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1.
An experiment was carried out in 1992 and 1993 to examine the effect of white clover content of perennial ryegrass/white clover swards on the performance of Limousin × Friesian heifers. Swards with low (L), medium (M) and high (H) white clover contents were established and managed by continuous variable stocking. A compressed sward height of 5·5 cm was maintained using a buffer fence to vary plot areas, with herbage surplus to grazing requirements cut, removed and yields measured. The mean white clover proportions for treatments L, M and H were 0·02, 0·19 and 0·18 in 1992 and 0·13, 0·16 and 0·31 in 1993 respectively. White clover contents of the swards reached a maximum in August and September, and differences between treatments diminished. There was no significant difference between treatments in the content of white clover in the swards in autumn 1993.
Liveweight gains of heifers increased asymptotically with increasing white clover content of the sward. Below a white clover herbage mass of 300 kg DM ha–1 , there was little effect on liveweight gain, which was 0·70 kg day–1 over the grazing season. Between 400 and 450 kg DM ha–1 white clover, liveweight gains were 0·85–0·90 kg day–1 . While clover content of the sward did not significantly affect utilized metabolizable energy output; the mean output over the grazing season in the two years from liveweight gain and herbage yield was 78 GJ ha–1 . It is suggested that, using this grazing system, white clover reached an equilibrium with a mean herbage mass of about 400 kg DM ha–1 over the grazing season. 相似文献
Liveweight gains of heifers increased asymptotically with increasing white clover content of the sward. Below a white clover herbage mass of 300 kg DM ha
2.
An experiment was conducted to examine how variation in the composition and structure of mixed grass/white clover swards affected diet selection by sheep and goats. Sward composition in a mixed perennial ryegrass/white clover sward was manipulated by continuous grazing from 28 May to 28 July (pre-experimental phase) with cattle, sheep or goats, and then from 29 July to 2 September (experimental phase) with sheep or goats in a factorial design replicated twice. Sward surface height was maintained at 6 cm by regular adjustment of stocking density. Grazing by different sequences of animal species resulted in significant differences in the proportions of white clover in the sward, and especially in the proportion of clover lamina and petiole. Grazing by goats in the pre-experimental phase led to greater proportions of clover lamina and petiole in the whole sward and the sward surface. The proportion of white clover in the diet selected by sheep in the experimental phase was consistently higher than that in the sward as a whole, but was closely related to that near to the sward surface (approximately the top 2 cm). For goats there was no significant relationship between the proportion of clover in the diet and in the whole sward, and they generally selected a diet with a lower proportion of white clover than was present in approximately the top 2 cm of the sward. It is concluded that on mixed grass/white clover swards goats do not graze as deeply into the sward as sheep and that this results in a lower proportion of white clover in their diet and therefore allows higher proportions of white clover to develop under grazing by goats than by sheep. 相似文献
3.
Sward composition, animal performance and the potential production of grass/white clover swards continuously stocked with sheep 总被引：1，自引：0，他引：1
The potential productivity of perennial ryegrass/ white clover swards (GC) under continuous stocking management was assessed by comparing their performance, when grazed by sheep at sward surface heights of 3, 6 and 9 cm, with that of an all–grass sward (G) maintained at 6 cm and fertilized with 420 kg N ha–1 The grass/clover swards received no nitrogen fertilizer. The different grazing treatments had a marked effect on animal performance. In the first year for example, for treatments GC3, GC6, GC9 and G6–420 respectively, mean stocking rates to weaning were 19–7, 14–3, 8–9 and 18–4 ewes ha–1 (plus twin lambs); lamb growth rates were 223, 268, 295 and 260 g d–1 and so total lamb live weight gain was 1054, 920, 630 and 1148 kg h a–1 . The relative performance of the treatments was similar in all three years. All three grazing treatments had a similar effect on the composition of the grass/clover swards. Clover content increased in 1985, and was sustained in 1986 and 1987 during the main grazing season, although a marked decline in clover content during the winter led to a progressive long–term decline in both the proportion and the amount of clover.
