THE EFFECTS OF LEVEL OF NITROGEN FERTILIZER ON BEEF PRODUCTION FROM GRAZED PERENNIAL–RYEGRASS/WHITE–CLOVER PASTURES

The treatments in this summer–grazing experiment were designed as a 2 × 3 factorial, there being two levels of nitrogenous fertilizer (nitro–chalk), supplying 0 and 336kg of N/ha per annum (NO and N3, respectively) and three stocking rates. The fertilizer was applied in 7 dressings at approximately three–weekly intervals. The animals used were Hereford x Friesian steers; these were slaughtered at the end of the grazing season. The stocking rates were calculated on the basis of expected herbage production. The experiment was laid out in 6 randomized blocks which were grazed in rotation. Two blocks were cut for conservation before grazing each year; up to the end of June only 4 blocks were used for grazing.
There was little contamination of the swards with unsown species. With the NO swards the clover contents declined each year, but remained fairly high at over 20% in 1965. Clover contents also declined each year in the N3 swards and by 1965 were only 2 to 4%.
The quantities of herbage cut for conservation were higher from the swards receiving N. The live–weight gains of the cattle (per head) were higher at the lower stocking rates, the effect of stocking rate being more noticeable in the July to Oct. period. Live–weight gains per ha increased at the higher stocking rates. In 1963 and 1965, as stocking rates increased carcass weights per animal decreased and carcass quality, as indicated by the commercial grades, was poorer. In 1964, a dry spell from July to Oct. necessitated the removal of cattle from the experiment and the effects of treatment on carcass weight and quality were not apparent.     

EFFECT OF HIGH FERTILIZER NITROGEN AND STOCKING RATES ON LIVEWEIGHT GAIN PER ANIMAL AND PER HECTARE

The effect of increasing annual fertilizer N application rate from 400 to 800 kg/ha (357 to 714 lb N/ac) and stocking rate from 5.0 to 7.5 animals per forage ha (2.02 to 3.04 animals per forage ac) on herbage availability, digestible OM intake and live weight gain was investigated in a grazing experiment repeated in 3 consecutive years. A 21×1 day rotational paddock grazing system was used in which the grazing area was increased in the ratio of 1:1.5:3 on two predetermined occasions. Increasing the fertilizer N application rate increased herbage availability by 12% but failed to increase live weight gain. Increasing stocking rate decreased herbage availability per ha and per animal, and also live weight gain per animal, but increased live weight gain per forage ha by 17.6%.     

THE EFFECT OF NITROGEN, STOCKING RATE AND GRAZING METHOD ON THE OUTPUT OF PASTURE GRAZED BY BEEF CATTLE

An experiment was conducted in 1971 and 1972 to study the effects of two levels of fertilizer N (50 and 504 kg/ha) on the productivity of pastures grazed by young beef cattle. Two stocking rates were imposed at the lower N level and three at the higher. In addition to rotational grazing, set-stocking and an integrated grazing-conservation system were included. The responses/kg N were approximately 1 kg live-weight gain, 19–24 Meal ME and 8–9 kg DM. Maximum yields of 1200–1300 kg live-weight gain/ha and 25,000–27,000 Meal ME/ha were recorded. Productivity of set-stocked pasture was similar to rotational grazing at the high N level, but lower at low N. The integrated system yielded comparable results to high-N rotational grazing. Performances and herbage intakes per animal reflected the stocking rates imposed.     

A PORTABLE-CORRAL TECHNIQUE FOR MEASURING THE EFFECT OF GRAZING INTENSITY ON YIELD, QUALITY AND INTAKE OF HERBAGE

A grazing experiment using four stocking rates of sheep, equivalent to 34, 45, 57 and 68 sheep/ha on an assumed 200-day grazing season, was conducted using a portable grazing corral technique. Plots were subjected to fotir grazing periods between mid May and early September. The effect of stocking rate on herbage yield and quality and the influence of these factors and feed intake on liveweights of the sheep were recorded. The mean daily herbage organic matter available over the trial was 9.6, 5.8, 3.3 and 23% of the total liveweight of the sheep at each of the four stocking rates. The highest grazing pressure led to the production of high-quality herbage, but also led to reduced productivity, low feed intake and liveweight losses. The most lenient grazing pressure failed to provide adequate herbage utilization. Even at the most intensive stocking pressure, only 66% of the herbage available to ground level was utilized in grazings after July. Intake results suggested that sheep of 45 kg liveweight required 1000–1200 g digestible organic matter per day to maintain body weight. Despite the higher in vitro digestibility of herbage on offer at the higher stocking rates, intake was limited through lack of herbage; a high degree of correlation existed between herbage availability and herbage intake over the four stocking rates and at all grazings. It is concluded that the portable corral technique is well suited for grazing studies and the assessment of sward response to varying stocking rates and is particularly useful where facilities for more extensive studies are limited.     

