Pastures are fields growing plants for grazing animals. New Zealand farmers have developed systems for efficiently grazing large numbers of animals in open pastures all year round. Pasture is cost-effective feed, but it has to be of good quality to produce economically worthwhile quantities of milk, meat or wool from livestock.
Grass, the most common pasture plant, is familiar to most people, who come into contact with it when mowing lawns, playing sports, or pulling weeds out of their gardens.
There are many varieties of grass. They have a wide range of sizes and growth rates, and can grow in different situations. Weed grasses that invade gardens are mainly annual species, which germinate from seed each year. If grasses are left to go to seed, the seeds may survive for many years in the soil, providing a continuing source of new plants.
Lawn grasses, and those on golf courses and sports fields, usually have fine leaves, grow along the ground, and have an ability to withstand trampling. The tall unmown or ungrazed grasses along roadsides are generally broadleaf types, with upright, rapid growth, which can successfully compete with other species. These are usually a mix of weed grasses and those from adjacent farm pastures.
Pastures are not just grass; they are usually sown as a mixture of one or more grasses, and one or more legume species, such as clover. Some herbs may also be included. However, pastures usually end up with some weeds in them as well.
A farmer aims to sow the species mix that will grow the best, and that stock will like to eat. Pasture plants generally must be able to regrow quickly after they have been defoliated by cutting or grazing, several times per year.
All pasture plants that are eaten by grazing animals are collectively described as forage plants.
In the mid-19th century the open country in the eastern North and South islands provided the pastures for sheep grazing and the new wool industry. These open areas had been largely created earlier by forest fires – both accidental (from lightning strikes and volcanic activity) and deliberately lit by Polynesian and European settlers to clear the bush.
After forest was burnt in the drier eastern regions, the absence of grazing animals allowed tussock grasslands to develop. South Island hills, downlands and plains were dominated by tall tussock (Chionochloa species), with larger snow tussock at higher altitudes.
The natives preferred by grazing animals were wheatgrass (Elymus species), plume grass (Dichelachne crinita), blue tussock (Poa colensoi) and holy grass (Hierochloe redolens). Farmers soon found native grasses inadequate due to their poor growth rate and low nutrient value. They believed that introduced species, especially clovers, were needed if farming was to succeed.
Most of the plants that now grow in New Zealand pastures came from England. There grasses were used not only for feeding animals, but also for roof thatching, for which the common reed grass was preferred.
English grasses and clovers were introduced into New Zealand in the mid-1800s. Many weeds were also accidentally introduced in seed mixtures.
In 1861 there were 158,000 acres (63,200 hectares) of planted pasture, which increased to 3.5 million acres (1.4 million hectares) in 20 years. The success of these pastures encouraged more forest burning and land clearance to develop new grasslands. In a letter to the London Times in 1882, the New Zealand agent general in London asserted that New Zealand had more land laid down in English grasses than all of Victoria, New South Wales, Queensland and South Australia put together. By 1925 pasture covered 16.5 million acres (6.6 million hectares), almost a quarter of the country.
In the early years of pasture development, especially on hill country, bush-burn mix was often sown on land that had been cleared by burning. The seed mixture included grass, legumes and herbs, in the hope that if you put them all in, something would grow. Seed was applied generously – usually 20–40 kilograms per hectare.
One of the most popular introduced English grasses was cocksfoot (Dactylis glomerata), which thrived on the Banks Peninsula hills, where it was sown after the native tussock and remnant forest had been burnt. It was in demand for pastures in the North Island and for a few years Banks Peninsula farmers earned good money from selling cocksfoot seed – growing 83% of New Zealand’s supply in 1905.
Once the initial supply of nutrients from ash and organic matter were depleted, introduced pasture plants needed fertiliser to continue to grow well. In areas where English grasses could not survive, native grasses were preferred.
In 1905 the first fertiliser trials showed that phosphate was needed by pasture. Superphosphate was a particularly useful fertiliser because it allowed other nutrients to be easily added into the mix where needed.