It is suggested that a management based on maintaining a sward surface height close to 6 cm (as in all–grass swards) leads to optimum performance in grass/white clover swards grazed using continuous stocking with sheep. Despite the presence of a small and declining clover content, the output of the mixed grass/clover sward managed in this way was 80%, 80% and 82% of that of a grass sward supplied with 420 kg N ha–1 in 1985, 1986, and 1987 respectively and, similarly, 83% of the output in 1987 of a grass sward receiving 210 kg N ha–1 . 相似文献
It is suggested that a management based on maintaining a sward surface height close to 6 cm (as in all–grass swards) leads to optimum performance in grass/white clover swards grazed using continuous stocking with sheep. Despite the presence of a small and declining clover content, the output of the mixed grass/clover sward managed in this way was 80%, 80% and 82% of that of a grass sward supplied with 420 kg N ha
4.
Effects of grazing by sheep or cattle on sward structure and subsequent performance of weaned lambs 总被引：1，自引：0，他引：1
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
5.
Three experiments designed to investigate different facets of autumn management on white clover stolon development are described. The effects of defoliation interval (2, 4, 6 and 8 weeks during 16 weeks from 27 July) were investigated. The shortest interval resulted in the shortest length of stolon material per unit area but cutting interval had no effect on growing point density nor on hardiness of stolon tips evaluated in October, December and January.
Chemical grass suppressants were employed to reduce grass biomass during winter in two experiments to evaluate the influence of grass on white clover development. One experiment involved varying grass tiller density by spraying a perennial ryegrass/white clover sward in October with three rates of three chemical suppressants (Clout, Kerb and Checkmate). Although tiller and clover growing point density were inversely related in January, the overall relationship was not strong.
Clout at l·5kg a.i. ha−1 was sprayed in October on one of two subplots in each of twelve grazed grass/white clover plots that had been maintained at 7 or 9 cm from July to October then grazed to 3–4 cm with sheep. Sward height had no effect on clover population density but the shorter sward had a greater mean node number per secondary stolon branch. By March, suppressing grass resulted in more than double the stolon population density, a higher proportion of plants with tertiary and quaternary branches, and on marked stolons, five times more branches and 60% higher dry matter (DM) produced during winter but with shorter petioles compared with clover in untreated plots.
It is concluded that white clover has the capacity to branch during a mild winter and as stolon branch numbers can suffer a net loss as a result of the presence of the grass canopy, management that controls grass growth during winter should aid over-wintering and improve persistence of white clover. 相似文献
Chemical grass suppressants were employed to reduce grass biomass during winter in two experiments to evaluate the influence of grass on white clover development. One experiment involved varying grass tiller density by spraying a perennial ryegrass/white clover sward in October with three rates of three chemical suppressants (Clout, Kerb and Checkmate). Although tiller and clover growing point density were inversely related in January, the overall relationship was not strong.
Clout at l·5kg a.i. ha
It is concluded that white clover has the capacity to branch during a mild winter and as stolon branch numbers can suffer a net loss as a result of the presence of the grass canopy, management that controls grass growth during winter should aid over-wintering and improve persistence of white clover. 相似文献
6.
