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.     

Effects of spring defoliation and fertilizer nitrogen on the growth of white clover in ryegrass/clover swards

An examination was made of the effects of different spring treatments on the growth of white clover in a ryegrass/white clover sward. Plots were either cut once (in February, March or April) or twice (in February and April) or left uncut. Nitrogen was applied to half of the plots in each instance. The clover was sampled at intervals of approximately 3 weeks from February to June to determine numbers of leaves and growing points and weights of plant parts. Rates of leaf appearance were also observed and estimates were made of total herbage mass from ground-level cuts.
Percentages of white clover in the herbage were higher in unfertilized than in fertilized plots and in defoliated than in undefoliated plots. The percentage increases that followed defoliation were usually maintained into later regrowth, showing that clover content was not automatically reduced as herbage mass increased. Increases in growing points were recorded after the beginning of April in defoliated unfertilized plots but not in undefoliated fertilized plots or in plots fertilized and defoliated twice during the spring period, in which numbers fell substantially.
Inverse relationships were found between rates of leaf appearance, or the number of green leaves retained per stolon, and herbage mass, whereas heights of clover and grass leaves and the percentage of dry matter allocated to petiole rather than leaf in the clover increased with increasing herbage mass.
We suggest that the observed differences between spring treatments in clover percentage result primarily from their differential effects on the formation and death of tillers and growing points in the early stages of regrowth.     

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

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

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.     

The effects of nitrogen fertilizer applied in spring on swards of ryegrass sown with four cultivars of white clover

Nitrogen fertilizer was applied at 0, 30,60 and 90 kg N ha^-1 in March 1976, 1977 and 1978 to plots containing perennial ryegrass cv. Barlenna sown either alone or with white clover cv. Blanca, Sabeda, Olwen and S100 in four replicated blocks.
Dry matter (DM) yield of all swards responded positively to N with the response being highest in the no-clover swards in two of the three years. Annual DM yields were lower in the no-clover than in the mixed swards at any given N level. The higher levels of N reduced DM yield in mixed swards at some harvests in midsummer.
Swards of S100 were consistently among the lower yielding mixed swards, whereas the other three clover cultivars varied in their relative yields. There were no N x cultivar interactions for white clover yields; irrespective of cultivar, N application reduced annual white clover yield by similar amounts.
It is concluded that it is beneficial to apply moderate amounts of N fertilizer to mixed swards in spring and that under these conditions the yield differences between swards including medium-large and smaller leaved white clover cultivars are similar to differences between the inherent yield potential of these cultivars in mixed swards receiving no N.     

Herbage growth, white clover content and lamb production on grazed ryegrass-white clover swards

Two contrasting Gremie perennial ryegrass and Blanca white clover seeds mixtures were established. Each sward type was either continuously or rotationally (four paddocks) grazed at two stocking rates by lambs of 26–28 kg initial mean live weight in two 12-week experiments. Dry matter production, assessed by the cage method, was lower on the high-clover sward during the first experiment but overall was similar between seeds mixtures. Clover content, and differences between sward types, declined with time and was lowered by continuous grazing in both experiments and by the higher stocking rate in the first experiment. Animal performance was related to intake and both were increased by lowering stocking rate, increasing clover content and adopting a continuous grazing system. The results are discussed in relation to the experimental methods used and to other published findings.     

Effect of cultivar and seed rate of perennial ryegrass and strategic fertilizer nitrogen on the productivity of grass/white clover swards

