Forage yield and persistency of Trifolium repens × Trifolium nigrescens hybrids under rotational sheep grazing

Introgression of reproductive traits from the annual, profuse flowering, ball clover (Trifolium nigrescens Viv.) into white clover (Trifolium repens L.) is one breeding strategy to improve seed yields of T. repens that must be achieved without sacrificing agronomic performance and persistency under grazing. The yield and persistency of hybrids between white clover and T. nigrescens were compared under rotational sheep grazing over three harvest years. The hybrids included the backcross (BC) 2 and 3 generations produced using white clover as the recurrent parent. The large‐leaved T. repens variety Olwen, medium‐leaved varieties AberDai and Menna and the small‐leaved variety S184 were sown as controls. Hybrids and control varieties were sown with a perennial ryegrass companion; between April and the end of October in each harvest year the plots were rotationally grazed with sheep with clover and perennial ryegrass (DM) yield and the proportion of clover present measured over the growing season. The clover and total DM yields of the BC2 and BC3 were generally comparable with the small‐ and medium‐leaved varieties within the experiment and significantly greater than the yields of the large‐leaved variety Olwen. Throughout the 3 years of the experiment the BC2 maintained a clover content above 0·30 and comparable with the small‐leaved varieties, while the clover content of the BC3 was comparable with the small‐ and medium‐leaved varieties in the first and third harvest years. No significant difference in perennial ryegrass production was observed when grown with the backcrosses or the control varieties. Differences in stolon and growing‐point density were observed at the end of the experiment with the density of the BC2 and BC3 less than the small‐leaved variety S184 but, in common with the medium‐leaved varieties, greater than the large‐leaved variety Olwen. The implication of these results for the use of this material in future experiments and in the white clover breeding programme is discussed.     

Individual and socially learned preferences for biserrula (Biserrula pelecinus L.) in sheep

This study examined how sheep develop a learned aversion to the annual legume biserrula (Biserrula pelecinus L.). Merino sheep were grazed on paddocks sown with either (i) biserrula, (ii) biserrula + ryegrass (Lolium rigidum Gaud.), (iii) crimson clover (Trifolium incarnatum L.), (iv) crimson clover + ryegrass or (v) ryegrass, for 4 weeks. Relative preference (Chesson–Manly selection index) was determined by offering randomly ordered monoculture plots of the three forage species. The groups of sheep were then combined into a single group and grazed a paddock containing a monoculture sward of each plant type for 5 d. Relative preference of sheep was tested again after the completion of the combined grazing. The experiment was repeated at three stages of plant phenology: vegetative, reproductive and senesced. Relative preference for biserrula was lower in sheep that had grazed the paddock sown with only biserrula compared with sheep that grazed a combination of biserrula + ryegrass, at both the vegetative (α; −0·11 vs. 0·32) and reproductive (α; 0·18 vs. 0·63) stages. At each stage of phenology, when groups were combined and grazed together, preference for biserrula became uniform. This supported the hypothesis that sheep develop an aversion to biserrula when they graze a pasture containing biserrula. However, we concluded that the familiarity of sheep with biserrula did not result in low relative preference; rather, the aversion was more likely a response to the high proportion of this plant in their diet. Social facilitation may have enabled sheep to overcome rapidly the food aversion.     

Forage selectivity by cattle and sheep co‐grazing swards differing in plant species diversity

Interactions between sward diversity and forage selectivity of cattle and sheep managed within mixed grazing systems are not fully understood. The objective of this study was to investigate the effect of either mono‐ or co‐grazing of sheep and cattle on swards differing in botanical composition (either diverse or grass‐dominated) on the intake choices of six target forage species. Jacobs' selection index (JSI) was employed to quantify the preference for single target species in relation to their proportion in the sward. Results revealed distinct intake preferences of sheep and cattle; as expected, sheep were more selective than cattle. To a lesser extent, the sward composition had an effect on intake preferences: cattle responded to botanical composition by changing their intake preferences, but to a lesser extent than sheep. Phleum pratense was the most preferred target forage species (JSI = 0.62). Lolium perenne, Taraxacum sect. Ruderale and Trifolium repens were also highly preferred regardless of sward composition or type of grazing (JSI = 0.47, 0.32 and 0.27 respectively). Dactylis glomerata and Festuca pratensis tended to increase in abundance after grazing events in both diverse and grass‐dominated swards. Co‐grazing of cattle and sheep facilitated a more homogeneous consumption of the target forage species evaluated.     

