Differences in the nitrogen use efficiency of perennial ryegrass varieties under simulated rotational grazing and their effects on nitrogen recovery and herbage nitrogen content

Eight varieties of perennial ryegrass (six new varieties and two old ones) grown at five levels of applied fertilizer (100, 200, 300, 400 and 500 kg of N ha^–1) were cut monthly during two growing seasons (March to October in 1997 and 1998) and their herbage dry‐matter (DM) yield and nitrogen (N) content were determined. Herbage leaf content and the N content of young fully expanded leaves were also measured in 1997, and monthly recovery of applied N was determined in both the first and second harvest years by using ¹⁵N. The rank order of varieties was similar for annual yield of DM and N at all five fertilizer levels. Proportional differences between varieties in DM yield were greatest in the first cut of each year, the late‐heading candidate variety Ba12151 out‐yielding the old late‐heading variety S23 by more than 70%. However, differences in annual DM yield were much more modest than in early spring yield, up to 10% in 1997 and up to 21% in 1998. The relatively small differences in total annual DM yield were attributed to only a small proportion of the applied N being recovered during a single regrowth period, most of the remainder becoming available for uptake in subsequent regrowth periods. There were small but highly statistically significant differences among varieties in the N content of their leaves, leaf N content being inversely related to yield of DM and N. This lends further support to the hypothesis that the metabolic cost of protein synthesis and turnover is a key factor controlling genetic variation both in leaf yield and in annual DM and N yield under frequent harvesting. Seasonal variation in herbage N content was much greater than differences among varieties in mean N content over all harvests. In May of both years at all applied fertilizer levels, herbage N content fell below the 20 g N kg^–1 DM level required by productive grazing animals.     

Temporal variation in nitrogen concentration of above ground perennial ryegrass applied different nitrogen fertiliser rates

Perennial ryegrass (Lolium perenne L.) was grown for seed in field trials in order to investigate the temporal variation in plant nitrogen (N) concentration during ontogeny. Crops were sown in three successive years and grown with five N fertiliser rates applied in the autumn and in the spring (autumn–spring): 0–0, 0–50, 0–100, 30–120 or 60–140 kg N ha⁻¹. Within each N fertiliser rate, N concentration in the plants increased from the initiation of spring growth and reached a maximum of 4.8% at 450–500 growing degree-days (GDD) after which it decreased to 0.8% at 1150–1200 GDD. This pattern of plant N concentration was consistently low at each N fertiliser rate and between years whereas the variation in plant N concentration within each year was high as a result of the different N fertiliser rates. Nitrogen fertiliser rate up to 150 kg N ha⁻¹ increased the seed yields.During spring growth 89% of the variation in plant N concentration could be explained by a non-linear function of GDD. Maximum variation occurred at 480 GDD, with a 95% confidence interval between 428 GDD and 540 GDD. Plant N concentrations measured at 424 GDD in 1998, 447 GDD in 1997, and 497 GDD in 1996, and the resulting correlation coefficients (r²) between N concentration and seed yield were 0.81, 0.71 and 0.92, respectively.It is concluded that the variation in plant N concentration during ontogeny in perennial ryegrass is related to different N fertiliser rates and that the greatest variation in plant N concentration was in the period from 428 GDD to 540 GDD.     

The influence of vernalization on response to nitrogen of perennial ryegrass

Vernalized and unvernalized perennial ryegrass (Lolium perenne cv. Gremie) tillers planted in microplots in a glasshouse in April 1974 and 1975 were exposed to natural daylength thus inducing vernalized plants to produce reproductive, and unvernalized plants vegetative growth. Nitrogen was applied at 0–30 g m^?2 (to 24 g m^?2 in 1975) to both types of herbage. At the first defoliation in each year yields from vernalized grass were greater than those from unvernalized grass; subsequently differences were minimal or reversed. Vernalization had no significant effect (P > 0.05) on total yields over four defoliations in either year. Apart from the first cut in 1974 nitrogen application increased dry matter yields of both types of herbage. Tiller numbers were usually increased by the lowest level of nitrogen application but at higher levels the effect was variable. There was no evidence of an interaction effect of level of nitrogen application and vernalization on dry matter yields.     

