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1.
A. R. Sibbald C. A. Marriott R. D. M. Agnew A. J. I. Dalziel 《Grass and Forage Science》2004,59(3):264-273
The sustainability of white clover in grass/clover swards of an upland sheep system, which included silage making, was studied over 5 years for four nitrogen fertilizer rates [0 (N0), 50 (N50), 100 (N100) and 150 (N150) kg N ha?1]. A common stocking rate of 6 ewes ha?1 was used at all rates of N fertilizer with additional stocking rates at the N0 fertilizer rate of 4 ewes ha?1 and at the N150 fertilizer rate of 10 ewes ha?1. Grazed sward height was controlled, for ewes with their lambs, from spring until weaning in late summer by adjusting the proportions of the total area to be grazed in response to changes in herbage growth; surplus pasture areas were harvested for silage. Thereafter sward height was controlled on separate areas for ewes and weaned lambs. Areas of pasture continuously grazed in one year were used to make silage in the next year. For treatments N0 and N150, white clover stolon densities (s.e.m.) were 7670 (205·4) and 2296 (99·8) cm m?2, growing point densities were 4459 (148·9) and 1584 (76·0) m?2 and growing point densities per unit length of stolon were 0·71 (0·015) and 0·67 (0·026) cm?1 respectively, while grass tiller densities were 13 765 (209·1) and 18 825 (269·9) m?2 for treatments N0 and N150 respectively. White clover stolon density increased over the first year from 780 (91·7) cm m?2 and was maintained thereafter until year 5, reaching 8234 (814·3) and 2787 (570·8) cm m?2 for treatments N0 and N150 respectively. Growing point density of white clover increased on treatment N0 from 705 (123·1) m?2 to 2734 (260·7) m?2 in year 5 and it returned to the initial level on treatment N150 having peaked in the intermediate years. Stolon density of white clover was maintained when the management involved the annual interchange of continuously grazed and ensiled areas. The non‐grazing period during ensiling reduced grass tiller density during the late spring and summer, when white clover has the most competitive advantage in relation to grass. The increase in stolon length of white clover in this period appears to compensate for the loss of stolon during periods when the sward is grazed and over winter when white clover is at a competitive disadvantage in relation to grass. The implications for the management of sheep systems and the sustainability of white clover are discussed. 相似文献
2.
An experiment was carried out to examine the changes in perennial ryegrass ( Lolium perenne L.) and white clover ( Trifolium repens L.) populations in mixed swards, under different grazing severities over three successive grazing seasons. In year 1, three paddocks were erected on a sward with a low initial content of clover (block 1). Sward heights were measured using a rising-plate meter, and were maintained at overall mean heights of 3·0, 5·5 or 7·0 cm by variable stocking with 8-month-old steers. In year 2, a further three paddocks were erected on an adjacent area with a high initial content of clover (block 2), and were maintained at the same three heights by similar management. Botanical analyses were carded out on samples collected at four times during the season. Maintaining swards at 5·5 or 7·0 cm led to a large proportion of the area being infrequently grazed. Block I paddocks had higher initial tiller densities, which increased as sward height was reduced, while block 2 paddocks, with their lower initial tiller density, showed little effect of sward height on tiller density. Initially, clover stolon growing-point densities and stolon masses increased more rapidly in the taller swards. Later, however, large losses in the clover populations occurred on all paddocks during long wet winters and there was a general reversal in these trends for stolon growing-point densities and stolon masses, 3·0>5·5>7·0. By year 3, swards with differing 相似文献
3.
Two experiments are described in which the effect of grazing or defoliating mixed swards at different times over winter and spring on clover content and development was investigated. In the first experiment swards were grazed with sheep (to about 3 cm) for a short period in (a) November, (b) November, January and March, (c) March or (d) not at all, in three consecutive years. All swards were grazed intermittently during the grazing season with cattle and cut for silage once each year. Each plot received either 0 or 50 kg N ha?1 in March. The effect of N fertilizer was to reduce clover content in each summer and clover growing point density in the third year. In two of the three years, treatments involving grazing in March had lower subsequent net annual herbage accumulation compared with the other two treatments and higher clover content in summer of the third year. Reduction in growing point density in all plots during the grazing season was associated with cattle grazing when conditions were wet, suggesting that stolon burial was implicated. Grazing with sheep in November, January and March resulted in significantly more visible (when counted in situ) clover growing points in April in year 2 and more total growing points (counted after dissection of turves) in the third year than the November grazed and ungrazed treatments which had, on occasions, higher grass tiller density. In a microplot experiment, high herbage mass standing over winter was associated with lower potential photosynthesis per unit clover lamina area and lower growing point density in March. Cutting herbage in March to 2-3 cm resulted in higher clover content and higher growing point number per unit stolon length. The latter was significantly correlated with total irradiance and red: far red at the canopy base. Potential photosynthesis of clover was not affected by cutting in March. It is concluded that growing point density can be increased by grazing or cutting during winter or spring. However, in order for these new stolons to contribute to clover yield during the summer, they have to be maintained until then by ensuring that competition from grass is minimized by keeping the sward short in winter and spring and avoiding the burial of stolons during grazing. 相似文献
4.