A. R. Sibbald T. J. Maxwell A. J. I. Dalziel & R. D. M. Agnew 《Grass and Forage Science》2002,57(1):33-47
The implications for UK upland sheep systems of reducing nitrogen fertilizer application to perennial ryegrass/white clover swards were studied over 3 years. Sward height (3·5–5·5 cm) was controlled for ewes with lambs until weaning using surplus pasture areas for silage; thereafter, ewes and weaned lambs were grazed on separate areas, and sward height was controlled by adjusting the size of the areas grazed and using surplus pasture areas for silage if necessary. Combinations from three stocking rates [10, 6 and 4 ewes ha−1 on the total area (grazed and ensiled)] and four nitrogen fertilizer levels (150, 100, 50 and 0 kg ha−1 ) provided six treatments that were replicated three times. Average white clover content was negatively correlated with level of nitrogen fertilizer. The proportion of white clover in the swards increased over the duration of the experiment. Control of sward height and the contribution from white clover resulted in similar levels of lamb liveweight gain on all treatments. All treatments provided adequate winter fodder as silage. It is concluded that the application of nitrogen fertilizer can be reduced or removed from upland sheep pastures without compromising individual animal performance provided that white clover content and sward height are maintained. Resting pastures from grazing by changing ensiled and grazed areas from year to year sustained white clover content over a 3-year period. 相似文献
7.
White clover varieties, potentially suitable for inclusion in seed mixtures for mixed stock-rearing farm systems, were evaluated when growing with S23 perennial ryegrass under rotational sheep grazing with a silage cut in late May or early June, as practiced on farms. Monoculture grass swards were also included to enable the direct and indirect contribution of white clover to total sward production to be evaluated.
White clover increased total sward production during all three years of the trial by an average of 50%. Although clover content of swards were similar, large differences occurred in their grass content, especially in the third year, when difference in total yields of swards based on large–leaved clover varieties was 2 t ha−1 while difference in clover yield was only 0-6 to ha–1 The indirect contribution of white clover, namely the extra grass resulting from N transfer, was greater in the spring than in the autumn. It was also greater for Nesta than for other varieties. and exceptional for this variety in that the increase in grass yield above that of grass monoculture was maintained over three harvest years. 相似文献
White clover increased total sward production during all three years of the trial by an average of 50%. Although clover content of swards were similar, large differences occurred in their grass content, especially in the third year, when difference in total yields of swards based on large–leaved clover varieties was 2 t ha
8.
P. Carrère F. Louault P. C. De Faccio Carvalho M. Lafarge & J. F. Soussana 《Grass and Forage Science》2001,56(2):118-130
Mixtures of perennial ryegrass ( Lolium perenne L.) and white clover ( Trifolium repens L.) sown in alternate rows or in a thoroughly mixed matrix were grazed by sheep, either continuously or during short grazing tests, and were used to investigate the influence of the vertical and horizontal components of the sward structure on defoliation by sheep.
In an experiment under continuous grazing, the defoliation intensity was greater for white clover compared with perennial ryegrass leaves (0·80 and 0·58 respectively). In spring, perennial ryegrass leaves were more defoliated than white clover leaves, whereas the reverse was observed in summer. The ratio of the proportion of white clover to perennial ryegrass leaves grazed was negatively correlated with the difference between the surface height of the perennial ryegrass and white clover rows in spring. In both spring and summer, white clover leaves of the same extended leaf length had a higher proportion of them grazed than perennial ryegrass leaves.
In another experiment, during short grazing tests with perennial ryegrass–white clover swards that were grazed at the same sward surface height and at the same white clover content as in the previous experiment, there were no significant differences in the proportion of white clover and perennial ryegrass leaves grazed between strips of the two species and thoroughly mixed structures. The proportion of white clover leaves grazed was higher than that of perennial ryegrass leaves.
These results show that the differential defoliation by sheep of perennial ryegrass and white clover leaves varies according to their vertical distribution in the mixed canopy, but is little affected by their horizontal distribution. Even small differences in sward surface height between mixed perennial ryegrass and white clover can affect diet selection by sheep to a rather large extent. 相似文献
In an experiment under continuous grazing, the defoliation intensity was greater for white clover compared with perennial ryegrass leaves (0·80 and 0·58 respectively). In spring, perennial ryegrass leaves were more defoliated than white clover leaves, whereas the reverse was observed in summer. The ratio of the proportion of white clover to perennial ryegrass leaves grazed was negatively correlated with the difference between the surface height of the perennial ryegrass and white clover rows in spring. In both spring and summer, white clover leaves of the same extended leaf length had a higher proportion of them grazed than perennial ryegrass leaves.