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.     

Comparison of herbage production under continuous stocking and intermittent grazing

The possibility of increasing the herbage utilized over a grazing season was investigated in a study comparing continuously stocked steady-state swards maintained at optimum height (3.5 cm) with intermittently grazed swards. The intermittent systems were designed (a) to allow periodic increase in leaf area and hence growth rate, (b)to ensure that the accumulated herbage was eaten before it senesced, and (c) lo retain high tiller density by alternating periods of herbage accumulation with periods of continuous stocking. Two treatments (no animals or animal numbers reduced to half those on the 3.5 cm steady-state treatment) were used during the 17-18-d periods of herbage accumulation. Grazing down was completed in 3–4 d, after which two treatments (14 d or 28 d) were used for the intervening periods of continuous stocking when sward height was maintained at 3.5 cm. Herbage production was estimated using the tissue turnover technique, with tiller population densities and rates of growth, senescence and net production per tiller measured at frequent intervals. Intermittent grazing treatments where animals were removed during herbage accumulation resulted in changes in tiller size and number, and in growth rates, but not senescence rates, per tiller such that short-term deviations in the net rate of herbage production occurred compared with the continuously stocked control. The periods of advantage during phases of herbage accumulation were counterbalanced by those of disadvantage during the subsequent steady-state phases. Where animal numbers were reduced during herbage accumulation, sward conditions differed little from those of the continuously stocked control, implying that intake per individual animal was increased. It was concluded that intermittent grazing systems offered no advantage over simpler continuous stocking systems, provided that a flexible approach to conservation was incorporated to allow control of sward conditions on the grazed area.     

A NOTE ON THE LIVEWEIGHT CHANGE OF SHEEP GRAZING AT THREE STOCKING RATES AND TWO LEVELS OF NITROGENOUS FERTILIZER

The liveweight changes of sheep grazing at 3 stocking rates and 2 levels of N fertilizer were recorded. The results are discussed in relation to the model proposed by Owen and Ridgman (1) for short–term periods of grazing.     

The effect of applying cattle slurry using the trailing‐shoe technique on dairy cow and sward performance in a rotational grazing system

The effects of applying cattle slurry using the trailing‐shoe technique on dairy cow and sward performance were examined in two experiments in Northern Ireland. In Experiment 1, forty‐eight cows were allocated to two treatments, with or without slurry application. In Experiment 2, sixty cows were allocated to four treatments, a combination of high and normal grazing stocking rate, with or without slurry application. In Experiment 1, slurry was applied during the first and fourth rotations. In Experiment 2, slurry was applied prior to the first grazing rotation and during the second, fifth and sixth grazing rotations. In Experiments 1 and 2, the total inorganic fertilizer nitrogen (N) inputs applied within the slurry treatments were 200 and 133 kg N ha^?1, with 280 and 285 kg N ha^?1 used within the fertilizer‐only treatments in each experiment respectively. Varying responses of milk yield to slurry application were observed. In Experiment 1, with a normal stocking rate, no effect was observed. In Experiment 2 with two stocking rates, reduced milk yields were observed at both stocking rates. Although not significant, there were indications that this reduction in milk yield when slurry was applied was higher at higher stocking rates.     

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.     

THE EFFECT OF NITROGEN, STOCKING RATE AND FREQUENCY OF GRAZING BY BEEF CATTLE ON THE OUTPUT OF PASTURE

Two successive grazing experiments were conducted over 12 weeks on perennial ryegrass pastures with 50 and 44 young cattle to study the effect of N fertilizer when applied at a daily rate of 1 or 3 kg N/ha. At each level of N two stocking rates differing hy 20% were imposed. At the liigher N level and stocking rate, three frequencies of grazing were imposed. At the stocking rates imposed N tended to reduce the daily liveweight gain per head, but increased the total liveweight gain per ha by from 0.79 to 1.58 kg/kg N. A 20% increase in stocking rate depressed gain per head in both years. In the first year it did not improve gain/ha, hut in the second year gain/ha was increased by 12–17%. There was a tendency for performance per animal and per ha to increase as the grazing cycle was lengthened. In 1969 the highest yield in the whole season was 1880 grazing days and 1260 kg gain/ha. The overall response to N fertilizer was similar to that recorded in other reports, but it is possible that a lack of K had limited pasture growth.     

