Growth and colonization of a range of white clover cultivars strip-seeded into an upland perennial ryegrass sward

Seven cultivars of white clover (Trifolium repens L.) (Kent, S184, Huia, Menna, Donna, Alice and Nesta) and a commercial mixture, ‘Ensign’, were strip-seeded into an upland perennial rye-grass (Lolium perenne L.) sward in late June 1986. Swards were first grazed by sheep, either on 5/6 August (early) or on 19/20 August (late) and then every 14–21 days (frequently) or 28–42 days (infrequently) during 1986, followed by a common grazing regime in 1987. During April to mid-June 1988 the swards received either a moderate amount of nitrogen or none and were cut frequently or once only in mid-June. Growth of individual seedlings was assessed before and after grazing during 1986 and stolon accumulation and distribution and sward colonization were assessed during 1987 and 1988. All cultivars emerged rapidly and satisfactorily and there were no consistent significant differences in the overall dry matter accumulation per seedling during establishment. During the first autumn the proportion of the aboveground biomass removed during grazing was smallest in Kent (c. 20%) and largest in Nesta (c. 40%). Kent and S184 produced most leaves and stolons and the greatest length of stolons per seedling and per individual stolon, and Nesta and Alice the fewest leaves and stolons and shortest stolons. Seedlings grazed early had heavier and longer stolons than those grazed late; those grazed frequently had more leaves, stolons and growing points than those grazed infrequently, especially following early grazing. During 1987 Kent and S184 had consistently the largest number of stolon growing points, and weight and length of stolons per unit area; these two cultivars and Nesta also colonized the sward more rapidly than the other cultivars. All cultivars contributed substantially and similarly to herbage production in late September. There were no residual effects of the 1986 treatments after the summer of 1987. During 1988 additions of nitrogen fertilizer at 100 kg N ha^-1 or allowing the herbage to remain undefoliated between mid-April and mid-June both independently halved the number of stolon growing points per unit area; together they reduced it by 80%. Nitrogen also, on average, halved stolon weights but less so in Nesta, Alice and Huia and more so in all other cultivars. Infrequent defoliation greatly decreased stolon weights in Kent and S184 but had no significant effects on the other cultivars. Sward colonization was almost complete by June and entirely so by October for all cultivars in all treatments. Implications of the results for the after-management of strip-seeded white clover are discussed.     

Turnover of grass laminae and white clover leaves in mixed swards continuously grazed with steers at a high-and low-N fertilizer level

Turnover rates of grass laminae and clover leaf tissue were estimated over a range of intervals within three periods each year in the second to fourth years (1983-85) of a trial involving swards continuously grazed by steers and receiving either 60 kg N ha-1 in spring (60N) or 360 kg N ha^?1 throughout the year (360N). Within the 60N swards initial stocking rates at turnout were low (60N LS) at 7-2 steers ha^?1 and high (60N HS) at 90 steers ha^?1 in 1983, and in 1984 and 1985 corresponding rates were 10-8 and 13-5 ha^?1. The 360N swards were initially stocked at turnout at 96 (360N LS) and 120 (360N HS) steers ha^?1. Stocking rates were reduced by 33% in midsummer except for 60N in 1984 and 1985 when they were reduced by 50%. Meaned over 3 years, 360N HS had lower herbage mass than 60N LS. Tiller density in 360N was almost 50% higher than in 60N and clover growing point density was only one quarter that of 60N with the 60N LS having lower clover densities than 60N HS in 1985. Generally, leaf extension rate per tiller was higher in 360N than 60N and, when significant, 60N LS had higher senescence rates per tiller than 360N HS. Rate of increase in new clover lamina tissue per stolon was not affected by treatments, whereas in 1983 LS had higher senescence rates of clover laminae than HS. Petiole growth per stolon was higher in LS than HS in 1983 and 1984, the mean over these years for 360N HS being 77% that of 60N LS. Petiole senescence per stolon was lower in 360N HS than 60N LS only in 1983. When comparing 60N HS and 360N LS (representing similar levels of grazing intensity, having similar herbage mass) the gross growth of leaf material in the former was 75% of the latter, in contrast to 57% for net growth. Clover contributed 18% to the estimated growth of leaves compared to a mean of 7% in herbage mass. Taking inflorescence and pseudostem into account in 1984 and 1985,60N HS had 7% clover in standing herbage and 14% in net growth. Therefore, the contribution of clover to growth is considerably higher than its presence in herbage mass would suggest in continuously grazed swards. It is concluded that low-N swards, owing to their lower tiller density and slower grass leaf extension rate, will be less efficiently grazed than swards at higher N levels at a given herbage mass, but the presence of clover will partly offset that disadvantage.     