In another experiment, during short grazing tests with perennial ryegrass–white clover swards that were grazed at the same sward surface height and at the same white clover content as in the previous experiment, there were no significant differences in the proportion of white clover and perennial ryegrass leaves grazed between strips of the two species and thoroughly mixed structures. The proportion of white clover leaves grazed was higher than that of perennial ryegrass leaves.
These results show that the differential defoliation by sheep of perennial ryegrass and white clover leaves varies according to their vertical distribution in the mixed canopy, but is little affected by their horizontal distribution. Even small differences in sward surface height between mixed perennial ryegrass and white clover can affect diet selection by sheep to a rather large extent. 相似文献
9.
An experiment was carried out to examine the effect of supplementation on the performance of spring-calving dairy cows grazing swards of differing perennial ryegrass and white clover content. Seventeen heifers and sixty-four Friesian cows in their third to ninth week of lactation were turned out onto one of three pastures with different proportions of perennial ryegrass and white clover. Nine animals on each pasture received either 0, 2 or 4 kg d−1 of a concentrate with a crude protein concentration of 180 g kg−1 dry matter (DM). Prior to grazing, swards contained proportionately 0·01 (L), 0·15 (M) and 0·20 (H) of total DM as clover. During the experiment, grazing pressures were adjusted by movement of buffer fences to maintain compressed sward heights at 6 cm. Samples taken 26 and 68 d after the start of grazing showed little change in the proportion of clover in sward L (< 0·01 and 0·02 respectively), but convergence in the proportion of clover in swards M and L (0·08-0·16 and 0·10-0·15 respectively). Mean daily yields of milk, fat, protein and lactose increased significantly with increased clover content and, even without supplementation, daily yields were 25·4, 0·98, 0·73 and 1·09 kg respectively on sward H. Of the milk components, only protein was significantly increased by increasing sward clover content. The response in milk yield to supplementation was greater on sward L than on swards M and H. 相似文献
10.
An established sward of binary mixtures of meadow fescue (Festuca pratensis) and white clover (Trifolium repens) (either AberHerald, Grasslands Huia or Sandra) was subjected to (A) no further defoliation, (B) a defoliation in late September or (C) a defoliation in late October after four harvests had been taken during the grazing season. About a tonne of dry matter (DM) was removed by the autumn defoliations. There were two levels of nitrogen application in spring, either 0 or 90 kg ha?1. The development of grass and clover morphology and population sizes from early autumn until the first harvest the following year was followed by regular sampling of the above-ground material. Stolons were analysed for total non-structural carbohydrates (TNCs), and the temperature at stolon level was continuously recorded. There were no interactions between autumn defoliation, clover cultivar or nitrogen treatments on any of the parameters studied. White clover growing-point numbers and stolon morphological characteristics were reduced in size during the winter and did not recover during the spring. A defoliation in late September resulted in the greatest reduction, whereas there were no differences between the other two treatments. The grass tiller population increased from early autumn until the last sampling occasion in May, but both autumn defoliations resulted in a smaller increase. Defoliation in late September had the greatest impact. The TNC content of white clover stolons fell from about 350 g kg?1 to 150 g kg?1 DM from late autumn until late April. There were small differences between the treatments, but a defoliation in late September resulted in a significantly lower level in late autumn. The temperature amplitude at stolon level was consistently greater in plots defoliated in late September. Total DM harvested in spring was 4367, 2564 and 3536 kg ha?1, of which 388, 352 and 460 kg ha?1 was white clover, from treatments A, B and C respectively. It is concluded that an autumn defoliation may affect the overwintering of white clover negatively, but that the effect on the grass may be even more detrimental. 相似文献
11.
