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 combined use of fertilizer nitrogen and white clover on grazed ryegrass swards

A 1-year grazing experiment with dairy cows is described in which the milk yield and herbage intake from a sward of S23 perennial ryegrass alone receiving fertilizer N at an annual rate of 360 kg ha⁻¹ were compared with those from a ryegrass-white clover var. Blanca sward given a total N application of 180 kg ha⁻¹. Both treatments gave virtually the same total milk yield of about 12500 kg ha⁻¹ over a 20-week grazing season.     

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.     

South-west England grassland survey 1983

A survey of grassland on 127 farms in south-west England was conducted in order to investigate the cutting and grazing management of grassland, botanical composition and the use of fertilizer N, and to quantify recent trends in reseeding and the age structure of swards. Twenty-six percent of the grassland surveyed was classified as arable grassland (in rotation with crops) and 74% as permanent grassland. Only 37% of the established grassland on dairy farms was aged over 20 years compared with 53% on livestock farms. Mowing was practised on 52% of the grassland, two-thirds of it every year, and virtually all grassland was grazed for part of the year. The average fertilizer N input was 168 kg ha⁻¹ with considerable variation with sward age (average 113 kg ha⁻¹ for over-20-year-old swards) and between dairy farms (average 217 kg ha⁻¹) and livestock farms (100 kg ha⁻¹)- The average proportion of sown species (mainly Lolium perenne) ranged from 90% in young swards to 36% in swards aged over 20 years, with considerable variation within age groups. L. perenne was associated with high inputs of fertilizer N, good drainage, sheep grazing and organic manures, e.g. among swards aged over 20 years it contributed 38% on average where >250 kg N ha⁻¹ were applied, but only 12% where no fertilizer N was applied. A continuous network of Trifolium repens occurred in 27% of the grassland–this was associated with low inputs of fertilizer N, good drainage and sheep grazing. Agrostis spp. were the most abundant unsown species and Cirsium arvense, Ranunculus spp. and Rumex spp. the most common broad-leaved weeds. Features of the sample are compared with those in the south-west England region and in England and Wales as a whole.     

The utilized metabolizable energy output of grassland on hill farms in Northern Ireland

Forty hill farms in Northern Ireland were surveyed to obtain information on stocking rates and output and to identify factors affecting output. The mean farm area of 194 ha was composed of 155 ha hill land and 39 ha inbye land with a mean stocking rate of 0–7 cow-equivalents ha⁻¹.
On the average farm most of the grassland (88%) was over 20 years old. The preferred species content of the swards averaged 22% over the whole farm and 42% in cut swards. This latter result may be attributed to the relatively high level of fertilizer N applied to these swards (131 kg ha⁻¹) compared to the mean application rate over the whole farm of only 29 kg N ha⁻¹ and 93 kg ha⁻¹ applied to the inbye land.
Output data calculated as utilized metabolizable energy (UME) per unit area for the whole farm and separately for hill and inbye components showed that although only 21% of the farm area was inbye land almost half the annual total metabolizable energy requirements of stock had to be met by grazing inbye. The capacity of herbage to meet stock energy demands was much lower on the hill with supplementary feed having to be provided over the winter.
Calculated output from inbye land was 39 GJ ha⁻¹ compared to 7 GJ ha⁻¹ from the hill and 15 GJ ha⁻¹ from the whole farm. UME output of the whole farm was negatively correlated with farm size (r=−0 55) and positively correlated with stocking rate (r = 0 89), applied N level (r = 0 63)     

Comparative studies of the influence of sward conditions on the ingestive behaviour of cows and sheep

Separate groups of non-lactating cows and wether sheep grazed at similar herbage allowances for two successive 5-d periods on swards that had previously been grazed frequently or infrequently with the intention of creating differences in canopy structure. Measurements were made of sward structure and composition, ingestive behaviour and diet composition. The preliminary treatments had little effect upon either sward conditions or animal behaviour.
Herbage mass was reduced from 4020 kg dry matter (DM) ha⁻¹ to 3290 kg DM ha⁻¹ on average over a 5-d grazing period as a consequence of the relatively low grazing pressure imposed. This resulted in a mean decline in intake per bite of 28%, and the changes for cattle and sheep did not differ significantly. However, there was a marked difference in the other behavioural responses of the two species; in the sheep biting rate fell and grazing time increased with declining herbage mass, particularly in the sward previously grazed infrequently, whereas the changes in the cattle were small.
Differences in the botanical composition of the herbage eaten by cattle and sheep were minor, but there was a small but consistent advantage to the sheep in the digestibility of the herbage eaten.
In the first of the two periods the variation in surface height after grazing was substantially greater for sheep-grazed than for cattle-grazed swards, indicating more patchy grazing by the sheep.
Estimates of daily herbage organic matter (OM) intake calculated from ingestive behaviour variables were high (means 38 and 32 g (kg LW) ⁻¹ for cattle and sheep respectively) and usually declined substantially over a grazing period.     

