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1.
The productivity of a mixed sward comprising perennial ryegrass cv. Fantoom and white clover cv. Aran was measured under eight defoliation management systems and two fertilizer N rates (0 and 75 kg ha-1) applied in spring. The defoliations involved a basic six-harvest simulated grazing system together with the interposition of silage cuts once or twice at varying times during the growing season; evaluation was made over three harvest years, 1983-85. Mean annual production of total herbage DM over the three years was 8.351 tha-1 without N and 9.49 tha-1 with 75 kg N ha-1, a mean response of 15.2 kg DM per kg applied N. The responses for individual treatments occurred mainly at the first cuts, whether for simulated grazing (a mean of 12 9 kg DM) or for silage (a mean of 259 kg DM); however, this influence of spring N was not sustained at other cuts over the season. Mean annual white clover DM production was 4.19 t ha-1 with no N and 3.32 t ha-1 with 75 kg ha-1 N, but the reduction due to N was not significant in any year. The mean amount of clover stolon DM present post harvest over all management systems was 1.33 t ha-1 with no N and 1.03 t ha-1 with 75 kg ha-1 N. Mean annual DM production of total herbage from the six-harvest system was 8.11 t ha-1 Compared with 8 88 t ha-1 (a 9% increase) from the systems with one silage cut and 9.241 ha-1 (a 14% increase) from the systems with two silage cuts. Corresponding white clover DM production was 4.02, 3 87 and 3 53 t ha-1, respectively, and mean stolon DM amounts post harvest, 1 12,1.15 and 1-23 t ha-1, respectively. It is concluded that grass/white clover swards are suitable for management systems which involve cutting for conservation. Spring N application did not greatly reduce white clover production in this experiment where white clover was at higher levels than are likely in farming practice and the swards were not grazed. More knowledge of spring N rates, and indeed of N application rates generally, would be advantageous in future assessment of silage cutting systems.  相似文献   

2.
Persistence of white clover (Trifolium repens) in mixtures was studied in a long-term experiment. Mixtures of two cultivars of perennial ryegrass (Lolium perenne) with contrasting growth habits and three white clover cultivars differing in leaf size were sown in 1991 and evaluated at two cutting frequencies. During 1995 and 1996 mixtures with large-leaved white clover cv. Alice had the highest dry-matter (DM) content, clover and N yield, and the highest white clover content, and mixtures with medium-leaved Retor the lowest, whereas mixtures with small-leaved Gwenda yielded most grass DM. In 1995 averaged over cutting treatments and mixtures, the mixtures yielded 11·8 t DM ha?1 with a white clover content of 0·6; the apparent N fixation was 393 kg N ha?1. In 1996 these values declined to 8·5 t DM ha?1, 0·48 white clover and 236 kg N ha?1. There was no significant effect of cutting frequency on DM yield or white clover content, whereas the effects of grass cultivar were not consistent. In spring there was a peak in the DM production of the mixtures, coinciding with a peak in production of the grass component. However, in summer and autumn the seasonal pattern of DM production of the mixtures was similar to that of the white clover component. Both cultivars of perennial ryegrass showed the same seasonal response, but the seasonal growth pattern of white clover differed slightly between clover cultivars and cutting treatments. In later years only one cutting frequency was imposed, and no yield measurements were taken. White clover was judged to have performed well during 1997; the clover content in September was very high (0·76), whereas in October 1998 it was 0·45. Mixtures with Alice contained most white clover. Despite fluctuations in white clover content during 1991–98, all clover cultivars had persisted 7 years after sowing, irrespective of companion grass cultivar, at both cutting treatments.  相似文献   