The effect of delayed autumn harvest on the survival of varieties of perennial ryegrass

The reactions of five early and five late varieties of perennial ryegrass to stimulation of bulky autumn growth and deferment of harvesting were compared in terms of spring growth and subsequent recovery during three winters. Winterkill was marked in 1971–72, particularly when harvesting was deferred to late November, in early varieties S24 and Presto Pajbjerg and in the late variety S23. Least affected among early varieties were Premo and Barvestra (tetraploid) and among late varieties, Perma and Barpastra (tetraploid). All varieties showed rapid recovery. The results are discussed in terms of the significance of winterkill, and the effects of age of sward, variety susceptibility and deferment of autumn defoliation. It is concluded that the form of winterkill which occurs in the west of Scotland can have serious consequences to farm productivity in severe winters. Autumn growth left standing into November can also lead to winterkill. Under good management, varietal differences are unimportant. In a severe winter, no varieties of perennial ryegrass are reliable.     

An investigation into the grazing efficiency of perennial ryegrass varieties

The objective of this study was to compare the grazing efficiency of 30 perennial ryegrass varieties, differing in ploidy and heading date. Plots were grazed by lactating dairy cows and managed under a rotational grazing system with 19 grazing events occurring over two years. Pre-grazing and post-grazing compressed sward heights were measured with a rising plate meter. A mixed model was used to predict the post-grazing sward height of each variety based on year, grazing event, block and pre-grazing sward height. Residual grazed height (RGH) was derived as the difference between the actual and predicted post-grazing sward height and was used as the measure of grazing efficiency. Negative RGH values indicated that the actual herbage removed was greater than that predicted and so indicated a superior grazing efficiency. Varieties differed in their level of grazing efficiency (p < .001), with RGH values ranging from −0.38 to +0.34 cm. Tetraploid varieties exhibited significantly greater grazing efficiency performance than diploids (p < .001), with average RGH values of −0.13 and +0.13 cm respectively. A significant difference in grazing efficiency was found among recommended perennial ryegrass varieties that are not being recorded by mechanically harvested simulated grazing protocols. A variety reappraisal that included grazing efficiency could identify varieties capable of improving on-farm livestock productivity from grass.     

Response of perennial ryegrass varieties to annual changes in sward management

The effect of annually switching sward management between cutting regimes that simulated rotational grazing and those for forage conservation vs. maintaining a constant management regime was studied by testing for ranking-order changes between six perennial ryegrass varieties.
Total dry-matter (DM) yields were found to change in response to an annual switch in management. When under a conservation management and switched in the next year to simulated grazing, all six varieties yielded more in that year than when they were maintained constantly under simulated grazing. Similarly, when under a simulated grazing management and switched in the next year to conservation, all six varieties yielded less than when maintained constantly under a conservation management. These yield differences were largely expressed in spring of the year following the management switch.
Differences in the ranking order of varieties were observed between the constant sward management treatments and the alternating managements. However, in these changes in variety ranking, no variety was consistently favoured or disadvartaged by the annual switch in management. Therefore, no clear evidence was produced that an alternating management system had any consistent effect on variety ranking and the observed changes were possibly due to the normal year-to-year variation frequently recorded in variety performance trials.     

The effect of strategic nitrogen application and defoliation systems on the productivity of a perennial ryegrass/white clover sward

