The response of mini-swards of perennial ryegrass/white clover to simulated rainfall following slurry application

Perennial ryegrass/white clover mini-swards were used lo determine whether sward responses to slurry were modified by subsequent simulated rainfall (SR). Combinations of two SR volume rates (6.5 and 13 mm), three SR timings (3, 24 and 48 h after slurry application) and two slurry types (cattle, pig) were compared with a fertilizer control (no SR). Scorch, smother and growth of marked stolons and tillers were monitored after slurry application, and yields of both species were recorded. Slurry coverage of plastic squares indicated that smother may be greater on horizontally orientated leaves (clover). Reduced grass leaf growth and numbers of clover growing points in the week following slurry application were attributed mainly to smother, and possibly other phytotoxic effects of slurry. Reasons for the superior clover growth with cattle slurry arc unknown, although its higher P and K content may have contributed. Timing of rainfall is important in influencing sward responses to slurry application. Results suggest that application of slurry may be most beneficial when it immediately precedes rainfall and that longer intervals between slurry application and rainfall reduce grass and clover growth through either greater ammonia loss or slurry negative effects.     

Effects of grazing by sheep or cattle on sward structure and subsequent performance of weaned lambs

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.     

Effects of grazing by sheep or goats on sward composition in ryegrass/white clover pasture and on subsequent performance of weaned lambs

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.     

RESPONSE OF GRASSLAND TO NITROGENOUS FERTILIZER IN THE WEST OF ENGLAND

Extensive replicated plot experiments were carried out at Henley Manor Farm from 1956–1961 to obtain accurate measurements of herbage production and response to nitrogenous fertilizers under West of England conditions. 356 plots were used; use of the herbage by both cutting and grazing was studied. The principal results are: Grass/ clover swards (containing approx. 35% clover) grown without nitrogenous fertilizer averaged 75 cwt dry matter per acre per annum. Application of nitro-chalk to initially grass/clover swards reduced the clover content of the herbage. About 133 lb N/annum was required by an all-grass sward to equal the production of a grass/clover sward without N. Attempts to increase production of grass/clover swards by using N for early growth and relying on clover for mid-season growth were unsuccessful in 2 out of 3 years. Swards (initially grass/clover) gave significant increases in total dry-matter production from regular use of the lowest level of N (26.0 or 34.7 lb N/acre/cut or graze) in 44 out of 49 cases. Extremely high yields were obtained from the heaviest use of N (104.2 lb N/acre/silage cut). 52.1 lb N/acre/cut or graze was the optimum rate of application on ail-grass and grass/clover swards. Up to about 350 lb N/acre/annum the dosage-response curve was very nearly straight for all-grass and grass/clover swards. On the grazed plots herbage left ungrazed amounted on average to only 6% of the total. The health of all stock on the high nitrogen plots (as well as all others) was excellent.     

Sward composition, animal performance and the potential production of grass/white clover swards continuously stocked with sheep

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^–1and 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.     

Effect of sward surface height on the performance of ewes and Iambs continuously grazed on grass/clover and nitrogen-fertilized grass swards

In three successive years, sward height was maintained at 3, 5, 7 or 9 cm on grass swards receiving a total of 300 kg N ha^?1 in six equal monthly dressings from April, and on grass/clover swards receiving 50 kg N ha^?1 as a single dressing in early spring. From turnout in April until weaning in July, 64 ewes and their lambs (mean litter size 1·5) were continuously grazed at the four sward surface heights on the two sward types. White clover content of grass/clover swards remained low throughout the experiment ranging from 0·2 to 7·4% of the herbage mass. During the first two years, lamb gains averaged over sward types were 204, 260, 285 and 308 g d^?1 up to weaning, while in the third year gains were 238, 296, 296 and 260 g d^?1 on 3, 5, 7 and 9 cm swards respectively. Ewes lost live weight on 3 cm swards but apart from this sward height had little effect on performance. During the autumn, weaned lambs gained — 27, 87, 147 and 167 g d^?1 on 3, 5, 7 and 9 cm swards respectively. Sward type had only a small effect on the performance of lambs up to weaning but in the autumn, mean gains of weaned lambs were lower on grass/N swards (73 g d^?1) than on grass/clover swards (115 g d^?1). Relative to 3 cm swards, carrying capacities of 5, 7 and 9 cm swards were 0·76, 0·57 and 0·52 respectively from turnout to weaning and 0·66, 0·52 and 0·44 respectively during autumn. Grass/clover swards carried 0·67 of the ewes carried by grass/N swards from turnout to weaning and 0·51 of the live weight carried by grass/N swards during autumn. The reaction of the two sward types to sward height did not appear to differ but in the third year there was evidence of a reduction in white clover content when swards were grazed at 9 cm. The data suggest that lamb growth rates will increase as sward height increases up to 9 cm and the evidence for this was stronger with weaned lambs in autumn than with suckling lambs in spring.     