Productivity and nutritional value of 20 species of perennial legumes in a low‐rainfall Mediterranean‐type environment in southern Australia

In the rain‐fed mixed‐farming systems of southern Australia, the consistent supply of high‐value forage is limited by a range of climatic, edaphic and systems constraints. Over 2 years, we compared biomass production and nutritional value of 30 accessions of perennial legumes, and predicted intake, grazing days and growth of ewes and lambs. There was significant variation in nutritional value and biomass production between and within species. Lucerne (Medicago sativa) and sulla (Hedysarum coronarium) produced the greatest amount of biomass and energy. There was variability among accessions in digestibility (DMD), acid detergent fibre (ADF) and crude protein, and the rate of change in these traits as plants matured. Trifolium species had the highest DMD across all growth stages. Hairy canary clover (Dorycnium hirsutum), erect canary clover (Dorycnium rectum), greater birdsfoot trefoil (Lotus uliginosus), Australian trefoil (Lotus australis) and running postman (Kennedia prostrata) had energy levels that would not maintain liveweight of mature sheep. In the second year, species differed in response to harvesting treatments. Lucerne and sainfoin (Onobrychis viciifolia) were more productive under a frequent cutting regime. Accessions of white clover (Trifolium repens), red clover (Trifolium pratense), alsike clover (Trifolium hybridum), cullen (Cullen australasicum), strawberry clover (Trifolium fragiferum), sainfoin and birdsfoot trefoil (Lotus corniculatus) showed some promise, while Tedera (Bituminaria bituminosa) and milkvetch (Astragalus cicer) performed poorly under the experimental conditions. We conclude by discussing additional agronomic and nutritional factors that need consideration when developing novel perennial legumes for mixed‐farming systems in the context of a changing climate.     

Forage yield and persistency of Trifolium repens × Trifolium nigrescens hybrids when sown with a perennial ryegrass companion

Abstract Introgression of reproductive traits from ball clover (Trifolium nigrescens Viv.) into white clover (Trifolium repens L.) is one breeding strategy to improve seed yields of T. repens that must be achieved without sacrificing agronomic performance and persistency. The yield and persistency of hybrids between white clover and the annual, profuse flowering species T. nigrescens were compared under a cutting regime over three harvest years. The hybrids included the F1 and the backcross (BC) 1, 2 and 3 generations produced using T. repens as the recurrent parent. Parental species and hybrids were sown with a perennial ryegrass companion; clover and perennial ryegrass dry‐matter (DM) yield and the proportion of clover present were measured over the growing season. In the third harvest year, a portion of each plot was grazed. Differences were observed between T. nigrescens, the F1 and the backcross hybrids and T. repens. In the first and second harvest years, clover DM yield, the proportion of clover present and total DM yield of the backcross hybrids were similar to T. repens, whereas that of the T. nigrescens and the F1 hybrid were negligible. No significant difference in perennial ryegrass production was observed between the parental species and the hybrids when grown, respectively, in combination with these species and hybrids. In the third harvest year, clover DM yield and the proportion of clover present with the BC3 was lower than with T. repens. Throughout the growing season the DM production of T. repens and the backcross hybrids was similar. In the third harvest year, under cutting, DM yield of T. repens was greatest and that of the BC3 lowest, but under grazing, the yields of the BC1 and BC3 were greater than T. repens and the BC2. The implication of these results for the future development of these hybrids is discussed.     

