Assessment of contrasting perennial ryegrasses, with and without white clover, under continuous sheep stocking in the uplands. 5. Herbage production, quality and intake in years 4–6

Herbage characteristics were studied over years 4–6 (1988–90) in three perennial ryegrass ( Lolium perenne L.) varieties as grass-only (200 kg N ha^-1) and grass/clover ( Trifolium repens L.) swards which received 75kg N ha^-1 in 1988 and 0kg N ha^-1 in 1989 and 1990 when continuously stocked with sheep. Mean total annual herbage production of Aurora, a very early flowering variety, was 11% more than that of late-flowering Aberystwyth S23 due to 21% higher growth as grass/clover pasture. The grass/clover sward of Meltra, a tetraploid late-flowering variety, out-yielded S23/clover by 17%. Herbage production of grass/clover was 86% of that of grass only in 1988 but only 54% of the grass-only swards averaged for 1989 and 1990.
In vitro organic matter digestibility (OMD) of Meltra was 38g kg^-1 OM and 27g kg^-1 OM higher than that of S23 and Aurora respectively. OMD of grass/clover was 15g kg^-1 OM higher than that of grass only during the post-weaning period. Herbage intake was positively correlated with OMD of herbage.
The herbage attributes were related to lamb performance reported previously. Lamb output was positively correlated with intake of digestible organic matter.
Differences between the three varieties in herbage characteristics were greater as grass/clover than as grass-only swards, reflecting their compatibility with white clover. In this respect Meltra was the best and S23 the poorest variety.     

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.     

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.     

The contribution of different white clover cultivars to the nitrogen yield of mixed swards

The annual contribution of clover to a mixed sward for 5 years was compared for a range of cultivars, viz. S1OO, Sabeda, Blanca and Olwen, in order of increasing leaf size. The contribution referred to as'clover-derived nitrogen N', was measured as the difference between N harvested in mixed swards and that in similarly treated swards devoid of clover. The swards were harvested four or five times each year and received N fertilizer, annually, at 0, 30, 60 or 90 kg N ha⁻¹ in March.
Blanca swards had the highest clover-derived N yield in the second year and lowest in the fourth year. By the fifth year Sabeda and S100 (medium leaved cultivars) were contributing more N than the other two cultivars. When related to the amount of clover harvested, S100 had the highest value in the second year and S100 and Sabeda in the third year. Relating the total lover-derived N harvested over the 5 years to the amount of clover harvested, S100 had an efficiency of contribution of 54-3 kg N t⁻¹ dry matter (DM) compared to a mean of 49 0 kg N t⁻¹ clover DM for the other three cultivars. Nitrogen fertilizer reduced the contribution of clover N in the first 3 years owing to a reduction in clover yield, but it did not affect clover's efficiency to contribute N.
It is concluded that although the smallest leaved type of the four (S100) made the most efficient N contribution to the sward more information is required to relate morphology of clover to its capability to contribute N directly or indirectly to the sward.     

The liveweight gain of Limousin × Friesian heifers grazing perennial ryegrass/white clover swards of different clover content and the effects of their grazing on sward botanical composition

An experiment was carried out in 1992 and 1993 to examine the effect of white clover content of perennial ryegrass/white clover swards on the performance of Limousin × Friesian heifers. Swards with low (L), medium (M) and high (H) white clover contents were established and managed by continuous variable stocking. A compressed sward height of 5·5 cm was maintained using a buffer fence to vary plot areas, with herbage surplus to grazing requirements cut, removed and yields measured. The mean white clover proportions for treatments L, M and H were 0·02, 0·19 and 0·18 in 1992 and 0·13, 0·16 and 0·31 in 1993 respectively. White clover contents of the swards reached a maximum in August and September, and differences between treatments diminished. There was no significant difference between treatments in the content of white clover in the swards in autumn 1993.
Liveweight gains of heifers increased asymptotically with increasing white clover content of the sward. Below a white clover herbage mass of 300 kg DM ha^–1, there was little effect on liveweight gain, which was 0·70 kg day^–1 over the grazing season. Between 400 and 450 kg DM ha^–1 white clover, liveweight gains were 0·85–0·90 kg day^–1. While clover content of the sward did not significantly affect utilized metabolizable energy output; the mean output over the grazing season in the two years from liveweight gain and herbage yield was 78 GJ ha^–1. It is suggested that, using this grazing system, white clover reached an equilibrium with a mean herbage mass of about 400 kg DM ha^–1 over the grazing season.     