The effect of nitrogen in cattle slurry and mineral fertilizers on nitrogen fixation by white clover

The influence of N in slurry or in mineral fertilizers on herbage yield and nitrogen fixation by white clover grown in mixed swards was investigated. Two levels of N in cattle slurry were compared with a range of mineral N fertilization. The percentage of N derived from symbiosis (% Nsym) was measured by the ¹⁵N-isotope dilution method. The measurements were made in spring 1987 in two 4-year-old field trials, and included two out of five harvests.
The % N_sym was approximately 90% without N fertilization. It decreased in response to both mineral N and N in slurry but did not fall below 63%. The sum of two harvests revealed that 51·2 kg N ha⁻¹ were fixed in the absence of N fertilization. With 75 kg mineral N ha⁻¹ or 50 m³ cattle slurry ha⁻¹, the yield of fixed N decreased to 17·2 and 24·9 kg ha⁻¹, respectively. When compared on the basis of the fertilizer effect on dry matter yield and N concentration of perennial ryegrass, the decrease in yield of N fixed due to treatment with cattle slurry was less than that due to mineral N fertilizer. This was owing to the smaller extent of the depression in the proportion of white clover in the sward when the same amount of N was applied in cattle slurry, as compared with mineral fertilizer, although % N_sym responded similarly to both types of N fertilization.     

Managing grass/clover swards to produce differing clover proportions

Management treatments were applied to an established ryegrass/white clover sward with the aim of producing differences in clover content. The treatments were: mowing (M) with no fertilizer N (intended to give high clover), grazing by cattle (C) with no fertilizer N (medium clover) and grazing by sheep (S) with 300 kg N ha⁻¹ applied (low clover). Following treatments significant differences ( P < 0.001) were observed, with M, C and S containing respectively. 237, 81 and 3 kg DM ha⁻¹ of live clover. Treatment M swards had fewer ryegrass tillers but greater numbers of clover growing points than did treatment S, with values being intermediate on treatment C. Following overwintering most of the differences in the clover component between treatments C and M were lost, but those on treatment S still persisted. Management can be used to manipulate the botanical composition of ryegrass/white clover swards, but these changes may be only transient.     

Sward dynamics of a smooth-stalked meadowgrass dominantwhite clover sward rotationally grazed by cattle and/or sheep

This experiment was carried out to study the responses of sward components (particularly white clover, Trifolium repens ) to grazing management in a natural sward dominated by smooth-stalked meadowgrass ( Poa pratensis ) syn. Kentucky bluegrass. Treatments during two grazing seasons (1989–90) were: cattle grazing alone (C); cattle grazing followed by topping (CT); cattle grazing followed by sheep grazing (CS); and sheep grazing alone (S). Mean target pre- and post-grazing herbage masses were 2200 and 1100 kg DM ha⁻¹, estimated by single-probe electronic capacitance meter. Sward component dynamics were monitored using turf dissections, marked white clover stolons, and ring-toss white clover leaf counts. Component and sward data for the C, CT, CS and S treatments respectively, were: number of white clover leaves m⁻², 1295, 1384, 1408, 900 (s.e. ± 108); number of leaves per growing point, 3·2, 3·4, 3·0, 2·8 (s.e. ± 0·2); herbage accumulation (t DM ha⁻¹), 5·16, 5·02, 5·87, 8·28 (s.e. ±0 08); rejected herbage (% pasture area) 39·7, 7·7, 16·0, 0 (s.e. ± 75); and annual net herbage production (t DM ha⁻¹) 3·39, 4·35, 4·99, 8·28 (s.e. ± 0.07). Swards grazed by sheep alone contained less white clover, but regrew quicker and produced more herbage than other treatments. Close topping or grazing by sheep following dairy cattle grazing decreased sward rejection by cattle. These treatments maintained more of the pasture in better condition for subsequent cattle grazing, resulting in greater net herbage production than where no post-cattle grazing treatment was used.     

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.     

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.     