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
5.
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
6.
S. J. Cowlishaw 《Grass and Forage Science》1960,15(1):6-11
An experiment was carried out in two parts to investigate lack of persistency of white clover in a meadow fescue/white clover sward when grazed by poultry. It was found that poultry manure was responsible for a considerable part of this depressing effect. Grazing by poultry in the autumn and winter was nearly as effective in reducing the clover conlent of the sward as grazing for the whole year, autumn grazing being particularly harmful. Autumn and winter grazing alone increased the number of sown grass tillers and reduced Poa tririalis tillers in comparison wilh all-the-year-round grazing. Range and fold grazing at a high stocking rate (312 per acre in the first winter) both had the same effect on the sward. The effects of drought and continual close mowing on white clover persistence are discussed. Fertilizers containing calcium, potassium and phosphorus might counteract the depressing effect of poultry grazing and manure on white clover. 相似文献
7.
Z. N. Nie A. D. Mackay D. J. Barker I. Valentine & J. Hodgson 《Grass and Forage Science》1997,52(2):190-198
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
8.
Small plots of a Festuca-Agrostis upland sward on a peaty gley podsol were strip-seeded during late June 1986 with white clover cvs Aberystwyth S184 or Menna at 4 kg ha−1 and defoliated early (20 August) or late (3 September) and then frequently or infrequently (every 2 weeks or 4 weeks) until the end of September. All plots were defoliated in early November, at 3-weekly intervals during the growing season in 1987 and then grazed rotationally during 1988.
Satisfactory seedling establishment, representing 46% emergence, was achieved 5 weeks after sowing. The differential defoliation regimes had no persistent significant effects on clover development. S184 soon produced more leaves per seedling than Menna and a smaller proportion of its leaf number and weight were removed at each defoliation. Following large losses of leaves over the 1986–87 winter, SI84 had significantly more leaves per stolon than Menna; subsequently it also colonized the sward at a quicker rate. During 1987 amounts of herbage harvested (6.1 t ha−1 ) were similar with the two clover cultivars, with S184 contributing 47% and Menna 44% of this respectively. SI84 made a larger contribution to yield during May and June but Menna was more productive during September and October. During 1988 clover populations were maintained with rotational grazing without additional fertilizer inputs.
The results show that, despite initial soil and climatic contraints, both small and medium-leaved clovers can be strip-seeded into upland swards with large subsequent benefits to yield and herbage quality. However, they also indicate the need for further experiments to determine the influence of sward morphology and defoliation regime on stolon branching rates and accumulation of growing points which, in turn, govern sward colonization. 相似文献
Satisfactory seedling establishment, representing 46% emergence, was achieved 5 weeks after sowing. The differential defoliation regimes had no persistent significant effects on clover development. S184 soon produced more leaves per seedling than Menna and a smaller proportion of its leaf number and weight were removed at each defoliation. Following large losses of leaves over the 1986–87 winter, SI84 had significantly more leaves per stolon than Menna; subsequently it also colonized the sward at a quicker rate. During 1987 amounts of herbage harvested (6.1 t ha
The results show that, despite initial soil and climatic contraints, both small and medium-leaved clovers can be strip-seeded into upland swards with large subsequent benefits to yield and herbage quality. However, they also indicate the need for further experiments to determine the influence of sward morphology and defoliation regime on stolon branching rates and accumulation of growing points which, in turn, govern sward colonization. 相似文献
9.