A comparison of diploid and tetraploid perennial ryegrass and tetraploid ryegrass/white clover swards under continuous sheep stocking at controlled sward heights. 3. Sward characteristics and animal output, years 4–8

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.     

Persistence and colonization of gaps in sown swards of grass and clover under different sward managements

The effects of extensive sward management and patch size on the persistence and colonization of gaps in sown swards was examined by creating gaps of five different sizes (2·3, 7, 10, 14 and 19 cm in diameter) in four different sward treatments: a fertilized sward grazed to 4 cm, i.e. relatively intensive management, and three extensively managed unfertilized swards, which were not grazed or grazed to 4 cm or 8 cm. The swards were originally sown with ryegrass (Lolium perenne L.) and white clover (Trifolium repens L.), but had developed differences in species composition as a result of the management treatments imposed 2 years before and during the experiment. Light quality measurements, i.e. red-far red (R/FR) ratio, were used to determine when the light environment in the gaps no longer differed from that in control, uncut patches and this was used as an estimate of gap persistence. Persistence of gaps depended on both sward management and gap size. Gaps disappeared most rapidly in the ungrazed sward and fertilized 4-cm sward, and most slowly in the unfertilized 8-cm sward. Small gaps persisted for up to 2 weeks in all but 8-cm swards, whereas larger gaps were estimated to persist for up to 20–25 weeks in unfertilized, grazed swards. There was no evidence that the number of grass or dicotyledonous species increased in the gaps compared with the control areas. There were significant positive linear relationships between the vegetation that developed in gaps and that in the control, uncut patches, reflecting the different species composition of the established sward of the grazed (grass-dominant) and ungrazed (Ranunculus repens-dominant) treatments. For total grass dry matter and tiller numbers, as well as L. perenne tiller numbers, there was a small, but significant, effect of both patch size and sward management on the slopes of the regressions between the controls and gaps. The results are discussed in relation to the potential for species composition of sown swards to change as a result of gap creation.     

Surface application and shallow injection of cattle slurry on grassland: nitrogen losses, herbage yields and nitrogen recoveries

An experiment was carried out over 2 years on grass and grass/clover swards in SW England lo compare herbage yields and N recovery following surface application or shallow injection of cattle slurry at three different times of application. In the second year, losses of N via ammonia volatilization, denitrification and nitrate leaching were measured from applications to the grass sward. On the grass sward, there was no significant effect of time or method of application on dry-matter (DM) yield in the first year, although shallow injection reduced apparent N recovery (ANR) in the herbage by 45% when compared with surface application. In the second year, shallow injection reduced DM yields by 26% and ANR by 48%. On the grass/clover sward, there were no significant effects of time or method of application on DM yields or ANR in either year Inclusion of dicyandiamide (DCD) in the October slurry applications had no significant effect in the first year, but in the second year on the grass sward increased DM yield by 31% and 14% and ANR by 156% and 42% for shallow injection and surface applications respectively. Measurements in the second year on the grass sward showed a reduction in N loss by ammonia volatilization using shallow injection of 40% and 79% for March and June applications respectively. Losses due to denitrification were greatest following October application. Shallow injection increased denitrification losses following March application, but there were no significant differences following October or June applications. N losses due to leaching were small, with no significant difference between treatments. Reasons for the reductions in DM yield and ANR following shallow injection, despite the large reduction in N loss by ammonia volatilization, are discussed.     

Factors affecting the stolon growth of white clover in ryegrass/clover patches

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.     

THE EFFECT OF FERTILIZER NITROGEN AND WHITE CLOVER ON HERBAGE PRODUCTION

The effect of a range of N rates on herbage production from grass/white-clover and grass swards was investigated in two long-term grazed experiments. The mixed sward yielded more than the grass swards over the range of fertilizer rates tested which were 0–120 lb N/ac (134.5 kg/ha), but the response of the mixed sward to fertilizer N was less than that of tbe grass sward. Tbis was due to the direct and indirect effect of clover, which was considerable with no fertilizer N but decreased witb increasing rates of application. However, clover was not completely suppressed by N at eitber site and contributed to berhage yields at all N rates. Rate and time of N application and the amount of clover in tbe sward affected tbe seasonal distribution of DM yields. The mid-season decline was less marked at bigb- tban at intermediate-levels of N supply.     