The milk-production potential of different sward types was measured in each of the four seasons of the year in a replicated experiment in south-west Victoria, Australia. Dairy cows were offered ad libitum allowances of a 'short-term winter' sward, based on Italian ryegrass (treatment STW), a 'long-term winter' sward, based on a winter-active tall fescue (treatment LTW), a 'long-term summer' sward, based on a summer-active tall fescue (treatment LTS) and a Control sward (perennial ryegrass) in four seasons (days in milk in parentheses): spring (November dairy cows, 124), summer (February, 227), autumn (May, 234) and winter (August, sixty-four). A 'short-term summer' sward, based on chicory and white clover (treatment STS), was also included in summer. There was a significant season × treatment interaction caused by a more gradual decline in milk yield from peak for cows grazing treatment LTS compared to the Control treatment in the transition period from spring to summer. In summer, cows grazing treatment STS produced more milk (1·41 kg fat plus protein per cow d−1 ) than cows grazing all other treatments (0·92 kg per cow d−1 ) because of the superior nutritive value of herbage of pre-grazing pasture and higher apparent dry-matter intakes. Swards based on alternative species to perennial ryegrass are capable of supporting milk production that is at least comparable over an annual cycle. 相似文献
12.
The effect of cutting for conservation on a grazed perennial ryegrass-white clover pasture 总被引：2，自引：0，他引：2
Continuous stocking with sheep at high stocking rates may reduce the content of white clover (Trifolium repens) in mixed grass-clover swards. The present experiment was carried out to investigate the effects on sward production and composition of resting a perennial ryegrass (Lolium perenne)- white clover sward from grazing and taking a cut for conservation. Swards were set-stocked with 25 and 45 yearling wethers ha?1 either throughout a grazing season, or on swards that were rested for a 6-week period and then cut in early, mid- or late season. In an additional treatment swards were cut only and not grazed. Net herbage accumulation was higher at the lower of the two stocking rates and was marginally increased by the inclusion of a rest period at the high but not the low stocking rate. Clover content was higher at the lower stocking rate and was increased by the inclusion of a rest period by 30% at 45 sheep ha?1and by 11% at 25 sheep ha?1 The effect was most marked at the end of the rest period before cutting. When rested from grazing the tiller density of ryegrass decreased although tiller length increased, and clover stolon length, petiole length and leaflet diameter increased though leaf and node number per unit length of stolon decreased; the reverse applied when the sward was returned to grazing after cutting. At the high stocking rate, rest periods in mid-season or later maintained the greatest clover content and marginally increased total net herbage accumulation. At the low stocking rate the timing of the rest period had no significant effect on total net herbage accumulation or on clover content. These results show that the combination of grazing and cutting is of benefit where the stocking rate is high enough to threaten clover survival and limit sheep performance. However, at such a stocking rate, feed reserves are at a minimum throughout the grazing season and so opportunities for resting the sward are probably low. 相似文献
13.
The effect of the initial N-supplying capacity of soils (SoilN, 90–230 kg N ha–1 year–1 ) was tested on the dry-matter and N yields of pure or mixed white clover and perennial ryegrass swards, managed under simulated grazing over a 5-year period. The cumulated N harvested in the mixed swards was similar, both for white clover and perennial ryegrass, but the proportion of white clover showed oscillations over a 2-year period. In the first year, the SoilN effect was similar to that of fertilizer N. During the course of the experiment, the effect was always positive on the pure perennial ryegrass sward, alternately negative and nil for the white clover in the mixed sward and alternately positive and nil for the perennial ryegrass in the mixed sward; the period of these oscillations was 2 years. From the third regrowth period after sowing, the ratio between the actual N concentration and the concentration non-limiting to growth for the perennial ryegrass in the mixed sward, increased above that of the pure perennial ryegrass sward. It was in turn greater in the soils that were initially poor and then greater in those that were initially rich in soil N. The periodic oscillation of the initial SoilN effects implies that the initial SoilN gradient was alternately compensated and restored. It was concluded that N fluxes are partly responsible for the temporal oscillations in the proportion of white clover in mixed swards. 相似文献
14.
