Interactions between seedlings of perennial ryegrass and white clover cultivars in establishing swards

Interactions between perennial ryegrass (grass) and white clover (clover) cultivars were investigated at the seedling stage in two experiments: (a) a field experiment in which two clovers, AberHerald and Grasslands Huia, were grown in binary mixture with two grasses, Preference and Ba 10761; (b) a glasshouse experiment in which the same clover/grass combinations were grown in low-N soil either with (+ N) or without (-N) added N. In the field experiment both clovers produced larger and more complex seedlings with Preference, and this was particularly evident in Huia. In the glasshouse experiment grass dry-matter yield was greater in the +N treatment, and this effect increased with time. Clover seedling density and development were suppressed in the +N treatment, and the development of AberHerald was affected more than Huia. Morphological measurements of the clovers showed interactions between clover, grass and N level. In the -N treatment Huia plants were larger and more complex than those of AberHerald, but in +N conditions there was little difference between them. Grass cultivar had an effect on clover via N-level interactions: in +N plants there was no grass effect, but -N plants were significantly larger with Preference. Comparison of the root and shoot morphology of the two grasses revealed no obvious differences that would account for these effects.     

Survivor populations of S23 perennial ryegrass from zero-grazed and set-stocked swards

Perennial ryegrass tillers were collected from intensively used set-stocked and zero-grazed leys and from an old permanent pasture, grown on and compared at 30 cm spacing. All swards except the permanent pasture had been sown with cv. S23 and were of known age, ranging from 6 months to 11 years from sowing. Each genotype was scored for date of inflorescence emergence, and subsequently in vitro dry matter digestibility (DMD), D-value of green leaf and the ratio of leaf dry weight: stem dry weight were determined. Both DMD and D-value declined significantly in green leaf samples of populations from the older zero-grazed swards but no significant changes were detected in populations from set-stocked swards. In set-stocked populations there was a shift towards later flowering. In zero-grazed populations there was a consistent increase in the amount of leaf relative to stem with the age of the sward from which the plants were sampled. The survivor plants were more prostrate and leafier and it is suggested that under zero grazing, where cutting was to a uniform height, plants of this form were less severely defoliated and thus at a selective advantage.     

The nature of competition between perennial ryegrass and white clover

Perennial ryegrass and white clover were grown in boxes with either no competition, root competition only, shoot competition only, or both root and shoot competition between them, Boxes received either no nitrogen or 200 kg N ha⁻¹ as a split application. The experiment was harvested at 8, 12, 16 and 20 weeks after sowing. Perennial ryegrass was more competitive than white clover throughout the experiment and its overall competitive ability increased with Lime. The effects of root competition were greater than those of shoot competition at the first harvest, with both forms of competition having similar affects at the second harvest, while at the third and final harvests shoot competition had greater effects than root competition. At the later harvests N application increased the overall competitive ability of perennial ryegrass, relative to white clover, mainly owing to the increase in its shoot competitive ability.     