The effects of stocking rate and nitrogen fertilizer on a perennial ryegrass-white clover sward

The effects of stocking rate and N fertilizer on a mixed sward of perennial ryegrass ( Lolium perenne) and white clover ( Trifolium repens ) set-stocked with sheep were examined. Sward production and composition, and sheep production were studied.
Increasing the stocking rate over the range 25–55 yearling sheep ha⁻¹ reduced herbage accumulation by about 40%, whether or not N fertilizer was applied. Increasing the stocking rate increased the density of ryegrass tillers, but reduced the density of clover stolons and the clover content of the swards. Applications of N fertilizer (200 kg N ha⁻¹ a⁻¹) increased herbage accumulation by about 20% but substantially reduced the clover content.
Liveweight gain per animal and per unit area were greater at the lower stocking rates where the clover content and nutritive value of the diet were greatest. Wool growth per unit area was greater at the higher stocking rates. Applications of 1M fertilizer increased liveweight gain at stocking rates above 25 sheep ha⁻¹, but had no effect on wool production at any stocking rate.
The results demonstrate that a stable and productive grass-clover association was maintained under conditions of set-stocking at around 23 yearling sheep ha⁻¹and that at this stocking rate, which appears to be about the biological optimum, there was no advantage in using N fertilizer.     

Seasonal patterns of grass production under cutting or continuous stocking managements

A comparison was made between the seasonal pattern of net herbage accumulation under cutting and the pattern of intake under continuous variable stocking on a Lolium perenne sward, which was well supplied with nitrogen fertilizer and irrigated to minimize moisture stress.
The seasonal pattern of production under monthly cutting showed characteristic asymmetry with a marked peak in production in late May/early June, a rapid decline in June followed by an increase in rate in August and the total amount harvested over the season was 9–28 t organic matter ha⁻¹.
By contrast, the seasonal patterns of production on swards grazed by ewes to maintain sward surface heights of 30, 50 and 70 mm all differed fundamentally from that observed under cutting. Production was more evenly distributed throughout the season under these grazing treatments which, it has been proposed, should optimize performance. Total amounts harvested by grazing were 10–84, 10.12 and 8.51 t OM ha⁻¹, respectively. The different patterns of production under cutting and grazing were considered to be associated with differences in the expression of reproductive development in the grass crop and the maintenance of a smaller leaf area per unit ground area under grazing.
The results of the study suggest that it is not appropriate to regard the seasonal pattern of net accumulation under a standard cutting regime as representing the potential production of grass under continuous stocking. Moreover, in practice, the more uniform seasonal pattern of production seen in swards maintained on the basis of a controlled sward surface height makes it easier to match the supply of herbage to the appetite of grazing animals as the season progresses.     

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.     

Response of permanent and reseeded grassland to fertilizer nitrogen. 1. Herbage production and herbage quality

The productivity of permanent swards of mixed species composition was compared with that of sown Lolium perenne , cv. Melle at five fertilizer-N rates (0, 150, 300, 450 and 900 kg N ha⁻¹) and with L. perenne/Trifolium repens , cv. Grasslands Huia at 0 kg N ha⁻¹. The investigation was conducted under two cutting frequencies at sixteen sites in England and Wales, representing a range of grassland environments.
Annual total herbage dry matter (DM) production from both permanent and reseeded swards increased with successive increments of fertilizer-N up to 450 kg N ha⁻¹. Herbage DM production from reseeded swards in the first year after sowing was signficantly higher than from the permanent swards, at all fertilizer-N treatments. In subsequent years the production advantage of the L. perenne reseeds was maintained only at the higher N rates, though sown L. perenne/T. repens was the most productive sward type at 0 N. Average differences in modified acid-detergent fibre suggested small advantages in herbage quality to the reseeded swards.
It is concluded that, while reseeded swards are more productive in the year after sowing, many permanent swards are capable of high levels of production and that reseeding to a L. perenne sward cannot always be justified, particularly for grassland receiving low or moderate inputs of fertilizer-N.     

The effect of sward height on the liveweight gain of farmed yearling red deer (Cervus elaphus) stags

The effect of sward height on the liveweight gain of yearling farmed red deer stags grazing permanent upland pastures in the UK in two successive years is described. The swards received nitrogen fertilizer at a rate of 218 kg ha⁻¹. Red deer stag calves, which had been weaned in September and housed over winter on a hay and concentrate diet to gain on average 57 g d⁻¹ in year 1 and 75 gd⁻¹ in year 2, grazed at one of fourmean sward heights of 4, 6, 8 and 10cm from the beginning of June until September. Liveweight gains were recorded over a period of 15 weeks. All animals were slaughtered and carcass weights were recorded after the end of the grazing period. Liveweight gains and final live weights and carcass weights were significantly ( P <0·05) lower on the 4-cm sward than on the other swards, but there were no differences between the performance of animals on the 6-, 8- and 10-cm swards.     