Seven cultivars of white clover (Trifolium repens L.) (Kent, S184, Huia, Menna, Donna, Alice and Nesta) and a commercial mixture, ‘Ensign’, were strip-seeded into an upland perennial rye-grass (Lolium perenne L.) sward in late June 1986. Swards were first grazed by sheep, either on 5/6 August (early) or on 19/20 August (late) and then every 14–21 days (frequently) or 28–42 days (infrequently) during 1986, followed by a common grazing regime in 1987. During April to mid-June 1988 the swards received either a moderate amount of nitrogen or none and were cut frequently or once only in mid-June. Growth of individual seedlings was assessed before and after grazing during 1986 and stolon accumulation and distribution and sward colonization were assessed during 1987 and 1988. All cultivars emerged rapidly and satisfactorily and there were no consistent significant differences in the overall dry matter accumulation per seedling during establishment. During the first autumn the proportion of the aboveground biomass removed during grazing was smallest in Kent (c. 20%) and largest in Nesta (c. 40%). Kent and S184 produced most leaves and stolons and the greatest length of stolons per seedling and per individual stolon, and Nesta and Alice the fewest leaves and stolons and shortest stolons. Seedlings grazed early had heavier and longer stolons than those grazed late; those grazed frequently had more leaves, stolons and growing points than those grazed infrequently, especially following early grazing. During 1987 Kent and S184 had consistently the largest number of stolon growing points, and weight and length of stolons per unit area; these two cultivars and Nesta also colonized the sward more rapidly than the other cultivars. All cultivars contributed substantially and similarly to herbage production in late September. There were no residual effects of the 1986 treatments after the summer of 1987. During 1988 additions of nitrogen fertilizer at 100 kg N ha-1 or allowing the herbage to remain undefoliated between mid-April and mid-June both independently halved the number of stolon growing points per unit area; together they reduced it by 80%. Nitrogen also, on average, halved stolon weights but less so in Nesta, Alice and Huia and more so in all other cultivars. Infrequent defoliation greatly decreased stolon weights in Kent and S184 but had no significant effects on the other cultivars. Sward colonization was almost complete by June and entirely so by October for all cultivars in all treatments. Implications of the results for the after-management of strip-seeded white clover are discussed. 相似文献
10.
Growing point dynamics and spring growth of white clover in a mixed sward and the effects of nitrogen application 总被引：2，自引：0，他引：2
The effects of N applied in spring on the growth and development of white clover ( Trifolium repens L.) in a mixed sward were investigated at Uppsala, Sweden. In early spring, the plots received 0 or 90 kg N ha−1 in the form of nitrochalk. The formation and loss of stolon branches were followed on marked stolons. The proportion of white clover in the total above-ground dry matter (DM) of the sward fell substantially in both treatments during the 8-week growth period, but more so in N fertilized than in unfertilized plots; fertilizer N increased the accumulation of grass DM, whereas it reduced the accumulation of white clover DM. Over time, there was a loss of white clover growing points and this loss was greatest in plots where N was applied. Branching occurred predominantly during the first half of the growth period and was unaffected by N application, whereas the loss of branches was more confined to the latter period and was increased in plots receiving N. Irrespective of node position, the size of the branches that died was comparatively small, and more branches were lost from young than from old node positions. It is concluded that the decline in the number of growing points in the N fertilized sward was mainly due to an increased loss of recently formed branches. As a consequence of its stimulating effect on grass growth, the N fertilized treatment initially led to a reduction in the R:FR ratio of light and subsequently also in the availability of photosynthetically active radiation within the canopy. These changes in the light environment of the sward caused morphological adjustments to be made by the white clover and may have contributed to the observed loss of branches. 相似文献
11.
Five white clover populations of Swiss origin and three bred varieties were grown in binary mixtures with two perennial ryegrass varieties, Aurora and S23. The seasonal yields of clover and grass plus clover were measured under a cutting regime during the second and third years after establishment. A series of destructive detailed sward measurements was made during the late autumn to spring period preceding each harvest year. In this way changes in the amounts of stolon, leaf plus petiole and numbers of growing points were monitored during the winter.
There were large differences in clover yield between populations in both years. These were evident from the first (spring) harvest in each year. Higher-yielding clovers in spring tended to produce higher annual clover yields. No grass × clover interaction was evident at any harvest. Large differences between clovers were also apparent in the morphological characteristics measured, with the Swiss material generally having greater amounts of stolon, leaf plus petiole and numbers of growing points present in early spring. It is proposed that these factors contribute to the high spring yield in the Swiss populations. Loss of stolon length over each winter was less in the Swiss material, indicating that its good spring growth was not obtained at the expense of winter hardiness. Annual clover yield was found to be significantly positively correlated with the amount of stolon present in spring, exemplifying the importance of stolon survival over the winter. 相似文献
There were large differences in clover yield between populations in both years. These were evident from the first (spring) harvest in each year. Higher-yielding clovers in spring tended to produce higher annual clover yields. No grass × clover interaction was evident at any harvest. Large differences between clovers were also apparent in the morphological characteristics measured, with the Swiss material generally having greater amounts of stolon, leaf plus petiole and numbers of growing points present in early spring. It is proposed that these factors contribute to the high spring yield in the Swiss populations. Loss of stolon length over each winter was less in the Swiss material, indicating that its good spring growth was not obtained at the expense of winter hardiness. Annual clover yield was found to be significantly positively correlated with the amount of stolon present in spring, exemplifying the importance of stolon survival over the winter. 相似文献
12.
