LECTURE NOTES 2 1959
By Dr Deric Charlton
Preparing Winter Pastures
In autumn the livestock farmer has nature against him, as pasture plants are preparing to become dormant as the cool season approaches.
Vigour is needed in the pastures, so continuous grazing should be avoided in autumn as grass vigour has declined. The right species are needed for cool-season growth, as some will grow better then than others. Fertiliser application should be undertaken in early autumn for full advantage before growth has ceased.
The farmer’s skill is important at this time – whether he grazes or rests his pastures. If the pasture rested during autumn tillers will be developed but in cold areas, frost may kill many tillers and no young tillers will be able to form.
The best approach is to allow a good root system to be established, but not to let it grow “too proud” that there are no new tillers in late winter. Stopping grazing in late autumn allows the pasture to rest then and gives the tiller buds a chance to grow, providing late winter grazing and enabling the pasture to survive for another growing season. If the pasture is rested over winter the roots become vigorous and store nutrients, enabling the farmer to graze the pasture from late winter on into spring.
In pasture management the livestock farmer must always consider the future – the next seasons. His aim in summer is to prevent primordia growing into seedheads – keep the pasture leafy – and in autumn he must keep the pasture growing but avoid letting become “too proud”. The farmer should always consider clover content in his pastures as this contributes greatly to the feed quality obtained. Clover provides protein whereas the grass provides bulk and fibre.
Plant competition
There are three main factors to consider in plant competition in a pasture:
- Early season growth
- Growth form
- Palatability
Early season growth
Resting a ryegrass-clover pasture in early spring will lower the clover content, as there is strong competition from the ryegrass then. The earlier-growing grasses will win any competition with clover and later-developing grasses in early spring when there is no grazing.
However, if the pasture is grazed the early grasses will use their reserves by late spring when the later-growing species still have stored reserves. These later growers are not so closely grazed, as there is plenty of forage by then, so they are favoured.
Growth form
Without any spring grazing the erect-growing plants are favoured, whereas when a pasture is grazed the low-growing prostrate plants, such as white clover, will gain in growth. Carbohydrates from animal droppings will benefit the clover growth whereas the grasses absorb any nitrogen. The carbohydrate supplied in this way probably helps the nitrogen-fixing bacteria in the clover root nodules to survive and perform effectively.
Palatability
If the animal stocking rate is maintained at the optimum level, palatability is unimportant. Grasses, however, are more palatable when their tillers are young, and the farmer should graze them then, to keep the grass tillers young and leafy. When there is excessive growth in a pasture then palatability comes into play and causes selective grazing, and each livestock type has a particular preference among the pasture plants.
Pasture Types in Britain
Four main types of pasture occupy nearly all of the British grasslands:
- Finishing (fattening) pastures
- Breeding pastures
- Ranching pastures
- Meadows
These carry stock from 1 sheep to 2ha to 12 per ha. In the 1920s Welsh Plant Breeding Station scientists led by Sir George Stapledon and William Davies undertook a vegetation survey of Britain, assessing permanent natural land by its productivity. However they found it was impossible to classify grassland productivity according to the individual productivity of grasses, in that, for example, cocksfoot was found everywhere.
Some grasses however did indicate productivity – species like browntop (Agrostis) and fescues had fine leaves in poorly productive land but had broader leaves in higher productive land. There was always a range within a species, but which was the dominant plant? Cocksfoot, for example could be found dominating a very productive pasture but could also dominate a less productive one.
Davies selected perennial ryegrass as the standard indicator of productive land. The fine-leaved fescues (Festuca rubra and F. ovina) were present on good land under adverse conditions but dominated pastures on infertile land, so he selected these grasses as indicators of low-class land. Browntop (Agrostis Spp) was selected as the intermediary indicator.
They found that the Midlands was the largest area of productive pasture and the estuaries featured the next best grasslands. They felt that three factors determined this:
Soil – the soil types found in the Midlands are too heavy for arable farming but highly priced, so had been put into pasture. In these areas the arable farmers became animal farmers and livestock farming became the tradition, So although the soil wasn’t the best, the conditions determined their use as pastures. These soils are retentive alluvial deposits that are fairly quick in weathering, whereas the granite soils of Wales weather only very slowly.
Climate – affects the soil as well as the pasture growth.
Pasture and livestock management – farmers sow different seeds mixtures on their land when they resow it, and some land in the Midlands cannot carry stock over winter. The pasture use determines the botanical composition of a pasture.