The performance of summer-calving cows grazing perennial ryegrass swards

The objectives of this experiment were to study the effects of different grazing managements in spring on herbage intake and performance of summer-calving dairy cows and to examine the effects of regrowth in early June on herbage intake and cow performance. Four spring-grazing treatments were applied to predominantly perennial ryegrass swards: Control (C), sward grazed by cows to 6–8 cm sward surface height (SSH); CG16, sward grazed by cows to 3–4 cm SSH in May and allowed to regrow to a target SSH of 16cm in early June; CG8, sward grazed by cows to 3–4 cm SSH in May and allowed to regrow to 8cm in early June; and SG8, sward grazed by sheep to 2–3 cm SSH in May and allowed to regrow to 8 cm in early June, All swards were continuously stocked by summer-calving (May and July) primiparous and multiparous cows from 16 June to 7 September, to a target SSH of 8–10cm. Spring treatments bad marked effects on herbage intakes and milk production. Estimated in July by n alkane analysis, the mean herbage intake ± s.e.d. of cows on each treatment were 1·8, 1·4, 1·4 and 3·0 ± 0·31 kg dry matter (DM) 100 kg live weight (LW)^?1 d^?1 (P < 0·01) for treatments C, CG16, CG8 and SG8 respectively. Measured in August, intakes were 1·8, 20, 2·1 and 2·4 ± O·33kg DM 100kg LW^?1 d^?1 respectively. Severe spring grazing led to increased milk yield and reduced milk fat content from summer-calving cows fed 5·2 kg d^?1 of a proprietary concentrate. Average milk yields for the eleven experimental cows on each treatment were 24·3, 23·4, 26·2 and 29·0 ± 1·20 kgd^?1 (P < 0·01) for C, CG16, CG8 and SG8, and average milk fat contents were 45·4. 42·4, 43·9 and 40·9 ± 1·02gkg^?1 (P<0·05) respectively. The results suggest that severe grazing of swards in early season could improve herbage intake and milk yield of summer-calving cows in mid- and late season. The most favourable spring treatment in this respect was severe grazing by sheep. However, this advantage could be negated in midseason by lax grazing at that time.     

The ingress of Poa annua into perennial ryegrass swards

The ingress of Poa annua into established swards of perennial ryegrass was recorded in four experiments aimed at determining whether ingress was due to P. annua aggression or to a decrease in ryegrass vigour. Emphasis was placed on severity of defoliation, effect of bare spaces and the time of year most favourable to colonization.
In Experiment 1, P. annua ingress was greatest in the autumn, especially where ryegrass had been sown in rows rather than broadcast sown. In Experiment 2, seedlings of P. annua only established successfully in mature ryegrass swards that had been defoliated at intervals of two weeks. Experiment 3 showed that ingress was inversely related to the vigour of the ryegrass cultivar, being particularly high on frequently defoliated plots. In Experiment 4, which involved a study of the colonization of poached areas, more seedlings established in quadrats surrounded by P. annua -dominant pasture compared with patches surrounded by perennial ryegrass.
It is concluded that P. annua is not an aggressive species; it colonizes only open ryegrass swards that have become weakened by intensive management.     

Dynamics of perennial ryegrass and white clover in sown swards in NW Greece

Seasonal dynamics of white clover and perennial ryegrass were examined in sown perennial ryegrass/white clover swards subject to a 2 × 2 factorial treatment combination of defoliation (rotational grazing by sheep and cutting) and nitrogen fertilizer application (0 and 40 kg N ha^–1 year^–1) in NW Greece. Sward surface height and percentage cover were measured before and after five defoliation periods in 1996 within permanent microplots (30 × 30 cm, divided into nine cells) in which white clover was either initially present or absent. Both white clover and perennial ryegrass achieved maximum height and cover in April–May. Defoliation treatment and whether white clover was present initially significantly affected height and cover of both species. Total plant cover was similar prior to all defoliation periods except in July, a time of drought. Cover of perennial ryegrass was greater where white clover was initially absent, but total plant cover was greater in microplots containing white clover and the extent of the differences varied during the year. In contrast, N fertilizer application had little effect on species cover, other than small reductions in white clover cover. When white clover was present in April, it was found in virtually every microplot cell until July, but if it was absent in April there was little colonization of the microplot.     

Water use and water-use efficiency of perennial ryegrass swards as affected by the height and frequency of cutting and seed rate

The effects of cutting height (20 and 44 mm), frequency (once every 2 weeks April-September inclusive and twice a year) and seed rate (250 and 20 kg ha^-1) on the water use and herbage yield of perennial ryegrass swards, for 3 years after sowing, were compared.
Frequent cutting and a low cutting height reduced water use in the first year only. In later years infrequent cutting led to higher yields and higher water-use efficiencies, but did not affect total water use or the shape of the soil water profile. Seed rate influenced sward composition and the pattern of water use, but not total water use. The swards from the low seed rate had a lower stubble biomass and tiller density, and extracted relatively more water at depths of 75 and 85 cm and less at depths of 15 and 35 cm, than the swards derived from the high seed rate.
The ratio of actual: potential evapotranspiration was reduced as the soil water deficit increased and was lowest in the summer after a dry spring. Cutting height and frequency during summer were shown not to be effective methods of either conserving water or manipulating the effective rooting depth of an established sward.     