The productivity of a mixed sward comprising perennial ryegrass cv. Fantoom and white clover cv. Aran was measured under eight defoliation management systems and two fertilizer N rates (0 and 75 kg ha^-1) applied in spring. The defoliations involved a basic six-harvest simulated grazing system together with the interposition of silage cuts once or twice at varying times during the growing season; evaluation was made over three harvest years, 1983-85. Mean annual production of total herbage DM over the three years was 8.351 tha^-1 without N and 9.49 tha^-1 with 75 kg N ha^-1, a mean response of 15.2 kg DM per kg applied N. The responses for individual treatments occurred mainly at the first cuts, whether for simulated grazing (a mean of 12 9 kg DM) or for silage (a mean of 259 kg DM); however, this influence of spring N was not sustained at other cuts over the season. Mean annual white clover DM production was 4.19 t ha^-1 with no N and 3.32 t ha^-1 with 75 kg ha^-1 N, but the reduction due to N was not significant in any year. The mean amount of clover stolon DM present post harvest over all management systems was 1.33 t ha^-1 with no N and 1.03 t ha^-1 with 75 kg ha^-1 N. Mean annual DM production of total herbage from the six-harvest system was 8.11 t ha^-1 Compared with 8 88 t ha^-1 (a 9% increase) from the systems with one silage cut and 9.241 ha^-1 (a 14% increase) from the systems with two silage cuts. Corresponding white clover DM production was 4.02, 3 87 and 3 53 t ha^-1, respectively, and mean stolon DM amounts post harvest, 1 12,1.15 and 1-23 t ha^-1, respectively. It is concluded that grass/white clover swards are suitable for management systems which involve cutting for conservation. Spring N application did not greatly reduce white clover production in this experiment where white clover was at higher levels than are likely in farming practice and the swards were not grazed. More knowledge of spring N rates, and indeed of N application rates generally, would be advantageous in future assessment of silage cutting systems.     

The effect of cutting frequency and applied nitrogen on production and digestibility of perennial ryegrass

Grass swards were cut at intervals of 2, 3, 4, 5, 6 and 8 weeks and received 336 or 673 kg ha^?1 nitrogen the higher level being applied as a single or as split dressings. Reducing cutting interval from 8 to 2 weeks reduced mean DM yield by 37% from 14·2 to 9·0 t ha^?1 and digestible DM yield by 24% from 9·4 to 7·2 t ha^?1. The response to the extra N at the highest level of application was greatest under the most frequent cutting regimes. Application of N did not affect the digestibility of DM. Results are discussed in relation to the comparative effects of frequency of cutting at different seasons of the year and at different levels of N.     

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.     

Comparative sheep production and herbage characteristics on four perennial ryegrass varieties in the uplands

Ewe and lamb performance, herbage production and feed quality components on four late-flowering perennial ryegrass ( Lolium perenne L.) varieties were assessed under a fixed stocking management at an upland site (305 m OD) in mid-Wales. Averaged over four years (1981–84) there was no significant difference (P>0·05) between Aberystwyth S23, Aberystwyth Ajax, Perma and Meltra (tetraploid) in ewe and iamb liveweight gains. There were, however, considerable differences between varieties during individual years and their relative ranking also changed substantially over the four years. Lamb production on Perma was 22% more than on S23 in the first year but by the fourth year it was 21 % less than on the latter variety.
Differences between varieties were observed in herbage production. Net herbage accumulation was 15% more on Meltra than on Ajax whilst the calculated quantity of OM consumed was 19% higher from Meltra than from both Ajax and S23. Net animal liveweight gains were positively correlated with herbage production (r = 0·95, P < 0·05) and DOM consumed (r=0·96. P<0·05).     

The development of response to fertilizer nitrogen in the first regrowth of perennial ryegrass

The experiment was undertaken to examine the interactions between yield responses to secondary applications of fertilizer N and length of regrowth interval following three levels of primary N. A sward of S24 perennial ryegrass received all combinations of three fertilizer treatments, nil, 50, and 100 kg ha^-1 N for primary growth harvested on 21 May and four treatments, nil, 33, 66 and 100 kg ha^-1 N for the second growth harvested 2, 3, 4, 5, 6 or 7 weeks later.
Cubic equations of growth were derived from the yields of dry matter and both the direct response to secondary N and the residual responses to primary N increased as regrowths developed. A positive residual effect to increasing primary N was obtained at the three lower levels of secondary N for weeks 4–7 but a negative response was obtained with the highest level of secondary N. The implications are discussed in terms of target responses and yields and the growth interval required to attain these targets.     

