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1.
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2.
An experiment was conducted to determine the genetic variation among diploid perennial ryegrass (Lolium perenne L.) varieties for sward structural characteristics considered to be important for intake by cattle. Assessments were made between June and September in 2000 and 2001. Six varieties (Abergold, Respect, Agri, Herbie, Barezane and Barnhem) were subjected to a cutting experiment where swards were cut after 3 to 4 weeks of regrowth during the growing season. The variables, measured in three 2‐week periods, were herbage mass of dry matter (DM), sward surface height (SSH), bulk density, proportion of green leaf, tiller density, tiller weight, extended tiller height, length of sheath and length of leaf blade. Significant differences among varieties were found in both years for herbage mass of DM, SSH, bulk density, proportion of green leaf, tiller density, tiller weight and length of sheath. The results show that there is significant genetic variation among diploid perennial ryegrass varieties for sward characteristics important for intake during grazing.  相似文献   

3.
The effect of sward structure of four temperate grass species on the bite mass of cattle was evaluated. Micro‐swards (79 cm × 47 cm; approximately the area of a feeding station) of orchardgrass (Dactylis glomerata L.), quackgrass [Elymus repens (L.) Gould], meadow fescue [Schedonorus pratensis (Huds.) P. Beauv] and reed canarygrass (Phalaris arundinacea L.) were offered to Holstein dairy cows in short‐term grazing sessions in 2006 and 2007 using a 4 × 4 Latin square design. Cows were allowed to take fifty bites in each session. Bite mass was calculated by dividing the adjusted change in weight of the micro‐sward by the number of bites. Sward surface height, bulk density and distribution of herbage dry matter (DM) in the canopy were measured pre‐ and post‐grazing. Sward structure differed among the grass species within years but bite mass (on a fresh or DM basis) was not affected. Higher surface heights and bulk densities in 2006 compared with 2007 (averaged across grass species) resulted in greater bite masses of DM in 2006. Values were 25·7 cm vs. 17·0 cm for surface height; 1219 g m?3 vs. 926 g m?3 for bulk density; and 1·05 g DM bite?1 vs. 0·50 g DM bite?1 for 2006 and 2007 respectively. Within the context of this study, differences between years in bite mass, associated with greater changes in sward structure, were more important than differences among grass species.  相似文献   

4.
Three cultivars (two diploid and one tetraploid) in each of three maturity groups (early, intermediate and late) of perennial ryegrass were sown in 10 m2 plots, replicated four times, in Northern Ireland in June 1997 in a study of the effect of heading date on tiller development (including initiation to flower) and turnover of tillers produced at specific times in spring in 1998 and 1999. The plots were harvested seven times in each year. Annual dry‐matter production was similar for all groups in each year. In spring and early summer of both years, tiller density of the diploid cultivars was 1·5 times greater than that of the tetraploid cultivars and the mean tiller density over all swards in June was about 0·40 times greater than that in April. Maximum proportions of reproductive tillers in the early, intermediate and late maturity groups, determined from apical dissections, were found in early April, mid‐May and early June, respectively. Although a high proportion of tillers, which were present when annual observations commenced in spring, was decapitated at the first harvest in the early group, the previous population density was maintained by rapid production of new tillers during May, including those from suppressed tiller buds during reproduction. It is concluded that the relationship between heading date and rate of tiller turnover (including flowering) at specified times in spring is important in sward management throughout the early part of the growing season and should be taken into account in tiller‐based grass growth models.  相似文献   

5.
During an experiment in which the height of mixed perennial ryegrass/while clover swards was maintained throughout the season at 3 or 7 cm (S and T, respectively), or were maintained al those heights until 30 June then changed (ST and TS), a limited study was made of the effects on the population densities and masses of the two species. During the earlier part of the season the short swards (S and ST) developed higher tiller and stolon growing point (sgp) densities, but with a reduced mass of ryegrass, principally of the pseudostem fraction, than the tail swards (T and TS). Thiere was little effect of sward height on the mass of clover. Whilst there was a general tendency for tiller and sgp densities to increase during the latter part of the season, tiller density increased greatly where sward height was reduced (TS) and both tiller and sgp densities were reduced where sward height was allowed to increase (ST). Changing sward height, whilst limiting the accumulation of dead grass material (TS), allowed grass leaf and dead masses to increase (ST), and adversely affected the increase in the clover component, principally of stolon material, in both ST and TS.  相似文献   