Populations of two annual clover species evolved in response to 13 years of grazing management and phosphate fertilizer application

A Syrian grassland was subject to 13 years of replicated management treatments, namely a factorial design of 0 or 60 kg/ha annually of phosphate fertilizer, combined with relatively low or high sheep stocking intensities. Previous work found that differences in grazing intensity and phosphate induced changes in the structure of the legume community, presumably due to changes in competitive relationships. The aim of this study was to investigate how the populations of the predominant clover species, Trifolium campestre and Trifolium tomentosum, changed as a consequence of management treatments. We hypothesized that the populations from the fertilized or low grazing intensity treatments would express phenotypic traits associated with increased competitive ability and/or with risk mitigation. Populations of both ruderal-type clover species provided evidence of evolution but were largely responsive to different management factors. Assuming that heavy grazing and no fertilizer are the natural state of the grassland, addition of phosphate led to T. tomentosum plants that were wider and had larger seeds, traits associated with improved competitive ability. The populations from the fertilized paddocks had increased fecundity and a trend towards greater dormancy, traits associated with risk mitigation. In contrast, T. campestre plants became wider and more erect when stocking intensities were reduced and had greater seed dormancy in fertilized paddocks. The implication of this work is that the collection of germplasm from grasslands with a history of heavy grazing and fertilizer application may assist agronomists to find genotypes that are better adapted to pastures within ley farming systems in Australia.     

Seedling recruitment dynamics of forage and weed species under continuous and rotational sheep grazing in a temperate New Zealand pasture

Understanding the grazing conditions under which plant populations are limited by seed availability (seed limitation) is important for devising management schemes that aim to manipulate the establishment of weed and forage species. Seeds of three weed species (Cirsium arvense, C. vulgare and Rumex obtusifolius) and five forage species (Lolium perenne, Lotus uliginosus syn. L. pedunculatus, Paspalum dilatatum, Plantago lanceolata and Trifolium repens) were broadcast sown into L. perenne–T. repens pastures in Manawatu, New Zealand and five sheep‐grazing and two slug‐grazing (with and without molluscicide) treatments were imposed in a split‐plot design. Of the five sheep‐grazing treatments, four compared continuous grazing with rotational grazing at intervals of 12, 24 and 36 d in spring, with all four grazed under a common rotation for the remainder of the year. The fifth treatment was continuous grazing all year. Seed sowing increased seedling emergence of C. vulgare, L. perenne, P. lanceolata, R. obtusifolius and T. repens under all sheep‐ and slug‐grazing treatments, with differences in seedling densities persisting for at least 21 months. Seed sowing did not increase seedling densities of C. arvense, L. uliginosus or P. dilatatum. The effects of sheep‐grazing management on seedling emergence and survival were uncoupled. For the five seed‐limited species, seedling emergence was greater on pastures that were rotationally grazed during spring compared with those that were continuously grazed. However, seedling survival was lower in pastures grazed rotationally during summer, autumn and winter, so that after 21 months seedling numbers were greater on plots that were continuously grazed all year. Exclusion of slugs increased seedling recruitment of T. repens but had no impact on the other species. As weed and forage species responded in a similar way to sheep‐grazing management (increased under continuous, decreased under rotational), it is unlikely that the goals of reducing weed invasions and enhancing forage species establishment could be carried out concurrently in established pastures with the same management.     

Impact of spatial heterogeneity of plant species on herbage productivity,herbage quality and ewe and lamb performance of continuously stocked,perennial ryegrass–white clover swards

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.     

Changes in species composition of abandoned sown swards after imposing seasonal cutting treatments

