Laidlaw / Frame Improved Grassland Management

1. Auflage 2013
ISBN: 978-1-84797-727-4
Verlag: Crowood
Format: EPUB
Kopierschutz: 6 - ePub Watermark

E-Book, Englisch, 352 Seiten

This new, fully updated and revised edition of Improved Grassland Management covers all aspects of grassland management and is of particular relevance to the UK and the Republic of Ireland, although the principles discussed apply to all temperate grassland zones. Almost twenty years ago, when the original edition of this book was written by John Frame, issues such as efficiency in the use of nutrients in manures, grassland biodiversity and greenhouse gas emissions from ruminant production were either nascent, or of no relevance to mainstream grassland farming. The intervening two decades have seen the introduction of water and, latterly, air quality directives by the EU, cross compliance, the single farm payment, and an ever-increasing need for grassland farmers to be conscious of the economics of their business. The present edition, which has been thoroughly revised by Scott Laidlaw, covers the full scope of modern grassland management. Accordingly the application of technical developments in supplying and utilizing grass and forage, which remain central to grassland management, is presented in the context of these changes.Topics covered include: breeding and evaluation of new varieties of grass to meet current needs; new technology in establishing swards; legislative constraints, background science and practice in determining forage quality and the utilization of forage either for grazing or silage; feed budgeting, grassland biodiversity, grassland and climate change, and transferring knowledge and technology; wide-ranging list of sources and references, which provides the reader with further detailed information. Essential reading for all those involved in modern grassland management including grassland farmers, agricultural consultants and advisory officers, as well as agricultural, land use and biology students. Written in a reader-friendly advisory style, it can be read and understood without an in-depth technical or scientific background. Fully illustrated with 61 colour photographs.

Autoren/Hrsg.

Laidlaw, A S

Frame, John

Leseproben

2

Characteristics of Grasses and Legumes

Next in importance to the profusion of water, light and air, those three great physical facts which render existence possible, may be reckoned the universal beneficence of grass.

J.J. Ingalls (1872)

Although temperate grasses share many features in common, especially their general form, they differ widely in their responses to soil conditions and other environmental variables. As pointed out in Chapter 1, botanical composition of sown swards changes with age. Although many factors influence the relative competitiveness of species some are more important than others. The most important within a climatic zone, after management, are mainly soil-based.

Main factors that influence sward composition:

• Type of management

• Nutrient availability

• Soil moisture

• Soil pH.

Source: Peeters

This chapter provides information on the main sown and natural grass species in lowland, particularly with regard to their agronomic characteristics and their response to some of the factors listed above.

SOWN GRASS SPECIES

Perennial Ryegrass

This is clearly the most important and widely used grass species in seed mixtures, exhibiting rapid establishment, good tillering ability, excellent production response to fertilizer N and high acceptability to stock. At equivalent growth stages to other species, both perennial and Italian ryegrasses produce higher DM yields at specific levels of digestibility. Production of perennial ryegrass at a given level of digestibility can be at least 20 per cent more than that of cocksfoot, for example. However, more recently bred varieties of other sown species suggest that the gap is narrowing.

Inflorescences of perennial ryegrass.

Perennial ryegrass is persistent if soil fertility is high, particularly the intermediate and late heading varieties. It is also tolerant of intensive grazing and of cutting, provided interval between defoliations is not excessively long. It regrows quickly after defoliation provided swards are not cut for repeated heavy crops of silage or for hay at a mature stage of growth, since these managements reduce tiller density.

There are numerous recommended varieties and seed is normally readily available, except perhaps the most recently recommended varieties. As the varieties exhibit a wide range of characteristics, for example in heading dates, earliness of growth, disease resistance and persistency, perennial ryegrass can fulfil the needs of most farming systems. It is also an important grass in other temperate regions of the world, such as New Zealand.

However, perennial ryegrass does not grow well under very dry conditions, where summers are hot or on infertile soils. When grown under infertile conditions the sward becomes weak and stemmy, lacking longevity and susceptible to invasion by indigenous grasses and weeds. Its susceptibility to winter damage during cold periods or frost damage on first spring growth has been greatly reduced due to progressive improvement in cold hardiness of varieties and less frequent occurrence of cold winters in recent years.

Distinctive varieties of the different ryegrass species have been bred with double the number of chromosomes of normal diploid varieties. These commercial tetraploid ryegrasses were introduced in the 1960s. Tetraploidy can also occur as ‘sports’ in natural populations. Some of these were developed, and cocksfoot grass and white clover, for example, are natural tetraploids. Timothy is a hexaploid, that is it has six sets of chromosomes.

Perennial ryegrass (left) and red fescue tillers. Leaves of red fescue are thin and bristle-like.