Assessment of contrasting perennial ryegrasses, with and without white clover, under continuous sheep stocking in the uplands. 3. Herbage production, quality and intake

Herbage characteristics were monitored over 3 years (1985–1987) in three perennial ryegrass ( Lolium perenne L.) varieties as grass/only (200 kg N ha⁻¹) and grass/clover ( Trifolium repens L.) (75 kg N ha⁻¹) swards when continuously stocked with sheep. Although mean total annual herbage production was similar from the grass varieties, growth of Aurora, a very early-flowering variety, was higher than that of Aberystwyth S23 and Meltra (tetraploid) late-flowering types in spring. Herbage production from grass-only swards was 15% higher than from grass/clover swards.
In vitro organic matter digestibility (OMD) of Aurora and Meltra was 34 g kg ⁻¹ and 26 g kg ⁻¹ higher ( P < 0·01) than that of S23. Averaged over varieties, the OMD of grass/clover was 25 g kg ⁻¹ higher ( P < 0·05) than grass-only during the post-weaning period. Individual lamb digestible organic matter intake (DOMI) was 22% higher ( P < 0·05) on grass/clover than on grass-only during this period. Water-soluble carbohydrates content of Aurora was 42% higher ( P < 0·001) than that of both Meltra and S23.
Herbage characteristics were related to lamb performance reported previously. Lamb production was positively correlated with DOMI. However, the magnitude of differences in lamb performance between treatments was much greater than the extent of differences detected in herbage characteristics.     

Frequency of stocking rate adjustments required on contrasting upland perennial ryegrass pastures continuously grazed to a sward height criterion from May to July

The use of sward height as a criterion for determining the time and extent of stocking-rate changes on continuously grazed swards was investigated over a 2-year period (1985–86) in a sheep production experiment. Swards of three contrasting perennial ryegrass ( Lolium perenne L.) varieties were established with and without Aberystwyth S184 small-leaved white clover ( Trifolium repens L.) at an upland site (310–363 m) in mid-Wales. From spring (late April) until weaning (mid-July) the pastures were continuously stocked with Beulah Speckled Face ewes and Suffolk cross lambs. During this period sward heights of 4 ± 0.5 cm were obtained and maintained by regular adjustment of animal number on individual paddocks. Grass-only swards received 160 and 200 kg N ha⁻¹ and the grass clover swards were given 80 and 75 kg N ha⁻¹ in 1985 and 1986 respectively.
Differences were observed between the treatments in sward height profiles over the season necessitating contrasting adjustments to stocking rates. Mean stocking rate necessary on early flowering Aurora (22 6 ewes ha⁻¹) was respectively 27% and 17% higher than on late-flowering Aberystwyth S23 and Meltra (tetraploid) ryegrasses; mean stocking rate on grass-only swards was 19% higher than on the grass-clover pastures.
It is concluded that sward height is a useful criterion on which to make adjustments to stocking rates to compare the potential performance of contrasting swards, under continuous grazing. The infrequent adjustments required to maintain a constant sward height, especially on the late flowering diploid perennial ryegrass variety on which many upland pastures are based, suggest that the criterion of sward height could be successfully employed on farms as an aid to efficient grazing management.     

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.     

The effect of strategic fertilizer nitrogen and date of primary harvest on the productivity of a perennial ryegrass/white clover sward

Four management systems involving different dates for first harvest (simulated grazing, early silage, late silage and hay) and two fertilizer N rates in spring (0 and 80 kg ha^-1) were imposed on a perennial ryegrass cv. Talbot/white clover cv. Blanca sward during 1981-82. In each year, annual total herbage DM was increased by spring application of N but white clover production and content in the total herbage were reduced; however, white clover, which was depressed in the harvests immediately after N application, recovered during the season to amounts and contents in the total herbage similar to those given no spring N.
Annual total herbage DM production increased as the date of primary harvest was delayed (935 to 1197 t ha^-1 over two years) but mean organic matter digestibility values for the same period decreased (0-769 to 0700). First-harvest production made up substantial proportions of the annual production in the conservation systems. White clover, as shown by its production and the amount of stolon present, was tolerant of conservation systems, especially with no applied N.
It is concluded that grass/white clover swards are suitable for management systems which involve cutting for conservation. The use of strategic spring N seems a viable option, but more knowledge of rates would be valuable since this experiment only compared 80 kg ha^-1 with no applied N.     