Abstract Seasonal cutting treatments were imposed on abandoned perennial ryegrass/white clover swards at three sites in the UK to determine the impact on species diversity and the contribution of different species to biomass. Before the cutting experiment, the abandoned swards had received no fertilizer applications and had been neither grazed nor cut for 3 years. The original sown species, Lolium perenne and Trifolium repens, had virtually disappeared during this period. Self‐sown grasses, including Agrostis capillaris, Dactylis glomerata, Festuca rubra, Holcus mollis, Poa pratensis and P. trivialis, had become dominant at two sites. Ranunculus repens was the dominant species at the third site, and self‐sown grasses, such as Holcus lanatus and P. trivialis, and Juncus and Carex species were also present. The standing herbage in 2·5 m × 2·5 m subplots was cut to 2·5 cm above ground level and removed annually in either June or October for 7 years at two sites and 6 years at the third site. Total biomass removed was generally < 4 t dry matter (DM) ha^?1, and both total and live biomass decreased over time in the June cutting treatment at two sites. There were large changes in species composition after initiating the two cutting treatments. The numbers of grass and dicot species increased, although many new species had a low frequency of occurrence. The contribution of species to biomass changed over time, with species showing a vegetative regenerative strategy decreasing over time at one site. At this site, annual cutting in June was slightly more effective than cutting in October in reducing the dominance of R. repens; cutting in early October effectively reduced Juncus spp. At two sites, there was a decrease in the contribution of the species group showing seasonal regeneration by seed, and differences between cutting dates for two species within this group at one site. L. perenne and T. repens remained at much lower levels than in adjacent unfertilized, grazed swards. Reseeding may be necessary to create species assemblages for ecological and agricultural objectives.     

Forage quality of white clover (Trifolium repens L.) × Caucasian clover (T. ambiguum M. Bieb.) hybrids and their grass companion when grown over three harvest years

Interspecific hybrids between white clover (Trifolium repens L.) and Caucasian clover (Trifolium ambiguum M. Bieb.) have been developed to introgress the rhizomatous growth habit into white clover, to increase persistence and drought tolerance. The forage quality of T. repens, T. ambiguum and the backcross 1 (BC1) and backcross 2 (BC2) hybrids and companion grass, when grown in mixtures with an intermediate perennial ryegrass (Lolium perenne L.) under a cutting‐only management, was measured. In vitro dry‐matter digestibility (DMD), water‐soluble carbohydrate (WSC) and crude protein (CP) concentrations of the legume and grass fractions were measured throughout the growing season over three harvest years. Trifolium repens had a lower WSC but a higher CP concentration than the perennial ryegrass companion in all harvest years and at all cuts. The legume fractions from the BC1 and BC2 hybrid plots had a higher WSC and a lower CP concentration but an in vitro DMD value comparable with white clover throughout the growing season and in each harvest year. The grass fractions from the mixtures with the backcross hybrids had a higher WSC and a lower CP concentration than the grass fraction from the T. repens plots, in all harvest years and throughout the growing season. No difference in in vitro DMD between parental species and backcross hybrids was observed. The implications of these results for the development of these hybrids and animal performance are discussed.     

Selection by sheep and goats for perennial ryegrass and white clover offered over a range of sward height contrasts

The selection by sheep (six Coopworth ewe hoggets, 44·3 ± 4·6 kg live weight) and goats (six Saanen/Anglo‐Nubian yearling males, 38·1 ± 3·8 kg live weight) for perennial ryegrass (Lolium perenne) and white clover (Trifolium repens) and for sward height was measured in two experiments involving paired turves. Pairs of turves with herbage of differing height and of either the same or different plant species were offered. One sward (fixed height species, FHS) was always offered at 130 mm and the other (variable height species, VHS) at 130, 90 or 50 mm. Turves (450 mm × 220 mm) were cut to a soil depth of 100–150 mm from areas of perennial ryegrass and white clover regrown to the desired height after previously being cut to 30 mm. Each turf in a pair was weighed (±1 g) before and after grazing by penned animals maintained on a barley‐based pelleted diet. The number of prehending bites taken from each turf was recorded over a grazing period (128 ± 12 s). Bite mass, bite rate and intake rate were calculated. As the sward height of the VHS turf declined, an increasing proportion of the diet was selected from the 130 mm turf. When averaged over all height contrasts, both animal species selected a higher proportion (0·776 ± 0·026) of their diet from 130‐mm white clover than from 130‐mm perennial ryegrass (0·591 ± 0·018) turves. On average, goats selected a higher proportion (0·721 ± 0·022) of their dry‐matter (DM) intake from the 130‐mm turf than sheep (0·646 ± 0·019), but the effect was not consistent. In contrasts with perennial ryegrass as the VHS (and both perennial ryegrass and white clover as FHS), the proportion of the diet selected from the 130‐mm turf was very similar for both animal species. However, with white clover as the VHS (and both perennial ryegrass and white clover as FHS), goats selected a higher proportion of their intake from the 130‐mm turf to the extent that in the 130‐mm perennial ryegrass/50‐mm white clover contrast sheep showed as strong selection for 50‐mm white clover as goats did for 130‐mm perennial ryegrass. This lesser selection of goats for white clover as its height in a sward declines is likely to contribute to the higher white clover content observed in swards grazed by goats. Bite mass was greater on white clover (246 ± 5 mg DM bite^–1) than on perennial ryegrass (173 ± 5 mg DM bite^–1) and was greater for goats (255 ± 6 mg DM bite^–1) than for sheep (195 ± 5 mg DM bite^–1). Bite rate was greater on perennial ryegrass (45·9 ± 1·0 bites min^–1) than on white clover (39·9 ± 1·0 bites min^–1) and was greater for sheep (45·5 ± 1·1 bites min^–1) than for goats (42·5 ± 1·1 bites min^–1). Apparent intake rate by both sheep and goats was lower (mean, 5·0 ± 0·29 g DM min^–1) on 130 mm perennial ryegrass/white clover than on 130 mm perennial ryegrass/perennial ryegrass (7·0 ± 0·27 g DM min^–1), but was higher (9·62 ± 0·29 g DM min^–1) on 130‐mm white clover/perennial ryegrass than on 130‐mm white clover/white clover (8·2 ± 0·29 g DM min^–1) combinations.     