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
13.
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
14.
The effects of variety, cutting interval and nitrogen application on the morphology and development of stolons and leaves of white clover 总被引：1，自引：0，他引：1
Six varieties of white clover, each grown with perennial ryegrass, four intervals between cuts and two levels of applied nitrogen in all combinations, were compared in a field experiment during the first 27 months after sowing. Information about yields, crop fractions, heights and ryegrass tillers has been presented in an earlier paper (Wilman and Asiegbu, 1982). The present paper is concerned with the more detailed studies of white clover, which help to explain the yield results and contribute to the understanding of the response of this species to management when grown in competition with grass. Increasing the interval between harvests increased the length of clover stolon per unit area of ground and increased stolon diameter, petiole length, weight per leaf and number of leaves harvested as a proportion of the number present in the sward while only slightly reducing the rate of leaf emergence, helping to explain the positive effect of increasing the interval on clover yield noted in the earlier paper. During regrowth, successive leaves had longer petioles and the length of individual petioles increased beyond the stage at which the leaflets were fully opened. Weight per leaf in clover increased considerably from April to June and declined to below the April value by October. It was shown that weight per leaf can be greatly increased by increasing the interval between harvests without reducing the number of leaves harvested per unit area per year. The stolon length measurements provided some support for the view that medium large-leaved varieties of white clover can with advantage be defoliated rather less frequently than small-leaved varieties. Stolon length was less adversely affected by applied N in the medium large- than in the small-leaved varieties. The small-leaved varieties had thinner stolons than the medium large-leaved varieties but about twice the stolon length when no N was applied, and a relatively high proportion of leaves which escaped defoliation. The application of N reduced stolon diameter, increased petiole length and had little or no effect on weight per clover leaf. 相似文献
15.
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
16.
Two field experiments were carried out at North Wyke, Devon in 1985 (Experiment A) and 1986 (Experiment B) to investigate the effectiveness of either cutting or rotational sheep-grazing managements for raising the clover content of clover-depleted swards. Subplots were pretreated in March with (a) propyzamide at 0·4kg a.i. ha-1, (b) chlorpyrifos at 0·72 kg a.i. ha-1 and methiocarb at 0·22 kg a.i. ha-1, (c) carbofuran at 1·3 kg a.i. ha-1, or (d) not so treated, in order to reduce grass tiller density, control insect and mollusk pests, or control all invertebrate pests respectively (a-c), Carbofuran was not applied to swards that were to be grazed subsequently. The propyzamide pretreatment (a) significantly reduced the quantity of herbage dry matter (DM) grazed and the silage DM yields in both years, but raised the numbers of active clover buds, and clover stolon density and its weight in 1986, though not in 1985, The pesticide package (b) raised the quantity of herbage DM grazed in both years, and the silage DM yield in 1986, Carbofuran (c) raised silage yields in 1985. Neither pretreatment (b) nor (c) significantly affected clover performance. In comparison with sheep grazing, cutting showed a trend to higher DM yields, and significantly raised clover stolon density and weight in both years, and active bud numbers in 1986. The periodic sheep grazing management included recovery intervals of 14 d and 35 d. In 1986 (but not 1985) the longer recovery interval raised herbage DM consumption, but had no effect on clover development. The cutting management included nitrogen inputs of either 100 kg ha-1 in March, or none. N input raised annual DM yields in 1986 (but not 1985) but did not affect clover DM yields or performance in either year. The experiments at North Wyke were supported by on-farm experiments using exclosure cages at ten sites in 1985 and nine in 1986, in Yorkshire, Wales, the Midlands and Devon. In both years, application of propyzamide as in treatment (a) reduced DM yields (P<0.001) and raised the proportion of clover (P<0.001) in May harvests. The density of active clover buds (P<0.05), stolon density (P<0.001) and stolon weight (P<0.001) were increased by October. A combined carbofuran and methiocarb treatment significantly (P<0.001) increased herbage yields, but did not affect measures of clover performance. Unlike the main experiments, a comparison of grazing (outside the cages) and cutting management (within the cages) showed no effect on clover development. It was concluded that cutting, or rotational sheep grazing with a long recovery interval, would promote clover development in the clover depleted sward. Though successful in the overall assessment, application of propyzamide gave highly variable results on different sites and was not sufficiently reliable. 相似文献
17.