Apart from a lack of moisture, a shortage of nitrogen is usually the main thing that limits pasture growth. The cheapest form of nitrogen is that provided by legumes.
Legumes – plants like peas, clovers, soya, gorse and broom – all develop nodules or growths on their roots due to infection from bacteria in the soil. The bacterial activity converts nitrogen from the air in the soil into a form that can be taken up by other plants when the nodules die and disintegrate.
Legumes have the ability to fix atmospheric nitrogen into a form that other plants can use. This avoids the need to apply expensive nitrogen fertiliser, and has allowed New Zealand to develop relatively low-cost, year-round, pasture-based farming systems. No other country relies so heavily on legume-based pastures for its primary industries.
Perennial ryegrass (Lolium perenne) is the most common grass on New Zealand farms. Its main advantage is its ability to keep growing over many years. In Europe some perennial ryegrass pastures have been growing for centuries – hence the name.
Perennial ryegrass needs moist fertile soils to grow well and struggles during hot dry summers because of its shallow roots. In wet winters it can recover well from treading and hard grazing by stock.
The feed quality is better if it is grazed every three to four weeks during spring and autumn to remove emerging flower heads and encourage leafy, resilient regrowth.
Perennial ryegrass usually contains a fungus called endophyte, which lives inside the plant and is transferred to the next generation through seed.
Endophyte produces toxins that can make grass less palatable, but also benefits the grass by deterring insect pests and over-grazing by animals. Plants with endophyte are especially resistant to Argentine stem weevil, a major cause of ryegrass plant loss in pastures. Ryegrass types with little or no endophyte are used in the southern South Island, where pasture pests are much less common.
In the early 1980s endophyte in ryegrass was found to be the cause of ryegrass staggers, a summer-to-autumn disorder in stock. Endophyte can also reduce milk and beef production in summer and early autumn. Perennial ryegrasses are now available with endophyte types that do not produce the animal toxins, but still deter insects.
Italian ryegrass (Lolium multiflorum) is erect and large-leafed, and grows a large amount of high-quality forage for up to three years. Some types survive for only a year (annuals) and are usually sown in autumn, between other winter feed crops.
Italian ryegrass needs highly fertile soils. Its endophyte content is seldom a problem to livestock.
Hybrid ryegrasses are widely used to boost winter pasture in cooler regions. They combine the best features of perennial and Italian ryegrasses, and are sown alone or mixed with perennial ryegrass.
They range from ‘short-rotation’ ryegrasses similar to Italian ryegrass, which have high yields of leafy forage over one to four years, to long-rotation ryegrasses that survive longer. Some contain the same endophyte as perennial ryegrass.
By using drugs to double the sets of chromosomes, researchers have created modified Italian and perennial ryegrasses that are larger, establish faster, are more drought persistent and hardier in winter. They are also preferred by stock because of their high sugar content; and so animals eat more and grow faster.
Cocksfoot (Dactylis glomerata) is a hardy, drought-tolerant grass, which grows strongly during summer because of its deep roots. It must be regularly grazed or it becomes coarse and unpalatable.
Cocksfoot contains no endophyte fungus, so can be safely grazed during dry summers. It grows well with perennial ryegrass, but dense types of cocksfoot can be aggressive competitors with other grasses. It can withstand close grazing. It is generally very tolerant to pest attack, but can suffer fungal rust disease.
Tall fescue (Festuca arundinacea) is another deep-rooted grass that tolerates heat and drought. It also withstands acid, alkaline and saline soils with poor drainage, and is becoming a popular alternative to ryegrass in drier regions. It thrives on highly fertile soils and responds well to nitrogen fertiliser.
Tall fescue is normally planted with clover. It is never sown with ryegrass as tall fescue establishes itself more slowly, and so is overtaken by the faster-growing ryegrass. Tall fescue is best sown on warm soils in February or October. Grazing should be frequent during spring to prevent the development of seed heads and a slowing of growth.