Soil compaction effects on second-harvest yields of perennial ryegrass for silage

Variation in dry-matter yield at second harvests was studied in a long-term comparison of wheel traffic systems and soil compaction in grassland for silage in Scotland. Yields were obtained from compacted soil subjected to conventional traffic (C), from less compacted soil in a reduced ground-pressure traffic system (R) and from non-compacted soil in a zero-traffic system (Z). Relationships between the ratios of second-harvest yields, C₂/Z₂ and C₂/R₂, and a number of soil, rainfall and crop parameters were tested by correlation analysis. The yield ratios increased significantly with the number of days after mowing before 2 mm of rain fell in 1 d ( r = 0·923*** and 0·715*, for C₂/Z₂ and C₂/R₂ respectively), and C₂/Z₂, but not C₂/R₂, decreased with increasing amount of rainfall in the 14 d after first mowing ( r = 0·787*). It was concluded that yield from compacted soil was greater than that from non-compacted soil because the former depended less on rainfall in the weeks after first mowing. The degree of soil compaction in the reduced ground-pressure traffic system, although maintaining first-harvest yield benefit, reduced the risk of significantly diminished yield at second harvest in dry summers.     

The effect of drying temperature on in vitro dry-matter digestibility and water-soluble carbohydrate content of perennial ryegrass varieties

In official forage grass variety trials in the UK, herbage samples are dried at 100°C or more to facilitate quick drying of the large numbers of samples that are currently needed. When assessing herbage quality, however, 80°C has been recommended as the highest temperature that can be used during drying without serious deterioration. Herbage from six perennial ryegrass varieties, which were known to show a range of variation in in vitro concentration of digestible dry matter (DMD) and water-soluble carbohydrate concentration (WSC) during the vegetative phase of growth, was dried in an oven with forced ventilation at 100°C and at 80°C before analysis. Mean DMD over all varieties was slightly lower [6 g kg⁻¹ dry matter (DM)] and mean WSC over all varieties was considerably lower (24 g kg⁻¹ DM) at 100°C. Varieties differed in mean DMD over both drying temperatures by 37 g kg⁻¹ DM and in mean WSC by 63 g kg⁻¹ DM. There was, however, no significant interaction between variety and drying temperature for either DMD or WSC. Although drying at the higher temperature underestimated both DMD and WSC, it did not significantly alter the ranking of varieties or the range among them.     

The impact of defoliation frequency and nitrogen fertilizer application in spring on summer survival of perennial ryegrass under grazing in subtropical Australia

Abstract This field study investigated the effect of timing of nitrogen (N) fertilizer application in spring on the survival of grazed perennial ryegrass (Lolium perenne cv. Dobson and Yatsyn) over summer in a subtropical environment. There were five N fertilizer treatments: no applied N, 46 kg N ha^?1 on 22 October or 22 November or 22 December, or on 22 October and again on 22 December. Water‐soluble carbohydrate (WSC) concentration of perennial ryegrass plants entering the summer was altered by varying defoliation frequency, with defoliation interval based on the number of leaves per tiller. Frequent defoliation was set at a regrowth level of one leaf per tiller and less frequent defoliation at a regrowth level of three leaves per tiller, over a total of two by three‐leaf per tiller regrowth periods. Application of N fertilizer was found to have no significant effect (P > 0·05) on survival of perennial ryegrass plants over summer. On the other hand, defoliation had a marked effect on perennial ryegrass persistence, with frequent defoliation decreasing ryegrass plant density (51 vs. 88 plants m^?2; P < 0·001) and increasing the density of tropical weed grasses (99 vs. 73 plants m^?2; P < 0·001) by autumn. Frequently defoliated plants had a lower stubble WSC content on a per plant basis than less frequently defoliated plants in spring (103 vs. 201 mg per plant; P < 0·001) and summer (59 vs. 101 mg per plant; P < 0·001). The lower WSC content was associated with a smaller root system in spring (1·50 vs. 2·14 g per plant; P < 0·001) and autumn (1·79 vs. 2·66 g per plant; P < 0·01), and this was reflected in 0·29 more plants being pulled from the soil by livestock between November 1996 and April 1997. Rhizoctonia fungus was associated with roots of pulled plants, but not with roots of seemingly healthy plants, indicating that this fungus may have a role in a weakened root system, which was more prone to sod pulling. Nitrogen applied in October and November resulted in a reduced WSC concentration, although the effect was restricted to 1 month after N application. The present study indicates that survival of perennial ryegrass plants over the summer in a subtropical region is prejudiced by frequent defoliation, which is associated with a lower WSC concentration and a shallower root system. Under grazing, sod pulling is a reflection of this weaker root system and contributes to plant mortality.     