3.
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   

4.
The productivity of a mixed sward, comprising perennial ryegrass cvs Barlano and Bastion and white clover cvs Donna and Aran, was measured under sixteen fertilizer N treatments. These involved 0.25, 50 and 75 kg N ha-1 in spring only, in autumn only and in all combinations of spring N and autumn N. A simulated grazing regime of six cuts annually at 3- to 6-week intervals was imposed. Increasing rates of total N application increased total herbage DM regardless of application pattern. Yield response was greater with N applied in the spring, and total herbage DM was higher with high spring N-low autumn N than the reverse. Mean yield responses at the first harvest to 25, 50 and 75 kg ha-1 N in spring were 13.6, 10.8 and 11.6 kg DM per kg N. Corresponding responses at the final harvest to N rates in the autumn were 7.2, 5.8 and 6.8 kg DM per kg N. Responses were similar at these times for treatments receiving combined spring and autumn N. Over all treatments, mean annual production of total herbage was between 7.08 t ha-1 DM with no N and 8.19 t ha-1 with 75 kg ha-1 N in both spring and autumn. Owing to drought, mean production in year 2 fell by 32% compared with year 1. White clover production fell progressively with increasing N application. Treatments with spring-applied N gave the most marked decrease. White clover was more markedly depressed than the associated grass by the drought in the second year. The mean reductions in white clover content were 0.17, 0.07 and 0.12 percentage units per kg applied N for spring N, autumn N and combinations. Autumn N use depressed white clover less than spring N but the yield response of grass was less. It is concluded that any applied N adversely affects white clover performance to some degree. Where management factors are unfavourable to white clover even strategic N use may not be wise. Instead, it is suggested that a ‘dual-sward’ approach be adopted in practice, namely, grass/white clover swards with no N. and complementary grass swards receiving optimum applied N to give better production at times when grass/white clover swards are relatively less productive.  相似文献   

5.
The effect of sowing date (SD) and sowing rate of perennial ryegrass (PRG) on the establishment of Caucasian and white clovers in New Zealand was assessed. Clovers were sown in spring on 24 September (SD1) and 9 November (SD2) 1999, and in autumn on 4 February (SD3) and 31 March (SD4) 2000. On each date, clovers were sown with 0, 3, 6 or 12 kg ha?1 of PRG. Total herbage dry matter (DM) production up to 6 November 2000 was 13–16 t DM ha?1 for SD1 and SD2 when sown with 3–12 kg ha?1 of PRG, and 7–10 t DM ha?1 for sown clover monocultures. For SD3 and SD4, total herbage production was 6–9 t DM ha?1 with PRG, while total herbage production of clover monocultures was 5·4 t DM ha?1 for SD3 and 2·6 t DM ha?1 for SD4. By 6 November 2000, white clover contributed proportionately more than 0·15 of herbage mass when sown with 3–12 kg ha?1 of PRG on SD1, SD2 or SD3, but less than 0·09 when sown on SD4. The proportion of Caucasian clover never exceeded 0·09 of herbage mass in any of the swards. White clover was successfully established in spring and in autumn with 3–12 kg ha?1 of PRG provided the 15‐mm soil temperature was above 14 °C. None of the combinations of Caucasian clover and PRG provided an adequate proportion of legumes during the establishment year. This unsuccessful establishment of Caucasian clover with PRG was attributed to its inability to compete for available light as a seedling due to slow leaf area expansion from secondary shoot development and a high root:shoot ratio. Alternative establishment strategies for Caucasian clover may include the use of slow establishing grasses, cover crops and temporal species separation.  相似文献   

6.
In a small-plot trial five grass varieties bromegrass cv. Grasslands Matua, perennial ryegrass CVS. Melle (diploid) and Bastion, Condesa and Meltra (tetraploid) were established as grass/white clover swards with white clover cv. Menna. Productivity was measured under 6-weekIy cutting both without N fertilizer (No) and with 100 kg N ha?1 applied in spring (N100) Evaluation was made over 2 harvest years, 1986–87. Total mean annual production of herbage dry matter (DM) in the first harvest year at No and No was 5·07 t ha?1 and 6·93 t ha?1 respectively. In year 2, corresponding values were 11·81 and 12·67 t ha?1. In year 1, Matua swards at No and N100 yielded 5·08 and 6·65 t DM ha?1 compared with 507 and 70 t DM ha?1 for the mean of the four ryegrass varieties. In year 2, corresponding values were 12·90 and 12·29 for Matua and 11·54 and 12·78 for the four ryegrasses. In year 1, the digestable organic matter in the dry matter (DOMD) of the Matua swards was lower than that of Melle, Bastion and Condesa at NO, particularly at the first cut. In year 2, differences in DOMD between treatments and varieties were not significant. The proportion of white clover was found to be higher in the No than the N100 treatment, and also higher in year 2 in most treatments. For the No treatment Matua swards had the highest proportion of white clover in year 1 (32% compared with 24% for the mean of the ryegrass varieties) but the lowest proportion in year 2 (27% compared with 60% for the ryegrasses). For the No treatment in year 1 clover production was also 43% higher, on average, from the tetraploid treatments than with Melle as the companion grass; for this comparison in year 2 the differences were not significant. It is concluded that Matua bromegrass/white clover swards receiving no N fertilizer may have a good potential under cutting management. However, the evidence from this trial is that in the second year the proportion of white clover is lower with Matua swards than with perennial ryegrass as the companion grass.  相似文献   