Effect of supplementation on production by spring-calving dairy cows grazing swards of differing clover content

An experiment was carried out to examine the effect of supplementation on the performance of spring-calving dairy cows grazing swards of differing perennial ryegrass and white clover content. Seventeen heifers and sixty-four Friesian cows in their third to ninth week of lactation were turned out onto one of three pastures with different proportions of perennial ryegrass and white clover. Nine animals on each pasture received either 0, 2 or 4 kg d⁻¹ of a concentrate with a crude protein concentration of 180 g kg⁻¹ dry matter (DM). Prior to grazing, swards contained proportionately 0·01 (L), 0·15 (M) and 0·20 (H) of total DM as clover. During the experiment, grazing pressures were adjusted by movement of buffer fences to maintain compressed sward heights at 6 cm. Samples taken 26 and 68 d after the start of grazing showed little change in the proportion of clover in sward L (< 0·01 and 0·02 respectively), but convergence in the proportion of clover in swards M and L (0·08-0·16 and 0·10-0·15 respectively). Mean daily yields of milk, fat, protein and lactose increased significantly with increased clover content and, even without supplementation, daily yields were 25·4, 0·98, 0·73 and 1·09 kg respectively on sward H. Of the milk components, only protein was significantly increased by increasing sward clover content. The response in milk yield to supplementation was greater on sward L than on swards M and H.     

The effect of fertilizer nitrogen rate, white clover variety and closeness of cutting on herbage productivity from perennial ryegrass/white clover swards

Four varieties of white clover (small-leaved cv. Aberystwyth S184. medium-leaved cv. Grasslands Huia and large-leaved cvs Linda and Olwen) were sown at 3 kg ha^-1 together with 10 kg ha^-1 perennial ryegrass cv. Talbot. Herbage productivity was measured for three harvest years, 1979-81, over four annual rates of fertilizer N (0,120,240 and 360 kg ha^-1) and two closeness of cutting treatments (80 and 40 mm from ground level). A simulated grazing regime of six cuts per year at 3- to 6-week intervals was used.
Production of total herbage DM was increased by increasing N rate; mean annual DM production ranged from 783 1 ha^-1 with no N to 11701 ha^-1 at 360 kg ha^-1 N. Mean herbage response to N (kg DM per kg N applied) was 73,90 and 108 for the three successive N increments relative to no N. Mean white clover DM production was reduced from 4 14t ha^-1 with no N to 051 t ha^-1 at 360 kg ha^-1 N.
The large-leaved clover varieties were more productive than the small- or medium-leaved varieties at all N rates. Close cutting increased total herbage and white clover by a mean annual 16% and 31%. respectively. White clover varieties did not interact with either N rate or closeness of cutting.
It is concluded that repetitive N application over the growing season is incompatible with white clover persistence and production, even with large-leaved clover varieties or with close cutting, two factors which improved clover performance in the experimental swards.     

Assessment of contrasting perennial ryegrasses, with and without clover, under continuous sheep stocking in the uplands. 4. Animal performance in years 4–6

Relative sheep production from Aurora (very early flowering), Mellra (late-flowering tetraploid) and Aberystwyth S23 (late flowering) perennial ryegrass ( Lolium perenne L.) varieties was compared during harvest years 4-6 (1988-90) as grass only (200 kg N ha⁻¹) and grass/clover (75 kg N ha ⁻¹ in 1988, 0 kg N ha⁻¹ in 1989 and 1990) at Bronydd Mawr Research Centre (310-363 m) in mid-Wales. The pastures were continuously stocked with Beulah Speckled Face ewes and their Suffolk cross lambs from spring to mid-July. From late July to early November only the weaned lambs grazed the swards.
Mean (1988-90) total annual lamb production per hectare from Aurora and Meltra was 70% and 16% more than that from S23. However, the difference between both varieties and S23 was much greater as grass/clover (Aberystwyth S184 small-leaved type) than as grass-only swards. Differences between the grasses in individual lamb growth rates were most pronounced during the post-weaning period, when that on Meltra was 38% and 23% more than on Aurora and S23 respectively.
Mean annual lamb output from grass/clover swards was only 70% of that from grass-only swards during the 2 years when the former swards received no fertilizer N. Averaged over the 3 years (1988-90) individual lamb liveweight gain post weaning was 38% higher on grass/clover than on grass-only swards.
The results are discussed in relation to those for the first 3 harvest years (1985-87). It is concluded that, although Aurora was less persistent than both late-flowering varieties, its superiority in providing an average of 29% more lamb output than S23 during the critical spring period (up to early June) would be of considerable practical significance in upland sheep systems, as would be the overall superiority of the tetraploid Meltra over S23.     