Four cultivars of perennial ryegrass (intermediate diploid cv. Talbot and tetraploid cv. Barlatra, and late diploid cv. Parcour and tetraploid cv. Petra) were each sown at 10,20 and 30 kg ha^-1, all with 3 kg ha^-1 of white clover cv. Donna. Herbage productivity was measured over 3 harvest years, 1982–84. under two annual rates of fertilizer N (0 and 150 kg ha^-1); the 150 kg ha^-1 rate was split equally between March and August applications. Fertilizer N increased total herbage DM production; the 3-year means for the 0 and 150 kg ha^-1 N rates were 8·04 and 8·91 t ha^-1, respectively. In successive years, total herbage responses to N (kg DM (kg N applied)^-1) were 6·6, 35 and 72 (overall mean, 58). Mean white clover DM production over the 3 years was reduced from 4·48 t ha^-1 at nil N to 2·82 t ha^-1 at the 150 kg ha^-1 rate, a fall of 37%. Grass seed rate did not influence total herbage production or white clover performance. The two intermediate perennial ryegrass cultivars had a marginal advantage in total herbage production over the two late cultivars, but white clover content and production were higher with tetraploids than diploids. It is concluded that the value of increased herbage production from strategic use of fertilizer N has to be weighed against its depressive effect on white clover performance; application of 75 kg ha ha^-1 N in both spring and autumn was excessively high if maintenance of a good white clover content in the sward is an objective. There is considerable flexibility in the grass: clover seed ratio in seeds mixtures. Modern highly-productive perennial ryegrass varieties do not differ substantially in compatibility with white clover but tetraploids permit better clover performance than diploids.     

Changes in contribution of white clover to canopy structure in perennial ryegrass/white clover swards in response to N fertilizer

Twelve plots were laid down on an existing perennial ryegrass/white clover sward, one plot in each of six replicated blocks receiving 100 kg  N ha⁻¹ (100N) and one plot receiving no N (0N). Biomass, canopy development (stratified cuts and point quadrat records at 2–4-week intervals) and changes in stolon population density were recorded during one 8-week regrowth period (25 July–23 September) to investigate the likely causes of N effects on white clover in mixed swards.
Over the period, N fertilizer resulted in an increase of 74% in perennial ryegrass biomass and a reduction of 24% in white clover biomass. There was also a reduction of 44% in stolon growing point density, mainly due to lower density of younger stolon branches. White clover's contribution to the upper three leaf area index (LAI) units (taken as an estimate of the proportion of photosynthetically active radiation (PAR) intercepted) was, on average, 70% at 0N producing 74% of the sward biomass, compared with 46% contribution to interception and 37% contribution to biomass at 100N.
While there was no evidence of overtopping, it is concluded that N fertilizer application increased the LAI of perennial ryegrass in the upper layers of the canopy thereby reducing the share of available PAR to white clover. This, coupled with a lower radiation use efficiency at high N and lower population density, results in white clover's reduced performance in mixed swards receiving N fertilizer.     

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.     

The effect of some invertebrate species on persistence of white clover in ryegrass swards

In two experiments in established swards of perennial ryegrass and white clover, plots were treated with pesticides to control slugs, leather-jackets, weevil larvae and lucerne flea as selectively as possible. Other plots were treated to control ail of these pests.
Chlorpyrifos application in early summer (to control weevil larvae) and methiocarb pellets (to control slugs) also gave partial control of leather-jackets. Other effects on non-target species were considered to be unimportant, as pest status could not be attributed to the species. A high level of control of lucerne flea by methiocarb pellets, noted previously, was confirmed.
At both sites combined treatment against insect pests and slugs produced large increases in clover content and yield over a 3-year period, in comparison with untreated plots, although clover tended to decline In alt plots. At one site, where the clover content of untreated plots reached 33% at one stage, specialist clover herbivores such as weevils and lucerne flea were more common. Treatments directed against weevils and slugs gave the highest clover yields, and leatherjacket control may also have contributed, particularly when the population reached 0.9 m ha⁻¹ in the final year. At the other site, where the clover content was low (ultimately 01.1–6%), leather-jacket populations reached 2.1 m ha⁻¹ and slug numbers were also relatively high. Control of these species contributed most to the relative increase in clover content and yield.     

Short-term effects of nitrogen on the growth and nitrogen nutrition of small swards of white clover and perennial ryegrass in spring

Small swards of white clover and perennial ryegrass were established in Perlite in a heated glasshouse, as either monocultures or mixtures of equal plant numbers. On 26th March, 1984 the swards were moved outside and their growth studied over the period to 29th May. All swards received a basal level of nitrate N to simulate soil mineralization and two-thirds received additionally the equivalent of 80 kg N ha⁻¹. Over the experimental period (26th March-29th May) clover maintained its proportion of total mixture dry weight In swards given 'fertilizer'-N and increased its proportion in those given only 'basal' N, However, clover declined as a percentage of total mixture dry weight during the first period of the experiment when total leaf area index (LAI) and ambient temperatures were low, and increased its percentage later when temperature and LAI had risen. Changes in tiller and stolon growing point numbers were not good indicators of changes in dry weight. Relative yields and relative replacement rates also were not good indicators of relative performance in mixture. Where 'fertilizer'-N was applied, clover derived less of its nitrogen from that source than grass although their uptakes per unit shoot dry weight were similar.     