The influence of rates of nitrogen and potassium application on the cooking quality of four potato varieties

Summary The influence of four nitrogen and four potassium levels on sloughing, mealiness, softness, colour and discoloration of cooked potatoes was investigated with the varietiesAristo, Irene, Libertas andIJsselster, grown on twelve trial fields on sandy soils. Both these types of fertilizer had an influence on all cooking properties but the response varied considerably between varieties. In general, the varietyAristo responded most strongly, whereasLibertas usually showed the weakest reaction. The effect of potassium was to produce in all varieties a linear decrease in sloughing, mealiness and softness. The response to nitrogen was more varied in thatAristo responded with a nearly linear decrease, whereas the other varieties, especiallyLibertas, showed a weaker reaction. Nitrogen decreased yellowness and increased discoloration after cooking, whereas potassium had the opposite effect. Nitrogen was especially harmful with respect to discoloration after cooking if the potassium level was low. Field influence was very strong with regard to textural properties, but only slight with regard to colour and discoloration after cooking.

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Zusammenfassung Der Einfluss von 0, 80, 160 und 240 kg N/ha (je zur H?lfte als Salpeter und Ammoniak), je kombiniert mit 0, 100, 200 oder 300 kg K₂O/ha (als Sulfat) auf das Zerkochen, die Mehligkeit, die Weichfleischigkeit, die Farbe und das Nachdunkeln gekochter Kartoffeln wurde an den SortenAristo, Irene, Libertas undIJsselster aus 12 Versuchsfeldern (Sandb?den) untersucht. Sowohl Stickstoff wie Kalium übten einen Einfluss auf alle Eigenschaften aus (Abb. 1), aber die Reaktion der Sorten wich betr?chtlich voneinander ab, besonders in bezug auf Stickstoff. Im allgemeinen reagierteAristo am st?rksten, w?hrendLibectas oft die schw?chste Reaktion zeigte (Abb. 3). Die Reaktion in bezug auf Eigenschaften im Zusammenhang mit der Textur gegenüber Kalium bestand in einer linearen Verminderung des Zerkochens, der Mehligkeit sowie der Weichfleischigkeit, und das Verhalten der Sorten war in dieser Hinsicht gleich. Die Reaktion dieser Eigenschaften gegenüber Stickstoff fiel unterschiedlicher aus, indemAristo mit einer nahezu linearen Abnahme reagiert, w?hrend die andern Sorten, und besondersLibertas, eine schw?chere Reaktion in Form einer optimalen Kurve zeigten (Abb. 3). Die durch die Herkunft bedingten Unterschiede in bezug auf die Textur waren betr?chtlich und bedeutend gr?sser als die Unterschiede infolge der Düngung (Abb. 2). Stickstoff schw?chte die gelbe Farbe ab und verst?rkte das Nachdunkeln nach dem Kochen, w?hrend Kalium eine gegenteilige Wirkung erzeugte (Abb. 5). Der Einfluss von Stickstoff auf das Nachdunkeln war bei der SorteLibertas am ausgepr?gtesten. Stickstoff verst?rkte das Nachdunkeln am meisten, wenn die Kaliumgabe niederig war (Abb. 7). Der Herkunftseinfluss auf die Farbe und das Nachdunkeln war kleiner als auf die Eigenschaften im Zusammenhang mit der Textur und war mit dem Einfluss von Düngern vergleichbar (Abb. 6).

