美国宾州大学草坪学

Turfgrass management

一、turf management

Turfgrasses are plants that form a more or less continuous ground cover that persists under regular mowing and traffic. An interconnecting community of turfgrasses and the soil adhering to their roots and other belowground organs form a turf. The terms turf and turfgrass are thus different in that one refers only to the plant community while the other represents a higher level of ecological organization by including a portion of the medium in which the turfgrasses are growing. When the surface layer of a turf is harvested for transplanting, it is called sod.

Turfgrasses evolved under the selection pressure of grazing animals. By close grazing, these large herbivors ensured the survival of only those plants with their growing points near the surface of the ground. In contemporary turfs, the uses to which the turf is subjected impose additional selection pressure and usually determine, along with management, how well a particular turf will perform.

Turfgrasses play a variety of roles in our lives. In this aerial photograph, notice how turfgrasses provide a fabric linking together different parts of the landscape.

The most basic function of any turf is soil stabilization. Then, the function of residential and commercial lawns is primarily aesthetic. And, finally, sports turfs are expected to withstand the physical stresses associated with specific sports and recreational activities.

These functions correspond to the intensity of culture employed to sustain the turf. Once established, turfs used exclusively for soil stabilization require infrequent mowing, little or no fertilization or irrigation, and no supplementary cultural practices. Lawn turfs typically require higher - and sports turfs the highest - intensity of culture to achieve and maintain the desired level of quality.

Thus, golf and athletic-field turfs provide for spectator sports and recreation, while lawn and roadside turfs serve decorative and utilitarian purposes, respectively.

This is an example of a utility turf along a roadside. While some portions of this turf are unmowed, others are mowed only three or four times per year to provide areas on which automobiles can stop during emergencies.

Utility turf also occur as grass strips on airports. Their purposes include stabilizing soils adjacent to runways and to serve as landing areas for light planes.

In addition to soil stabilization, lawn turfs enhance the aesthetic value of the residential or commercial landscape while providing arenas for play.

Some residential landscapes employ exotic plantings of turfgrasses and ornamental plants. In this photograph, the "lawn" is maintained like a golf green.

Golf turf is actually a composite of different turfs sustained at a broad array of cultural intensities. While the greens are the most intensively cultured turfs, they usually constitute less than two percent of the area on a golf course. Tees and collars add up to an additional one or two percent. Fairways and aprons might make up as much as thirty percent. The rest of the golf-course turf is the rough; the intermediate rough adjacent to fairways is maintained at a higher intensity of culture than the remaining roughs, which are often maintained as utility turfs.

A football field is an example of a turf used for spectator sports. In addition to stabilizing the soil and providing an attractive site, the turf must withstand the physical stresses associated with this sport. To the extent to which damage occurs, the turf should have the capacity to recover between games.

As much of the traffic is confined to non-turf areas, the turf on a baseball field is less of a challenge to maintain; however, at major stadiums, the quality of the turf is expected to be excellent.

Tennis turf is rare in the United States, but popular in the England. Its cultural requirements are similar to those of a golf green; however, because of the severe traffic stress, tennis turfs are a challenge to maintain at a consistently high level of quality.

This shows the Royal Ascot Racecourse in London, England. The track itself is mowed high to enhance its traffic tolerance and recuperative capacity, but the surrounding grounds are often intensively cultured for aesthetics and ceremonial purposes. The turf is predominently colonial bentgrass and annual bluegrass. Some yarrow was intentionally seeded to improve the wear tolerance of the turf.

This shows a dog-racing track in New Zealand. The track was seeded to perennial ryegrass and tall fescue.

Croquet is a sport popularly played on lawns; this "croquet court" at a country club in England is maintained like a golf green.

Lawn bowling is very popular throughout the British Commonwealth. Usually, bentgrasses and annual bluegrass are the predominent turfgrasses used; however, in New Zealand, Cotula - a broadleaf species - is used in place of grass.

Regardless of the particular use to which turfs are subjected and the intensity of culture imposed, they are incredibly complex and fascinating systems. In these ecosystems, turfgrass communities exists in intimate association with their climatic, edaphic and biotic environments. The quality and persistence of these turfs reflect how well all of the components interact to form a sustainable and effective association.