A comparison of diploid and tetraploid perennial ryegrass and tetraploid ryegrass/white clover swards under continuous sheep stocking at controlled sward heights. 1. Sward characteristics

Two 1·0 ha plots of a late-heading diploid perennial ryegrass (var. Contender) and a late-heading tetraploid ryegrass (var. Condesa), and two 1·4 ha plots of the tetraploid with Aberystwyth S184 small-leaved white clover, were direct sown in May 1987. Over the three years 1988–90 they were continuously stocked by Mule ewes with Suffolk-cross twin lambs, from early April to the end of August, at a target sward surface height (SSH) of 4–6 cm on one set of plots (constant swards) and, on the other set, al 4–6 cm rising after June to a target 6–8 cm (rising swards). The heights were achieved by variable stocking. Fertilizer N was applied only to the grass plots at the rate of 150- 180kgN ha^-1 annually.
SSH was mainly within the target 4–6 cm, after higher initial heights at turnout in 1988and 1990. Mean heights of the constant swards (April- August) averaged 5·53, 4·43 and 5·04cm in the three years. The rising swards (July-August) increased in height over the constant swards by an average of 0·88, 0·48 and 0·55 cm, in successive years.
Clover content of the herbage mass dry matter in the grass/clover swards increased over each grazing season to average 13·0, 26·5 and 21·2% in the three years, with a high mean stolon density of 130 in m^-2 in August 1990. Ryegrass tiller densities in year 3 were 23% higher in the diploid than in the tetraploid swards, which had 43% more than the 10000 tillers m^-2 of the tetraploid ryegrass/clover swards.
It is concluded that the combination of a densely stoloniferous small-leaved clover with the open growth habit of a tetraploid ryegrass can achieve swards of high clover content under continuous sheep stocking.     

THE EFFECT OF STAGE OF GROWTH AT DEFOLIATION ON WHITE CLOVER IN MIXED SWARDS

Four experiments are described in which various defoliation methods and frequencies were imposed on grass/white-clover swards. Clover was not reduced in any of these hy increasing the length of growth period or hy cutting at a late stage of growth, but intensive sheep grazing reduced clover compared nitb cutting and taking a silage cut in a grazing sequence improved clover yield. These results do not support the contention that cutting a mixed sward for hay or silage suppresses clover because of competition for light: with a ‘big white’ type of clover infrequent defoliation may cause no more shading than frequent. Alternatively, any additional shading may be compensated for by an increase in clover growth, stimulated hy the longer growth period. It is suggested that, in practice, competition for nutrients and moisture also contrihute towards clover suppression when swards are cut for hay or silage.     

A comparison of diploid and tetraploid perennial ryegrass and tetraploid ryegrass/white clover swards under continuous sheep stocking at controlled sward heights. 2. Animal production

Performance of continuously stocked Mule ewes nursing Suffolk-cross twin lambs over three grazing seasons, between April and August, was compared on swards of N-fertilized diploid perennial ryegrass (D), tetraploid perennial ryegrass (T) and tetraploid perennial ryegrass with white clover (TC), the latter receiving no fertilizer N. Sward height was maintained by variable stocking rate close to a target of 4–6 cm (constant treatment) from turnout and compared in July and August with a rising sward height treatment (target 6–8 cm). Lambs on TC swards had significantly higher (P <0·001) liveweight gains compared with lambs on T swards by 41 gd^-1 in April–June and by 68gd^-1 in July-August. Live weight and body condition score of ewes in August were significantly higher (P<0·001) on TC compared with T swards, by 11·3 kg and 0·75 respectively. Rising sward heights in July–August increased live-weight gain of lambs compared with constant sward heights by 102, 39 and 54gd^-1 in consecutive years, associated with sward height increases of 0·9, 0·5 and 0·6cm respectively. Rising sward height increased ewe live weight and body condition score by 5·1 kg and 0·3 respectively, compared with results from constant sward heights. Effects of sward height and sward type were additive. T swards had a significantly (P<0·01) 16% greater overall lamb output than the D swards due mainly to a 10% higher achieved stocking rate. Stocking rates of ewes on TC vs T swards were 40, 13 and 12% lower in April-August in successive years. The higher liveweight gain of lambs on the TC swards resulted in lamb outputs of 76, 105 and 101% of the T swards in successive years, showing that grass/clover swards containing over 20% clover could produce similar lamb output ha^-1 to grass swards given 150–180 kg N ha^-1.     