The implications of controlling grazed sward height for the operation and productivity of upland sheep systems in the UK: 7. Sustainability of white clover in grass/clover swards with reduced levels of fertilizer nitrogen

The sustainability of white clover in grass/clover swards of an upland sheep system, which included silage making, was studied over 5 years for four nitrogen fertilizer rates [0 (N₀), 50 (N₅₀), 100 (N₁₀₀) and 150 (N₁₅₀) kg N ha^?1]. A common stocking rate of 6 ewes ha^?1 was used at all rates of N fertilizer with additional stocking rates at the N₀ fertilizer rate of 4 ewes ha^?1 and at the N₁₅₀ fertilizer rate of 10 ewes ha^?1. Grazed sward height was controlled, for ewes with their lambs, from spring until weaning in late summer by adjusting the proportions of the total area to be grazed in response to changes in herbage growth; surplus pasture areas were harvested for silage. Thereafter sward height was controlled on separate areas for ewes and weaned lambs. Areas of pasture continuously grazed in one year were used to make silage in the next year. For treatments N₀ and N₁₅₀, white clover stolon densities (s.e.m.) were 7670 (205·4) and 2296 (99·8) cm m^?2, growing point densities were 4459 (148·9) and 1584 (76·0) m^?2 and growing point densities per unit length of stolon were 0·71 (0·015) and 0·67 (0·026) cm^?1 respectively, while grass tiller densities were 13 765 (209·1) and 18 825 (269·9) m^?2 for treatments N₀ and N₁₅₀ respectively. White clover stolon density increased over the first year from 780 (91·7) cm m^?2 and was maintained thereafter until year 5, reaching 8234 (814·3) and 2787 (570·8) cm m^?2 for treatments N₀ and N₁₅₀ respectively. Growing point density of white clover increased on treatment N₀ from 705 (123·1) m^?2 to 2734 (260·7) m^?2 in year 5 and it returned to the initial level on treatment N₁₅₀ having peaked in the intermediate years. Stolon density of white clover was maintained when the management involved the annual interchange of continuously grazed and ensiled areas. The non‐grazing period during ensiling reduced grass tiller density during the late spring and summer, when white clover has the most competitive advantage in relation to grass. The increase in stolon length of white clover in this period appears to compensate for the loss of stolon during periods when the sward is grazed and over winter when white clover is at a competitive disadvantage in relation to grass. The implications for the management of sheep systems and the sustainability of white clover are discussed.     

Management options for increasing white clover contents of swards, without resowing

Two field experiments were carried out at North Wyke, Devon in 1985 (Experiment A) and 1986 (Experiment B) to investigate the effectiveness of either cutting or rotational sheep-grazing managements for raising the clover content of clover-depleted swards. Subplots were pretreated in March with (a) propyzamide at 0·4kg a.i. ha^-1, (b) chlorpyrifos at 0·72 kg a.i. ha^-1 and methiocarb at 0·22 kg a.i. ha^-1, (c) carbofuran at 1·3 kg a.i. ha^-1, or (d) not so treated, in order to reduce grass tiller density, control insect and mollusk pests, or control all invertebrate pests respectively (a-c), Carbofuran was not applied to swards that were to be grazed subsequently. The propyzamide pretreatment (a) significantly reduced the quantity of herbage dry matter (DM) grazed and the silage DM yields in both years, but raised the numbers of active clover buds, and clover stolon density and its weight in 1986, though not in 1985, The pesticide package (b) raised the quantity of herbage DM grazed in both years, and the silage DM yield in 1986, Carbofuran (c) raised silage yields in 1985. Neither pretreatment (b) nor (c) significantly affected clover performance. In comparison with sheep grazing, cutting showed a trend to higher DM yields, and significantly raised clover stolon density and weight in both years, and active bud numbers in 1986. The periodic sheep grazing management included recovery intervals of 14 d and 35 d. In 1986 (but not 1985) the longer recovery interval raised herbage DM consumption, but had no effect on clover development. The cutting management included nitrogen inputs of either 100 kg ha^-1 in March, or none. N input raised annual DM yields in 1986 (but not 1985) but did not affect clover DM yields or performance in either year. The experiments at North Wyke were supported by on-farm experiments using exclosure cages at ten sites in 1985 and nine in 1986, in Yorkshire, Wales, the Midlands and Devon. In both years, application of propyzamide as in treatment (a) reduced DM yields (P<0.001) and raised the proportion of clover (P<0.001) in May harvests. The density of active clover buds (P<0.05), stolon density (P<0.001) and stolon weight (P<0.001) were increased by October. A combined carbofuran and methiocarb treatment significantly (P<0.001) increased herbage yields, but did not affect measures of clover performance. Unlike the main experiments, a comparison of grazing (outside the cages) and cutting management (within the cages) showed no effect on clover development. It was concluded that cutting, or rotational sheep grazing with a long recovery interval, would promote clover development in the clover depleted sward. Though successful in the overall assessment, application of propyzamide gave highly variable results on different sites and was not sufficiently reliable.     