The effects of spatial location of white clover ( Trifolium repens L.) within a perennial ryegrass ( Lolium perenne L.)/white clover pasture on stolon and petiole extension were investigated in two experiments, where patch size containing white clover (0·5 m, 1·5 m and 4 m diameter), location within the patch (inside and edge) and cutting height (4 cm and 8 cm) were varied. Stolon extension rate was greater on the edge of a patch (12·1 mm week−1 ) than inside the patch (7·2 mm week−1 ). Patch size affected both stolon and petiole extension rate, which were both greater in small and medium-sized than in large patches. It is suggested that the fastest spread of white clover in patchy sward environments should occur from small patches, which could double in diameter during a growing season. Manipulating the heights of vegetation within and outside large patches affected light quality (red-far red; R/FR) at ground level, which was greater under shorter than taller swards and greater under the canopy of the grass matrix than the grass/white clover patch. However, the height differences between adjacent vegetation had little effect on stolon or petiole growth. In May only, stolon extension at the patch boundary was greatest when both patches and the grass matrix had a height of 8 cm. 相似文献
18.
J. E. Vipond G. Swift A. T. Cleland J. Fitzsimons & E. A. Hunter 《Grass and Forage Science》1997,52(1):99-109
Results for years 4–8 of a long-term grazing experiment on swards of a diploid perennial ryegrass (Lolium perenne), var. Contender (D swards), a tetraploid ryegrass, var. Condesa (T swards) and Condesa with S184 white clover (Trifolium repens) (TC swards), direct sown in May 1987, are presented. The swards were continuously stocked with sheep from 1988 to 1990, as previously reported, and for a further 5 years, 1991–95, at a target sward surface height (SSH) of 4–6 cm. Control of sward height was successfully achieved by variable stocking, except in 1993 when paddocks were set stocked and the resulting mean SSH was 9·3 cm. Grass swards received on average 160 kg N ha?1 year?1; grass/clover swards were mainly not fertilized with N with the exception that they were given 30 kg N ha?1 as a remedial mid-summer application during a period of low herbage mass on offer in 1994 and 1995. Mean white clover content of the swards fell from 18·2% of herbage dry-matter (DM) in 1992 to 8·5% in 1993, whereas stolon lengths fell from 120 to 58 m m?2. A return to lower sward heights in 1994–95 resulted in an increase in white clover content to 12·8% by the final sampling in August 1995. Perennial ryegrass content of the grass swards remained high throughout (mean 96·7% in 1995). Perennial ryegrass tiller densities recorded in August 1991, 1993 and 1994 showed consistently significant (P < 0·001) sward differences (3-year mean 16 600, 13 700 and 10 100 perennial ryegrass tillers m?2 for the D, T and TC swards). In 1994, the year after lax grazing, a low perennial ryegrass tiller density (9100 m?2) and low white clover content (mean 4·3%) in the TC swards resulted in a much lower herbage bulk density than in the grass swards (April–July means 72, 94 and 44 kg OM ha?1 cm?1 for the D, T and TC swards). There was a consistent 40 g d?1 increase in lamb liveweight gain on the TC swards over the T swards, except in 1994. In that year there was a reduction in lamb liveweight gain of 33 g d?1 on the TC swards and a significant increase in ewe liveweight loss (117 g d?1) associated with low herbage bulk density despite optimal sward height. Lamb output (kg liveweight ha?1) on TC swards reflected white clover content, falling from a similar output to that produced from grass given 160 kg N ha?1, at 18% white clover DM content, down to 60% of grass + N swards with around 5% clover. A 6% greater output from the T than the D swards was achieved mainly through higher stocking rate. The experiment demonstrated a rapid, loss in white clover under lax grazing, and showed that the relationship between performance and sward height is also dependent on herbage density. High lamb output from a grass/clover sward was only achieved when the clover content was maintained at 15–20% of the herbage DM. 相似文献
19.