Finishing (fattening) pastures
These pastures are usually found on heavy soils with a good water table. They are grazed each year and droppings are returned to the land. By returning animal droppings and a pasture management that encourages clover growth, the soil fertility is gradually built up. The only crop being sold off is the livestock and these pastures are usually only grazed in winter at a very low stocking rate (2-3 sheep/ha) and this encourages spring growth, insuring against drought. Accordingly the earlier-growing grasses (perennial ryegrass) have the advantage and hard grazing during late spring-early summer removes the cocksfoot and timothy content. So in these best pastures perennial ryegrass and white clover are the dominant pasture species.
The cattle usually graze the fields nearer the farm buildings most and in spring. This depletes the early-growing grass content and the pasture consists of ryegrass mixed with browntop. The fields furthest away from the buildings tend to be grazed least, so these become ryegrass-dominant.
In the past the market for beef determined the period that cattle were kept on the farm, so some Midland pastures deteriorated due to winter stocking. In the North of England famers tend to buy cattle in for winter stocking as the land can stand this use, so the pastures tend to be cocksfoot dominant.
Breeding pastures
The pastures are grazed hard in spring and then rested for a hay crop. Accordingly ryegrass and clover disappear and they become cocksfoot-dominant. Where there is a tendency towards mixed farming, the pasture quality deteriorates and browntop takes over.
Ranching pastures
In these situations stock are left to roam within the enclosed land so they take the best grasses when they can and gradually rob the land, as they defecate and sleep elsewhere. The land usually suffers from a lack of one essential, such as water or a mineral, so there is little capitol invested in the livestock.
In some countries where ranching is the normal practice there is so much drought that stocking rates must be very light. When drought sets in all the fodder is eaten, but when there is a wet season the grass beats the stock and so it survives. Any little artificial input will result in a great overall improvement. All water conservation methods are practised on these lands and holes up to 150mm deep are made using tractor equipment, to avoid water run-off.
In north-western Victoria, Australia there is an area called the Simpson Desert. As the land was settled in the 1800s and 1900s cultivation developed all around the Desert and a farmer called Anderson discovered this desert sand reacted strongly to molybdenum and managed to cultivate a large area of it.
Irrigation is the most used improvement method for ranching pastures. The cost of water distribution can be very high, but it can often be financially worthwhile.
Meadows
Meadows are found in all types of climate and they receive different managements so vary a lot. The soil fertility level is usually maintained by return of farmyard manure.
When farmers sow seed mixtures to renovate meadowland they protect the component they want to keep growing, and so it persists longer than the other species. For example timothy has remained the dominant grass in pastures around Sterling since the mid-1880s, because the swampland on the Carse of Sterling was stripped of 2-3m of peat by returning soldiers who were given blocks of this land. This left a heavy clay soil that suits timothy perfectly, and green-cut hay was in great demand to feed the draught horses then used in Glasgow and Edinburgh.
Eventually the horses were replaced by motorised transport but the timothy farmers had by that time developed a persistent form of timothy that was labelled Scots timothy, and this grass was in demand for seeds mixtures in England. This practice – and the timothy – persists to this day.
The well-known Cockle Park seeds mixture, developed by Gilchrist in Northumberland after extensive research on farms, has been a favourite mixture for farmers with meadowland. When they sow the mixture as a long ley, the perennial ryegrass dominates in the first year, as the farmer wants a hay crop then, so he doesn’t graze it very much. By the second season the ryegrass has been exploited and so cocksfoot and timothy dominate. However the ryegrass can be maintained by keeping its seedheads down as summer comes, and by returning droppings.
Spring grazing checks the ryegrass more than cocksfoot and so a mid-summer hay crop is dominated by the cocksfoot. This species stores food after the hay is taken, and quickly develops an aftermath, where it is rather unpalatable and so it protects itself to grow in future seasons.
In The Netherlands the water table tends to be high in winter but is lowered in spring, allowing the early grasses to grow. In summer the water table rises again and so hay crops on this land consist mainly of meadow fescue. But this grass tends to be unpalatable there, so the pasture is ploughed in and renovated with Italian and perennial ryegrass. However in Britain, timothy and meadow fescue grow well together, are palatable and are therefore grown in drier meadows.
In meadowland when no other grasses dominate, Poa species (meadow-grasses) invade but tend to be unpalatable and this protects them from overgrazing. Crested dogstail (Cynosurus cristatus) also thrives in less fertile overgrazed meadows. This grass is easy to harvest for seed so was included in seeds mixtures, but it invades with Poa species anyway and is rather a nuisance as it is very early into seedhead and bears very few tillers.
Whichever grass dominates a meadow depends on the farmer’s grazing management. However white clover only tends to persist with perennial ryegrass – the two are excellent for growing high quality livestock feed.
By making silage, rather than hay, a farmer can control the feed quality of such species mixtures more easily. Better feed quality can also be conserved for winter supplementary feeding, thus relieving pressure on pastures at this time.
No comments:
Post a Comment