The influence of autumn management and companion grass on the development of white clover over winter in mixed swards

Three experiments designed to investigate different facets of autumn management on white clover stolon development are described. The effects of defoliation interval (2, 4, 6 and 8 weeks during 16 weeks from 27 July) were investigated. The shortest interval resulted in the shortest length of stolon material per unit area but cutting interval had no effect on growing point density nor on hardiness of stolon tips evaluated in October, December and January.
Chemical grass suppressants were employed to reduce grass biomass during winter in two experiments to evaluate the influence of grass on white clover development. One experiment involved varying grass tiller density by spraying a perennial ryegrass/white clover sward in October with three rates of three chemical suppressants (Clout, Kerb and Checkmate). Although tiller and clover growing point density were inversely related in January, the overall relationship was not strong.
Clout at l·5kg a.i. ha⁻¹ was sprayed in October on one of two subplots in each of twelve grazed grass/white clover plots that had been maintained at 7 or 9 cm from July to October then grazed to 3–4 cm with sheep. Sward height had no effect on clover population density but the shorter sward had a greater mean node number per secondary stolon branch. By March, suppressing grass resulted in more than double the stolon population density, a higher proportion of plants with tertiary and quaternary branches, and on marked stolons, five times more branches and 60% higher dry matter (DM) produced during winter but with shorter petioles compared with clover in untreated plots.
It is concluded that white clover has the capacity to branch during a mild winter and as stolon branch numbers can suffer a net loss as a result of the presence of the grass canopy, management that controls grass growth during winter should aid over-wintering and improve persistence of white clover.     

Implications of nitrogen fertilizer applications and extended grazing for the N economy of grassland

The response of swards which have been previously grazed to N fertilizer applied in early February was studied in two experiments in Northern Ireland. The effect of N fertilizer applied at a range of dates in autumn and spring on swards for out-of-season utilization was studied in a further experiment. Deep soil coring was also undertaken, subsequent to grazing with dairy cows, in grazed and protected areas in November and March to investigate the effect of out-of-season grazing on soil mineral N levels.
Dry-matter (DM) yield response to early spring N application in previously grazed swards was low, with no effect on DM yield in February or March. Progressively delaying N application (and commencement of herbage accumulation) in autumn from 8 September until 18 October reduced herbage availability in late autumn and early spring but increased leaf lamina content. The greater the amount of herbage accumulated to 1 December, the lower the tiller density in the following April.
N fertilizer had a greater impact on soil mineral N in spring than in late autumn/early winter, suggesting that fertilizer N was more prone to loss in the latter. Soil mineral N was not significantly affected by out-of-season grazing.
It is concluded that in well-fertilized, previously grazed swards response to N for out-of-season herbage is low and the probability for N loss is increased. Herbage quality will decline and the sward may be damaged if about 2 t DM ha⁻¹ or more of harvestable herbage accumulates for use in winter or in early spring.     