7.
Growth of grass herbage in Ireland is highly seasonal with little or no net growth from November to February. As a result, feed demand exceeds grass supply during late autumn, winter and early spring. At low stocking rates [≤2 livestock units (LU) ha?1], there is potential to defer some of the herbage grown in autumn to support winter grazing. This study examined the effects of four autumn‐closing dates and four winter‐grazing dates in successive years on the accumulation of herbage mass and on tiller density in winter and subsequent herbage production at two sites in Ireland, one in the south and one in the north‐east. Closing swards from grazing in early and mid‐September (north‐east and south of Ireland respectively) provided swards with >2 t DM ha?1 and a proportion of green leaf >0·65–0·70 of the herbage mass above 4 cm, with a crude protein (CP) concentration of >230 g kg?1 DM and dry matter digestibility (DMD) of >0·700. The effects of autumn‐closing date and winter‐grazing date on herbage production in the subsequent year varied between the two sites. There was no significant effect of autumn‐closing date in the north‐eastern site whereas in the south earlier autumn closing reduced the herbage mass in late March by up to 0·34 t DM ha?1 and delaying winter grazing reduced the herbage mass in late March by up to 0·85 t DM ha?1. The effects of later grazing dates in winter on herbage mass continued into the summer at the southern site, reducing the herbage mass for the period from late March to July by up to 2 t DM ha?1. The effects of imposing treatments in successive years did not follow a consistent pattern and year‐to‐year variation was most likely linked to meteorological conditions.  相似文献   

8.
The provision of grass for early spring grazing in Ireland is critical for spring calving grass‐based milk production systems. This experiment investigated the effect of a range of autumn closing dates (CD), on herbage mass (kg DM ha?1), leaf area index (LAI) and tiller density (m?2) during winter and early spring. Thirty‐six grazing paddocks, closed from 23 September to 1 December 2007, were grouped to create five mean CD treatments – 29 September, 13 October, 27 October, 10 November, 24 November. Herbage mass, tiller density and LAI were measured every 3 weeks from 28 November 2007 to 20 February 2008; additionally, herbage mass was measured prior to initial spring grazing and tiller density was measured intermittently until September 2008. Delaying CD until November significantly (P < 0·05) reduced herbage mass (by approximately 500 kg DM ha?1) and LAI (by approximately 0·86 units) in mid‐February. On average, 35% of herbage mass present on swards on 20 February was grown between 28 November and 30 January. LAI was positively correlated with herbage mass (R2 = 0·78). Herbage mass increased by approximately 1000 kg DM ha?1 as spring grazing was delayed from February to April. Tiller density increased from November to February, although it did fluctuate, and it was greatest in April (9930 m?2). This experiment concludes that in the south of Ireland adequate herbage mass for grazing in early spring can be achieved by delaying closing to early mid‐October; swards required for grazing after mid‐March can be closed during November.  相似文献   

9.
Four cultivars of perennial ryegrass (intermediate diploid cv. Talbot and tetraploid cv. Barlatra, and late diploid cv. Parcour and tetraploid cv. Petra) were each sown at 10,20 and 30 kg ha-1, all with 3 kg ha-1 of white clover cv. Donna. Herbage productivity was measured over 3 harvest years, 1982–84. under two annual rates of fertilizer N (0 and 150 kg ha-1); the 150 kg ha-1 rate was split equally between March and August applications. Fertilizer N increased total herbage DM production; the 3-year means for the 0 and 150 kg ha-1 N rates were 8·04 and 8·91 t ha-1, respectively. In successive years, total herbage responses to N (kg DM (kg N applied)-1) were 6·6, 35 and 72 (overall mean, 58). Mean white clover DM production over the 3 years was reduced from 4·48 t ha-1 at nil N to 2·82 t ha-1 at the 150 kg ha-1 rate, a fall of 37%. Grass seed rate did not influence total herbage production or white clover performance. The two intermediate perennial ryegrass cultivars had a marginal advantage in total herbage production over the two late cultivars, but white clover content and production were higher with tetraploids than diploids. It is concluded that the value of increased herbage production from strategic use of fertilizer N has to be weighed against its depressive effect on white clover performance; application of 75 kg ha ha-1 N in both spring and autumn was excessively high if maintenance of a good white clover content in the sward is an objective. There is considerable flexibility in the grass: clover seed ratio in seeds mixtures. Modern highly-productive perennial ryegrass varieties do not differ substantially in compatibility with white clover but tetraploids permit better clover performance than diploids.  相似文献   