New Zealand seed does not contain any toxic endophyte, but an endophyte has been introduced in some types to protect against insect pests.
Prairie grass (Bromus willdenowii, B. catharticus or B. unioloides) is a large-leafed grass with broad foliage. It grows well during winter and early spring, and tolerates drought, but it persists for only about four years. Prairie grass thrives on free-draining fertile soils and does not tolerate waterlogged conditions, animal treading or acidic soil. It grows well on the eastern coasts of the North and South islands.
Its large-seeded flowerheads are quite palatable to grazing stock, unlike those of most other grasses.
Grazing brome (Bromus stamineus) is closely related to prairie grass, but has finer leaves and tillers (shoots from the base of the stem), which help it tolerate close grazing. Like prairie grass, it grows well in dry eastern regions as quality winter and summer feed. Grazing brome grows best on medium-to-light-textured soils with free drainage.
Timothy (Phleum pratense) grows only on moist, heavy soils in the cooler southern regions of the South Island. It is highly palatable to stock but is uncompetitive with other plants, so needs light grazing. However, it grows well with clover.
Timothy starts growing later in spring than ryegrass and lacks drought tolerance. It is an excellent stock feed, even when seed heads emerge. It has been shown to give high milk yields in dairy cows, and makes good hay.
Phalaris (Phalaris aquatica) is a hardy, blue-green perennial, which grows best on drier soils and in autumn and winter. It withstands hard grazing and treading once established, and is very resistant to pests.
It contains an alkaloid that can cause the nervous disorder phalaris staggers in grazing stock, especially on cobalt-deficient soils when little other feed is available. Because of this, phalaris should be sown with other dryland grasses.
Yorkshire fog (Holcus lanatus) commonly grows wild in wet conditions and thrives on infertile and acidic soils with high aluminium levels. Generally considered a weed, it produces a rank, hairy-leafed, unpalatable pasture and soon dominates other species unless kept closely grazed.
Browntop (Agrostis species) is regarded as a weed grass, because of its low quality. However, because it persists in low-fertility soil, it dominates unimproved hill and upland pastures, or poorly managed lowland pastures. Its quality can be improved with nitrogen fertiliser. Its fine, dull leaves densely cover the ground and tend to smother clover growth. It is one of the main grasses used in lawns.
The most prominent native grasses in New Zealand are tussock grasses, which abound in high-country landscapes. They shelter exotic grasses and legumes, which supply feed for livestock.
Other native grasses are scarce in well-grazed pastures, but can be seen in natural grassy areas and in some less fertile hill-country pastures.
Subtropical grasses have been introduced from warmer continents (notably Africa and South America) and are now well-established in northern regions of New Zealand. These grasses need relatively high temperatures for photosynthesis compared with the more-common temperate grasses in New Zealand pastures.
Subtropical grasses grow coarser, less palatable foliage than the temperate grasses, and are vigorous during the warm seasons. However, they are frost-tender and grow poorly in the cold seasons. As a result, subtropical grasses have a mixed reputation and, as they often suppress higher-quality pasture species, many farmers consider them to be weeds. If farmers can maintain good clover content in pastures dominated by subtropical grasses, then the pasture feed value is adequate. Otherwise these species offer poor nutrition for grazing animals.
Annual subtropical species (commonly called summer grasses) in northern pastures often colonise dead patches caused by summer drought.
Some species can exist for many years as dormant seeds in the soil, whereas ryegrass seed tends to be short-lived, so cultivation or livestock treading can result in reinvasion by the less valuable subtropical grasses.
Kikuyu grass (Pennisetum clandestinum) is a very vigorous, coarse, low-quality grass, which can take over pastures in frost-free regions. It is present throughout Northland.
A perennial grass, it is low-growing and deep-rooted, with stolons (stems that grow along the soil surface) and rhizomes (roots that grow horizontally in the soil). It forms a dense turf, which is very resistant to heavy grazing and attempts to remove it.