The impact of grazing severity on perennial ryegrass/white clover swards stocked continuously with beef cattle

An experiment was carried out to examine the changes in perennial ryegrass ( Lolium perenne L.) and white clover ( Trifolium repens L.) populations in mixed swards, under different grazing severities over three successive grazing seasons. In year 1, three paddocks were erected on a sward with a low initial content of clover (block 1). Sward heights were measured using a rising-plate meter, and were maintained at overall mean heights of 3·0, 5·5 or 7·0 cm by variable stocking with 8-month-old steers. In year 2, a further three paddocks were erected on an adjacent area with a high initial content of clover (block 2), and were maintained at the same three heights by similar management. Botanical analyses were carded out on samples collected at four times during the season. Maintaining swards at 5·5 or 7·0 cm led to a large proportion of the area being infrequently grazed. Block I paddocks had higher initial tiller densities, which increased as sward height was reduced, while block 2 paddocks, with their lower initial tiller density, showed little effect of sward height on tiller density. Initially, clover stolon growing-point densities and stolon masses increased more rapidly in the taller swards. Later, however, large losses in the clover populations occurred on all paddocks during long wet winters and there was a general reversal in these trends for stolon growing-point densities and stolon masses, 3·0>5·5>7·0. By year 3, swards with differing     

The effect of cutting for conservation on a grazed perennial ryegrass-white clover pasture

Continuous stocking with sheep at high stocking rates may reduce the content of white clover (Trifolium repens) in mixed grass-clover swards. The present experiment was carried out to investigate the effects on sward production and composition of resting a perennial ryegrass (Lolium perenne)- white clover sward from grazing and taking a cut for conservation. Swards were set-stocked with 25 and 45 yearling wethers ha^?1 either throughout a grazing season, or on swards that were rested for a 6-week period and then cut in early, mid- or late season. In an additional treatment swards were cut only and not grazed. Net herbage accumulation was higher at the lower of the two stocking rates and was marginally increased by the inclusion of a rest period at the high but not the low stocking rate. Clover content was higher at the lower stocking rate and was increased by the inclusion of a rest period by 30% at 45 sheep ha^?1and by 11% at 25 sheep ha^?1 The effect was most marked at the end of the rest period before cutting. When rested from grazing the tiller density of ryegrass decreased although tiller length increased, and clover stolon length, petiole length and leaflet diameter increased though leaf and node number per unit length of stolon decreased; the reverse applied when the sward was returned to grazing after cutting. At the high stocking rate, rest periods in mid-season or later maintained the greatest clover content and marginally increased total net herbage accumulation. At the low stocking rate the timing of the rest period had no significant effect on total net herbage accumulation or on clover content. These results show that the combination of grazing and cutting is of benefit where the stocking rate is high enough to threaten clover survival and limit sheep performance. However, at such a stocking rate, feed reserves are at a minimum throughout the grazing season and so opportunities for resting the sward are probably low.     

Growth, colonization and productivity of two white clover cultivars strip-seeded into an upland Festuca-Agrostis sward

Small plots of a Festuca-Agrostis upland sward on a peaty gley podsol were strip-seeded during late June 1986 with white clover cvs Aberystwyth S184 or Menna at 4 kg ha⁻¹ and defoliated early (20 August) or late (3 September) and then frequently or infrequently (every 2 weeks or 4 weeks) until the end of September. All plots were defoliated in early November, at 3-weekly intervals during the growing season in 1987 and then grazed rotationally during 1988.
Satisfactory seedling establishment, representing 46% emergence, was achieved 5 weeks after sowing. The differential defoliation regimes had no persistent significant effects on clover development. S184 soon produced more leaves per seedling than Menna and a smaller proportion of its leaf number and weight were removed at each defoliation. Following large losses of leaves over the 1986–87 winter, SI84 had significantly more leaves per stolon than Menna; subsequently it also colonized the sward at a quicker rate. During 1987 amounts of herbage harvested (6.1 t ha⁻¹) were similar with the two clover cultivars, with S184 contributing 47% and Menna 44% of this respectively. SI84 made a larger contribution to yield during May and June but Menna was more productive during September and October. During 1988 clover populations were maintained with rotational grazing without additional fertilizer inputs.
The results show that, despite initial soil and climatic contraints, both small and medium-leaved clovers can be strip-seeded into upland swards with large subsequent benefits to yield and herbage quality. However, they also indicate the need for further experiments to determine the influence of sward morphology and defoliation regime on stolon branching rates and accumulation of growing points which, in turn, govern sward colonization.     