The diet ingested by sheep grazing swards differing in white clover and perennial ryegrass content

A series of twenty-four swards containing different proportions of white clover (0·20-0·25) and perennial ryegrass were created by using different seed mixtures, herbicide applications and previous cutting Frequencies. These swards were used to study the diet of oesophageally-fistulated wether sheep which grazed the various swards for a 30-min period after 1, 2 and 3 weeks of regrowth.
The proportion of white clover in the diet was generally greater than that in the sward. Fifty-seven percent of the variation in the proportion of white clover in the diet could be attributed to the proportion of white clover in the sward. White clover and perennial ryegrass leaf and stem were grazed to the same height and the proportion of white clover in the grazed horizon of the sward explained 83% of the variation in the proportion of white clover in the diet. The proportion of white clover in the diet was greater than the proportion in the grazed horizon of the sward in week 3 of regrowth, but not in weeks 1 and 2, and greater when the proportion of white clover in the grazed horizon was lower than 0·20. Both these observations were interpreted as indicating selection for white clover by the sheep within the grazed horizon.
There was a positive and linear relationship between the depth of the grazed horizon and sward height which, together with the relationship between the proportion of white clover in the grazed horizon and in the diet, would allow the prediction of the proportion of white clover of the diet from the height and the white clover content of the grazed horizon of the sward.     

Dry-matter production and botanical composition of multispecies and perennial ryegrass swards under varying defoliation management

Multispecies swards, comprised of different plant functional groups have comparable production potential to high N input L. perenne swards at reduced N when legumes are included. However, information on the appropriate management of multispecies swards is limited. The effect of differing management practices on the herbage dry-matter (DM) production and botanical composition of different sward types was investigated using a 3 × 2 × 2 factorial design plot experiment. The experiment consisted of three sward types: L. perenne-only receiving (LP; 250 kg N ha⁻¹ a⁻¹); L. perenne-Trifolium repens (LP-TR); multispecies sward containing L. perenne, Phleum pratense, Trifolium repens, Trifolium pratense, Plantago lanceolata and Cichorium intybus (MSS). LP-TR and MSS received 90 kg N ha⁻¹ a⁻¹. Harvesting of plot herbage took place every 21 or 28 days to a defoliation height of 4 or 6 cm, over two growing seasons (March to November 2020 and 2021 inclusive). Annual herbage produced by both LP and LP-TR was not significantly affected by defoliation frequency. However, MSS produced 1923 kg DM ha⁻¹ a⁻¹ more herbage when harvested less frequently. Unsown species contributed significantly less to the herbage DM of MSS compared to LP and LP-TR and remained similar in 2020 and 2021, whereas the contribution of unsown species to herbage DM increased in LP and LP-TR from 2020 to 2021, with noxious species more associated with LP and LP-TR than MSS. Results demonstrate the role of multispecies swards in improving the sustainability of grass-based agricultural systems in an environment of reduced fertilizer inputs.     

Effect of ryegrass endophyte in mixed swards of perennial ryegrass and white clover under two levels of irrigation and pesticide treatment

In a small-plot experiment at Hurley, UK, infection of perennial ryegrass with the endophytic fungus Acremonium lolii had no apparent effect on seedling populations and herbage yield of ryegrass and white clover sown in mixture. The plots were maintained under two levels of irrigation with or without pesticide (carbosulfan granules) to study possible interactions with stress due to drought or pest damage. The higher level of irrigation consistently increased yield of both grass and clover during 1989 and 1990, but the effects of endophyte and pesticide on yield were not consistent, nor were the few significant interactions between factors. It is concluded that infection of ryegrass does not appear to increase ryegrass production or to decrease white clover production in the UK, in contrast to reports from New Zealand.     