The use of herbage nitrogen status to optimize herbage composition and intake and to minimize nitrogen excretion: an assessment of grazing management flexibility for dairy cows

A framework for managing rotationally grazed pastures for dairy cattle which enables the cows’ energy and protein requirements to be met while simultaneously limiting the amount of N excreted in order to reduce N losses is described. The first objective is achieved by ensuring that lamina mass and the N concentration of herbage do not limit herbage intake or feeding value. The second objective is achieved by limiting N fertilizer supply or increasing the interval between defoliations to reduce the N concentration of herbage. Lower and upper thresholds for the N concentration of herbage and lamina mass were estimated from published data. The method is illustrated using two vegetative regrowths (beginning and end of spring) in a cutting experiment with two fertilizer treatments, 0 or 120 kg N ha^?1 (?N and +N), and early or late cutting. Decreasing N supply led to a reduction in grazing management flexibility, i.e. the defoliation interval ranges which were compatible with the required sward characteristics (minimum lamina mass and N concentration of lamina) for herbage intake and to meet the protein requirements of dairy cows. Aiming for the upper threshold N concentration of herbage increased the minimum interval between defoliations only for the +N treatments. Nevertheless, grazing management flexibility remained the highest for the +N treatments.     

Manipulation of herbage production by altering the pattern of applying nitrogen fertilizer

The redistribution of herbage production during the growing season to synchronize herbage supply with feed demand by livestock by altering the application pattern of a range of nitrogen (N) fertilizer rates was studied. Application rates of N were 50, 150 and 250 kg N ha^?1 per annum and patterns were with 0·60 of N fertilizer applied before June (treatment RN) and with only 0·20 of N fertilizer before June (treatment IN). Treatments were imposed in a cutting (simulated grazing) experiment (Experiment 1), which was conducted for 2 years and a grazing experiment (Experiment 2) which was conducted for 3 years. In both experiments, herbage production was reduced in April and May and increased in the June–October period on treatment IN relative to RN, but annual herbage production was not significantly affected except in the third year of Experiment 2, when treatment RN had significantly (P < 0·05) higher herbage production than treatment IN. Crude protein (CP) concentration of herbage was lower in April and May on treatment IN than treatment RN. However, CP concentration of herbage was rarely below 150 g kg^?1 DM and so it is unlikely that livestock productivity would be compromised. On treatment IN, concentrations of CP in herbage were higher in the late summer than on treatment RN, which may increase livestock productivity during July and August when livestock productivity is often lower. Altering the strategy of application of N fertilizer did not affect in vitro dry matter digestibility of herbage.     

Effect of different grazing management systems on the herbage mass and pasture height of a Nardus stricta grassland in western Scotland, United Kingdom

The aims of this study were to examine the effect of three grazing treatments (year‐round stocking rates of 0·8 ewes ha^?1, 0·5 ewes ha^?1 and 0·5 ewes ha^?1 plus grazing cattle in summer), imposed for 4 years, on the herbage mass and surface height of a Nardus stricta‐dominated grassland in western Scotland and to obtain estimates of annual productivity of this grassland. Nardus stricta‐dominated grassland comprised proportionately 0·20 of the grazing area. Stocking rate of sheep had no significant effect on the herbage mass of the grassland in the first 2 years of the experiment, although mean summer pasture heights were significantly higher under the lower stocking rate of sheep. The pasture on the treatment with cattle grazing in summer had a significantly lower herbage mass and lower surface height than the two sheep‐only grazing treatments. Year‐to‐year variation in the herbage mass and surface height of herbage in summer was greater than the effect of treatments. Despite changes in surface height, the structural diversity of the grasslands was not increased by the treatments. The annual production of vascular plant material ranged from 417 g DM m^?2 in 1994 to 628 g DM m^?2 in 1996.     