Seasonal changes in herbage mass and nutritive value of a range of grazed legume swards under Mediterranean and cool temperate conditions

Seasonal changes in herbage mass and herbage quality of legume‐based swards under grazing by sheep or cattle were investigated at four locations in climatically different zones of Europe: Sardinia (Italy), southern France, northern Germany and south‐west England (UK). At each location standard treatments were applied to legumes typical of species widely used in each locality: Medicago polymorpha in Italy, Medicago sativa in France, and Trifolium repens in Germany and in UK. At each site comparisons were made of two other legumes: Trifolium subterraneum and Hedysarum coronarium in Italy, Onobrychis sativa and Trifolium incarnatum in France, Trifolium pratense and Lotus corniculatus in Germany, and Trifolium ambiguum and L. corniculatus in UK. Legumes were sown in mixture with locally appropriate companion grasses, and measurements were made over two or three grazing periods. In Italy M. polymorpha swards gave the greatest herbage mass in grazing period 1 but H. coronarium was more persistent. At the French site all legumes established poorly with no significant herbage mass differences between treatments. At both the UK and German sites L. corniculatus maintained a high proportion of legume in the sward; T. repens showed poor persistence under continuous sheep grazing in UK but persisted under cattle grazing in Germany, while T. ambiguum was slow to establish in the UK, and T. pratense proved to be of comparable herbage mass to the standard T. repens‐based sward in the last year of the experiment. The concentration of crude protein and in vitro digestibility of organic matter in the dry matter of herbage showed greater within‐season variation than between treatments at each site. It is concluded that, in addition to currently used species, legume‐based swards containing H. coronarium, O. sativa and L. corniculatus all have potential to contribute to forage production for low‐input grazing and their use merits further consideration in systems of livestock production in Europe.     

Dry matter production of white clover (Trifolium repens L.), Caucasian clover (T. ambiguum M. Bieb.) and their associated hybrids when grown with a grass companion over 3 harvest years

Abstract The dry matter (DM) production of Trifolium repens, T. ambiguum and the backcross 1 (BC1) and backcross 2 (BC2) hybrids with T. repens as the recurrent parent were compared in mixtures with an intermediate heading variety of perennial ryegrass (Lolium perenne L.) under a cutting‐only management over 3 harvest years. Plots of parental legume species and backcross hybrids were established from small plantlets and oversown with the companion grass. In the first harvest year, the DM yield of clover in T. repens plots was greater than that in the BC2 plots and both greater than in the BC1 plots, whilst in the second and third harvest years differences between the DM yield of clover in the T. repens and the BC1 and BC2 hybrid plots were small. Similar results were obtained for the DM yield of total herbage. There were also differences in seasonal growth in the first harvest year, when yield of clover in T. repens plots was greater than in the BC1 and BC2 hybrid plots at early cuts but not at later cuts. Few differences in seasonal growth were observed between parental species and hybrids in subsequent harvest years. Comparison of above‐ and below‐ground biomass showed more DM in roots and rhizome of clover in the backcrosses than in the T. repens plots in the second harvest year but differences were less evident in the third harvest year. The clover in the backcross hybrid plots also had fewer stolon growing points per quadrat than the T. repens plots, but the BC2 had more than the BC1 plots. The exploitation of these hybrids in breeding programmes as a strategy to improve the persistence and drought tolerance of white clover is discussed and implications for forage production considered.     

