Effects of interval between harvests and application of fertilizer N in spring on the growth of perennial ryegrass in a grass/white clover sward

A perennial ryegrass/white clover sward, which had been grazed for over 2 years, was cut at 1-, 2-, 3- or 6-week intervals from 18 April to 28 November 1986. Two rates of fertilizer N application in spring, 0 and 66 kg N ha⁻¹, were compared. Perennial ryegrass growth was studied in three 6-week periods, beginning on 18 April, 18 July and 17 October. Clover growth was studied in the same three periods and described by Fisher and Wilman (1995) Grass and Forage Science , 50 , 162–171.
Applied N increased the number of ryegrass tillers m⁻², the rate of leaf extension and the weight of new leaf produced tiller⁻¹ and m⁻²per week. Increasing the interval between cuts reduced the number of ryegrass tillers m⁻² and increased the rate of leaf extension, weight tiller⁻¹and the weight of new leaf produced tiller⁻¹week⁻¹. Increasing the interval between cuts increased the weight of new ryegrass leaf produced m⁻² where N had recently been applied, but otherwise had little effect on the weight of new leaf produced m⁻². Applying N favoured the grass in competition with the clover in every respect, whereas increasing the interval between cuts only favoured the grass, compared with clover, where N had recently been applied; where N had not been applied, the ratio of ryegrass tillers to clover growing points in the sward was very little affected by the interval between cuts.     

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.     

Seasonal changes in the crude protein concentration of mixed swards of white clover/perennial ryegrass grown without fertilizer N in an organic farming system in the United Kingdom

Changes in the crude protein (CP) concentration of white clover and perennial ryegrass herbage from a mixed sward were determined on six sampling dates from May to October in each of 2 years. The swards were grown without fertilizer N in an organic farming system and continuously grazed by dairy cows during the grazing season. The annual mean contents of white clover in the dry matter (DM) of the sward were 272·3 and 307·0 g kg⁻¹ in Years 1 and 2. The mean CP concentrations of the white clover and perennial ryegrass herbage were 251·6 and 151·9 g kg⁻¹ DM in Year 1 and 271·9 and 174·0 g kg⁻¹ DM in Year 2 respectively. The CP concentration of the white clover increased significantly during the grazing season from 220·0 to 284·1 g kg⁻¹ DM in Year 1 and from 269·0 to 315·5 g kg⁻¹ DM in Year 2. In the perennial ryegrass herbage the CP concentration increased from 112·2 to 172·6 g kg⁻¹ DM in Year 1 and from 142·7 to 239·5 g kg⁻¹ DM in Year 2. The rate of increase during the season in the CP concentration of the perennial ryegrass herbage was similar to the rate of increase recorded in the white clover herbage.     

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.     

Effects of application of nitrogen fertilizer on concentrations of P, K, S, Ca, Mg, Na, Cl, Mn, Fe, Cu and Zn in perennial ryegrass/white clover pastures in south-western Victoria, Australia

Effects of timing and rate of N fertilizer application on concentrations of P, K, S, Ca, Mg, Na, Cl, Mn, Fe, Cu and Zn in herbage from perennial ryegrass/white clover pastures were studied at two sites in south-western Victoria, Australia. Nitrogen fertilizer (0, 15, 25, 30, 45 and 60 kg ha^–1) was applied as urea in mid-April, early May, mid-May, early June and mid-June 1996 to pastures grazed by dairy cows. At Site 1, N fertilizer resulted in a linear increase in P, K, S, Mg and Cl concentrations in herbage and a linear decrease in Ca concentration. For all times of application, concentrations of P, K, Ca, Mg and Cl in herbage increased by 0·0048, 0·08, −0·010, 0·0013 and 0·053 g kg^–1 dry matter (DM) per kg N applied respectively. For S concentration, maximum responses occurred in mid-May (0·012 g kg^–1 DM per kg N applied). At Site 2, N fertilizer resulted in a linear increase in P, S and Na concentrations in herbage, a linear decrease in Ca concentration and a curvilinear increase in K and Cl concentration. The maximum responses for P, S and K concentrations in herbage occurred for the N application in mid-June and were 0·015, 0·008 and 0·47 g kg^–1 DM per kg N applied respectively. For Cl concentration, the maximum response occurred for the N application in early June and was 0·225 g kg^–1 DM per kg N applied. Overall, applications of N fertilizer up to 60 kg ha^–1 did not alter herbage mineral concentration to levels that might affect pasture growth or animal health.     

