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

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

The implications of controlling grazed sward height for the operation and productivity of upland sheep systems in the UK. 2. Effects of two annual stocking rates in combination with two levels of fertilizer nitrogen

When grazed sward surface height was controlled within the range 3·75-5·25 cm during spring and summer, the effects of two annual stocking rates of twenty (SR20) and twelve (SR12) Cheviot ewes per hectare with their lambs and two rates of nitrogen fertilizer, 100(N100) and 200(N200)kg Nha⁻¹ per year on animal performance and yield of silage from areas of pasture surplus to grazing requirements were measured. Decision rules for management of sward height resulted in good control of swards and consistent and satisfactory individual animal performance across treatments. Total output of lamb was greater for SR20 than for SR12 (699 vs 424kg live weight ha⁻¹; P < 0·001). Yield of silage was less for SR20 than for SR12 [27 vs 184 kg dry matter (DM) per ewe; P < 0·001] and less for N100 than for N200 (65 VS 146 kg DM per ewe; P < 0·01). Around the mating period, when sward height fell below 3·5cm, supplementary feed was offered. More concentrates were offered to the SR20 than to the SR12 ewes (12·3 vs 1·2kg DM per ewe; P < 0·001) and to the N100 than to the N200 ewes (8·3 vs 5·2kg DM per ewe; P < 0·01); trends in the amounts of hay offered during that period were similar.     

The implications of controlling grazed sward height for the operation and productivity of upland sheep systems in the UK: 6. The effect of reducing stocking rate and application of fertilizer nitrogen in Wales

Abstract The implications for the agricultural productivity of the UK upland sheep systems of reducing nitrogen fertilizer application and lowering stocking rates on perennial ryegrass/white clover swards were studied over 4 years at a site in Wales. The system involved grazing ewes and lambs from birth to weaning on swards maintained at a constant height with surplus herbage made into silage, thereafter ewes and weaned lambs grazed on separate areas until the onset of winter with adjustments to the size of the areas grazed and utilizing surplus pasture areas for silage. Four stocking rates [SR 18, 15, 12 and 9 ewes ha^?1 on the total area (grazed and ensiled)] and two levels of annual nitrogen fertilizer application (N 200 and 50 kg ha^?1) were studied in five treatments (N200/SR18, N200/SR15, N50/SR15, N50/SR12 and N50/SR9). Average white clover content was negatively correlated with the level of annual nitrogen fertilizer application. White clover content of the swards was maintained over the duration of the experiment with an increasing proportion of clover in the swards receiving 50 kg N ha^?1. Control of sward height and the contribution from white clover resulted in similar levels of lamb liveweight gain from birth to weaning in all treatments but fewer lambs reached the slaughter live weight by September at the higher stocking rates and with the lower level of fertilizer application. Three of the five treatments provided adequate winter fodder as silage (N200/SR15, N50/SR12 and N50/SR9). Because of the failure to make adequate winter fodder and the failure of white clover to fully compensate for reduction in nitrogen fertilizer application, it is concluded that nitrogen fertilizer can only be reduced on upland sheep pastures if accompanied by reduced stocking rates.     

The implications of controlling grazed sward height for the operation and productivity of upland sheep systems in the UK. 4. The effect of seasonal pattern of nitrogen fertilizer application and annual stocking rate