The effect of subsequent mangement on the success of introducing white clover to an existing sward

Two experiments, each lasting approximately 12 months, were carried out at North Wyke, Devon, in 1982-83 (A) and 1983-84 (B), to investigate various sward managements following oversowing of white clover (Trifolium repens, cv. Grasslands Huia) at 4 kg ha^-1 with a Hunter Rotary Strip-Seeder in June or July into the stubble of a permanent grass sward following conservation. Experimental managements comprised cutting, grazing with wether sheep or grass suppression by herbicide, as appropriate, in late summer/autumn (Phase I), winter (Phase II) and spring/early summer (Phase III). During Phase I, there was no differential effect on clover stolon development of lenient grazing at approximately 4-weekly intervals or topping at the same frequency to a similar height. Early in Phase II of Experiment A, grazed paddocks became so badly poached that no differences occurred between grazing either to early January or throughout the winter. Under drier conditions in Phase II of Experiment B, continuous grazing at either five (L) or ten (H) sheep ha^-1 had no immediate effect on clover stolon development, but in a silage cut in June, paddocks formerly stocked at the lower rate yielded 40% more DM than those at the higher rate. Experiment A compared the use of a grass-suppressing herbicide, propyzamide, applied at 0.6 kg a.i. ha^-1 in either October or February; in Experiment B it was applied in October. Prophyzamide applied at either time in Experiment A increased the clover content of herbage regrowing after the end of the experimental period from 16% to 36% (s.e.d. ± 3.9). In Experiment B, October application raised the clover contents of herbage cut in June 1984 from 10% (H) and 17% (L) to 32% (s.e.d.±5.9), and stolon lengths per m² at the end of the summer period from 33 (H) and 56 (L) to 86m (s.e.d. ± 11.7). However, the effect of spraying propyzamide on subsequent herbage yields was erratic, and appeared to depend on the incidence of frost after application. In Phase III of Experiment A, continuous grazing was compared with a silage cut in June. At the end of the experiment there were 31 m m^-2 of clover stolon in silaged areas compared with only 2.5 m m^-2 following grazing (s.e.d.±6.6). Clover content and herbage yields were also significantly higher following conservation. In Experiment B in the same period, rotational grazing with a 14- or 35-day recovery interval was compared with a silage cut in June, with or without 100 kg N ha^-1 applied in March. Application of N to the conservation treatment reduced clover stolon length per unit area, and in the regrowth in the post-experimental period the conservation treatment without N had the largest clover content (31% compared with 16-23% for other treatments, s.e.d. ± 3.6)     

Some effects of herbage composition, as influenced by previous grazing management, on milk production by cows grazing on ryegrass/white clover pastures. 2. Milk production in late spring/summer: effects of grazing intensity during the preceding spring period

Three experiments (2a, 2b and 2c) were carried out to examine the effects of different grazing intensities imposed during spring on subsequent herbage composition and milk production measured in summer.
Increased intensity of grazing imposed during spring (including the period of reproductive development in ryegrasses) produced swards in early summer with lower pre-grazing herbage masses, which contained higher concentrations of green leaf, clover and digestible nutrients, but lower concentrations of grass stem and senescent material.
In the first and second experiment cows were given a common daily allowance of total herbage dry matter (DM). The cows grazing on low-mass swards in early summer produced larger daily yields of milk, fat and protein than those grazing on the high-mass swards.
In the third experiment, cows were given a common daily allowance of green leaf DM from three swards which differed in pre-grazing herbage mass and in herbage composition. The allowances of total DM required differed widely between the treatments. There were no significant differences in milk yields between the swards despite the large differences in herbage composition.
The practical implications of these results are discussed.     

A COMPARISON OF THE HERBAGE YIELD OF ITALIAN RYEGRASS AND TALL FESCUE MIXTURES IN THE SECOND AND THIRD YEAR AFTER SOWING

The annual yield of tall fescue was higher than that of Italian ryegrass in the third year after sowing, but the total yield of herbage from grass plus clover swards was similar.
In both the second and third year after sowing, the yield of herbage in the spring grazing was higher when fescue was used as the sown grass. The method of establishment of both tall fescue and Italian ryegrass affected the total and seasonal yield in the second and third year after sowing, but the magnitude of these effects was not nearly as marked as it was earlier in the life of the leys. In the second year after sowing, swards of both Italian ryegrass and tall fescue had a higher yield of total herbage and of white clover, and a lower ingress of unsown species, when established without a cover crop and grazed frequently in the year of sowing.
The inclusion of red clover did not increase total yield of DM in the second and third year after sowing, and it slightly decreased the yield of the tall fescue mixture in the third year following sowing when N was applied. S170 tall fescue was readily grazed by sheep in spring and autumn.
The apparent recovery of applied N varied with the mixture sown, and the management given during establishment.     