Almost everyone in Northland hates kikuyu. Farmers hate it because it has poor feed value and crowds out better pasture species; orchardists hate it because it can climb up and partially smother fruit trees, and gardeners hate it because it can invade gardens and lawns. Even worse it is perennial and drought resistant, so once established is really difficult to get rid of.
Other subtropical grasses have steadily advanced south into new regions, possibly because of adaptation, farm management changes or climate change.
The most widespread of these is Paspalum dilatatum, which in recent decades has advanced in pastures (and lawns) well into the South Island. The content of paspalum in northern pastures has also increased.
White clover (Trifolium repens) is New Zealand’s most important pasture plant, due to its nitrogen-fixing abilities. It is sown throughout the country and grows well on fertile soils, but struggles in dry areas. However, pasture clover content is normally low – usually less than 10%. White clover is recognisable by its white flowers.
If a newly sown pasture isn’t grazed for up to six weeks from December until late January, then the clover will seed, and this seed crop can yield up to 50 kilograms per hectare. That’s 70 million seeds per hectare or 7,000 seeds for each square metre. Clover seeds develop an impermeable coat and can live for centuries in dry soil. Some clover seeds were recovered from under a 700-year-old church in England – and they germinated.
The clover root weevil (Sitona lepidus), which attacks white clover, was accidentally introduced to New Zealand in the 1990s and has since spread throughout the North Island and into the South Island, reducing pasture clover content. A parasitic wasp released in North Island during 2006 to control this pest appears promising.
White clovers with a dense mass of stolons and many small leaves are the most persistent because stolons spread, develop roots and split into plantlets, each eventually forming a separate plant. These types survive well in pastures closely grazed by sheep.
Large-leafed clovers have erect growth, large roots and flower heads, and thicker, but fewer, stolons. They are used in dairy pastures where grazing is relatively light and infrequent.
Small-leafed and large-leafed types are often mixed together to maintain good clover content for grazing and nitrogen fixation.
There are also medium-leafed types, which grow well in a broad range of grazing situations.
Each stem (or petiole) of a clover plant usually has three leaves, so if you find a rare four-leafed clover it is supposed to bring you good luck. These are different from a shamrock, which always has four leaves.
Red clover (Trifolium pratense) has a red flower, hairy, dull foliage, and a taproot. It is slower to flower than white clover. It can last up to seven years under favourable conditions – such as lax grazing or under long summer grazing rotations – but does not tolerate close grazing. When sown, it is important to ensure that it establishes itself well, as it does not reseed readily.
Red clover grows well on fertile, drier soils with other grasses, clovers and herbs. It makes good silage and hay. Deer prefer it to other plants, and it is acceptable to all livestock.
Red clover sometimes contains enough oestrogen to lower sheep fertility when fed in autumn, during mating; however, recent selections contain much lower oestrogen levels.
Also known as alfalfa, Medicago sativa is an upright legume grown for grazing or haymaking. It is commonly used in dryland pastures, as its taproots can extract water from deep in the soil, making it more tolerant to drought than other pasture plants.
Lucerne is best grown on fertile, well-drained soils. It does not reseed easily, but can survive for about eight years when managed well. It is best left to flower during the first summer, as this allows carbohydrate reserves to build up for regrowth and persistence. Lucerne should then be rotationally grazed or cut every four to six weeks.
Types of lucerne are now available with resistance to bacterial wilt, Phytophthora root rot, stem nematodes (worms) and aphids. Before sowing, the seed must be inoculated with the bacteria that enables it to fix nitrogen.
Subterranean clover (Trifolium subterraneum) is an annual that germinates in autumn and reseeds in late winter and spring. After flowering, it stops growing and pushes its seed heads into the soil, surviving over summer as dormant seeds, which germinate in autumn.