Greyface (Border Leicester × Scottish Blackface) ewes, mated in October, were housed in winter and turned out after lambing in late March to one of four treatments replicated three times on perennial ryegrass (Lolium perenne)-dominated pastures. On three of the treatments the stocking rate was 12·5 ewes plus lambs ha^?1 annum^?1 (SR_12·5), whereas on the fourth it was 15·0 ewes plus lambs ha^?1 annum^?1 (SR_15·0). There were two levels of applied fertilizer nitrogen (N), 152 kg N ha^?1 annum^?1 (N₁₅₂) and 205 kg N ha^?1 annum^?1 (N₂₀₅). Three patterns of nitrogen application were used: predominantly in spring (E), predominantly in autumn (L), and mainly in spring and autumn (E + L). Grazed sward surface height was controlled within the range 3·5–5·5 cm during spring and summer, and supplementary feed was offered when sward height was below 3·5 cm. The effects on animal performance, yield of silage and requirement for supplementary feed were measured over 3 years (1986–88). Management of the sward height within the specified limits resulted in similar levels of individual animal performance for all treatments, but treatment SR_15·0N₂₀₅E + L produced a significantly (P < 0·05) greater output of lamb per hectare. There was no evidence to suggest that, by increasing the amount of N fertilizer applied in the autumn, ewe reproductive performance was increased. Neither the treatment with the lower level of N applied in the spring (SR_12·5N₁₅₂L) nor the high stocking rate treatment (SR_15·0N₂₀₅E + L) was self-sufficient in winter feed (silage) production. SR_15·0N₂₀₅E + L also required more supplementary feed in both the lactation (38·1 kg ewe^?1) and the mating (9·1 kg ewe^?1) periods. SR_12·5N₁₅₂L required the second greatest amount of supplementary feed during lactation (36·1 kg ewe^?1), whereas SR_12·5N₂₀₅E + L required the least supplementary feed over both periods (27·8 kg and 4·8 kg ewe^?1). Taking all treatments together, there were significant (P < 0·05) differences between years in lamb weaning weight (kg), lamb output (kg ha^?1), yield of silage (kg ewe^?1) and supplementary feed required (kg ewe^?1), arising mainly from a lower level of herbage production in one year. Treatment SR_12·5N₁₅₂E generated the highest gross margin per hectare.     

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 implications of controlling grazed sward height for the operation and productivity of upland sheep systems in the UK. 1. Effects of two annual stocking rates in combination with two sward height profiles

The consequences of controlling sward height at two levels, around 5 cm (HS) and around 3·5 cm (LS), during spring and summer by adjusting weekly the proportion of the areas grazed in response to changes in rate of herbage production and utilizing the surplus pasture areas to conserve winter fodder were studied over three complete years for Greyface ewes with their lambs at 15ha⁻¹ (SR15) and 10ha⁻¹ (SR10). The rules used to control grazed sward height resulted in acceptable sward height control in three of four treatments and, by providing supplementary feed when sward height was below target, gave rise to similar levels of individual animal performance. Total output of lamb weaned was greater for the SR15 than for the SR10 flocks (607 vs 477 kg live weight ha⁻¹; P <0·001). Amounts of winter fodder produced were less for the SR15 than for the SR10 flocks [39 vs 213kg dry matter (DM) per ewe; P < 0·001]. Significantly more supplementary feed (10·0 vs 4·4kg DM per ewe; P < 0·01) and hay (13·7 vs 4·0kg DM per ewe; P7lt;0·05) were offered around mating to SR15 flocks than to SR10 flocks. It is concluded that, provided that sward height can be controlled between 3·5 and 5·0cm during the spring and summer and that supplementation is offered when the grazed sward is below 3·5 cm, flock performance will fall within acceptable and predictable limits.     

The effects of sward height and nitrogen fertilizer application on changes in sward composition, white clover growth and the stock carrying capacity of an upland perennial ryegrass/white clover sward grazed by sheep for four years