White clover growth patterns during the grazing season in a rotationally grazed dairy pasture in New York

White clover (Trifolium repens L.) is an important stoloniferous pasture legume in the Great Lakes region of the United States, but it often has limited persistence. Researchers in New Zealand and Wales have found that in spring, compared with other seasons, white clover plants have reduced branching complexity and have the fewest buds that produce leaves. They therefore suggested that in spring the plants are most vulnerable to grazing and climatic stress. Because of severe winter and cool, wet spring weather in New York State, it was hypothesized that white clover plants would also be of low branching complexity, smaller and have low axillary bud activity in spring compared with later in the grazing season. To test this, growth of white clover was monitored in an orchard grass (Dactylis glomerata L.)/white clover pasture in New York that was rotationally grazed with dairy cows during the 1993 and 1994 grazing seasons. Three sets of plants were sampled. The first set consisted of forty random plants sampled before each grazing event. Stolon branching order, number of each stolon branching type and area the plant occupied were determined. Approximately each month before one grazing event, a separate set of 32 random plants was measured in the field to determine the area they occupied; these plants were then removed to the laboratory for the measurement of stolon order, number of each stolon type, stolon lengths, total number of growing points, number of taproots and adventitious roots, root position and above-ground dry matter. Once a month, 12 additional plants were removed to measure axillary bud activity at each node. Leaf development from nodes tended to increase from spring to summer. However, the stolon branching order of white clover plants was not simpler in spring compared with summer or autumn. In 1994 during and after a dry and hot period, white clover plants were smaller, of lower stolon branching order and had fewer roots. Climate and associated soil organism activity appear to explain the different white clover growth patterns observed in New York and New Zealand. Severe winters in New York limit earthworm activity and stolon burial, which is important in contributing to stolon/plant breakdown in New Zealand. During the years of this study in New York, a hot and dry period had the most negative effect on the growth pattern of white clover.     

Effect of interval between harvests and spring-applied fertilizer N on the growth of white clover in a mixed sward

A perennial ryegrass ( Lolium perenne )-white clover ( Trifollum repens ) sward, that had been grazed for over 2 years, was cut at 1-, 2-, 3- or 6-week intervals from 18 April to 28 November 1986. The effects of two rates of N application in spring, 0 and 66kg Nha⁻¹, were compared. Clover growth was studied in three six-week periods that began on 18 April, 18 July and 17 October respectively. Increasing the interval between cuts increased the yield of herbage without reducing the proportion of clover in the harvested herbage, but the combination of applied N and the six-week interval was harmful to clover production. Increasing the interval between cuts tended to increase the proportion of resources allocated to stolons rather than to leaves, and to increase the weight of new dry matter (DM) per growing point rather than per m². In the third period of the study, when the ten youngest internodes per stolon were examined separately, all ten ages of internode were found to have been affected by the cutting management. This was indicated by the positive effect of the length of the interval between cuts on the weights of N, P and K per intemode. The concentrations of N, P and K were highest in the youngest intemodes. The application of N reduced the proportion of new DM allocated to stolen rather than to leaf and it reduced the number of clover growing points per m².     

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.     

Setting management limits for the production and utilization of herbage for out-of-season grazing

Three experiments were carried out on perennial ryegrass‐dominant swards to provide a basis for recommendations for the limits to (a) building up and timing of utilization of a herbage ‘bank’ for out‐of‐season grazing and (b) duration and intensity of early spring grazing in the United Kingdom and Ireland. In experiment 1, the effect of regrowth interval (from 7 September, 20 October, 17 November or 15 December) in autumn on herbage accumulation, leaf turnover and on subsequent spring growth was investigated. Swards regrown from early September reached maximum herbage mass (about 3 t ha^–1 DM) and leaf lamina content in mid‐November, by which time senescence rate exceeded rate of production of new leaves. New leaf production and senescence rates were greater in swards remaining uncut until December than in those cut in October or November. Time of defoliation up to December had no effect on spring herbage mass in the subsequent spring. Defoliating in March reduced herbage mass in late May by less than 20%. Experiment 2 investigated the progress in herbage growth and senescence in swards regrowing from different times in late summer and autumn to produce herbage for utilization beyond the normal grazing season. Treatments in a randomized block design with three replicates were regrowths from 19 July, 8 August, 30 August and 20 September. Based on a lower ceiling of leaf and total herbage mass being reached with progressively later regrowths, beyond which leaf senescence generally exceeded leaf production and herbage mass declined, it was concluded that currently recommended rotation lengths for this period should extend from 3 weeks in late July to 8 weeks for swards previously grazed in mid‐September. In both experiments, leaf senescence commenced earlier (by one leaf‐age category) than previously published estimates and so brought forward the time at which senescence rates balanced leaf growth rates. In experiment 3, designed to evaluate the effect of daily grazing period and intensity in early spring on herbage regrowth, dairy cows grazed successive plots (replicates) for 2 or 4 h each day at two intensities (target residual heights of 5 or 7 cm) in March to mid‐April. Regrowth rate was similar in all treatments including the ungrazed control, despite soil moisture content being relatively high on occasions. Tiller density was significantly reduced in May by grazing plots in early or mid‐April. It is concluded that in autumn there are limits to which rotation lengths should be extended to produce herbage for out‐of‐season grazing owing to attainment of ceiling yields. Although utilization in early spring may reduce herbage availability in spring, out‐of‐season utilization need not reduce herbage growth rates in early spring.     