Subterrranean clover is useful in east coast regions on soils too dry for white clover, where it can contribute more than 20% of winter pasture. It needs minimal grazing during spring flowering so it can reseed. Types that don’t flower until late spring appear best suited to New Zealand, as they stay in a vegetative state for longer before going to seed.
Lotus major (Lotus uliginosus) a perennial legume, grows well in wet, acidic, infertile soils where grazing pressure is light. Lotus has also been widely sown in agroforestry situations (where forestry and agriculture are combined) because it tolerates shade and needle litter better than clovers.
Lotus spreads by rhizome growth and can grow up steep banks. Lotus contains chemicals (condensed tannins) that prevent it causing bloat in cows – as may occur with some clovers – and that also reduce the effects of internal parasites in sheep and cattle. Resistant to some serious pasture pests, such as grass grub and porina, it is valuable for extensive farms where intensive chemical pesticides are not used.
Lotus normally takes a year to become established, though it is faster when soil temperatures are over 15°C. Light grazing is essential, as regrowth comes from lateral buds on the shoot stubble left behind after grazing. Grazing closer than 7–10 centimetres above the soil will slow down regrowth.
Livestock like, and benefit from, eating herbs, so New Zealand pasture-plant breeders have selected improved types of at least two common perennial herbs for grazing.
This large-leafed, succulent herb looks like a weed but gives up to 18 tonnes of high-quality dry matter per hectare from spring through to late autumn (other species may grow only 12–15 tonnes per hectare). Chicory (Cichorium intybus) is very acceptable to all livestock.
It grows best on fertile, free-draining soils and will persist for several years. Chicory’s forage is digested more rapidly than ryegrass and white clover pasture, and this may account for the fast growth rates of animals grazing chicory.
Plantain (Plantago lanceolata) grows well in many pasture situations. This flatweed has been developed into erect-growing types that are highly palatable to animals. It establishes itself rapidly, is very drought- and pest-tolerant and has a high mineral content, especially copper and selenium.
Plantain tolerates summer heat and is particularly valuable during summer in warmer regions. It can be included in many pasture mixtures. Plantain content rarely exceeds 20% of the pasture, though in warmer regions it may reach 50% or more.
Some small lawns are not grass – they are planted in other species such as cotula or dichondra. These are prostrate perennial herbaceous plants, with creeping stems and small roundish leaves, which take root readily at the leaf nodes and form a compact surface when regularly mown. Most bowling greens have a cotula cover.
Trees and shrubs can provide excellent livestock fodder during dry weather, when pastures brown off. Many farms have willows and poplars growing for erosion control or as shelter belts, and their prunings can provide inexpensive supplementary feed containing condensed tannins and other beneficial nutrients.
In drought conditions, feeding ewes with tree fodder for seven weeks prior to mating in February to March maintains the lamb weights and the number of lambs per ewe at non-drought levels.
Pastures based on perennial ryegrass and white clover grow well on most fertile, drought-free soils in moderate climates, but the east coasts of the North and South islands tend to suffer from summer droughts, which affect the pastures. In these regions, legumes that grow during winter and early spring, such as subterranean clover, often produce more animal feed than white clover, which is more productive in summer.
Deep-rooted grasses such as tall fescue and cocksfoot tolerate drought better than perennial ryegrass, and so are more productive in these regions.
Most seeds are sown after the soil has been cultivated and a fine seed bed produced. Another method, called direct drilling, is to kill the previous pasture by spraying with herbicide and then sow the seeds into grooves in the soil made by a special drill. This helps conserve soil moisture.
The South Island’s inland high country has cold winters and summer droughts. Sowing native tussock grassland with clover seed and sulphur-superphosphate fertiliser can produce a striking change to a clover-dominant cover. This may persist for a few years, but if it is not well grazed during this time the clover will disappear and the pasture revert to its original condition, perhaps with some poorer grasses such as Yorkshire fog and browntop.
On hill country, machinery cannot be used to cultivate the soil before sowing seed. One alternative is to graze the area with a large number of sheep or cattle, so that bare ground is exposed. The seed is sown into this seed bed and stock may be used to trample it in.