Some effects of added phosphorus on perennial ryegrass—white clover swards

The effect of applying 100kg P ha^-1 per year in the form of triple superphosphate to mixed swards of perennial ryegrass ( Lolium perenne ) and white clover ( Trifolium repens ) was examined on a soil of low P status.
The dry matter yield of total herbage was increased by 10'/i by added P. In the year of sowing the ryegrass benefited more than the clover from added P: in the subsequent four years the two species benefited equally. Both species responded 10 added P to a similar extent in terms of leaf size; the clover responded less well than the ryegrass in terms of rate of leaf emergence. However, clover responded positively to added P in terms of stolon internode length, length of stolon per m² and number of growing points per m². It is suggested that the application of P may promote the spread of white clover within an open sward, but that its application may not enhance the competitive power of white clover when growing with vigorous grasses.     

The effect of strategic fertilizer nitrogen and date of primary harvest on the productivity of a perennial ryegrass/white clover sward

Four management systems involving different dates for first harvest (simulated grazing, early silage, late silage and hay) and two fertilizer N rates in spring (0 and 80 kg ha^-1) were imposed on a perennial ryegrass cv. Talbot/white clover cv. Blanca sward during 1981-82. In each year, annual total herbage DM was increased by spring application of N but white clover production and content in the total herbage were reduced; however, white clover, which was depressed in the harvests immediately after N application, recovered during the season to amounts and contents in the total herbage similar to those given no spring N.
Annual total herbage DM production increased as the date of primary harvest was delayed (935 to 1197 t ha^-1 over two years) but mean organic matter digestibility values for the same period decreased (0-769 to 0700). First-harvest production made up substantial proportions of the annual production in the conservation systems. White clover, as shown by its production and the amount of stolon present, was tolerant of conservation systems, especially with no applied N.
It is concluded that grass/white clover swards are suitable for management systems which involve cutting for conservation. The use of strategic spring N seems a viable option, but more knowledge of rates would be valuable since this experiment only compared 80 kg ha^-1 with no applied N.     

Response to late season nitrogen of upland swards in Wales

During 1984 and 1985, trials at sixteen sites throughout Wales measured the yield response in upland swards from applying 40 and 80 kg N ha⁻¹ at three dates, 20 August, 4 September and 18 September. All sites were between 230 m and 345 m above sea level. Grass yields were measured by cutting plots during October and November.
Nitrogen increased the herbage dry-matter (DM) yield at all sites in both years. The yield response per kg N applied varied between sites. Mean yield response for the two years declined from 16·2 kg DM kg N⁻¹ with 40 kg N ha⁻¹ applied on 20 August to 8·9 kg DM kg N⁻¹ with 80 kg N ha⁻¹ applied on 18 September. In general there was a decline in response to N with increased rate and delay in time of application. The results indicate that responses above an optimum of 9 kg DM kg N⁻¹ can be obtained well into September. A general rule that 1 kg N can be economically applied per 4 summed day degrees air temperature >6 °C remaining in the autumn up to 30 November is suggested.
Delay in application and increasing N rate increased crude protein in the herbage but had only small effects on modified acid detergent (MAD) fibre and sugar. Generally, grass quality was good. Sward density assessed during the spring after nitrogen had been applied appeared to have been unaffected by the treatments.     

