is made up by the repeated application of nitrogenous fertilisers. In the New Zealand climate it is possible to grow legumes so well that they will supply enough nitrogen to enable the grasses also to thrive. Consequently, in this country, the basic principle of fertility raising is the production of nitrogen by the stimulation of the clovers. Depending on soil type, the main deficiencies have been found to be phosphorus, sulphur, potassium, and molybdenum. Lime is also important, not so much as a supplier of calcium, but as a means of reducing soil acidity. An essential part of a programme of fertility building is the recognition of the importance of the return of nutrients, particularly phosphorus, potassium, and nitrogen, through the animal to the pasture. Just as the pasture is grown to feed the stock, so do the stock in return feed the pasture with nutrients. The more stock carried, the greater and more useful is this return.
The finding of new and better species of pasture plants for New Zealand has long been the hope of many people.
A study of the seed mixtures now in general use will reveal that hardly any new species have come into general use during the last 60 years or so. The trend is in the opposite direction – the number of species now in general use or advocated is appreciably less than it used to be. Species such as sheeps parsley, sheeps fescue, red top, meadow foxtail, and Poa trivialis are seldom, if ever, sown now. The whole trend in the use of different species has been one of simplification rather than of complication. This is largely because of the realisation that the management imposed on a sward has a very marked effect on determining whether or not certain species will thrive.
Because current farm management practices favour ryegrass and white clover, these are still the main constituents of most mixtures. Other species which have stood the test of time are cocksfoot, timothy, paspalum, and crested dogstail; and of the legumes, subterranean clover, red clover, lucerne, and Lotus pedunculatus (Lotus major). Less used species include Phalaris tuberosa, doub, prairie grass, chewings fescue, alsike, and strawberry clover. Of all these species, the only comparatively recent introduction accepted for general use is subterranean clover, the value of which was being established about 30 years ago.
Many plants have since been tested and found wanting. One of the main areas in which plant testing was carried out until recently was the tussock grassland. After years of testing, several species had been found which were likely to be useful under the existing conditions of low fertility. At about the same time the rabbit was brought under control and aerial topdressing was introduced. This called for a complete revision of ideas. The outcome was that all the evidence pointed towards the somewhat surprising fact that, for introduction into the tussock grassland, cocksfoot was the most promising grass, and white clover and lucerne the most promising legumes.
Although the search for new and better species has been far from rewarding, it should not be abandoned, as there is always the possibility that something new and useful like subterranean clover will be found. The fact that it is unlikely that much advance will be made in regard to new species does not mean there is no chance of an improvement in plants. For the last 30 years improvement within species has been carried out mainly by the Grasslands Division of the Department of Scientific and Industrial Research at Palmerston North. This organisation has produced great improvements both by selection and by breeding in the ryegrasses, cocksfoot, timothy, and red and white clovers. Work has been carried out on inter-specific hybrids and in the improvement of several other species. This shows that the improvements which can be made within a species have an effect equivalent to, or greater than, the finding of a new species. It appears, therefore, that the most likely improvements in pasture plants will come not from new plant introductions but from the efforts of the plant breeder working on already commonly used species.
7. Weeds in Pastures
A plant survives in a pasture only because conditions are favourable. This applies to both desirable and undesirable plants. It is therefore not surprising to find adjoining paddocks with entirely different groups of weed plants present. For example, a high-fertility dairy pasture, rotationally grazed, may have a considerable proportion of the ground occupied by docks and perhaps chickweed, whereas in a low-fertility, hard-grazed pasture over the boundary fence the dominant weeds may be ribgrass and catsear. This is due mainly to differences in induced soil fertility and pasture management.
The important factor in the control of weeds in pastures is, therefore, one of so altering the fertility and management conditions that the weeds will not thrive under the newly created conditions. This procedure eliminates weeds which disappear with an increase in fertility and under conditions of management which favour high production. It must, however, be appreciated that as one alters conditions so that one group of weeds will disappear, another situation will be created which will suit other groups of weeds. For this reason it cannot be assumed that altered fertility and management will eliminate all weeds. All that can be expected is that one group of weeds may be replaced by another.
The crux of the weed problem is, therefore, the elimination of weeds which increase under the desirable conditions of high fertility and good pasture management. Because a reduction in fertility is undesirable as a weed-control measure, it is necessary to consider whether or not slightly modified management practices are warranted. For example, docks and ragwort decrease under sheep grazing. For this reason, and if the type of farming practised will allow it, both of these weeds can be kept under control by periodic grazing by sheep. They will, of course, return as soon as grazing by cattle is resumed. Usually such an approach is impracticable, and it is then necessary to resort to chemical or mechanical methods of control. These as a rule, provide only temporary relief, and consequently such treatment is necessarily repetitive.
Other weeds difficult to control are those which thrive under conditions which cannot be economically altered. Examples are sweet brier and nassella tussock. The former has been prevalent in Central Otago for many years, but did not spread sufficiently to cause any real alarm. With the reduction of the rabbit population, however, sweet brier is now growing vigorously and is regarded by runholders with great concern. Its increase has been due solely to the fact that the only known practicable method of control over large areas, namely, rabbits, has now been removed. The problem is therefore to find an alternative method of control at least as good as that of the rabbit and, at the same time, that is financially possible on country that is unlikely to be improved to the state where fertility is sufficiently high to allow enough sheep to control it efficiently. Several chemicals have been shown to be quite effective in killing sweet brier, but their use is limited to isolated plants solely because of the cost both of the chemical and of its application.
by Stephen Hector Saxby, DIP.AGR., Assistant Director, Farm Advisory Division, Department of Agriculture, Wellington.
- Grasslands of New Zealand, Levy, E. B. (1951)
- Grass to Milk, McMeekan, C. P. (1960)
- Pasture Production in New Zealand, Saxby, S. H. (1956)
- Chemical Methods of Weed Control, Matthews, L. J. (1956).