Perennial ryegrass/white clover pastures grazed by sheep and receiving either no fertilizer N (No) or 120 kg N ha^?1 year^?1 (N₀) were maintained with surface heights of 2·5, 3·5 and 5·0 cm for over four years. The treatments were replicated. The white clover (WC) population was greatest in the N₀treatment, and declined during the study. Between-year variation in WC was negatively related to rainfall and positively related to temperature, WC as a proportion of the total plant population decreased during the summer in the Nl treatment. The perennial ryegrass (PRG) population was greater in the Nl treatment, declined during the study and both within and between years was positively related to temperature. The population density of the unsown grasses was highest in the N-fertilized treatment and in the swards maintained at the lowest heights (these treatments also had the highest stocking rate); it increased during the study, within-years being positively related to temperature and between-years being positively related to rainfall. The WC stolon extension rate was largely unaffected by N fertilizer application and was greatest in the taller swards. Leaf appearance rate was unaffected by N fertilizer application and sward height; it was positively related to temperature and negatively related to rainfall. Branching rate was greater in the N₀ treatment with significant sward height effects confined to a negative relationship with local sward height within treatment plots on one occasion; it was negatively related to rainfall. The ground level red:far red light ratio was negatively related to local sward height. The total live weight of sheep carried in the No treatments was 0·7 of that in the N₁ treatments. Expected photomorphogenic responses by we were confined to stolon extension. It was concluded that on the poorly drained clay-loam soil used in this study the effects of sheep, in interaction with climatic factors, had an overriding effect on clover branching rate and the ultimate species composition.     

The implications of controlling grazed sward height for the operation and productivity of upland sheep systems in the UK. 3. The effect of choice of genotype, level of nitrogen fertilizer and lamb:ewe ratio

Grazed sward surface height was controlled within the range 3·25–4·75 cm during spring and summer in two experiments. In Experiment 1, the effects of stocking two breeds of ewe of similar size but different potential levels of reproductive performance [Brecknock Cheviot (C) and Beulah Speckled Face (B)] at different annual stocking rates of twelve (SR₁₂) and twenty (SR₂₀) per hectare, rates of nitrogen fertilizer of 100 (N₁₀₀) and 200 (N₂₀₀) kg N ha^?1 annum^?1 and different lamb:ewe ratios (C_1·2, B_1·2 and B_1·5) were measured in four treatments (SR₂₀N₂₀₀C_1·2; SR₂₀N₂₀₀B_1·2; SR₂₀N₂₀₀B_1·5; SR₁₂N₁₀₀C_1·2) replicated three times. In each of three years animal performance and yield of silage from areas of pasture surplus to grazing requirements were measured. In Experiment 2, breed B was compared with the Welsh Mule (W) breed, a larger with a higher potential reproductive performance, at two stocking rates, two rates of nitrogen fertilizer and two lamb:ewe ratios set on the basis of results from Experiment 1 (SR₁₈N₂₀₀B_1·5; SR₁₂N₁₀₀B_1·5; SR₁₈N₂₀₀W_1·5; SR₁₈N₂₀₀W_1·7). The treatments were replicated three times. The same terminal sire (Suffolk) was used in both experiments. A primary aim of the experiments was to test the validity of the experimental procedures used for comparing breeds of sheep where nutrition is provided predominately from grazed pastures. In Experiment 1, there was no difference between breeds C and B in the live weights of individual lambs at weaning at the same SR (20), N rate (200) and lamb:ewe ratio (1·2). Breeds C and B produced similar total yields of lamb (633 kg lamb ha^?1± 10·5) and silage (193 kg DM ewe^?1± 37·7), but breed B had a higher level of potential reproductive performance (1·59 vs. 1·37 lambs ewe^?1: P < 0·001). The treatments SR₂₀N₂₀₀B_1·5 and SR₁₂N₁₀₀C_1·2 produced, respectively, greater and lesser yields of lamb (725 vs. 384 kg lamb ha^?1, P < 0·001) and lesser and greater yields of silage (123 vs. 327 kg DM ewe^?1, P < 0·001). In Experiment 2, the live weight of lambs at weaning from breed W were heavier than from breed B (29·1 vs. 26·2 kg lamb^?1, P < 0·01) but there was no significant difference in total yield of lamb weaned between breeds W and B at the same SR (18), N rate (200) and lamb:ewe ratio (1·5) (747 kg lamb ha^?1± 19·2), or in the yield of silage (66 kg DM ewe^?1± 16·4), but breed W had a higher potential reproductive performance (1·85 vs. 1·58 lambs ewe^?1, P < 0·05). The treatments SR₁₈N₂₀₀W_1·7 and SR₁₂N₁₀₀B_1·5 produced, respectively, greater and lesser yields of lamb (840 vs. 473 kg lamb ha^?1, P < 0·001) and similar and greater yields of silage (60 vs. 141 kg DM ewe^?1, P < 0·05). The experimental approach adopted and the management protocols used provided a basis for ranking the performance of the breeds of ewes examined at appropriate levels of annual stocking rate, N-fertilizer input and lamb:ewe ratio.     