Sward herbage accumulation and nutritive value as affected by pasture renovation strategy

Perennial ryegrass pastures are the main feed for dairy cows in temperate regions. Alternatives to increase farm sustainability such as naturalized pastures have been proposed, and only limited knowledge exists regarding their potential as a forage source for grazing dairy systems. A field study was undertaken between September 2006 and September 2009 in Valdivia, Chile, to assess the effect of three pasture renovation strategies [naturalized fertilized (NFP); cultivated fertilized Lolium perenne and Trifolium repens mixture (RGWC); and cultivated fertilized Bromus valdivianus, Dactylis glomerata, Holcus lanatus, Lolium perenne and Trifolium repens mixture (MIXED)] over a naturalized degraded pasture on herbage production, botanical change and chemical composition. The three renovation strategies increased total herbage accumulation. During 2007–2008 and 2008–2009, the naturalized fertilized pasture produced similar amounts of dry matter as the cultivated fertilized mixtures. A higher grazing efficiency (the proportion of total herbage mass accumulation, removed by grazing dairy cows) was estimated for NNFP, RGWC and MIXED. Fertilization and liming increased the proportions of Lolium perenne and Bromus spp. at the expense of Agrostis capillaris and Trifolium repens. In the cultivated mixtures, the amount of Lolium perenne tended to decrease over time. Crude protein concentration and digestibility tended to be higher for naturalized fertilized and perennial ryegrass–white clover pastures throughout the experiment. These results suggest that fertilization and liming of a low-producing naturalized pasture might be a sound alternative for pasture improvement.     

The effect of different legume‐based swards on intake and performance of grazing ruminants under Mediterranean and cool temperate conditions

Intake and performance of sheep or cattle grazing legume‐based swards were assessed over 2 years at four locations in Europe with different climatic conditions: Sardinia (Italy), southern France, northern Germany and south‐west England (UK). Legume species were sown in mixtures with locally appropriate companion grass species. Standard legume species commonly used at the location (Medicago polymorpha in Italy, Medicago sativa in France, and Trifolium repens in Germany and UK) were compared with two alternative legume species characterized by different agronomic or nutritional characteristics. They were: Trifolium subterraneum and Hedysarum coronarium in Italy; Trifolium incarnatum and Onobrychis sativa in France; Trifolium pratense and Lotus corniculatus in Germany; and Trifolium ambiguum and L. corniculatus in the UK. Lactating milk sheep in Italy, non‐lactating ewes in southern France, growing cattle in Germany, and ewes and lambs in the UK were used in three replicates per treatment. Intake and performance of sheep and cattle in various treatments varied with location, year and period within year. In Germany, intake and performance by cattle were not affected by treatment. In contrast, at the other locations, sheep grazing standard or alternative legume species known to contain condensed tannins (sulla, sainfoin and birdsfoot trefoil) had higher proportions of legume and crude protein (CP) concentrations in the diet and higher CP intakes than those grazing the other alternative legume species. Sheep performance paralleled these results. It is concluded that there is potential for a greater use of alternative legume species, at least for sheep‐grazing systems, in both the Mediterranean and cool temperate zones of Europe.     