Dry-matter yield and herbage quality of a perennial ryegrass/white clover sward in a rotational grazing and cutting system

The expected reduction in the use of fertilizer nitrogen (N) on grassland in the Netherlands has led to renewed interest in white clover. Therefore, the performance of a newly sown perennial ryegrass/white clover sward on clay soil was assessed during 4 consecutive years. The experiment consisted of all combinations of two defoliation systems, i.e. one or two silage cuts per year (S1, S2), spring N application rate, i.e. 0 or 50 kg ha⁻¹ year⁻¹ (N₀, N₅₀), and the management system, i.e. rotational grazing and cutting, or cutting only (RGC, CO). The overall mean white clover cover was 30%. All treatments affected white clover cover, which was 8% higher with S2 than with S1, 6% higher with N₀ than with N₅₀ and 12% higher with CO than with RGC. The overall mean annual dry-matter (DM) yield (13·1 t ha⁻¹ year⁻¹) was significantly affected only by the management system: in two relatively wetter years, the annual DM yield was 1·19 t ha⁻¹ higher with RGC than with CO, whereas there was no difference in two relatively drier years. Nitrogen application increased the DM yield in the first cut by 7·0 kg kg⁻¹ N applied, but had no significant effect on the annual DM yield. Herbage quality was not affected by the experimental treatments. The average in vitro organic matter digestibility was 0.801, and the average crude protein content was 193 g kg⁻¹ DM. With the expected reduction in the use of fertilizer N, perennial ryegrass/white clover swards should be seriously considered as an alternative option to perennial ryegrass swards on these clay soils.     

Herbage production and nitrogen recovery from slurry injection and fertilizer nitrogen application

An experiment was carried out during 1986 and 1987 to examine the effects of mid-season slurry injection and fertilizer-nitrogen (N) application on herbage dry matter (DM) yield and N recovery. Cattle and pig slurry were injected at 56 and 112 m³ ha⁻¹ into an established sward. Five rates of fertilizer-N, as calcium ammonium nitrate, ranging from 0 to 120 kg ha⁻¹ in 30-kg increments, were superimposed on these treatments, and in both years DM yield was measured in one cut after 70 d regrowth. Slurry treatments increased herbage DM yields significantly ( P < 0-001). The efficiency of slurry total N compared with calcium ammonium nitrate-N averaged 53% in 1986 and 86% in 1987. The mean apparent recovery of slurry total N in herbage was 55% in 1986 and 40% in 1987. Fertilizer-N application increased ( P < 0.001) the mean yields of herbage in both years but when combined with some of the slurry treatments, DM yields over the five N-levels did not differ significantly, giving rise to interactions in 1986 ( P < 0-001) and 1987 ( P < 001). It is concluded that mid-season injection of slurry can be an effective means of utilizing slurry-N in terms of herbage DM production and consequent N use.     

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.     

Silage and milk production: studies with diets containing white clover silage

In three separate feeding experiments using a total of twenty-six individually-housed Ayrshire cows, three wilted silages made from Blanca white clover were offered ad libitum with either different supplements or different proportions of grass silage. The clover silages contained 680 g white clover kg⁻¹ on a DM basis, and had a mean DM concentration of 263 g kg⁻¹ with 231 g CP kg⁻¹ DM and 91 g ammonia-N kg⁻¹ N. The pH values averaged 4·16 and the DOMD concentrations 611 g kg⁻¹. In experiment 1 the daily intake of clover silage given alone was 15.2 kg DM per cow, i.e. 30·1 g kg⁻¹ live weight, and decreased by 0·76 kg DM kg⁻¹ barley DM and by 0·66 kg DM kg⁻¹barley plus soybean meal DM when these feeds were offered as supplements. Milk yield and fat concentration were higher on the supplement treatments than on the clover silage-only treatment. In experiments 2 and 3 the intakes of silage and total DM increased as the weight of clover in the diet increased from 0 to 700 g kg⁻¹ with parallel increases in milk yield. The effects on milk composition were small and generally non-significant. Although white clover silages with excellent fermentations were made, it is concluded that the main role of white clover in a silage system will be in mixed swards with grass to reduce the input of fertilizer N and to increase the voluntary intake of silage.     