10.
Performance of white clover/perennial ryegrass mixtures under cutting   总被引：4，自引：0，他引：4  
Clover persistence in mixtures of two varieties of perennial ryegrass (Lolium perenne) with contrasting growth habits and three white clover (Trifolium repens) varieties differing in leaf sizes was evaluated at two cutting frequencies. An experiment was sown in 1991 on a clay soil. The plots received no nitrogen fertilizer. In 1992, 1993 and 1994, mixtures containing the large-leaved clover cv. Alice yielded significantly more herbage dry matter (DM) and had a higher clover content than mixtures containing cvs Gwenda and Retor. Companion grass variety did not consistently affect yield or botanical composition. Cutting at 2 t DM ha?1 resulted in slightly higher total annual yields than cutting at 1.2 t DM ha?1, but did not affect clover content. In 1992 the mixtures yielded, depending on cutting frequency and variety, 10·6–14·6 t DM ha?1 and 446–599 kg ha?1 N, whereas grass monocultures yielded only 1·2–2·0 t DM ha?1 and 25–46 kg ha?1 N. From 1992 to 1994 the annual mean total herbage yield of DM in the mixtures declined from 12·2 to 10·5 to 8·7 t ha?1, the white clover yield declined from 8·7 to 6·5 to 4·1 t ha?1 and the average clover content during the growing season declined from 71% to 61% to 46%, whereas the grass yield increased from 3·4 to 4·0 to 4·5 t ha?1. The N yield decreased from 507 to 406 to 265 kg N ha?1 and the apparent N fixation from 470 to 380 to 238 kg N ha?1. Nitrate leaching losses during the winters of 1992–93 and 1994–95 were highest under mixtures with cv. Alice, but did not exceed 10 kg N ha?1. The in vitro digestible organic matter (IVDOM) was generally higher in clover than in grass, particularly in the summer months. No differences in IVDOM were found among clover or grass varieties. The experiment will be continued to study clover persistence and the mechanisms that affect the grass/clover balance.  相似文献   

11.
Under Irish conditions, the digestibility in May of grass managed for silage production is sometimes lower than expected. In each of two successive years, replicate field plots were established to examine the effects of three defoliation heights (uncut or cut to a stubble height of 10 or 5 cm) applied in winter and/or spring on herbage yields harvested in May and again in July, and on chemical composition and conservation characteristics associated with first‐cut silage. Swards that were not defoliated in December or March had a dry‐matter (DM) yield and in vitro DM digestibility (DMD) in mid‐May of 6597 kg ha?1 and 736 g kg?1, respectively, in Year 1, and corresponding values of 7338 kg ha?1 and 771 g kg?1 in Year 2. Defoliating swards to 5 cm in December reduced (P < 0·001) May DM yields compared to swards that were not defoliated in both December and March, while herbage DMD in May increased (P < 0·001) when defoliated in December or March. There were no clear effects of defoliation height or its timing on herbage ensilability or resultant conservation efficiency characteristics. The effects of defoliation on July yield were the reverse of those observed for May, while the total yield of the December and March defoliations plus the two silage harvests increased as defoliation height was lowered in Year 2 only. It is concluded that defoliation in winter and/or spring can increase herbage digestibility but will likely reduce DM yields in May.  相似文献   