Effect of regrowth interval on the productivity of swards defoliated by cutting and grazing

Over three grazing seasons (1984-1986) a sward of perennial ryegrass, cv. Talbot, which received a total of 336 kg N ha^-1 each season, was cut or grazed with ewes at 3- or 4-week intervals on a rotational basis.
Sward productivity was higher under cutting than under grazing irrespective of the interval between defoliations. Under cutting, mean herbage organic matter (OM) yields over both intervals were 8·66, 9·62 and 8·17 t ha-¹ in 1984, 1985 and 1986 respectively while under grazing the corresponding yields were 7·65, 8·63 and 7·50 t ha^-1. The mean annual yield of herbage defoliated at 3-week intervals was 7·50, 8·64 and 7 ·20 t OM ha^-1 compared with 8·80, 9·60 and 8·46 t OM ha^-1 for swards defoliated at 4-week intervals in the three years respectively.
The nitrogen (N) content of both the available and the residual herbage was consistently higher under grazing than under cutting. Available herbage contained 31·3 and 27·7 g N kg OM^-1 and residual herbage 26·1 and 22·7 g N kg OM^-1 under grazing and cutting respectively.
The mean yield of N under cutting was 284 kg ha^-1 compared with 304 kg ha^-1 under grazing. Defoliation interval had no effect on N yield, the overall mean yield being 294 kg ha^-1 under both 3- and 4-week defoliation intervals. The effect of the treatments on tiller population was slight and inconclusive.
The process of grazing reduced yield probably as a result of damage to the sward through trampling; the positive effect of excretal N on yield was minimal on account of the short grazing periods.     

Herbage growth rates on heterogeneous swards as influenced by sward-height classes

The contribution of four classes of sward height to daily herbage growth rates of a heterogeneous sward in eight periods throughout a grazing season was investigated in two continuous cattle-grazing systems differing in intensity (moderate stocking rate: MC; lenient stocking rate: LC). At the beginning and end of periods of 12 to 28 d, the compressed sward height (CSH) was measured in exclusion cages at eighteen fixed points per cage to derive daily growth rates for the four classes of sward height. Stratified calibrations were made to relate sward height to herbage mass for each treatment in each period. Quadratic regressions described the relationship between herbage growth rate and initial CSH for each treatment in each period. For scaling up to the scale of the plot, CSH was measured monthly at 100 points per plot. Daily herbage growth rates declined from more than 100 kg dry matter (DM) ha⁻¹ d⁻¹ on both treatments at the beginning of the grazing season to 20 kg DM ha⁻¹ d⁻¹ or less, especially on treatment LC. This was due to the larger area covered by tall herbage on treatment LC than on treatment MC. On treatment MC, daily herbage growth rate was predominantly derived from short sward areas of up to 12 cm in height while sward areas taller than 12 cm contributed most to daily growth rates on treatment LC in early summer. The method used is considered suitable for estimating daily herbage growth rates of different classes of sward height in extensively managed pastures and can easily be adapted to deal with more heterogeneous swards than used in this study.     

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.     

Quantifying the effect of nitrogen fertilizer applications in spring on white clover content in perennial ryegrass-white clover swards

Data are presented for the fourth (1979) and fifth (1980) harvest years of a trial in which four levels of N fertilizer (0, 30, 60 and 90 kg N ha⁻¹) were applied each spring to swards with grass (perennial ryegrass cv. Barlenna) and each one of four cultivars of while clover (Blanca, Sabeda, Olwen and S100) or grass alone. Results from the first three years have been published.
Dry matter (DM) harvested dropped from the fourth to fifth years over all swards by 1 −5 to 2 0 t ha⁻¹ but response to N was maintained (17.4 and 24.4 kg DM (kgN)^−l in response to 90 kg N ha⁻¹ in 1979 and 1980 respectively) despite reductions in summer yields relative to unfertilized swards. Blanca swards produced significantly less DM harvested than all other cultivars in 1979 and all cultivars in 1980 except for Olwen. Clover DM harvested continued to fall from 1977, the mean for the unfertilized treatment in 1980 being 55% of that in 1979. Up to 1980 Sabeda swards produced more clover DM harvested than Blanca swards. Linear regressions between annual clover content at zero N and at each spring N level for each sward type over 5 harvest years were very highly significant. It is concluded that all cultivars used responded similarly to spring N. Further work to develop a method for predicting the effect of spring N on clover content of given swards is required.