The effects of Rumex obtusifolius on the seasonal yield of two mainly perennial ryegrass swards

A preliminary field experiment on a sward cut six times during 1978 indicated that total grass herbage harvested was negatively related to the number of Rumex obtusifolius plants present; densities of five to ten plants m⁻² resulted in reductions of up to 30%, although the total quantity of herbage harvested (including Rumex ) may have remained constant. However, R. obtusifolius densities did not significantly affect grass yield during the first half of the growing season. A negative relationship between R. obtusifolius ground cover and grass yield, particularly from late July onwards, was shown in a second field experiment during 1979 and 1980 using a 3-cut management. It was estimated that to produce a 20% reduction in grass growth in July-August and October, R. obtusifolius ground covers of 30% and 20% respectively were needed. Sixty per cent of the total herbage harvested in 1980 consisted of R. obtusifolius. These results indicate the damage that can be caused by this species and suggest that control measures should be taken before early summer.     

Interaction between water-soluble carbohydrate reserves and defoliation severity on the regrowth of perennial ryegrass (Lolium perenne L.)-dominant swards

A field-study was undertaken in Hamilton, New Zealand to determine if there was an interaction between water-soluble carbohydrate (WSC) reserve content and defoliation severity on the regrowth of perennial ryegrass-dominant swards during winter. Perennial ryegrass plants with either low or high WSC content were obtained by varying the defoliation frequency. At the third defoliation at the one-leaf stage and at the first defoliation at the three-leaf stage (harvest H₁), swards were mown with a rotary lawnmower to residual stubble heights of 20, 40 or 60 mm. All swards were then allowed to regrow to the three-leaf stage before again defoliating to their treatment residual stubble heights (H₂). Frequently defoliated plants contained proportionately between 0·37 and 0·48 less WSC in the stubble after defoliation, depending on the severity of defoliation. There was no interaction between WSC content and defoliation severity for herbage regrowth between harvests H₁ and H₂. Herbage regrowth was lower from swards containing low WSC plants compared with high WSC plants (2279 vs. 2007 kg DM ha⁻¹). Furthermore, swards defoliated to 20 or 40 mm had greater herbage regrowth compared with those defoliated to 60 mm (2266, 2249 and 1914 kg DM ha⁻¹ for swards defoliated to residual stubble heights of 20, 40 and 60 mm, respectively). Regrowth of perennial ryegrass was positively correlated with post-defoliation stubble WSC content within defoliation severity treatment, implying that WSC contributed to the defoliation frequency-derived difference in herbage yield. However, the effect of defoliation severity on herbage regrowth was not associated with post-defoliation stubble WSC content.     

Genome-wide markers for seed yield and disease resistance in perennial ryegrass

The market success of perennial ryegrass(Lolium perenne L.) cultivars depends on sufficient seed production, as they are propagated by seed. However, breeding for high quality forage production reduces seed yield, and breaking the negative correlation would help to overcome the problem. The foliar disease crown rust is another factor affecting reproductive capacity and thereby seed yield. We evaluated seed yield-related traits and resistance to crown rust in a collection of commercial cultivars and ecotypes of perennial ryegrass and identified genome-wide markers associated with the traits. The study revealed high variation between the ecotype and cultivar groups as well as between years. A genome-wide association study identified 17 DNA single-nucleotide polymorphisms(SNPs) of which eight were associated with crown rust and nine with flag-leaf length. The SNP markers were located within or near predicted genes functioning in defense against pathogens. The identified genes are strong candidates for a further in-depth functional study to continue unravel determination of leaf architecture and crown rust resistance in perennial ryegrass.     