Cattle slurry as a source of nutrients for red clover: herbage production and clover contribution

An established sward of red clover cv. Hungaropoly sown pure received approx. 30 kg P ha^-1 and 200 kg K ha^-1 each year for 3 successive years. The P and K were applied either as cattle slurry, inorganic fertilizer or combinations of these. Treatments were applied either in spring or after the first harvest. There were a total of six treatments and these were harvested three times each year. The average yields of total herbage DM over all the treatments in the first, second and third years were 15·2, 14·2 and 14·2 t ha^-1 respectively and the various treatments had no significant effect on the overall yields.
Treatments had a significnt effect on red clover DM yields and percentage red clover in one harvest in each of the first 2 years and all three in the third year. Yields of red clover were lower and grass higher in treatments receiving cattle slurry only. On this treatment there was a total yield of 23·2 t ha^-1 red clover DM in the 3 years compared with 30·2 t ha^-1 on the inorganic fertilizer treatments. However, by applying P and K fertilizer in the spring, followed by cattle slurry after the first harvest, it was possible to maintain a high proportion of red clover in the sward and to produce yields of red clover DM similar to those on the inorganic fertilizer treatments.     

The productivity of four forage legumes sown alone and with each of five companion grasses

Four legumes—white clover cv. Blanca, red clover cvs Violetta (diploid) and Hungaropoly (tetraploid) and lucerne cv. Europe—were established as pure-sown swards and with each of five companion grasses: timothy cv. Timo, meadow fescue cv. Bundy, sweet brome cv. Deborah and perennial ryegrass cvs Talbot (diploid) and Barlatra (tetraploid), both ryegrasses being of 'intermediate' heading date. Two 'silage' crops and an 'aftermath grazing' crop were harvested in each of three successive years.
In the first harvest year, total herbage DM production of red clover ranged from 15·03 to 17·01 t ha^-1. White clover and lucerne swards produced considerably less at 7·12 to 11·01 t ha^-1. In the second harvest year, lucerne swards were the highest producing at 15·54 to 17·14 t ha^-1, while DM production from red clover and white clover swards ranged from 6·75 to 11·87 t ha^-1. Lucerne swards maintained their production superiority in the third year at 16·48 to 17·87 t ha^-1, while production from white clover swards ranged from 6·41 to 10·23 t ha^-1. However, red clover swards declined to 3·30 to 5·81 t ha ^-1; this above-average decline was mainly caused by the onset of red clover necrotic mosaic virus which affected all red clover plots uniformly in the second harvest year, and by winter conditions before the third harvest year. Total herbage DOM and CP yields of the swards were influenced in a similar manner to DM production.     

Forage availability from a temperate pasture managed with intensive rotational grazing

Successful integration of rotational grazing into livestock production systems requires estimates of pasture growth rates for feed budgeting of daily animal intake. By matching livestock nutrient demand with forage availability, over-feeding of supplements can be minimized, which reduces feed costs and the need lo manage surplus nutrients, A three-year grazing study was carried out on a Kentucky bluegrass ( Poa pratensis L.)-dominant pasture to estimate the daily quantity of herbage available to cattle in an intensive, rotational grazing system. Herbage production, species composition, and forage quality were determined in each of the six grazing cycles in a year, from April until September. The average length of a grazing cycle was 28·6 d, with 2·7 d for duration of grazing on a paddock. Pre-grazing and post-grazing sward heights, measured with a plate meter, were 14 and 7 cm, and the corresponding herbage masses were 1955 and 775 kg DM ha⁻¹ respectively. Under adequate soil moisture during 1989, herbage available for daily intake was 53 kg ha⁻¹ from April until mid- August, declining to approximately 32 kg ha⁻¹ d⁻¹ by the end of September. Distribution of this herbage was fairly uniform until the end of August. However, a dry summer in 1991 reduced herbage availability to 15 kg ha⁻¹ d⁻¹. Bluegrass and white clover ( Trifolium repens L.) formed 70% of the herbage yield during the period April–June. Later in the season, dead matter and other species increased, reducing the contribution of bluegrass and clover to approximately 60% of total dry matter. While these pastures have the potential to provide significant amounts of forage for 5–6 months in a year, additional on-farm forage reserves are needed during periods of water stress.     