This experiment was carried out to study the responses of sward components (particularly white clover, Trifolium repens ) to grazing management in a natural sward dominated by smooth-stalked meadowgrass ( Poa pratensis ) syn. Kentucky bluegrass. Treatments during two grazing seasons (1989–90) were: cattle grazing alone (C); cattle grazing followed by topping (CT); cattle grazing followed by sheep grazing (CS); and sheep grazing alone (S). Mean target pre- and post-grazing herbage masses were 2200 and 1100 kg DM ha−1 , estimated by single-probe electronic capacitance meter. Sward component dynamics were monitored using turf dissections, marked white clover stolons, and ring-toss white clover leaf counts. Component and sward data for the C, CT, CS and S treatments respectively, were: number of white clover leaves m−2 , 1295, 1384, 1408, 900 (s.e. ± 108); number of leaves per growing point, 3·2, 3·4, 3·0, 2·8 (s.e. ± 0·2); herbage accumulation (t DM ha−1 ), 5·16, 5·02, 5·87, 8·28 (s.e. ±0 08); rejected herbage (% pasture area) 39·7, 7·7, 16·0, 0 (s.e. ± 75); and annual net herbage production (t DM ha−1 ) 3·39, 4·35, 4·99, 8·28 (s.e. ± 0.07). Swards grazed by sheep alone contained less white clover, but regrew quicker and produced more herbage than other treatments. Close topping or grazing by sheep following dairy cattle grazing decreased sward rejection by cattle. These treatments maintained more of the pasture in better condition for subsequent cattle grazing, resulting in greater net herbage production than where no post-cattle grazing treatment was used. 相似文献
15.
Two experiments, each lasting approximately 12 months, were carried out at North Wyke, Devon, in 1982-83 (A) and 1983-84 (B), to investigate various sward managements following oversowing of white clover (Trifolium repens, cv. Grasslands Huia) at 4 kg ha-1 with a Hunter Rotary Strip-Seeder in June or July into the stubble of a permanent grass sward following conservation. Experimental managements comprised cutting, grazing with wether sheep or grass suppression by herbicide, as appropriate, in late summer/autumn (Phase I), winter (Phase II) and spring/early summer (Phase III). During Phase I, there was no differential effect on clover stolon development of lenient grazing at approximately 4-weekly intervals or topping at the same frequency to a similar height. Early in Phase II of Experiment A, grazed paddocks became so badly poached that no differences occurred between grazing either to early January or throughout the winter. Under drier conditions in Phase II of Experiment B, continuous grazing at either five (L) or ten (H) sheep ha-1 had no immediate effect on clover stolon development, but in a silage cut in June, paddocks formerly stocked at the lower rate yielded 40% more DM than those at the higher rate. Experiment A compared the use of a grass-suppressing herbicide, propyzamide, applied at 0.6 kg a.i. ha-1 in either October or February; in Experiment B it was applied in October. Prophyzamide applied at either time in Experiment A increased the clover content of herbage regrowing after the end of the experimental period from 16% to 36% (s.e.d. ± 3.9). In Experiment B, October application raised the clover contents of herbage cut in June 1984 from 10% (H) and 17% (L) to 32% (s.e.d.±5.9), and stolon lengths per m2 at the end of the summer period from 33 (H) and 56 (L) to 86m (s.e.d. ± 11.7). However, the effect of spraying propyzamide on subsequent herbage yields was erratic, and appeared to depend on the incidence of frost after application. In Phase III of Experiment A, continuous grazing was compared with a silage cut in June. At the end of the experiment there were 31 m m-2 of clover stolon in silaged areas compared with only 2.5 m m-2 following grazing (s.e.d.±6.6). Clover content and herbage yields were also significantly higher following conservation. In Experiment B in the same period, rotational grazing with a 14- or 35-day recovery interval was compared with a silage cut in June, with or without 100 kg N ha-1 applied in March. Application of N to the conservation treatment reduced clover stolon length per unit area, and in the regrowth in the post-experimental period the conservation treatment without N had the largest clover content (31% compared with 16-23% for other treatments, s.e.d. ± 3.6) 相似文献
16.