The implications of controlling grazed sward height for the operation and productivity of upland sheep systems in the UK. 5. The effect of stocking rate and reduced levels of nitrogen fertilizer

The implications for UK upland sheep systems of reducing nitrogen fertilizer application to perennial ryegrass/white clover swards were studied over 3 years. Sward height (3·5–5·5 cm) was controlled for ewes with lambs until weaning using surplus pasture areas for silage; thereafter, ewes and weaned lambs were grazed on separate areas, and sward height was controlled by adjusting the size of the areas grazed and using surplus pasture areas for silage if necessary. Combinations from three stocking rates [10, 6 and 4 ewes ha⁻¹ on the total area (grazed and ensiled)] and four nitrogen fertilizer levels (150, 100, 50 and 0 kg ha⁻¹) provided six treatments that were replicated three times. Average white clover content was negatively correlated with level of nitrogen fertilizer. The proportion of white clover in the swards increased over the duration of the experiment. Control of sward height and the contribution from white clover resulted in similar levels of lamb liveweight gain on all treatments. All treatments provided adequate winter fodder as silage. It is concluded that the application of nitrogen fertilizer can be reduced or removed from upland sheep pastures without compromising individual animal performance provided that white clover content and sward height are maintained. Resting pastures from grazing by changing ensiled and grazed areas from year to year sustained white clover content over a 3-year period.     

Breeding and evaluation of new white clover varieties for persistency and higher yields under grazing

Two experiments were established in 1989 and 1990 to evaluate the performance of white clover ( Trifolium repens ) varieties under grazing, using sheep and cattle, and also under a 'cutting-only' regime. The three potential medium/large-leaved varieties (AberVantage, AberCrown and AberDai) were selected and evaluated in a breeding programme that emphasized improving yield and persistency under grazing.
In Experiment 1, the potential varieties were sown with two different grass companions, and evaluated under a continuous cattle-grazing system, representative of their future role in actual farm practice, i.e. a set stocking system. Clover yield of the potential varieties in the second harvest year averaged 1–5 t ha⁻¹ more than the control variety Olwen. Total sward production of AberVantage, AberCrown and AberDai was 2.0–1.4 t ha⁻¹ higher than that of Olwen.
In Experiment 2, clover yields of the three potential varieties averaged 2.1 t more than Olwen in the second harvest year under continuous sheep grazing, but all three were lower yielding than Olwen in the cutting regime.
Both experiments illustrate how the use of grazing treatments during breeding and evaluation can improve the role of white clover varieties.     

Soil N contributes to the oscillations of the white clover content in mixed swards of perennial ryegrass under conditions that simulate grazing over five years

The effect of the initial N-supplying capacity of soils (SoilN, 90–230 kg N ha^–1 year^–1) was tested on the dry-matter and N yields of pure or mixed white clover and perennial ryegrass swards, managed under simulated grazing over a 5-year period. The cumulated N harvested in the mixed swards was similar, both for white clover and perennial ryegrass, but the proportion of white clover showed oscillations over a 2-year period. In the first year, the SoilN effect was similar to that of fertilizer N. During the course of the experiment, the effect was always positive on the pure perennial ryegrass sward, alternately negative and nil for the white clover in the mixed sward and alternately positive and nil for the perennial ryegrass in the mixed sward; the period of these oscillations was 2 years. From the third regrowth period after sowing, the ratio between the actual N concentration and the concentration non-limiting to growth for the perennial ryegrass in the mixed sward, increased above that of the pure perennial ryegrass sward. It was in turn greater in the soils that were initially poor and then greater in those that were initially rich in soil N. The periodic oscillation of the initial SoilN effects implies that the initial SoilN gradient was alternately compensated and restored. It was concluded that N fluxes are partly responsible for the temporal oscillations in the proportion of white clover in mixed swards.     

Silage and milk production: studies with diets containing white clover silage

In three separate feeding experiments using a total of twenty-six individually-housed Ayrshire cows, three wilted silages made from Blanca white clover were offered ad libitum with either different supplements or different proportions of grass silage. The clover silages contained 680 g white clover kg⁻¹ on a DM basis, and had a mean DM concentration of 263 g kg⁻¹ with 231 g CP kg⁻¹ DM and 91 g ammonia-N kg⁻¹ N. The pH values averaged 4·16 and the DOMD concentrations 611 g kg⁻¹. In experiment 1 the daily intake of clover silage given alone was 15.2 kg DM per cow, i.e. 30·1 g kg⁻¹ live weight, and decreased by 0·76 kg DM kg⁻¹ barley DM and by 0·66 kg DM kg⁻¹barley plus soybean meal DM when these feeds were offered as supplements. Milk yield and fat concentration were higher on the supplement treatments than on the clover silage-only treatment. In experiments 2 and 3 the intakes of silage and total DM increased as the weight of clover in the diet increased from 0 to 700 g kg⁻¹ with parallel increases in milk yield. The effects on milk composition were small and generally non-significant. Although white clover silages with excellent fermentations were made, it is concluded that the main role of white clover in a silage system will be in mixed swards with grass to reduce the input of fertilizer N and to increase the voluntary intake of silage.     