Influence of irradiance on branch growth of white clover stolons in rejected areas within grazed swards 总被引：3，自引：0，他引：3
Development of white clover stolons ( Trifolium repens ) was compared when grown in rejected areas and in adjacent defoliated areas over 28 days in May - June in continuously stocked grass/white clover swards. In the cut areas more branches were borne on stolons with more but shorter internodes and shorter petioles than in the rejected areas. Red (R)/far red (FR) ratio at the base of the cut sward was significantly higher than in the rejected sward.
Five experiments were carried out in which red light-emitting diodes (LEDs) supplied supplementary irradiation at the node of the youngest fully expanded leaf on white clover stolons growing in association with dense canopies of perennial ryegrass. Axillary bud/branch length was the only significantly affected aspect of development that was measured, irradiation enrichment increasing length by about three-fold over a 2–4 week period. One of the experiments involved identification of the site of perception of the R/FR effect. Natural and supplementary light were excluded from the stolon (by covering with a 2-cm layer of black beads), petiole (by wrapping in aluminium foil), both or neither and showed that exposure of the stolon/ petiole base to supplementary light was necessary to stimulate axillary bud growth.
It is concluded that the relative content of red light, and possibly absolute level, in irradiance at the base of the canopy in rejected areas is implicated in the young branch growth and that release of the buds can be achieved by defoliation, presumably due to increasing the red light content; however, the effect of increased photosynthetically active radiation (PAR) reaching stolons and young leaves cannot be discounted as an additional factor. 相似文献
Five experiments were carried out in which red light-emitting diodes (LEDs) supplied supplementary irradiation at the node of the youngest fully expanded leaf on white clover stolons growing in association with dense canopies of perennial ryegrass. Axillary bud/branch length was the only significantly affected aspect of development that was measured, irradiation enrichment increasing length by about three-fold over a 2–4 week period. One of the experiments involved identification of the site of perception of the R/FR effect. Natural and supplementary light were excluded from the stolon (by covering with a 2-cm layer of black beads), petiole (by wrapping in aluminium foil), both or neither and showed that exposure of the stolon/ petiole base to supplementary light was necessary to stimulate axillary bud growth.
It is concluded that the relative content of red light, and possibly absolute level, in irradiance at the base of the canopy in rejected areas is implicated in the young branch growth and that release of the buds can be achieved by defoliation, presumably due to increasing the red light content; however, the effect of increased photosynthetically active radiation (PAR) reaching stolons and young leaves cannot be discounted as an additional factor. 相似文献
20.
Changes in contribution of white clover to canopy structure in perennial ryegrass/white clover swards in response to N fertilizer 总被引：1，自引：0，他引：1
Twelve plots were laid down on an existing perennial ryegrass/white clover sward, one plot in each of six replicated blocks receiving 100 kg N ha−1 (100N) and one plot receiving no N (0N). Biomass, canopy development (stratified cuts and point quadrat records at 2–4-week intervals) and changes in stolon population density were recorded during one 8-week regrowth period (25 July–23 September) to investigate the likely causes of N effects on white clover in mixed swards.
Over the period, N fertilizer resulted in an increase of 74% in perennial ryegrass biomass and a reduction of 24% in white clover biomass. There was also a reduction of 44% in stolon growing point density, mainly due to lower density of younger stolon branches. White clover's contribution to the upper three leaf area index (LAI) units (taken as an estimate of the proportion of photosynthetically active radiation (PAR) intercepted) was, on average, 70% at 0N producing 74% of the sward biomass, compared with 46% contribution to interception and 37% contribution to biomass at 100N.
While there was no evidence of overtopping, it is concluded that N fertilizer application increased the LAI of perennial ryegrass in the upper layers of the canopy thereby reducing the share of available PAR to white clover. This, coupled with a lower radiation use efficiency at high N and lower population density, results in white clover's reduced performance in mixed swards receiving N fertilizer. 相似文献
Over the period, N fertilizer resulted in an increase of 74% in perennial ryegrass biomass and a reduction of 24% in white clover biomass. There was also a reduction of 44% in stolon growing point density, mainly due to lower density of younger stolon branches. White clover's contribution to the upper three leaf area index (LAI) units (taken as an estimate of the proportion of photosynthetically active radiation (PAR) intercepted) was, on average, 70% at 0N producing 74% of the sward biomass, compared with 46% contribution to interception and 37% contribution to biomass at 100N.
While there was no evidence of overtopping, it is concluded that N fertilizer application increased the LAI of perennial ryegrass in the upper layers of the canopy thereby reducing the share of available PAR to white clover. This, coupled with a lower radiation use efficiency at high N and lower population density, results in white clover's reduced performance in mixed swards receiving N fertilizer. 相似文献