Growth of grass/clover mixtures during winter 总被引：2，自引：0，他引：2
The percentage of clover in a mixture of Huia white clover and Melle perennial ryegrass decreased during each of three winters. In the most severe winter, both grass and clover suffered a net loss of weight, clover losing two–thirds of its maximum weight while grass lost about one–third. In the mildest winter, grass continued to gain weight throughout, while clover lost weight. Such losses, when combined with conditions such as the use of nitrogen fertilizer, which prevent a recovery of clover percentage during summer, will lead to a long–term decrease in the clover content of a sward.
The losses from the clover were contributed to by all plant parts especially leaf, which lost between 60% and 95% of lamina weight. The change from autumn to winter caused a greater decrease in the number of live leaves per shoot. and in the area and weight of individual leaves, in clover than in grass. Other work has shown that there is a greater decrease in photosynthesis in clover than in grass, probably owing to changes in canopy structure; this is one cause of clover's poor performance, though differences between the two species in the effect of winter on the distribution of the carbon fixed in photosynthesis and in losses of weight in respiration and tissue death may also be involved. 相似文献
The losses from the clover were contributed to by all plant parts especially leaf, which lost between 60% and 95% of lamina weight. The change from autumn to winter caused a greater decrease in the number of live leaves per shoot. and in the area and weight of individual leaves, in clover than in grass. Other work has shown that there is a greater decrease in photosynthesis in clover than in grass, probably owing to changes in canopy structure; this is one cause of clover's poor performance, though differences between the two species in the effect of winter on the distribution of the carbon fixed in photosynthesis and in losses of weight in respiration and tissue death may also be involved. 相似文献
17.
Effects of grazing by sheep or goats on sward composition in ryegrass/white clover pasture and on subsequent performance of weaned lambs 总被引：1，自引：0，他引：1
An experiment was conducted to assess the effects of grazing a perennial ryegrass (Lolium perenne) / white clover (Trifolium repens) sward by sheep or goats on sward composition and structure and on subsequent diet selection, herbage intake and liveweight gain by weaned lambs. From mid-May to late July (phase 1), ewes with twin lambs or yearling Scottish Cashmere goats grazed continuously swards maintained at 4- or 8-cm sward surface height. From mid-August to the end of September (phase 2), weaned lambs continuously grazed the same swards maintained at 4 cm (treatment 4–4) or at 8 cm (treatment 8–8) or which had been allowed to increase from 4 cm to 8 cm (treatment 4–8). By the end of phase 1, swards grazed by goats had higher proportions of white clover in the whole sward (0.377 vs. 0.181; s.e.d 0.0382; P < 0.001) than those grazed by sheep, irrespective of sward height treatment. This resulted in phase 2 in a higher proportion of white clover selected ( P <0.001), higher herbage intakes ( P < 0.001) and higher liveweight gains ( P < 0.001) by weaned lambs grazing swards previously grazed by goats compared with those previously grazed by sheep. There were higher proportions of clover present in the swards from treatment 4–8 at the beginning of phase 2 compared with the other sward height treatments and consequently weaned lambs had, on this treatment, a higher proportion of clover in their diet ( P <0.001), higher herbage intakes ( P <0001) and higher liveweight gains ( P <0.001). It is concluded that goats can be integrated into sequential grazing systems with sheep on grass/clover swards and this can result in an increase in the proportion of clover in swards and increased sheep performance. 相似文献
18.