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 productivity of four forage legumes sown alone and with each of five companion grasses

Four legumes—white clover cv. Blanca, red clover cvs Violetta (diploid) and Hungaropoly (tetraploid) and lucerne cv. Europe—were established as pure-sown swards and with each of five companion grasses: timothy cv. Timo, meadow fescue cv. Bundy, sweet brome cv. Deborah and perennial ryegrass cvs Talbot (diploid) and Barlatra (tetraploid), both ryegrasses being of 'intermediate' heading date. Two 'silage' crops and an 'aftermath grazing' crop were harvested in each of three successive years.
In the first harvest year, total herbage DM production of red clover ranged from 15·03 to 17·01 t ha^-1. White clover and lucerne swards produced considerably less at 7·12 to 11·01 t ha^-1. In the second harvest year, lucerne swards were the highest producing at 15·54 to 17·14 t ha^-1, while DM production from red clover and white clover swards ranged from 6·75 to 11·87 t ha^-1. Lucerne swards maintained their production superiority in the third year at 16·48 to 17·87 t ha^-1, while production from white clover swards ranged from 6·41 to 10·23 t ha^-1. However, red clover swards declined to 3·30 to 5·81 t ha ^-1; this above-average decline was mainly caused by the onset of red clover necrotic mosaic virus which affected all red clover plots uniformly in the second harvest year, and by winter conditions before the third harvest year. Total herbage DOM and CP yields of the swards were influenced in a similar manner to DM production.     

Some effects of added phosphorus on perennial ryegrass—white clover swards

The effect of applying 100kg P ha^-1 per year in the form of triple superphosphate to mixed swards of perennial ryegrass ( Lolium perenne ) and white clover ( Trifolium repens ) was examined on a soil of low P status.
The dry matter yield of total herbage was increased by 10'/i by added P. In the year of sowing the ryegrass benefited more than the clover from added P: in the subsequent four years the two species benefited equally. Both species responded 10 added P to a similar extent in terms of leaf size; the clover responded less well than the ryegrass in terms of rate of leaf emergence. However, clover responded positively to added P in terms of stolon internode length, length of stolon per m² and number of growing points per m². It is suggested that the application of P may promote the spread of white clover within an open sward, but that its application may not enhance the competitive power of white clover when growing with vigorous grasses.     

Dry-matter yield and herbage quality of a perennial ryegrass/white clover sward in a rotational grazing and cutting system

The expected reduction in the use of fertilizer nitrogen (N) on grassland in the Netherlands has led to renewed interest in white clover. Therefore, the performance of a newly sown perennial ryegrass/white clover sward on clay soil was assessed during 4 consecutive years. The experiment consisted of all combinations of two defoliation systems, i.e. one or two silage cuts per year (S1, S2), spring N application rate, i.e. 0 or 50 kg ha⁻¹ year⁻¹ (N₀, N₅₀), and the management system, i.e. rotational grazing and cutting, or cutting only (RGC, CO). The overall mean white clover cover was 30%. All treatments affected white clover cover, which was 8% higher with S2 than with S1, 6% higher with N₀ than with N₅₀ and 12% higher with CO than with RGC. The overall mean annual dry-matter (DM) yield (13·1 t ha⁻¹ year⁻¹) was significantly affected only by the management system: in two relatively wetter years, the annual DM yield was 1·19 t ha⁻¹ higher with RGC than with CO, whereas there was no difference in two relatively drier years. Nitrogen application increased the DM yield in the first cut by 7·0 kg kg⁻¹ N applied, but had no significant effect on the annual DM yield. Herbage quality was not affected by the experimental treatments. The average in vitro organic matter digestibility was 0.801, and the average crude protein content was 193 g kg⁻¹ DM. With the expected reduction in the use of fertilizer N, perennial ryegrass/white clover swards should be seriously considered as an alternative option to perennial ryegrass swards on these clay soils.