二、turf quality

The overall quality of a turf is determined by its visual and functional quality components.The most visible determinants of quality include: density, texture, uniformity, color, growth habit, and smoothness.Density is a measure of the number of aerial shoots per unit area. Density can vary with several factors, including: the particular turfgrass genotype, natural environmental conditions, and nature and intensity of cultural operations performed at the turfgrass site.Within the mowing tolerance range of a particular turfgrass, density decreases with increasing mowing height. At a particular mowing height density increases with increasing nitrogen fertility. Conversely, root growth and rhizome growth tends to increase with increasing mowing height.Texture is a measure of the width of the leaf blades.Texture varies widely among turfgrass species. Tall fescue is a relatively coarse textured species, while red fescue is quite fine textured. The bluegrasses, ryegrasses and bentgrasses are intermediate in texture.Texture and density are somewhat related in that coarse textured turfgrasses have relatively low densities, while fine textured turfgrasses can have very high densities.Uniformity is an estimate of the even appearance of a turf. The principal dimension of uniformity is compositional and deals with the mass of aerial shoots comprising the aerial portion of the turf. If each shoot is seen as having the same shape, size and orientation, the turf is said to be very uniform. Variations in turfgrass shoots, and the existence of weed species, disrupt the uniformity of the turf.Color is a measure of the light reflected by a turfgrass. Different turfgrasses vary in color from light to very dark green. Color is also a useful indicator of the general condition of the plants. A yellow or chlorotic appearance may indicate nutritional deficiencies, disease or some unfavorable factor affecting growth. Unusually dark color may be evidence of excessive fertilization, wilting, or the early stages of some disease.Growth habit describes the type of shoot growth evident in a particular turfgrass. The three basic types are: bunch-type, rhizomatous, and stoloniferous. Bunch-type turfgrasses spread primarily or exclusively by tillering. In addition to tillering, rhizomatous turfgrasses can spread by below-ground shoots called rhizomes, while stoloniferous turfgrasses spread by above-ground shoots called stolons.Smoothness is a surface feature of a turf that may affect both visual and functional quality. In this illustration, mowing with a dull mower can seriously reduce the smooth appearance of the turf and adversely affect putting quality on greens.The functional quality of a turf is determined not only by some of the visual characteristics already discussed, but by other characteristics as well, including: rigidity, elasticity, resiliency, recuperative capacity, yield, verdure, rooting, and putting speed. Rigidity refers to the resistance of the turfgrass leaves to compression, and is related to the wear resistance of a turf. It is influenced by the chemical composition of the plant tissue, water content, shoot size and density. Elasticity is the tendency of the turfgrass leaves to spring back once a compressing force is removed. It is an essential property of any turf since some traffic is inevitable with mowing and other activities. Elasticity is dramatically reduced when the turf is frozen; for this reason, traffic should be withheld on frosted turfs until the frost has disappeared. Resiliency is the capacity of a turf to absorb shock without altering its surface characteristics. While some resiliency is contributed by the turfgrass shoots, it is largely a feature of the medium in which the turfgrasses are growing. Layers of thatch and thatchlike derivatives add substantially to the resiliency of a turf. Ball roll is the average distance a ball travels upon being released to a turf surface. Mechanical devices may be used to release the ball at a consistent speed to obtain reliable measurements. An example is the stimpmeter used to measure ball on golf greens as an estimate of their putting speed. Recuperative capacity is the capacity of turfgrasses to recover from damage caused by disease organisms, insects, traffic and other factors. It varies with different turfgrasses and is strongly influenced by environmental conditions. Factors that reduce the recuperative capacity of a turf include: severely compacted soils, inadequate or excessive fertility and moisture, unfavorable temperatures, insufficient light, toxic soil residues, and disease. Yield is a measure of the clippings removed with mowing. It is an indication of turfgrass growth as influenced by fertilization, irrigation and other cultural as well as natural environmental factors. Excessively high yields may indicate excessive use of fertilizers, especially nitrogen, along with the often accompanying reductions in rooting, stress tolerance and disease resistance. Verdure is a measure of the amount of aerial shoots remaining after mowing. Within a particular turfgrass genotype, increasing verdure is correlated with increasing resiliency and rigidity. At higher mowing heights, the same genotype will often have more verdure and generally better wear resistance. With the same genotype and mowing height, verdure is directly proportional to density. Rooting is the amount of root growth evident at any one time during the growing season. It can be estimated visually by extracting a turf core with a soil probe or knife and carefully working the soil free with the fingers to expose the roots. Numerous white roots extending to a depth of several inches indicate favorable rooting in a turf. The overall turf quality level is determined by the relationship between factors that influence turfgrass growth and development - including climate, soil and culture - and those factors that influence decomposition and deterioration - including insects and other pests, disease-causing organisms, weeds and traffic. The ability of a turfgrass manager to maintain a desired level of turf quality reflects his or her ability to sustain satisfactory growth and development while controlling those factors that contribute to decomposition and deterioration.