6.
A perennial ryegrass (Lolium perenne L.)‐dominated sward on a well‐drained soil (Experiment 1) and a creeping bent (Agrostis stolonifera L.)‐dominated sward on a poorly drained soil (Experiment 2) were subjected to four treading treatments: control (C, no damage), light damage (L), moderate damage (M) or severe damage (S) to quantify the effects on herbage dry‐matter (DM) production and tiller density. In Experiment 1, treading damage was imposed in spring. In Experiment 2, one‐third of the site was damaged in autumn, one‐third in spring and one‐third in both spring and autumn. Both sites were rotationally grazed after treading treatments. Pre‐grazing herbage mass was measured eight times in Experiment 1 and seven times in Experiment 2 on each plot, and tiller density was assessed four times in each experiment. In Experiment 1, pre‐grazing herbage mass was reduced by 30% in S plots at the first harvest after damage, but cumulative pre‐grazing herbage DM production was not different between treatments (12·7 t DM ha?1). In Experiment 2, annual cumulative pre‐grazing herbage mass was reduced by between 14 and 49%, depending on intensity of treading damage event and season when damage occurred. Tiller density was not affected by treatment in either experiment. A perennial ryegrass‐dominated sward on a well‐drained soil was resilient to heavy treading damage. A creeping bent‐dominated sward on poorly drained soil requires a more careful grazing management approach to avoid major losses in cumulative pre‐grazing herbage mass production during wet weather grazing events.  相似文献   

7.
The use of plant phenology for determining the timing of management practices is poorly understood in species‐rich grasslands. The objectives were to assess the effect of management practices on the dates at which phenological stages occur and to compare different methods of calculating the growing degree‐days in order to predict them. Dates at which phenological stages of plant species occurred were recorded and plant strategy for resource capture and use was assessed through measurements of the dry matter content of leaves in two experiments in regions with contrasting climatic conditions. In Experiment 1, conducted near Toulouse, France, a set of 31 species was sown in pure stands at two levels of N availability. In Experiment 2, a network of 18 permanent grasslands, located in the French Pyrenees, was studied. In both experiments, the dry matter content of leaves, and flowering and ripening times, were measured. In Experiment 1, the dates on which a given phenological stage occurred were correlated with one another, and the grass species showed a significant ranking of dry weight of leaves for these dates. In Experiment 2, the difference between average flowering times of plant communities was shown to be around 40 d and resulted more from the species composition of the plant community than from their sensitivity to management practices. Plant communities were significantly ranked by dry weight of leaves for their flowering time. The minimum and maximum base temperatures which minimized the growing degree‐days between the two locations were 0 and 25°C, respectively, and the most appropriate date from which to start to accumulate temperatures was found to be 1 February.  相似文献   

8.
Abstract The effects of genotypic variation in ryegrasses on sward structure, bite dimensions and intake rate by dairy cows were investigated. Two experiments were conducted. In Experiment 1, swards were in a vegetative state whereas, in Experiment 2, they were partly reproductive and were taller with higher herbage mass but lower leaf proportion than in Experiment 1. Applicability of relationships between sward structure and bite characteristics, previously established from artificial or hand‐constructed swards, to field conditions were tested. Additional short‐term intake rates and/or sward structural characteristics were considered as indicators of potential intake for use in protocols for the evaluation of grass varieties. Four cultivars were studied: AberElan, Twins (diploid and tetraploid perennial ryegrasses respectively), Polly, a hybrid ryegrass (perennial × Italian ryegrass) and Multimo (Italian ryegrass), each established in 200‐m2 plots in four replicated blocks. Herbage intake rate was determined by short‐term liveweight change (taking account of insensible weight loss) using 16 dairy cows allocated to four balanced groups with each plot grazed by one group for a 1‐h assessment period. One block was grazed per day, over a 4‐d experimental period, with each group grazing each variety in a complete crossover design. Sward characteristics and bite rate were also measured in both experiments. Bite dimensions were subsequently estimated, with bite depth being determined as a function of extended tiller height (ETH) in both experiments. Within both experiments, bite mass and intake rate did not differ significantly between swards of different cultivars despite swards containing Multimo generally having a higher ETH and water‐soluble carbohydrate concentration and lower green leaf mass, sward bulk density and neutral‐detergent fibre concentration than the other swards. However, bite depth was significantly higher (P < 0·01) in swards containing Multimo swards than in the others and, in Experiment 1, bite depth, as a proportion of ETH, was higher in swards containing Multimo and lower in those containing Twins than in the other two cultivars, whereas there was no difference in Experiment 2. Taking both experiments together, the mean bite depth was 0·5 of ETH with sward bulk density accounting for almost half the variance in the relationship between bite depth and ETH. The bulk density of the bite (bite mass per unit bite volume), measured in Experiment 2, followed a similar pattern to sward bulk density, increasing in the order Multimo, Polly, AberElan and Twins. It is concluded that the relationships between sward characteristics and bite dimensions, derived from artificial swards, are applicable to field swards, although the range in natural ryegrass sward characteristics is usually not as wide as in experiments using artificial swards. Lack of precision in the measurement of short‐term intake and in sward‐based measurements is likely to preclude their use in the evaluation of grass varieties.  相似文献   