Relationship between vegetation state and bite dimensions of sheep grazing contrasting plant species and its implications for intake rate and diet selection

This study used both experimental evidence and a mathematical model to address some differences in interpretation in the literature on the relationship between sward height and the bite dimensions (bite depth, bite area and bite mass) of sheep grazing contrasting vegetation types. Individual non-fasted sheep were released onto small areas (10 × 10m) of white clover (Trifolium repens) and perennial ryegrass (Lolium perenne) and bite dimensions were measured as they grazed across patches (0·7 × 0·7 m) of predetermined sward surface height (SSH). Sward heights were 4, 7, 10, 13 and 16cm for white clover patches and 4, 6, 5, 9, 11·5 and 14cm for ryegrass patches. Four sheep were assigned to each plant species and each sheep grazed one patch of each height (five patches/sheep). Bite depth, bite area and bite mass increased linearly with SSH in both white clover and ryegrass. At a given SSH, bite depth was similar in white clover and ryegrass, but bite area and bite mass were greater in white clover than in ryegrass. The linear relationships observed between bite mass and SSH contrasted with the asymptotic relationships observed in some other studies, but it is suggested that different relationships may arise because of methodological differences between studies. Furthermore, when linear relationships for bite mass were compared with asymptotic relationships for bite mass in a mechanistic model of animals grazing from ryegrass-white clover pastures it was demonstrated that the nature of the relationship had relatively little effect on the relationship between intake rate and SSH. This was because intake rate depended on the fundamental mechanistic relationship between bite mass and prehension bite rate. This relationship meant that the greater bite masses found when linear relationship were assumed were associated with reduced prehension bite rates and thus the effect on intake rate was relatively small. In addition, the predictions of the model regarding the bases of diet selection by animals grazing ryegrass-white clover mixtures were simplified, and stabilized, when linear relationships were assumed.     

Sheep grazing and defoliation of contrasting varieties of organically grown winter wheat with and without undersowing

Field experiments in Gloucestershire, UK, in the 1990–91, 1991–92, 1993–94 and 1994–95 growing seasons explored the merits of grazing in spring a traditional tall wheat (Triticum aestivum) variety, Maris Widgeon, with more modern shorter varieties. In the first 2 years, defoliation was achieved by mowing at 7 cm in March and/or April. In the second 2 years, varieties sown at two sowing dates were grazed by sheep at a stocking rate of 42 × 50 kg sheep ha^?1 for 3 or 4 days in March. Defoliation reduced crop height and interception of photosynthetically active radiation (PAR). In 1991–92, mowing significantly reduced grain yield of some of the shorter varieties but not of Maris Widgeon. This interaction was related to the amount of PAR intercepted. In this year, mowing improved the establishment of undersown white clover (Trifolium repens) and perennial ryegrass (Lolium perenne), but in subsequent years the conditions were much drier and undersowing failed. In the last two experiments, grazing in March did not significantly reduce grain yield of any variety. The quality of the forage eaten by the sheep had a modified acid-detergent fibre (MADF) content of less than 300 g kg^?1 dry matter (DM) and a crude protein (CP) content of more than 200 g kg^?1 DM in both seasons. Yield of DM and calculated metabolizable energy (ME) of different varieties removed by the sheep interacted strongly with sowing date. September-sown Maris Widgeon provided ≈ 0·7 and 0·3 t DM ha^?1 (or 7·8 and 3·4 GJ ME ha^?1) in March 1994 and March 1995 respectively. However, the shorter wheat varieties, Hereward and Genesis, only provided 0·3 and 0·1 t DM ha^?1 when sown at the same time in the 2 years. At later sowing dates all of the varieties only provided about 0·1 t DM ha^?1 when sown in October 1993, or 0·01 t DM ha^?1 when sown in November 1994. Sheep grazing reduced total weed biomass in June, and reduced the emergence of weed seedlings from soil samples collected after the wheat harvest. Effects of defoliation on foliar infection by Septoria tritici were inconsistent.     