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Résumé L'auteur a étudié l'influence de 0, 80, 160 et 240 kg N/ha (moitié en nitrate, moitié en ammoniaque), chaque dose combinée avec 0, 100, 200 et 300 kg K₂O/ha (en sulfate), sur le délitement, la farinosité, la tendreté, la couleur et la décoloration de pommes de terre cuites, ces études portant sur les variétésAristo, Irène, Libertas et IJsselster, cultivées dans douze champs d'essais établis en sol sablonneux. L'azote et le potassium ont tous deux une action sur tous les caractères (Fig. 1) mais la réaction varie considérablement avec les variétés, spécialement pour l'azote. Généralement,Aristo réagit le plus fort, tandis queLibertas montre souvent la réaction la plus faible (Fig. 3). La réaction des caractères de texture au potassium est une décroissance linéaire du délitement, de la farinosité et de la tendreté et à cet égard le comportement des variétés est similaire. La réaction de ces caractères à l'azote est plus variée:Aristo réagit par une décroissance presque linéaire tandis que les autres variétés, et spécialementLibertas, montrent une réaction plus faible sous forme d'une courbe optimale (Fig. 3). Les différences entre champs sont considérables au regard de la texture et sont nettement plus grandes que les différences causées par les fertilisants (Fig. 2). L'azote diminue la coloration jaune et accroit la décoloration après cuisson, tandis que le potassium a l'effet contraire (Fig. 5). L'influence de l'azote sur la décoloration est la plus prononcée chez la variétéLibertas. L'azote accentue le plus la décoloration quand le niveau de potassium est bas (Fig. 7). L'influence du champ sur la couleur et la décoloration est beaucoup plus faible que sur les caractères de texture et est comparable avec l'influence des fertilisants (Fig. 6).

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Then stationed at the Provincial Research Centre for Agriculture in Drenthe, Assen, The Netherlands.     

In vitro rumen methane output of perennial ryegrass varieties and perennial grass species harvested throughout the growing season

The selection and feeding of perennial ryegrass (Lolium perenne L.) varieties (PRV) or perennial grass species (PGS) may affect enteric methane (CH₄) output because of changes in the fermentation dynamics in the rumen as a result of differences in herbage chemical composition. The objective of this study was to determine the effects of PRV and PGS harvested throughout the growing season on herbage chemical composition, and in vitro rumen fermentation variables and CH₄ output per unit of feed using a batch culture technique. Seven PRV (Experiment 1: Alto, Arrow, Bealey, Dunluce, Greengold, Malone, Tyrella) and six perennial grasses [Experiment 2: perennial ryegrass (Navan), perennial ryegrass (Portstewart), cocksfoot, meadow fescue, tall fescue, timothy; defined as PGS], managed under a simulated grazing regime, were incubated for 24 h with buffered rumen fluid in two separate experiments. The CH₄ output per unit of feed dry‐matter (DM) incubated was not affected (P > 0·05) by PRV (range of mean values across PRV of 23·9–25·3 (SEM 0·41) mL g^?1 DM) or by PGS (25·6–26·6 (SEM 0·37) mL g^?1 DM). The CH₄ output per unit feed DM disappearing during the in vitro rumen incubation was not affected by PRV (33·9–35·1 (SEM 0·70) mL g^?1 DM), and although there was an overall PGS effect (P < 0·05; 37·2–40·3 (SEM 0·71) mL g^?1 DM), none of the paired contrasts between PGS were significant when analysed using Tukey adjusted comparisons. This outcome reflected either small‐scale or a lack of treatment effects on individual herbage chemical composition (e.g. 454–483 g NDF kg^?1 DM, 215–224 g CP kg^?1 DM and 94–122 g water‐soluble carbohydrate (WSC) kg^?1 DM across PRV; 452–506 g NDF kg^?1 DM, 208–243 g CP kg^?1 DM and 73–131 g WSC kg^?1 DM across PGS) and in vitro rumen fermentation variables. Hence, these results provide no encouragement that choices among the grasses examined, produced within the management regimes operated, would reduce enteric CH₄ output per unit of feed in vivo. However, the technique utilized did not take account of animal × PRV or PGS interactions, such as potential differences in intake between animals, that may occur under farm conditions.     