THE EFFECT OF NITROGEN AND STOCKING RATE ON THE OUTPUT OF PASTURE GRAZED BY BEEF CATTLE

An experiment was conducted in two successire years to measure the effect of two levels of fertilizer N, 50 and 300 kg/ha (45 and 270 Ib/ac) on the productivity of pastures grazed by young beef cattle. Two stocking rates were imposed at the lower N level and 4 at the higher level. The responses per kg fertilizer N were approximately 1 kg liveweight gain, 20–24 Meal ME and 8–9 kg DM. Maximal yields of about 1000 kg gain/ha (890 Ib/ac) and 19,000 Meal ME/ha (7700 Mcal ME/acre) were recorded. Animal performance was similar on the low and the high N pastures. There was evidence that the chemical quality of pasture was lower on the low N pasture in the first year, but there was no difference in the second year. The numbers of dung pats per ha and the refusal of herbage due to fouling were reduced by Increasing the stocking rate.     

Effect of nitrogenous fertilizer on production per animal and per unit area by beef cattle offered similar daily allowances of herbage

An experiment repeated in 3 consecutive years in which 0, 200, 400 and 600 kg ha^?1 fertilizer N was applied annually is described. Cattle on all treatments were offered the same constant daily amount of 2.0 kg herbage DM per 100 kg liveweight above a 3.4 cm height of defoliation. Digestible OM intakes and daily rates of gain were in general not significantly different between treatments. Area required to support these intakes and gains however differed significantly between treatments (P < 0.001) and resulted in high outputs of liveweight gain per hectare on all treatments when compared with other published studies. These outputs together with other actual and theoretical outputs were used to predict optimum fertilizer N applications for grazing beef cattle and the predictions discussed in relation to commercial practice.     

Frequency and severity of defoliation of grass and clover by sheep at different stocking rates

The frequency and severity of defoliation of individual grass tillers and clover plant units was studied in Lolium perenne-Trifolium repens swards grazed by sheep at stocking rates ranging from 25 to 55 sheep ha^-1 and either receiving no N fertilizer or 200 kg N ha^-1. On average, sheep at the highest stocking rate defoliated individual tillers once every 4·2 d compared with once every 9·2 d at the lowest stocking rate with the removal of 58% and 47% of the leaf length of each tiller leaf at these stocking rates. Clover plant units were defoliated once every 4·2 d at the highest stocking rate and once every 7·2 d at the lowest stocking rate with the removal of 51% of its leaves and 12% of its stolon at the high stocking rate and 42% and 4% respectively at the low stocking rate. Differences in frequency and severity of defoliation between N fertilizer treatments were smaller than between stocking rates. Grass tillers and clover plant units were both defoliated less frequently and less severely in swards fertilized with N, though the difference in defoliation frequency between fertilizer treatments decreased as stocking rate increased. Defoliation frequency was related to the length of grass leaf per tiller or number of clover leaves per plant unit, and to the number of these tillers and the herbage on offer.     

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 EFFECT OF IRRIGATION AND STOCKING RATE ON THE OUTPUT FROM A SWARD

The dairy-cow results are presented from an experiment in which the response to grass irrigation was measured at two stocking rates. The method and herbage results have already been described (1).
Over two years, with an average application rate of 5·5 in of water per year, the main effect of irrigation was to increase the number of grazing days obtained by 35%. Neither yield per cow nor milk quality was significantly affected by the treatments.
The data emphasize the importance of high stocking rates for the full exploitation of irrigation. The practical implications of the results are discussed; they suggest that in the right circumstances of herd potential and grassland management, irrigation for milk production can be highly profitable.     

INTENSIVE SET-STOCKING OF DAIRY COWS

Farm-scale trials with Ayrshire dairy cows were conducted in South-West Scotland over two seasons to compare set-stocking and paddock grazing at similar stocking rates and N fertilizer rates. At a stocking rate of 1±9–2±0 cows/ac throughout the grazing season and a fertilizer N rate of about 400 units/ac, milk production per head from set-stocked cows was equal to that from paddock-grazed cows. No health problems arose as a result of applying fertilizer to the fields which were set-stocked. These trials hare established that set-stocking is a viable system for the intensive management of dairy cows on grassland in the UK, but further work is necessary to determine whether paddock-grazing has a higher potential for milk production than set-stocking.     

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.