9.
Soil occupation capacity via lateral expansion of tussocks in elephant grass (Pennisetum purpureum Schum.) may be associated with basal tillering. As grazing management alters the proportion of basal and aerial tillers in a tiller population, the hypothesis of this work was that grazing management affects tussock size and distribution with implications for plant population stability. The objective of this study was to evaluate the tiller population stability index, the proportion of basal and aerial tillers, tussock size, and the frequency of tussocks and bare ground in rotationally managed elephant grass cv. Napier. Treatments resulted from the combination of two post‐grazing heights (35 and 45 cm) and two pre‐grazing conditions (95% and maximum canopy light interception during regrowth – LI0·95 and LIMax) and were allocated to experimental units (850 m2 paddocks) according to a 2 × 2 factorial arrangement in a randomized complete block design, with four replications. Measurements were taken from January 2011 to April 2012. The post‐grazing height treatments affected the tiller population stability index, but did not influence the pattern of tussock distribution. On the other hand, the different grazing frequencies (targets of LI pre‐grazing) altered the pattern of tussock distribution and the proportion of bare ground. In general, the tiller population stability index and frequency of tussocks were higher and the frequency of bare ground lower on swards managed with the LI0·95 target relative to those managed with the LIMax target, regardless of the post‐grazing height used, indicating a larger soil occupation capacity of plants under the more frequent defoliation regime. Such responses were associated with larger population of basal tillers and highlight the importance of tiller category and perennation pathway in defining patterns of plant growth and tussock distribution.  相似文献   

10.
Prairie grass ( Bromus willdenowii Kunth) and a tetraploid Westerwolds ryegrass ( Lolium multiflorum Lam.) were established in a field trial in April 1987 and grown for a 3-month period of undisturbed growth. During this period the biomass partitioning and forage quality of each plant component was compared for the two species. Leaf, tiller and plant populations were assessed on ten occasions while accumulation of herbage and roots, chemical composition, leaf area and light interception were determined on six occasions. Herbage was divided into leaf lamina, inflorescence, vegetative and reproductive pseudostem. Nitrogen, water-soluble carbohydrates, ash, cell wall and in vitro digestibilities were determined.
Prairie grass had lower plant, tiller and leaf populations but larger tillers and more live leaves per tiller than Westerwolds ryegrass. Both species had similar light interception and leaf area index. Roots were distributed more evenly and to greater soil depths in prairie grass. Leaf lamina made major contributions to herbage DM accumulation and accumulation of the various chemical components, but as reproductive development occurred, reproductive pseudostem became a major component of the total sward. Harvesting herbage to gain optimum quantities of DM, herbage quality and regrowth is discussed. It is concluded that prairie grass is a high-yielding, high-quality forage grass, comparable with Westerworlds ryegrass.  相似文献   

11.
The objective of this study, which was part of a larger grazing‐systems experiment, was to investigate the cumulative impact of three levels of grazing intensity on sward production, utilization and structural characteristics. Pastures were grazed by rotational stocking with Holstein–Friesian dairy cows from 10 February to 18 November 2009. Target post‐grazing heights were 4·5 to 5 cm (high; H), 4 to 4·5 cm (intermediate; I) and 3·5 to 4 cm (low; L). Detailed sward measurement were undertaken on 0·08 of each farmlet area. There were no significant treatment differences in herbage accumulated or in herbage harvested [mean 11·3 and 11·2 t dry matter (DM) ha?1 respectively]. Above the 3·5 cm horizon, H, I and L swards had 0·56, 0·62 and 0·67 of DM as leaf and 0·30, 0·23 and 0·21 of DM as stem respectively. As grazing severity increased, tiller density of grass species other than perennial ryegrass (PRG) decreased (from 3,350 to 2,780 and to 1771 tillers m?2 for H, I and L paddocks respectively) and the rejected area decreased (from 0·27 to 0·20 and to 0·10 for H, I and L paddocks respectively). These results indicate the importance of grazing management practice on sward structure and quality and endorse the concept of increased grazing severity as a strategy to maintain high‐quality grass throughout the grazing season. The findings are presented in the context of the need for intensive dairy production systems to provide greater quantities of high‐quality pasture over an extended grazing season, in response to policy changes with the abolition of EU milk quotas.  相似文献   