Defoliation and productivity of a phalaris-subterranean clover sward, and the influence of grazing experience on sheep intake

Swards of Phalaris aquatica-Trifolium subterraneum were subjected to four defoliation treatments—zero, low (11 sheep ha⁻¹) and high (22 sheep ha⁻¹) stocking rates, and weekly cutting. At high stocking rate the annual grass Hordeum leporinum dominated while clover was dominant at low and zero stocking rates. Weekly cutting suppressed species other than clover and so failed to simulate grazing.
There were similarities in net herbage production between zero and lightly grazed swards and between heavily grazed and repeatedly cut swards. Net herbage production decreased in the order undisturbed sward < lightly grazed sward < heavily grazed sward < repeatedly cut sward.
When sheep grazed swards where herbage mass was low their daily consumption of herbage, and therefore liveweight change, depended on their recent grazing experience. Sheep accustomed to swards where herbage mass was low ate more because they grazed for much longer each day than unaccustomed sheep, although they selected a diet of similar digestibility.     

Contribution of white clover varieties to total sward production under typical farm management

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.     

Animal production evaluation of herbage varieties. 1. Comparison of Aurora with Frances, Talbot and Melle perennial ryegrasses when grown alone and with clover

Comparative herbage characteristics and sheep production (ewes and lambs until weaning and lambs thereafter) from swards of Aurora (very early flowering), Frances (early flowering), Talbot (intermediate flowering) and Melle (late flowering) varieties of perennial ryegrass ( Lolium perenne ) were studied under a continuous variable stocking management based on sward surface height guidelines. The varieties were assessed as grass-only (215 kg N ha⁻¹ fertilizer) and grass/clover (83 kg N ha⁻¹ fertilizer) pastures.
Over 2 years (1985-86) total annual lamb production per hectare from grass-only swards of Aurora was 19% more than that from Frances despite similar herbage productivity. Differences between the varieties in lamb output were more pronounced as grass/clover swards, with Aurora producing 29 and 18% more lamb than Melle and Talbot respectively and with Frances also giving 16% more than Melle. Overall lamb production from grass/clover swards was 10% more than that from the grass-only pastures, mainly due to 69% advantage in individual lamb growth rates after weaning. Herbage organic matter digestibility, during the post-weaning period, was higher on grass/clover than on grass-only swards, and similarly with Aurora versus the other varieties. Under a frequent cut simulated grazing regime the relative herbage productivity of the four varieties differed, with Aurora 13% less productive than Frances.
The results are discussed in relation to the limitations of assessing performance under cutting, and the significance of the interaction in animal productivity between the two sward types.     

Diet selection by sheep and goats and sward composition changes in a ryegrass/white clover sward previously grazed by cattle, sheep or goats

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.     

Effect of changing grazing severity on the composition of perennial ryegrass/white clover swards stocked with beef cattle

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.     

The spatial pattern of vegetation in cut and grazed grass/white clover pastures

The spatial patterns of white clover and sward surface height (SSH) that developed In established perennial ryegrass (Lolium perenne)/white clover (Trifolium repens) pastures undercutting lent every 4 weeks to 5 cm) and gracing (continuously grazed with sheep to 5 cm) were measured. While clover cover was recorded in 1000 contiguous 5 × 5-cm quadrats down 50-m permanent transects from early spring to late autumn. Measurements of SSH were made at 10-cm intervals down the same transect. Spatial pattern was analysed using two-term local quadrat variance and patch-gap analysis. At least two scales of spatial pattern existed for white clover when defoliation treatments began. White clover was not distributed at random but found in patches (mean size = 1.1 m) where it was finely intermixed with grass. Patches, separated by gaps (regions of no clover) (mean size = 2.3 m), were in turn aggregated into ‘patches of patches’, separated by larger gaps (mean size = 4.1 m). Under grazing the pattern of patches and gaps did not alter. Under cutting, patch size increased and gap size decreased, explaining in part the greater mass and cover of white clover that arose in cut than grazed swards during the experiment. No new patches of white clover due to seedling establishment or clonal growth were observed in either cut or grazed swards. The intensity of pattern increased in both cut and grazed swards, but the increase was greater m cut swards. The initial single scale of spatial pattern of SSH of tall patches (mean size = 1.2 m) separated by short patches (mean size = 2.7 m) did not change under grazing. SSH became uniform under cutting. It is suggested that the response of plants to selective (spatially heterogeneous) grazing is a crucial factor in the development and maintenance of spatial pattern in grasslands. The importance of spatial pattern to our understanding and interpretation of plant-plant and plant-animal interactions and to the composition of temperate grasslands is considered.