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.     

Reproductive tillers in cut tall fescue swards: differences according to sward age and fertilizer nitrogen application, and relationships with the local dynamics of the sward

The effects of sward age and fertilizer‐nitrogen (N) application rate on reproductive tillers and their involvement in the dynamics of swards of perennial grasses were investigated using sown swards of tall fescue (Festuca arundinacea). Treatments included plots representing two sward ages (two and six‐year‐old swards) and two fertilizer‐N rates (150 and 350 kg N ha^?1 yr^?1) on the same experimental field. In each of 2 years all plots were cut at the silage stage and three times afterwards. After each cut, during two growing seasons, the vegetative tillers and stubs of cut reproductive tillers were counted in ten permanent quadrats for each of the four treatments, using a grid of 150 cells, each of 2 cm × 2 cm. The results showed a higher density, and a greater proportion of reproductive tillers, on the higher fertilizer‐N rate treatment and on the older swards. The density of vegetative tillers was found to be greater in close proximity to the reproductive tillers in all sward treatments and in both assessment years. Thus, cutting the reproductive tillers did not result in thinning of the swards. It is suggested that a mother‐tiller effect, enhancing renewal of tillers, was likely, although zones bearing reproductive tillers during the second spring were sometimes already denser than zones in the rest of the quadrats before the winter.     

The effect of strategic use of fertilizer nitrogen in spring and/or autumn on the productivity of a perennial ryegrass/white clover sward

The productivity of a mixed sward, comprising perennial ryegrass cvs Barlano and Bastion and white clover cvs Donna and Aran, was measured under sixteen fertilizer N treatments. These involved 0.25, 50 and 75 kg N ha^-1 in spring only, in autumn only and in all combinations of spring N and autumn N. A simulated grazing regime of six cuts annually at 3- to 6-week intervals was imposed. Increasing rates of total N application increased total herbage DM regardless of application pattern. Yield response was greater with N applied in the spring, and total herbage DM was higher with high spring N-low autumn N than the reverse. Mean yield responses at the first harvest to 25, 50 and 75 kg ha^-1 N in spring were 13.6, 10.8 and 11.6 kg DM per kg N. Corresponding responses at the final harvest to N rates in the autumn were 7.2, 5.8 and 6.8 kg DM per kg N. Responses were similar at these times for treatments receiving combined spring and autumn N. Over all treatments, mean annual production of total herbage was between 7.08 t ha^-1 DM with no N and 8.19 t ha^-1 with 75 kg ha^-1 N in both spring and autumn. Owing to drought, mean production in year 2 fell by 32% compared with year 1. White clover production fell progressively with increasing N application. Treatments with spring-applied N gave the most marked decrease. White clover was more markedly depressed than the associated grass by the drought in the second year. The mean reductions in white clover content were 0.17, 0.07 and 0.12 percentage units per kg applied N for spring N, autumn N and combinations. Autumn N use depressed white clover less than spring N but the yield response of grass was less. It is concluded that any applied N adversely affects white clover performance to some degree. Where management factors are unfavourable to white clover even strategic N use may not be wise. Instead, it is suggested that a ‘dual-sward’ approach be adopted in practice, namely, grass/white clover swards with no N. and complementary grass swards receiving optimum applied N to give better production at times when grass/white clover swards are relatively less productive.