12.
To allow improved prediction of daily herbage intake of dairy cows in rotational grazing systems, intake behaviour was assessed throughout the day in 24‐h paddocks. Herbage intake in 16 lactating Holstein–Friesian cows was assessed using the short‐term (1‐h) weight gain method at four predetermined natural meal times throughout the day (early morning, T1; late morning, T2; mid‐afternoon, T3; and early evening, T4). The study comprised two 4‐day experiments, each with a cross‐over design of four blocks. In both experiments, cows grazed a 24‐h paddock daily, and the effect of the immediately previous grazing experience on intake behaviour was investigated throughout the day, taking account of daily fluctuations in the short‐term physiological condition of the cows. Experiment 1 was carried out to investigate overall grazing behaviour during meals as a sward is progressively depleted during the day, with intake being assessed within the paddock and, hence, on a depleted sward. Experiment 2 similarly investigated the effect of sward depletion and physiological condition throughout the day on intake, but cows were removed to fresh, undefoliated swards during intake measurement periods; thus, intake rate was not influenced by differences in sward condition. Intake behaviour from both experiments was compared to establish the effect on herbage intake of changes in sward state and non‐sward factors. In Experiment 1, sward surface height, available herbage mass, proportion of leaf and green leaf mass declined as the day progressed. Bite mass declined with sward depletion, and mean intake rate was 1·64 kg dry matter (DM) h–1, which was significantly lower at T3 (P < 0·01) than during other meals. In Experiment 2, plot sward conditions did not change throughout the day, and intake behaviour also remained constant, with a mean intake rate of 2·11 kg DM h–1. Mean bite depth as a proportion of pregrazing extended tiller height was constant throughout the day (mean 0·32). The results show that, although cows grazed throughout the day on progressively depleted swards, indicative of rotationally grazed paddocks (Experiment 1), bite mass declined linearly and intake behaviour was variable. However, where intake was assessed on high‐quality, undefoliated swards (Experiment 2), intake behaviour was similar regardless of the time of day and the immediately previous experience. There was some indication of an interaction between the effects of the sward and the physiological condition of the animal on herbage intake.  相似文献   

13.
Pasture managers seek to balance leaf appearance with utilization to sustain sward productivity while meeting livestock nutritional needs. Achieving this in silvopasture must account for the influence of light and defoliation on tillering. We determined tiller production, as a function of light availability and clipping height, for two forage grasses adapted to cool, humid temperate conditions of the Appalachian region of the USA. Tiller production of cocksfoot (orchard grass) (Dactylis glomerata L.) and tall fescue (Festuca arundinacea Schreb.) was greatest in unshaded and least in shaded sites, irrespective of residual clipping height. Juvenile plants produced more than twice as many tillers as mature plants, with differences accentuated by site, reflecting a shift in reproductive and resource‐use strategies. Trends in tiller production were as follows: cocksfoot > tall fescue; 10‐cm > 5‐cm residual clipping height; and unshaded > partially shaded > densely shaded sites. Tiller production reaches maximum earlier in the woodlot site, regardless of species or clipping height, than at the unshaded site. Plants at the wooded site extended leaves quickly, sustaining herbage production, but had less non‐structural carbohydrate and fewer tillers. Cocksfoot, but not tall fescue, sustained leaf and tiller production in the shaded sites, suggesting that cocksfoot is suited for use in silvopasture in this region.  相似文献   