Liveweight gains of lambs from Caucasian clover/ryegrass and white clover/ryegrass swards on soils of high and low fertility

The high nutritive value and persistence under a wide range of climatic and soil fertility conditions make Caucasian clover a potentially useful forage legume but there is little information about the performance of livestock grazing Caucasian clover/grass swards. This study compared liveweight gains of lambs grazing Caucasian clover/perennial ryegrass and white clover/perennial ryegrass swards on high fertility (Olsen P 20 mg L^?1, SO₄‐S 12 mg kg^?1) and low fertility (Olsen P 11 mg L^?1, SO₄‐S 7 mg kg^?1) soils from 1998 to 2001 in the South Island of New Zealand. Mean annual liveweight gains were 1178 kg ha^?1 for Caucasian clover/perennial ryegrass and 1069 kg ha^?1 for white clover/perennial ryegrass swards at high fertility compared with 1094 kg ha^?1 and 1015 kg ha^?1, respectively, at low fertility. There was a higher mean proportion of clover in Caucasian clover/perennial ryegrass (0·19) than white clover/perennial ryegrass (0·11) swards, but there were no differences in total herbage production between the two clover/perennial ryegrass swards. The mean concentration of crude protein in the herbage of Caucasian clover (302 g kg DM^?1) was higher than that in white clover (287 g kg DM^?1) and grass herbage (227 g kg DM^?1). Estimated mean metabolizable energy concentrations in the herbage were 12·5 MJ kg DM^?1 for the two clovers and 11·6 MJ kg DM^?1 for grass herbage. The difference in liveweight gain between swards on soils of high and low fertility was associated with an increase in total herbage production of similar composition and nutritive value, giving a greater number of grazing days for the swards on soils of high than low fertility.     

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

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

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

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

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

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

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.     

Effect of fertilizer nitrogen on six-year-old red clover/perennial grass swards

Three diploid red clover cultivars—Sabtoron, Violetta and Essex—and three tetraploid, Hungaropoly, Teroba and Red Head, were sown separately in pure culture and with each of three companion grasses: timothy (Aberystwyth S48), tall fescue (Aberystwyth S170) and perennial ryegrass (Aberystwyth S24).
The effects of fertilizer N on yield and on clover/grass ratio over a 2-year period (seventh and eighth harvest years) subsequent to 6 harvest years during which no N fertilizer was applied were investigated. The data for productivity and persistence have already been published (McBratney, 1981; 1984).
Application of fertilizer N increased DM yields in the eighth year. In this year, the highest yield, 11·9t ha^-1, averaged over the six clover cultivars, was given in association with tall fescue. Tall fescue contributed 90% of this yield. Clover content continued to decrease in all swards but the decrease was greatest in the swards receiving fertilizer N. The yield of clover DM averaged over the six cultivars under N treatment declined from 5·6t ha^-1 in the seventh year to only 0·4t ha^-1 in the eighth year.
The results from this trial demonstrate the potential of red clover sown either pure or in mixture with a suitable perennial grass, to maintain high output of quality herbage over a 6-year period without the aid of fertilizer N. They further demonstrate that following decline in red clover content, both herbage yield and quality may be restored by the application of N fertilizer, particularly where the clover was seeded with a highly productive companion grass.     

Herbage and nitrogen yields,fixation and transfer by white clover to companion grasses in grazed swards under different rates of nitrogen fertilization