Advanced analysis of dry-weight-rank data to discriminate direct and indirect interactions between white clover and grasses in a multi-species pasture under a range of management strategies

Infestations of pastures by species, such as creeping bentgrass (Agrostis stolonifera), may compromise the white clover (Trifolium repens) content in perennial ryegrass (Lolium perenne) mixtures. However, the interactions between white clover and species other than perennial ryegrass are not well understood. Strategies to prevent creeping bentgrass infestations require an understanding of its interactions with white clover, as the exclusion of white clover from infested pastures could be the result of either direct interaction or niche‐differentiation in response to management. A methodology is presented which enables the segregation of the effects of direct interaction and niche‐differentiation, based on existing dry‐weight‐rank measurements of a number of experimental pastures, subjected to a range of management strategies. Only between the two management extremities, i.e. permanent cutting of silage and lax grazing for long periods, did niche‐differentiation occur between white clover and creeping bentgrass. The white clover content was enhanced under the cutting regime, whereas lax grazing for long periods stimulated the content of creeping bentgrass. White clover was actively excluded from creeping‐bentgrass‐dominated patches by direct interaction, whereas it showed a high compatibility with perennial ryegrass. This direct interaction presents challenges to the prevention of creeping bentgrass by management, as creeping bentgrass and white clover showed nearly identical requirements in terms of environmental conditions and grassland management.     

Effects of systemic fungal endophytes on the performance of meadow fescue and tall fescue in mixtures with red clover

A symbiosis between grasses and systemic fungal endophytes exists in both natural and agricultural grassland communities. Our objective was to examine the effects of systemic endophytes on the competitive ability of two agronomically important grass species: meadow fescue [Festuca pratensis (Huds.) syn. Schedonorus pratensis (Huds.) P. Beauv] and tall fescue [Festuca arundinacea (Schreb.) syn. Schedonorus phoenix (Scop.)]. Plants of meadow and tall fescue were grown for 48 days in replacement series of interspecific mixture with a legume (red clover, Trifolium pratense L.) in different nutrient environments in a greenhouse. Neither of the grass species gained endophyte‐promoted competitive advantage over red clover in grass–clover mixtures. Endophyte infection increased the growth of meadow fescue monocultures by 89% compared to endophyte‐free monocultures in high‐nutrient soils, but plant competition or the cost of endophyte infection to the meadow fescue decreased the yield in resource‐limited conditions. On average, endophyte‐infected and endophyte‐free meadow fescues produced 0·15 and 0·17 g, and 0·14 and 0·14 g dry biomass per plant in mixtures with red clover in high‐ and low‐nutrient soils respectively. In contrast to meadow fescue, endophyte‐promoted growth of tall fescue monocultures was not detected. Endophyte‐infected and endophyte‐free tall fescue monocultures produced 0·76 and 0·95 g biomass per pot, respectively, in the high‐nutrient environment. Endophyte infection can increase the performance of the host grass, but the positive effects depend on the host species, the species composition and soil nutrient availability.     

Yield and nitrogen concentration of above- and below-ground biomasses of red clover cultivars in pure stands and in mixtures with three grass species in northern Europe

Three red clover (Trifolium pratense) varieties differing in productivity and winter hardiness, Jokioinen, Betty and Ilte, were sown in a 2‐year (2003–2004) pot experiment in pure stands and mixtures with the grasses, timothy (Phleum pratense), tall fescue (Festuca arundinacea) and meadow fescue (Festuca pratensis). Grass growth dominated until fertilizer‐N, applied when the stands were sown, was depleted. Timothy was the least competitive of the grass species. Red clover variety Ilte produced the highest dry‐matter (DM) yields. Variety Betty yielded less, but allocated as much biomass to the root and stubble (soil‐bound) fraction as variety Ilte. Variety Jokioinen allocated least to the soil‐bound fraction. While the root structure and the starch concentration of the crown‐root area were similar in all varieties, the high ratio of soil‐bound: harvested fractions could be a key to the higher winter survival and higher DM yields of Betty under field conditions. At the end of the experiment, 3–5 g N pot^?1 (49–81 g m^?2) had been harvested and 0·7–1·5 g N pot^?1 (11–24 g m^?2) was left in the soil‐bound fraction, amounts depending on the red clover variety and grass mixture, with pure clover stands containing the highest N amounts. Because of the high N concentrations in the biomass of red clover, the proportion of red clover and conditions prevailing during canopy and root death in mixed stands are crucial for N mineralization and incorporation into new growth.