14.
The objective of this study was to identify and understand grassland management practices employed on dairy farms in the Republic of Ireland, including grazing‐season length, concentrate‐feed input, uptake of new grassland‐management technologies and frequency and methods of sward renewal. The sample population for the survey was chosen from a proportionate representation of all milk suppliers taken from three of the largest dairy processors in the Republic of Ireland. The sample was subsequently broken down into three stocking rate (SR) and three size categories of milk quota (Qcat) to investigate their effects on the survey variables. Both SR and Qcat had significant effects on the proportion of participants adopting grass‐based technologies and on the amount of supplementary feed offered. Grazing‐season length increased from 228 d in Qcat1 to 249 d in Qcat 3 but was unaffected by SR (241 d; s.d. 3·05). The proportion of the grazing area reseeded annually was significantly affected by SR, increasing from 0·044 to 0·095 of the grassland area as SR increased from SR1 to SR3, with no effect of Qcat (0·068). The results show that on‐farm grass utilization is low, with significant potential for expansion and increased efficiency through increased SRs, greater adoption of grassland‐management technologies and higher levels of sward renewal.  相似文献   

15.
Appropriate pre-sowing methods for the introduction of improved forage legume and grass germplasm are an important issue for hill pasture improvement in New Zealand. A pastoral fallow, which involves not defoliating pasture for a period generally from late spring/early summer to autumn, could create a potentially favourable environment for introducing improved germplasm. A field study was conducted on two aspects (shady and sunny) of moist, low-fertility hill country with or without added fertilizer (phosphorus and sulphur) in the southern North Island of New Zealand, to investigate the changes in plant population density and sward structure during a full or partial pastoral fallow, compared with a rotationally grazed pasture. A 7-month (October to May) pastoral fallow dramatically decreased the densities of grass tillers by 72% (P < 0·01), white clover (Trifolium repens L.) growing points by 87% (P < 0·01) and other species by 87% (P < 0·05). The decline in tiller density by pastoral fallow was enhanced on the shady aspect. Fertilizer application increased white clover growing-point density on the shady aspect (P < 0·05) and grass tiller density on the sunny aspect (P < 0·05). Decreased plant density during pastoral fallowing was attributed to aboveground biomass accumulation, which altered sward structure, leading to interplant competition and mortality by self-thinning and completion of the life cycle of some matured plants. The plant size-density relationship during pastoral fallowing in this mixed-species sward followed the serf-thinning rule, particularly when the calculation was based on all plant species rather than grass alone. There was no significant (P > 0·05) difference in final plant population density between the 7-month pastoral fallow and a shorter term (October to December) pastoral fallow. It is concluded that pastoral fallowing effectively reduced the plant population density and altered sward structure of a hill pasture. Such changes create a more favourable environment for the introduction of improved forage species.  相似文献   

16.
The study was designed to test the hypothesis that grazing management in early season could alter sward structure to facilitate greater animal performance during critical periods. The effects of grazing a mixed perennial ryegrass/white clover sward at different sward surface heights, by cattle or sheep, in early season on sward composition and structure, and on the performance of weaned lambs when they subsequently grazed these swards in late season were determined. In two consecutive years, from mid‐May until mid‐July, replicate plots (three plots per treatment) were grazed by either suckler cows and calves or ewes and lambs at 4 or 8 cm sward surface heights (Phase 1). From mid‐August (Year 1) or early August (Year 2), weaned lambs continuously grazed, for a period of 36 d (Year 1) or 43 d (Year 2) (Phase 2), the same swards maintained at 4 cm (treatment 4–4), 8 cm (treatment 8–8) or swards which had been allowed to increase from 4 to 8 cm (treatment 4–8). Grazing by both cattle and sheep at a sward surface height of 4 cm compared with 8 cm in Phase 1 resulted in a higher (P < 0·001) number of vegetative grass tillers per m2 in Phase 2, although the effect was more pronounced after grazing by sheep. Sheep grazing at 8 cm in Phase 1 produced a higher number of reproductive tillers per m2 and a greater mass of reproductive stem (P < 0·001) than the other treatment combinations. The mass of white clover lamina was higher under cattle grazing (P < 0·05), especially on the 8‐cm treatment, and white clover accounted for a greater proportion of the herbage mass. These effects had mainly disappeared by the end of Phase 2. On the 4–4 and 8–8 sward height treatments the liveweight gain of the weaned lambs was higher (P < 0·05) on the swards previously grazed by cattle than those grazed by sheep. The proportion of white clover in the diet and the herbage intake also tended to be higher when the weaned lambs followed cattle. However, there was no difference in liveweight gain, proportion of white clover in the diet or herbage intake between swards previously grazed by cattle or sheep on the 4–8 sward height treatment. It is concluded that grazing grass/white clover swards by cattle compared with sheep for the first half of the grazing season resulted in less reproductive grass stem and a slightly higher white clover content in the sward, but these effects are transient and disappear from the sward by the end of the grazing season. They can also be eliminated by a short period of rest from grazing in mid‐season. Nevertheless these changes in sward structure can increase the performance of weaned lambs when they graze these swards in late season.  相似文献   