12.
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   

13.
The effect of defoliation interval on growth patterns of contrasting perennial ryegrass (Lolium perenne)–white clover (Trifolium repens) mixtures was studied. The dynamics of increase in leaf area, light interception and dry-matter (DM) production were measured within successive regrowth periods. No N fertilizer was applied. During 1995 six mixtures were cut eight (F1) or six times (F2) at a stubble height of 5 cm. The stubble composition was stable throughout the growing season: after harvest about 50 g DM m?2 (with a white clover proportion of 0·52) was present with a leaf area index (LAI) of 0·5 (0·38 white clover). The percentage of intercepted radiation after cutting was 20–30% and increased during 3 weeks to about 95%. The relative growth rate of leaf area and DM was higher for white clover than for perennial ryegrass, with the proportion of clover in the LAI and DM increasing during each regrowth period. Mixtures with large-leaved white clover cv. Alice had a lower initial clover content after harvest, but a more rapid increase in clover LAI and DM than mixtures with the smaller leaved cvs Gwenda or Retor. Alice had the highest total and clover LAI and DM at harvest. Cutting frequency affected the change in white clover–perennial ryegrass ratio during regrowth. This was significantly higher in mixtures with Alice than in mixtures with Gwenda, but only under less frequent cutting (F2). In spring there was a mean white clover proportion of about 0·55 in the LAI and 0·45 in the total harvested DM. In summer the white clover proportion in the LAI and DM increased to 0·70–0·75. There was a decline during autumn, especially in F2 and in the mixtures with the small-leaved white clover cv. Gwenda and the medium-leaved cv. Retor. In contrast, grass DM and LAI declined from spring to summer. The decline in clover LAI in autumn was similar in Alice and Gwenda at frequent cutting (F1), but stronger in Gwenda in F2. Retor had the lowest clover specific leaf area (SLA). The SLA values of Alice and Gwenda were similar, SLA being similar between cutting treatments. No differences were found for leaf weight ratio (LWR) among the three white clover cultivars or between the grass cultivars, and LWR was not affected by cutting treatment. Defoliation interval had limited effects on the growth pattern and leaf characteristics of perennial ryegrass–white clover mixtures.  相似文献   

14.
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   

15.
The benefits of white clover (Trifolium repens L.) in pastures are widely recognized. However, white clover is perceived as being unreliable due to its typically low content and spatial and temporal variability in mixed (grass‐legume) pastures. One solution to increase the clover proportion and quality of herbage available to grazing animals may be to spatially separate clover from grass within the same field. In a field experiment, perennial ryegrass (Lolium perenne L.) and white clover were sown as a mixture and compared with alternating strips of ryegrass and clover (at 1·5 and 3 m widths), or in adjacent monocultures (strips of 18 m width within a 36‐m‐wide field). Pastures were stocked by ewes and lambs for three 10‐month grazing periods. Over the 3 years of the experiment, spatial separation of grass and clover, compared with a grass–clover mixture, increased clover herbage production, although its proportion in the sward declined through time (0·49–0·54 vs 0·34 in the mixture in the first year, 0·28–0·33 vs 0·15 in the second year and 0·03–0·18 vs 0·01 in the third year). Total herbage production in the growing season in the spatially separated treatments decreased from 11384 kg DM ha?1 in the first year to 8150 kg DM ha?1 in the third year. Crude protein concentration of clover and grass components in the 18‐m adjacent monoculture treatment was greater than the mixture treatment for both clover (310 vs 280 g kg?1 DM) and grass (200 vs 180 g kg?1 DM). There was no clear benefit in liveweight gain beyond the first year in response to spatially separating grass and clover into monocultures within the same field.  相似文献   

16.
Microswards of white clover and perennial ryegrass were subjected to one of four treatments: weekly cutting to 3·5 cm, weekly cutting incorporating a period of no cutting for 6 weeks starting 27 April (early rest), weekly cutting incorporating a period of no cutting for 6 weeks starting 8 June (late rest), or cutting every 3 weeks. Two sward types were used: a mixture of white clover cv. Milkanova with perennial ryegrass cv. Melle, and white clover cv. Kent with perennial ryegrass cv. Melle. Growth measurements (leaf appearance, branching/tillering and stolon internode length) were confined to the first three treatments with records collected during contiguous 21-d measurement periods. Vertical height increments of clover and grass and red:far-red light ratios at the sward bases were also recorded at frequent intervals. At the end of the experiment population densities and unit weights were recorded for all treatments. Significant treatment effects on the rate processes were largely confined to the 21-d period immediately after weekly cutting of rested swards had resumed. On previously rested compared with weekly cut swards, clover leaf appearance rates were increased by 40% and branching rates by 164%. During the same period, grass leaf appearance rates were reduced by 50% and net tillering changed from positive to negative values. Though the rate responses were transient, effects were still apparent at harvest in September, when population density and content (proportion by population density and weight) of clover were significantly higher in the late rest treatment. The variety Kent showed a consistent, though usually nonsignificant, higher leaf appearance and branching rate compared with Milkanova, and in September was characterized by a higher population (7400 m?2 compared to 3200 m?2) of smaller units (27 compared to 46 mg/apical meristem) than Milkanova. The results are discussed in relation to defoliation effects and the role of light quantity and quality as they influence the component growth processes. Attention is drawn to the importance of canopy structure and the climatic and/or phenological differences in the relative seasonal behaviour of clover and grass, together with varietal variation within species in influencing responses to management manipulations.  相似文献   