Influence of root competition on compatibility between white clover and perennial ryegrass populations during seedling establishment

Plants of a white clover population, Ac 3785, were grown in binary mixtures with perennial ryegrass cv. Talbot and the 'coexisting' population, Ba 10281, in boxes. Treatments imposed were 'no root competition' and 'full competition', which prevented or allowed the root systems of the competing species to intermingle respectively. Shoot competition was permitted in both treatments. Measurements of dry-matter yield and leaf area of the clover and grasses were made on three occasions following sowing.
The dry-matter yield of both grasses was higher than that of clover at all three harvests and under both treatments, and this yield advantage tended to increase with time. Both grasses yielded more under full competition than where root competition was prevented. Talbot was higher yielding than the coexisting population under both treatments. Clover dry weight and leaf area index (LAI) were considerably higher under the 'no root competition' treatment. There was no effect of companion grass on clover dry weight, but clover LAI was significantly higher with its coexisting population than with Talbot in the 'no root competition' treatment.
The LAI and dry weight data indicate that clover leaf morphology changed in response to the companion grass where root competition was prevented. Thus, the superior aerial compatibility of Ac 3785 with its coexisting grass was limited by below-ground factors. Possible ecological reasons for this effect are discussed.     

The effect of time of initial defoliation and height of defoliation on the productivity of perennial ryegrass swards

Over a 3-year period the productivity of perennial ryegrass ( Lolium perenne L., cv. S24) swards as influenced by variations in the time of initial defoliation and close (2·5 cm) and lax (8 cm) defoliation was studied. Treatments with initial defoliations in the early vegetative stage, stem elongation and flowering stages of growth gave higher annual yields than treatments in which the initial defoliation was taken at an intermediate stage of growth when the majority of the stem apices had just been elevated above the height of defoliation. Initial defoliation treatments which removed a high proportion of apical meristems while the yield at the initial defoliation was still low produced the lowest annual yield. Consistent lax defoliation reduced yield by 14·5% compared with continual close defoliation. However, taking an initial lax defoliation followed by subsequent close defoliations produced a slight yield advantage of 4·8% over consistent close defoliation. The results are discussed in relation to other research findings and the practical implications commented upon.     

The interaction of perennial ryegrass and timothy in mixtures and their reaction to clover and nitrogen in cut swards

Results of experiments where timothy, perennial ryegrass and mixtures of these two in the presence and absence of white clover and receiving various nitrogen treatments were compared, have been considered in the light of previous related experiments. There is evidence that under certain conditions greater yields of sown grass can be achieved from mixed seedings than from either of the two grasses on its own. No yield advantage was gained from mixtures of species when cut infrequently after a late first cut. Inclusion of white clover changed the balance of species in favour of perennial ryegrass and no yield advantage occurred with mixtures in the presence of clover. Yield advantage may be related to seasonal changes in the order of dominance of the two grass species in mixed seedings.     

Production of perennial ryegrass cultivars of different maturity types when grown as pure swards and in certain combinations

A field investigation was carried out over 3 years to determine if there was a synergistic effect on total or seasonal yield when cultivars of perennial ryegrass were grown in combination. The three cultivars used were Stormont Zephyr, Hora and Perma, representing respectively early, medium late and late maturing groups. Each cultivar was grown as a pure stand and also as a 50:50 mixture with each of the other two cultivars. Each of these swards was maintained under two rates of nitrogen fertilization (300 and 600 kg per ha per annum) and under two harvesting treatments (4 and 8 harvests per annum). Mixture yield did not exceed significantly the pure sward yieid of the highest yielding component. Occasional yield improvements were detected for the mixtures averaged as a group over monocultures averaged as a group. There was a tendency, especially under frequent cutting, for the yield response to nitrogen to be greater from mixed than from pure swards.     