Perennial ryegrass cultivars are either diploid (natural number of chromosomes) or tetraploid (double the natural number of chromosomes). Plant breeders induce tetraploidy in ryegrasses by chemical, radiation or other treatment and they follow this by selection programmes. Compared with diploids, tetraploids have larger seed (two to four times heavier than corresponding diploids). Originally, tetraploids had a lower population density, larger tillers, higher water-soluble carbohydrate content, higher digestibility, lower dry matter content and higher dry matter yield than diploids. Some of these attributes conferred higher animal intake characteristics on tetraploids. However, the differences are now not so clear-cut as some tetraploids have relatively high tiller densities and some diploids have, for example, high dry matter yield potential, high water-soluble carbohydrate content and elevated digestibility. The high moisture content (low dry matter) of tetraploids is often cited as a disadvantage in silage or hay making, where wilting and drying are required, but in fact the differences are small in comparison to fluctuations brought about by nitrogen fertilization. The openness of most tetraploid ryegrass swards compared with diploid swards makes them compatible with clover.

To identify perennial ryegrass in a vegetative sward in the field, it is one of only two species whose tiller has a red base and shiny underside to its leaves. The other is red fescue, but its leaves are generally bristle-like.

Italian Ryegrass

This is the second most popular grass species sown, although its popularity has declined with the increasing trend towards long-term swards and greater use of the longer living hybrid ryegrasses. It is a biennial, that is it usually completes its lifecycle in two years, although some crops produce reasonable yields in their third year. It is most productive in the first full year after sowing.

Part of an Italian ryegrass inflorescence (right), showing awns (bristles) on the florets within its spikelets (i.e. structure comprising groups of florets), compared with the bristleless spikelets of perennial ryegrass (left).

Italian ryegrass commences growth early in spring, especially if sown in late summer rather than in spring the previous year. Under intensive fertilizing and cutting for conservation it gives good production of herbage of high digestibility. It can be grazed before cutting for silage since it is not an early heading grass, most varieties heading during the same period as intermediate perennial ryegrass. It is also productive in the year of sowing if sown in spring because of its rapid establishment and growth vigour. It can therefore be used as a catch crop or as a pioneer constituent in mixtures with forage rape.

The main drawback with Italian ryegrass is its short-lived nature, which is associated with a high degree of stem production; this lowers acceptability to grazing stock in midsummer if swards are not well grazed. Production from the second full harvest year is also substantially lower than in the first. Older swards of Italian ryegrass or swards that are allowed to enter winter with surplus growth are more susceptible to winter damage than other main sown species. In Recommended Lists Italian ryegrass varieties are rated lower for winter hardiness than perennial ryegrass varieties.

Hybrid Ryegrass

This is a bred hybrid between Italian and perennial ryegrass, with the aim of incorporating the more desirable characteristics of both parents, for example the rapid establishment and vigour of Italian ryegrass with the tillering ability of perennial ryegrass. Hybrids may resemble one or other of the parents or be intermediate in appearance. The Italian types have awned seedheads, form an open sward due to a low tiller density, give good spring growth and have higher yields than the perennial types. The majority of hybrids on Recommended Lists are tetraploids and the best hybrid ryegrasses are less productive than the best Italian ryegrasses but exhibit better ground cover and drought tolerance. The perennial types can potentially remain relatively productive for up to five years. Their main role is in high production swards that are mainly intended for silage production but they are not restricted to only-cutting swards. In grazed swards, their midseason acceptability is usually higher than that of Italian ryegrass.

Westerwolds Ryegrass

This is a rapidly establishing annual species (considered an annual form of Italian ryegrass) that gives high production in the season of sowing if seeded early and adequate moisture is available. It is therefore suitable for routine or emergency catch cropping. Both diploid and tetraploid varieties are available. Unlike Italian ryegrass, it heads profusely in the sowing year so defoliation, whether by cutting or grazing, must be sufficiently frequent to keep swards leafy to prevent a decline in their digestibility with maturity.

OTHER SOWN GRASS SPECIES

Timothy

This species occurs naturally as a hexaploid (six sets of chromosomes in its nucleus). It is better suited to cutting than grazing but it is very acceptable to grazing animals and, when mixed with competitive grasses such as perennial ryegrass, its slow regrowth leads to its being grazed out if grazing is intensive. It is useful for the cool wet conditions in the north and west and is invaluable on wet, peaty and heavy textured soils. Being the most winter hardy of the main grass species and also winter green, it produces valuable early growth in upland areas where it tolerates lower fertility than ryegrass. The seed is very small, 2 to 3 million per kg, slow to establish and should not be sown deeper than 10 to 15mm.

Timothy herbage has a low mineral content. Its digestibility declines less rapidly with maturity than the other major grasses, though the decline starts at an earlier growth stage. Therefore, it should be cut well before ear...