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.     

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.     

Assessment of contrasting perennial ryegrasses, with and without white clover, under continuous sheep stocking in the uplands. 5. Herbage production, quality and intake in years 4–6

Herbage characteristics were studied over years 4–6 (1988–90) in three perennial ryegrass ( Lolium perenne L.) varieties as grass-only (200 kg N ha^-1) and grass/clover ( Trifolium repens L.) swards which received 75kg N ha^-1 in 1988 and 0kg N ha^-1 in 1989 and 1990 when continuously stocked with sheep. Mean total annual herbage production of Aurora, a very early flowering variety, was 11% more than that of late-flowering Aberystwyth S23 due to 21% higher growth as grass/clover pasture. The grass/clover sward of Meltra, a tetraploid late-flowering variety, out-yielded S23/clover by 17%. Herbage production of grass/clover was 86% of that of grass only in 1988 but only 54% of the grass-only swards averaged for 1989 and 1990.
In vitro organic matter digestibility (OMD) of Meltra was 38g kg^-1 OM and 27g kg^-1 OM higher than that of S23 and Aurora respectively. OMD of grass/clover was 15g kg^-1 OM higher than that of grass only during the post-weaning period. Herbage intake was positively correlated with OMD of herbage.
The herbage attributes were related to lamb performance reported previously. Lamb output was positively correlated with intake of digestible organic matter.
Differences between the three varieties in herbage characteristics were greater as grass/clover than as grass-only swards, reflecting their compatibility with white clover. In this respect Meltra was the best and S23 the poorest variety.     

The utilization of N fertilizer, applied to perennial ryegrass/white clover pasture growing on a humus iron podzol in N.E. Scotland

Applications of N fertilizer (0.40, 80, 120 and 240 kg N ha⁻¹ year⁻¹ in dressings of 40 or 80 kg N ha⁻¹) were made to a perennial ryegrass/white clover ( Lolium perenne L. Trifolium repens L.) pasture growing on a humus iron podzol reclaimed from heather ( Calluna vulgaris L.) moor in 1982 and 1983. Where no N was applied, estimates of Ni fixation and mineralization were almost equal, being approximately 50 kg N ha⁻¹ year⁻¹ from each source. Apparent efficiencies of fertilizer use were generally low; for each dressing they ranged between –0·7 and 25·5 kg dry matter (DM)kgN⁻¹. Also, responses to N fertilizer were affected by previous dressings. The net N recovery in harvested herbage from application of 120 kg N ha⁻¹ year⁻¹ was 30 kg N ha⁻¹ year⁻¹.     

The effect of height and frequency of mowing on the yield and composition of perennial ryegrass—white clover swards in the autumn to spring period

Ninety-six plots (3 × 2 m) of well-established perennial rye grass/white clover pasture were mown to heights of 2·7 (Low) or 3·96 (High) cm (rising plate meter) at 14-, 28-, 84- or 112-d intervals in autumn-winter. A 7-, 14- and 28-d mowing interval was superimposed in spring on each autumn–winter mowing interval treatment with the low and high mowing heights altered to 2·92 and 4·80 cm, respectively.
With the low cutting height, accumulated herbage DM was more than doubled (1806 ± 79 kg DM ha^-1) compared to a 'high' (754 ± 49 kg DM ha^-1) cutting height in autumn–winter and this was due to increased harvesting efficiency rather than growth as estimated by leaf extension. Although defoliation interval had no effect on DM yield, the grass component increased and clover decreased. The composition effect carried over into spring. On average, 3·5 tillers were produced over winter for each ryegrass tiller present in autumn and tiller densities were higher in spring. Tillers produced over autumn–winter contributed more than 60% of ryegrass growth by early spring.
In early spring (16–30 September), the low cutting height increased herbage DM yield, in mid-spring (1–14 October) it reduced DM yields particularly in combination with short defoliation intervals, while in late spring (14 October to 11 November) cutting height had no effect on DM yields.
Over the entire spring period there was a very marked effect of defoliation interval on DM yields.