In grass–legume swards, biologically fixed nitrogen (N) from the legume can support the N requirements of the grass, but legume N fixation is suppressed by additional fertilizer N application. This study sought to identify a fertilizer N application rate that maximizes herbage and N yields, N fixation and apparent N transfer from white clover to companion grasses under intensive grazing at a site with high soil‐N status. During a 3‐year period (2011–2013), swards of perennial ryegrass and of perennial ryegrass–white clover, receiving up to 240 kg N ha^?1 year^?1, were compared using isotope dilution and N‐difference methods. The presence of white clover increased herbage and N yields by 12–44% and 26–72%, respectively. Applications of N fertilizer reduced sward white clover content, but the effect was less at below 120 kg N ha^?1. The proportion of N derived from the atmospheric N fixation was 25–70%. Nitrogen fixation ranged from 25 to 142 kg N ha^?1 measured using the isotope dilution method in 2012 and from 52 to 291 kg N ha^?1 using the N‐difference method across all years. Fertilizer N application reduced the percentage and yield of fixed N. Transfer of N from white clover to grass was not confirmed, but there was an increased N content in grass and soil‐N levels. Under intensive grazing, the maximum applied N rate that optimized herbage and N yields with minimal effect on white clover content and fixation rates was 60–120 kg N ha^?1.     

A comparison of the output from permanent swards containing clover or receiving nitrogen fertilizer when continuously grazed by ewes and lambs

A 2-year experiment was designed to compare the output from a permanent grass sward, either containing clover (GC) or receiving 200kg N ha^-1 (GN), when continuously grazed by sheep stocked at 12 and 15 ewes ha^-1 on GC and 15 and 18 ewes ha^-1 on GN. Sward surface height (SSH) was controlled within designated guidelines by adjusting the size of the grazing area with an electrified ‘buffer’ fence; the herbage surplus to grazing requirement was cut and conserved. A dried grass supplement was offered to the sheep during periods of low herbage availability. The experiment was carried out during 1989 and 1990. No silage was made on GC15 in either year compared with 28 and 90kg DM ewe-¹ on GN15 in 1989 and 1990 respectively; supplementation was consistently and significantly greater on GC15 than on GN15. Clover proportion was generally higher on GC12 than GC15 (significant (P <0·01) in September 1989) and reached a maximum level of 14%on GC12 in August 1990. Herbage organic matter digestibility was little affected by the inclusion of clover in the sward. Differences in lamb growth rate were not significant and, at the common stocking rate, there was no difference in lamb output between GC and GN. In 1990, GC12 and GN15 treatments proved to be successful after weaning in balancing the increasing nutritional requirements of the ewes during the period prior to mating, the requirements of a declining lamb population as the lambs satisfied the criteria for slaughter and were sold, and a continuing need to conserve surplus herbage. The metabolizable energy requirements of the ewes and lambs over 2 years were 75·8 and 74· 7 GJ ha-¹ for GC15 and GN15 respectively, and the differences in total utilized metabolizable energy output of the two systems were due to the amounts of herbage conserved and supplement consumed. The 2-year mean total UME output on GC15 was 80% of that on GN 15 (67·8 and 84·4 GJ ha^-1 for GC15 and GN15 respectively) and the experiment provided further evidence that grass/white clover swards with no fertilizer N applied are capable of producing about 80% of the total output of grass swards receiving 200 kg N ha^-1.     

Influence of irradiance on branch growth of white clover stolons in rejected areas within grazed swards

Development of white clover stolons ( Trifolium repens ) was compared when grown in rejected areas and in adjacent defoliated areas over 28 days in May - June in continuously stocked grass/white clover swards. In the cut areas more branches were borne on stolons with more but shorter internodes and shorter petioles than in the rejected areas. Red (R)/far red (FR) ratio at the base of the cut sward was significantly higher than in the rejected sward.
Five experiments were carried out in which red light-emitting diodes (LEDs) supplied supplementary irradiation at the node of the youngest fully expanded leaf on white clover stolons growing in association with dense canopies of perennial ryegrass. Axillary bud/branch length was the only significantly affected aspect of development that was measured, irradiation enrichment increasing length by about three-fold over a 2–4 week period. One of the experiments involved identification of the site of perception of the R/FR effect. Natural and supplementary light were excluded from the stolon (by covering with a 2-cm layer of black beads), petiole (by wrapping in aluminium foil), both or neither and showed that exposure of the stolon/ petiole base to supplementary light was necessary to stimulate axillary bud growth.
It is concluded that the relative content of red light, and possibly absolute level, in irradiance at the base of the canopy in rejected areas is implicated in the young branch growth and that release of the buds can be achieved by defoliation, presumably due to increasing the red light content; however, the effect of increased photosynthetically active radiation (PAR) reaching stolons and young leaves cannot be discounted as an additional factor.