17.
Estimates of the frequency of absence of rooted perennial ryegrass tiller bases from concentric sampling quadrats of different sizes are recommended for characterizing the open space structure of perennial ryegrass swards. It is proposed that these estimates are useful for evaluating the persistence of grass species and cultivars in swards. Data on this aspect of sward structure could provide criteria for the productivity of a sward and thus for the need to reseed grassland.  相似文献   

18.
Bite depth was measured in four experiments in which grazing cows were offered, individually, patches of perennial ryegrass swards, typically 0·9 m × 0·9 m, of contrasting structural composition within linear sequences of eighteen to twenty‐seven patches. Bite depths were analysed in relation to the independent effects of pseudo‐stem height, re‐growth depth, stubble height and sward height. In vegetative swards comprising predominantly leaf, with re‐growth and stubble strata of vegetative origin, bite depth was strongly related to sward height. However, when the leaf–stem contrast between strata increased, bite depth was strongly correlated with the depth of re‐growth. Cows were observed to penetrate into a mature stubble stratum with increasing sward height, indicating that stubble height is only a partial regulator of bite depth. In an experiment designed to investigate the independent effects of pseudo‐stem and sward height, pseudo‐stem was only a partial regulator of bite depth. Evidence to support the concept that bite depth is a fixed proportion of sward height across swards of different structure was inconsistent, but there was evidence of a maximum bite depth of 0·70 of sward height. There were also indications that bite depth was conditioned by the number of bites removed. This suggested that cows initially took a cautious approach to grazing, building up bite depth with feedback over the first 20–30 bites in a new patch. Behaviour at the current patch was not affected by the characteristics of the preceding or succeeding patch in sequence.  相似文献   

19.
The potential of imaging spectroscopy for the assessment of seasonal dry‐matter (DM) yield and sward quality was studied. Relationships between spatial heterogeneity of tiller density, light interception, ground cover and seasonal DM yield were developed. Sward heterogeneity was quantified by the spatial standard deviation of ground cover and of logarithmically transformed ground cover, and patterns in ground cover transects were quantified by wavelet entropy. An experiment was conducted with eight control (C) swards, eight naturally damaged (ND) swards and twelve artificially damaged (AD) swards. Swards were established in containers and spectroscopic images were recorded twice weekly. Seasonal DM yield was linearly related to a combination of means of ground cover and index of reflection intensity (r2 = 0·93). Spatial variation of tiller density was larger for AD and ND swards than for C swards. Values of the spatial standard deviation of ground cover and wavelet entropy were larger for AD and ND swards than for C swards. A single spatial standard deviation of ground cover value of 13% discriminated ND and AD swards from C swards. Seasonal means of wavelet entropy (r2 = 0·70) and the spatial standard deviation of ground cover (r2 = 0·63) at harvest were linearly related to seasonal DM yield. It is concluded that imaging spectroscopy can be used for assessing seasonal DM yield and sward heterogeneity.  相似文献   

20.
Two experiments were carried out on a tall fescue sward in two periods of spring 1994 and on a tall wheatgrass sward in autumn 2001 and spring 2003 to analyse the effect of sward surface height on herbage mass, leaf area index and leaf tissue flows under continuous grazing. The experiment on tall fescue was conducted without the application of fertilizer and the experiment with tall wheatgrass received 20 kg P ha?1 and a total of 100 kg N ha?1 in two equal dressings applied in March (autumn) and end of July (mid‐winter). Growth and senescence rates per unit area increased with increasing sward surface height of swards of both species. Maximum estimated lamina growth rates were 28 and 23 kg DM ha?1 d?1 for the tall fescue in early and late spring, respectively, and 25 and 36 kg DM ha?1 d?1 for tall wheatgrass in autumn and spring respectively. In the tall fescue sward, predicted average proportions of the current growth that were lost to senescence in early and late spring were around 0·40 for the sward surface heights of 30–80 mm, and increased to around 0·60 for sward surface heights over 130 mm. In the tall wheatgrass sward the corresponding values during spring increased from around 0·40 to 0·70 for sward surface heights between 80 and 130 mm. During autumn, senescence losses exceeded growth at sward surface heights above 90 mm. These results show the low efficiency of extensively managed grazing systems when compared with the high‐input systems based on perennial ryegrass.  相似文献   

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