17.
The effects of different defoliation regimes on the growth and development of three contrasting white clover cultivars (S184, Menna and Alice) were assessed in three experiments in the glasshouse. Experiment 1, with clover growing on its own, investigated the effects of three times of onset × two intensities of defoliation. In Experiment 2, clover was grown with grass and there were two times of onset × two heights × two frequencies of defoliation. Experiment 3, also with grass, investigated the effects of changing defoliation frequency at different intervals from sowing. All clover cultivars responded similarly to the various treatments and there were no interactions between time of onset and subsequent defoliation regimes in Experiments 1 and 2. Without competition from grass (Experiment 1), defoliating early at the three leaf-stage of clover decreased the number of growing points by 32% and stolon weights and lengths by 50% compared with delaying defoliation until the nine leaf-stage. Maintaining one compared with two leaves per growing point had similar effects. Over 17 weeks undefoliated seedlings produced ten times more stolon than early defoliated or intensively defoliated seedlings. In competition with grass (Experiment 2) delaying defoliation significantly decreased all aspects of stolon growth. Seedlings growing in swards defoliated frequently and closely had most growing points whereas those defoliated infrequently had least. Stolon lengths and weights were larger for seedlings growing in swards defoliated frequently than for those defoliated infrequently at both heights of cutting. Mean weight of stolon per unit length was greater when swards were defoliated at 6 cm than at 2 cm height. Changing defoliation from every 2 weeks to every week (Experiment 3) decreased stolon growth slightly when the change was made early but increased it when the change was made late, although similar amounts of stolon were produced by seedlings continuously defoliated throughout every week and every 2 weeks. The results are discussed in relation to the seedlings' leaf complements and growth habit; the over-riding influence of grass competition is highlighted. The possibility of devising optimal defoliation strategies and the need to test these in the field are also outlined.  相似文献   

18.
Developing sustainable grazing management systems based on perennial species is critical to preventing land degradation in marginal land classes. A field study was conducted from 2002 to 2006 to identify the impacts of deferred grazing (no defoliation of pastures for a period generally from spring to autumn) and fertilizer application on herbage accumulation, soil seed reserve and nutritive value in a hill pasture in western Victoria, Australia. Three deferred grazing strategies were used: short‐term deferred grazing (no defoliation between October and January), long‐term deferred grazing (no defoliation from October to the autumn break) and optimized deferred grazing (withholding time from grazing commenced between annual grass stem elongation and seed head emergence and concluded in February/March). These treatments were applied with two fertilizer levels (with or without fertilizer at 50 kg phosphorus ha?1 and 2000 kg lime ha?1 applied in year 1 only) in a factorial arrangement and two additional treatments: continuous grazing (CG) and no grazing (NG) in year 1. The deferred grazing treatments on average produced herbage dry matter of 4773 kg ha?1, the NG produced 4583 kg ha?1 and the CG produced 3183 kg ha?1 in year 4 (2005–06) of the experiment. Deferred grazing treatments with and without fertilizer application produced an average of 5135 and 4411 kg DM ha?1 respectively. Averaged over 4 years, deferred grazing increased the germinable seed pool of perennial grasses by 200% and annual grasses by 50% (except optimized deferred grazing that considerably decreased the annual grass seed pool) compared with the CG. The best of the deferred grazing strategies increased the digestibility of pastures by 7% compared with the CG. The results demonstrated that deferred grazing from spring to autumn followed by rotational grazing could be an effective tool to increase herbage production and soil seed pool and improve the digestibility of native pastures in the steep hill country of southern Australia.  相似文献   