P. Phelan B. Keogh I. A. Casey M. Necpalova J. Humphreys 《Grass and Forage Science》2013,68(4):548-563
White clover can reduce fertilizer‐N requirements, improve sward nutritive value and increase environmental sustainability of grazed grasslands. Results of previous experiments in glasshouse conditions and on mown plots have suggested that white clover may be more susceptible than perennial ryegrass to treading damage on wet soils. However, this phenomenon has not been investigated under actual grazing conditions. This experiment examined the effects of treading on clover content, herbage production and soil properties within three clover‐based grazing systems on a wet soil in Ireland for 1 year. Treading resulted in soil compaction, as evidenced by increased soil bulk density (P < 0·001) and reductions in the proportion of large (air‐filled) soil pores (P < 0·001). Treading reduced annual herbage production of both grass and white clover by similar amounts 0·59 and 0·45 t ha?1 respectively (P < 0·001). Treading reduced the sward clover content in June (P < 0·01) but had no effect on annual clover content, clover stolon mass or clover content at the end of the experiment. Therefore, there was little evidence that white clover is more susceptible to treading damage than perennial ryegrass under grazing conditions on wet soils. 相似文献
19.
J. Frame 《Grass and Forage Science》1972,27(3):155-162
The agronomic value of Syn 1 tall fescue, a synthetic variety derived from North African parent material, was determined in three experiments. Herbage yield, sward purity and digestibility were measured under cutting treatments for incremental sward growth during autumn/winter, and for sward regrowths during autumn/winter, spring and a complete season. Similar data were obtained for sward regrowths during autumn/winter and spring under defoliation by grazing. Syn 1 was compared with several of the north-temperate region tall fescues, e.g. S170, Rozelle and Manade, also with S143 cocksfoot Syn 1 showed yield superiority in autumn/early winter when there were comparable populations of tall fescue. Under cutting management, Syn 1 swards thinned out rapidly because of lack of winter-hardiness and yields were depressed in the second season; the effects were worst under the winter foggage-type management. Under grazing, with probably less severe defoliation, Syn 1 swards maintained yields for an additional season, but thereafter failed to persist Syn 1 swards had low spring- and annual-yields. The yield advantage of Syn 1 in autumn/early winter was not sufficient to be of great agricultural value and with its shortcomings in winter-hardiness and annual yield, it was considered unsuitable for West of Scotiand conditions. The main value of plant material such as Syn 1 may lie in ccmferring autumn/winter growth potential to winter-hardy north-temperate tall fescues in a breeding programme. 相似文献
20.
To investigate the effect of sward height on liveweight change in goats grazing grass/white clover swards, an experiment was conducted from mid-August to mid-November with groups of non-lactating female cashmere goats that continuously grazed perennial ryegrass (Lolium perenne)/white clover (Trifolium repens) swards. Three replicated different sward height treatments — 10–8 cm (high), 7–5 cm (medium) and 5–3 cm (low) — were used to examine the effects on the competitive ability of grass and clover components within the sward canopy and their effect on liveweight. The pasture after grazing by goats had relatively higher ryegrass leaf (+0·26, high; +0·32, medium; and +0·18, low) and lower dead ryegrass proportions (?0·28, high; ?0·23, medium; and ?0·18, low) than at the beginning of the experiment, whereas the white clover fraction in the sward remained constant (+0·04, high; ?0·02, medium; and +0·03, low). Higher proportions of the white clover leaf lamina and petiole were found near the top of the sward canopy and were negatively correlated with the rate of liveweight gain by goats (P < 0·05). Goats gained 50·2 g Live weight (LW) d?1 on the tallest treatment (high) but lost 0·01 and 42·3 g LW d?1 on the medium and low sward height treatments respectively (s.e.d. 13·21, P < 0·001). Liveweight changes that occurred between sampling periods were also correlated (R2= 0·858, P < 0·001) with changes in the mean sward height and proportion of white clover lamina-petiole at the sward surface in relation to the proportion found within the whole sward. These results suggest that goat liveweight gains would be increased if another species was introduced to reduce the white clover proportion in the surface horizon. 相似文献