The West Coast receives high rainfall levels (up to 6 metres annually) but is almost frost-free, so perennial ryegrass and timothy thrive under these conditions.
Grasses such as timothy, grazing brome and prairie grass grow well in the southern South Island, where summers are cool and moist, and winters are colder. Summer growth here is strong but winter growth is slow.
Dairy cattle need a balanced diet, especially before and after calving, and good pasture growth is important in spring to boost early milk production. Throughout summer it pays to prevent cows grazing pastures to low levels, so they avoid eating the base of the plants and dead matter that could harbour toxins.
Cattle farmed for beef often graze a wider range of pasture types, from high-quality perennial ryegrass and white clover on flat and fertile soils, to pastures dominated by browntop on hill country.
The large areas of brown colouration often seen on hill pastures in the summer and autumn are mainly browntop seed heads.
White clover is an essential nitrogen source for dairy pastures. Red clover can be used under drier conditions where the white clover content of pasture is lower.
The regular use of nitrogen fertiliser, which occurs on many dairy farms, is detrimental to clover and reduces the clover-content of pastures to low levels.
Pasture productivity can be damaged by the treading of cattle and, in wet conditions, can also seriously compact the surface soil and reduce subsequent pasture growth.
Sheep graze pastures much more closely than cattle and are more selective grazers. They prefer clover to grass and enjoy a diet containing up to two-thirds clover. After lambing, in spring, sheep are usually kept in one paddock for about three to four weeks. This avoids unnecessary movement of ewes and lambs in order to reduce the likelihood of ewes abandoning their lambs.
After lambs are weaned, rotational grazing – where a mob of sheep graze the pasture very closely over a few days – can be resumed. They are then rotated or moved on to the next paddock.
The best pastures for sheep are mainly ryegrass and white clover, though poorer grasses, such as browntop and Yorkshire fog, often dominate hill-country sheep pastures. Where lamb production is important, perennial grasses (tall fescue, cocksfoot, timothy) and grazing herbs like plantain and chicory may be grown in special-purpose pastures.
Deer are very selective grazers and prefer red clover and broad-leafed herbs, such as chicory and plantain, to grasses. A mix of grasses, legumes and herbs will provide a useful deer pasture, but this must be rotationally grazed to avoid over-grazing of their preferred species.
Pasture for deer should be about 10 centimetres or taller. Deer also like to browse on trees such as willows, poplars and natural scrub.
Deer are very sensitive to the wild ryegrass endophyte and avoid it wherever possible, but readily graze endophyte-free pasture.
Horses are very selective grazers and avoid any ryegrass containing endophyte. They also avoid areas of unpalatable weeds and old dung patches (for at least six months), leading to patchy ungrazed and closely grazed areas. A pasture with a large ungrazed area is called ‘horse-sick’, but grazing with cattle will minimise this effect.
Goats prefer to browse taller grasses, weeds and shrubs, and are not sensitive to wild endophyte toxins in ryegrass. Because they graze taller herbage, they often create clover-dominant pastures, so some farmers graze sheep with goats as a complementary system.
As well as helping improve pasture quality, goats have other beneficial attributes – they don’t get fly-strike like sheep, they need less feed in a drought, angora goats are easier to shear than sheep, and in 2007 were much more profitable. Goat meat – which, despite its present lack of popularity in New Zealand, is eaten by more people in the world than sheep meat – is lean and low in cholesterol.
Llamas and alpacas are less selective but patchier grazers than sheep, and are sensitive to wild endophyte toxins in ryegrass. They deposit their dung in set areas, and this leads to a loss of fertility in the remainder of the paddock.
Ostriches and emus will selectively graze the best quality forage that is available. Their feed demand may increase during winter to compensate for cold stress. They prefer softer-leafed plants, such as clovers, herbs, lucerne and grasses, but will also eat brassicas.
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