19.
Tetraploid red clover (cv. Hungaropoly) was sown at seed rates of 6,12 or 18 kg ha?1 alone and in mixture with timothy (cv. Scots) at 2, 4 or 6 kg ha?1 or with tall fescue (cv. S170) at 6,12 or 18 kg ha?1. Two ‘silage’ crops and an ‘aftermath grazing’ crop were harvested in 2 successive years. In harvest years 1 and 2, total herbage production levels of 11.12 and 7.47 t dry matter (DM) ha?1 respectively were obtained from pure-sown red clover compared with 11.84 and 8.78 t DM ha?1 for red clover-timothy and 12.23 and 9.64 t DM ha?1 for red clover-tall fescue. Corresponding red clover production levels were 10.93 and 5.30 t DM ha?1 (red clover swards), 8.04 and 3.131 ha?1 (red clover-timothy), and 6.42 and 109 t ha?1 (red clover-tall fescue). Total herbage organic matter digestibility was improved by the timothy companion grass but not consistently by the tall fescue, whereas crude protein (CP) concentration was decreased by the addition of either grass. Increased seed rate intensified these effects, as well as the general effect of the companion grass in depressing red clover DM, digestible organic matter (DOM) and CP production. Total herbage DM, DOM and CP were not markedly affected by increasing red clover seed rate but red clover DM, DOM and CP were increased as red clover seed rate was raised, due to increases in the red clover component. The potential for silage cropping of red clover swards was confirmed but there was advantage in sowing a companion grass. Taking yield and quality parameters into consideration, timothy proved a better companion than tall fescue. A seed rate of 2 or 4 kg ha?1 timothy and 12 kg ha?1 red clover proved the most satisfactory.  相似文献   

20.
Five binary perennial grass/white clover (Trifolium repens, cv. Menna) mixtures were evaluated over a 3-year period under continuous sheep stocking together with the imposition of a rest period for either an early or a late conservation cut; the experiment with plot sizes of 0·16 ha was replicated three times. The grass species and cultivars used were Merlinda tetraploid and Magella diploid perennial ryegrass (Lolium perenne), Prairial cocksfoot (Dactylis glomerata), Rossa meadow fescue (Festuca pratensis) and Goliath timothy (Phleum pratense). The greatest total lengths of white clover stolon developed in the meadow fescue (171·6 m m?2) and timothy (151·9 m m?2) associations compared with those in tetraploid perennial ryegrass (98·6 m m?2), diploid perennial ryegrass (91·9 m m?2) and cocksfoot (74·6 m m?2) (s.e.d. 16·4, P < 0·001). On average, the proportion of white clover stolon that was buried was between 0·86 and 0·89 and this was more abundant in late than early season. Whereas timothy persisted, the persistence of meadow fescue was low under any of the managements tested and this was markedly reduced by the third grazing season. In the diploid perennial ryegrass sward, a late June to early August rest period for conservation enhanced white clover stolon length. An early April to late May rest period greatly reduced total white clover stolon length in both diploid perennial ryegrass and tetraploid perennial ryegrass associations (diploid perennial ryegrass-unrested 89 m m?2, early rest 56·1 m m?2, late rest 130·7 m m?2; tetraploid perennial ryegrass - unrested 125·1 m m?2, early rest 71 m m?2, late rest 99·7 m m?2; s.e.d. 19·19, P < 0·001). The numbers of white clover stolon growing points per unit stolon length were greatest when the sward was rested during late June to early August ?55·9 m?1 stolon length compared with 45·7 m?1 for an April to late May rest and 46 m?1 in the absence of a rest (s.e.d. 2·59, P < 0·001). Likewise, the percentage of stolon above ground was greatest with the late June to early August rest ?15·78% compared with 10·61% for the April to late May rest and 7·69% for no rest (s.e.d. 1·569, P < 0·001). The complementary percentages of buried stolon indicate the important role this fraction has and the need to study stolon behaviour in grazing studies generally. It is concluded that, in relation to perennial ryegrass as a companion grass, meadow fescue and timothy allow better white clover development and cocksfoot less. However, other attributes have to be considered, for example the poor persistence of meadow fescue and the slower regrowth of timothy, both of which allow the invasion of weed grasses, or the lower acceptability of cocksfoot to livestock. The timing of the rest period before the conservation cut can influence white clover development considerably, but the effects differed with different companion grasses.  相似文献   

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