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.     

Influence of structure and composition of ryegrass and prairie grass-white clover swards on the grazed horizon and diet harvested by sheep

Diet selection from ryegass-and prairie grass-white clover swards, vertically stratified into three horizons (A > 6 cm, B 3–6 cm, C > 3 cm), was studied using oesophageally fistulated sheep during summer and autumn. Animals grazed for 3-day periods. Apparent herbage intake was calculated from total herbage disappearance. The composition of each horizon and of the diet selected was measured daily.
Herbage mass (DM ha^-1) and sward height (cm) prior to grazing were not significantly different between swards in each season, and were 2·0 and 20 in summer and 1·6 and 10 in autumn. In summer, 36% and 5% of the green grass leaf (GGL) for prairie grass and ryegrass, respectively, was distributed in horizons A and B. In autumn 39% and 29% of GGL occurred above 3 cm for prairie grass and ryegrass, respectively. GGL distribution determined which sward horizons were grazed. Sheep grazed horizon C (0–3 cm) of summer ryegrass pasture, and the surface canopy (>3 cm) of all other swards.
In summer, apparent intake achieved by sheep grazing prairie grass swards was 87% higher than that achieved on ryegrass swards. In autumn a greater GGL distribution above 3 cm with prairie     

The relationships between stolon characteristics, winter survival and annual yields in white clover (Trifolium repens L.)

Five white clover populations of Swiss origin and three bred varieties were grown in binary mixtures with two perennial ryegrass varieties, Aurora and S23. The seasonal yields of clover and grass plus clover were measured under a cutting regime during the second and third years after establishment. A series of destructive detailed sward measurements was made during the late autumn to spring period preceding each harvest year. In this way changes in the amounts of stolon, leaf plus petiole and numbers of growing points were monitored during the winter.
There were large differences in clover yield between populations in both years. These were evident from the first (spring) harvest in each year. Higher-yielding clovers in spring tended to produce higher annual clover yields. No grass × clover interaction was evident at any harvest. Large differences between clovers were also apparent in the morphological characteristics measured, with the Swiss material generally having greater amounts of stolon, leaf plus petiole and numbers of growing points present in early spring. It is proposed that these factors contribute to the high spring yield in the Swiss populations. Loss of stolon length over each winter was less in the Swiss material, indicating that its good spring growth was not obtained at the expense of winter hardiness. Annual clover yield was found to be significantly positively correlated with the amount of stolon present in spring, exemplifying the importance of stolon survival over the winter.     

The effects of simulated continuous grazing on development and senescence of white clover

Two experiments investigating the effects of simulated continuous defoliation on white clover development and senescence are described. Stolons growing in boxes in a glasshouse were defoliated repeatedly by hand to simulate different intensities of continuous grazing by sheep. The experiments continued in both instances until eleven leaves had been produced on stolons in the most favourable treatment.
It was found that leaf dry matter production was reduced in proportion to the leaf complement of the stolon. Reduction of the leaf complement from two leaves to one leaf led to a reduction in subsidiary branch production of about 25% and an increase in percentage dead stolon from 33 to 44%, If no fully expanded leaves were retained branch production fell to 40% or less of that observed when two leaves were retained.
Stolons growing in swards continuously grazed by sheep usually have a green leaf complement varying between zero and two leaves per growing point. The consequences of maintaining different leaf complements in this range are discussed in the light of the current experiments.