Changes in the structure and physiology of a perennial ryegrass sward when released from a continuous stocking management: implications for the use of exclusion cages in continuously stocked swards

A perennial ryegrass sward was managed by continuous stocking with sheep (April–September) for 4 successive years after sowing. The sward was grazed to maintain a leaf (lamina) area index (LAI) close to 1.0. Areas of the sward were released from grazing on three occasions: once during summer in the third year after sowing, and twice during spring and summer in the fourth year after sowing. There were marked changes in the structure and physiology of the continuously stocked sward following release from grazing. After several successive years of continuous stocking, the sward comprised a large population of small tillers and the small LAI resulted in consistently low rates of photosynthesis. Following release from grazing, photosynthesis increased markedly as the LAI increased but this change was associated with the loss of a large proportion of the population of tillers. There were seasonal differences in the pattern of changes in photosynthesis and tiller numbers following release from grazing which were not apparent under continuous stocking. The changes in the structure and physiology of the sward following release from grazing suggest that the net accumulation of herbage in areas of sward from which the animals are excluded, for instance using cages, may be an unreliable estimate of production under continuous stocking.     

The influence of fertilizer nitrogen, white clover content and environmental factors on the nitrate content of perennial ryegrass and ryegrass/white clover swards

In a field experiment carried out over 3 years, the nitrate content of herbage from perennial ryegrass (Lolium perenne) swards increased exponentially with nitrogen application rate, but herbage nitrate content appeared to reach potentially dangerous concentrations only when nitrogen application rates were greater than those needed to stimulate dry-matter production. Thus, on average over all the harvests, maximum yield could be obtained with annual application rates of 400 kg N ha^–1 (six applications of 67 kg N ha^–1) for perennial ryegrass and 300 kg N ha^–1 (six applications of 50 kg N ha^–1) for perennial ryegrass/white clover (Trifolium repens) swards, whereas the mean nitrate concentrations were 3340 and 2929 mg NO₃ kg^–1 dry matter (DM) respectively. Nitrate content, however, varied considerably from harvest to harvest, reaching maxima of 9345 mg NO₃ kg^–1 DM at 400 kg N ha^–1 for perennial ryegrass and 6255 mg NO₃ kg^–1 DM at 300 kg N ha^–1 for perennial ryegrass/white clover. The nitrate content of herbage from perennial ryegrass/white clover swards was always greater than that of perennial ryegrass swards receiving the same rate of nitrogen application, even though in the herbage from the mixed sward the nitrate content of white clover was usually less than half that of the perennial ryegrass component. The physical environment did not have a clearly interpretable effect on nitrate content, although herbage harvested in May had a much lower nitrate content than that harvested at any other time of the season. It was not possible to find a single multiple regression equation relating herbage nitrate content to nitrogen application and to other environmental variables that explained more than 60% of the variance in herbage nitrate, but it is suggested that, by reducing the later-season nitrogen applications from 67 to 50 and finally to 33 kg N ha^–1 for perennial ryegrass and from 50 to 33 kg N ha^–1 for perennial ryegrass/white clover, it would be possible to achieve over 90% of the maximum yield while reducing average nitrate content to <40% of that at maximum yield, with no samples containing more than 2300 mg NO₃ kg ^–1 DM.     

Effects of spring fertilizer nitrogen and sward height on production from perennial ryegrass/white clover swards grazed by beef cattle

An experiment was carried out to compare the effects of two compressed sward height treatments, each at two fertilizer nitrogen (N) treatments (0 and 50 kg ha⁻¹ in spring), on the date of turnout and liveweight gain of steers grazing a perennial ryegrass/white clover ( Lolium perenne/Trifolium repens ) sward sited on clay loam in south-west England. The sward height treatments were 6 cm all season, and 4 cm in the spring rising to 6 cm in June; these were maintained using continuously variable stocking with Hereford × Friesian steers. Cattle were turned out on average 11·5 days earlier on the 4-cm sward height compared with the 6-cm sward height treatment. Liveweight gain early in the season was lower on the 4-cm swards than on the 6-cm swards. Liveweight gain ha⁻¹ over the whole season was similar for the two sward height treatments. Fertilizer N did not affect turnout date or liveweight gain.