Carbohydrate and crude protein fractions in perennial ryegrass as affected by defoliation frequency and nitrogen application rate

The objective of this study was to evaluate the effects of defoliation frequency (either at two‐ or three‐leaf stage) and nitrogen (N) application rate (0, 75, 150, 300, 450 kg N ha^?1 year^?1) on herbage carbohydrate and crude protein (CP) fractions, and the water‐soluble carbohydrate‐to‐protein ratio (WSC:CP) in perennial ryegrass swards. Crude protein fractions were analysed according to the Cornell carbohydrate and protein system. Carbohydrate fractions were analysed by ultra‐high‐performance liquid chromatography. Sward defoliation at two‐leaf stage increased the total CP, reduced the buffer‐soluble CP fractions and decreased carbohydrate fractions of herbage (P < 0·001). The effect of defoliation frequency was less marked during early spring and autumn (P < 0·001) than for the rest of the seasons. An increase in N application rate was negatively associated with WSC, fructans and neutral detergent fibre (P < 0·001), and positively associated with CP and nitrate (N‐NO₃) contents of herbage. Nitrogen application rate did not affect CP fractions of herbage (P > 0·05). The fluctuations in CP and WSC contents of herbage resulted in lower WSC:CP ratios during early spring and autumn (0·45:1 and 0·75:1 respectively) than in late spring (1·11:1). The herbage WSC:CP ratio was greater (P < 0·001) at the three‐leaf than the two‐leaf defoliation stage and declined as the N application increased in all seasons (P < 0·001). The results of this study indicate that CP and carbohydrate fractions of herbage can be manipulated by sward defoliation frequency and N application rate. The magnitude of these effects, however, may vary with the season.     

Comparison of the relative performance of perennial ryegrass varieties under upland and lowland conditions

Productivity, seasonal growth and persistence of 10 perennial ryegrass ( Lolium perenne L.) varieties were assessed al an upland (305 m) and lowland (30 m) site in mid-Wales. Averaged over 3 harvest years (1979–81), mean dry matter (DM) production at 8.8 t ha⁻¹ was 22% lower in the upland environment, with spring (April and May) growth showing greatest contrast varying from only 6% of that in the lowland in 1979, after a severe winter, to 113% in 1981.
Relative ranking of varieties differed considerably between the two environments and no correlation was found between DM production at the two sites ( r = 0.5945). Early heading varieties performed better in the spring than late types at the upland site. A comparison of the results with those published from official variety testing trials gave a positive relationship under lowland conditions ( r = 0.7162*) but no correlation with those from the upland centre ( r = 0.1969).
The findings of the study show that relative productivity of varieties, but not persistency, differs between upland and lowland environments.     

High perennial ryegrass seeding rates do not negatively impact pasture sward persistence

Poor persistence of perennial ryegrass swards is a common problem; however, there is a lack of long‐term studies to understand the mechanisms associated with poor persistence. This study describes an experiment to test the hypothesis that high ryegrass seeding rates (>18 kg seed per ha) reduce long‐term population persistence because of smaller plant size and poorer survival during the first year after sowing. Four cultivars, representing four functional types of perennial ryegrass, were sown at five seeding rates (equivalent to 6, 12, 18, 24 and 30 kg seed per ha) with white clover in three regions of New Zealand. Swards were monitored for 5 years. No evidence was found to indicate a lack of persistence of ryegrass‐based swards sown at higher seeding rates. During the first year, swards sown at higher seeding rates had greater herbage accumulation (except at the Waikato site), greater ryegrass tiller density and greater ryegrass content. This initial impact of high seeding rates had largely dissipated by the fourth year, resulting in swards with similar annual herbage accumulation, tiller density and botanical composition. Similarly, there were relatively few differences among cultivars for these variables. Although high seeding rates did not negatively impact sward persistence, geographical location did, with strong evidence of ryegrass population decline at the Waikato site for all treatment combinations, some decline in Northland, and stable populations in Canterbury. It is possible that productive perennial ryegrass pastures can only be sustained for 4–5 years in some situations, even when the best ryegrass technology and management practices are used.     

The effects of Rumex obtusifolius on the seasonal yield of two mainly perennial ryegrass swards

A preliminary field experiment on a sward cut six times during 1978 indicated that total grass herbage harvested was negatively related to the number of Rumex obtusifolius plants present; densities of five to ten plants m⁻² resulted in reductions of up to 30%, although the total quantity of herbage harvested (including Rumex ) may have remained constant. However, R. obtusifolius densities did not significantly affect grass yield during the first half of the growing season. A negative relationship between R. obtusifolius ground cover and grass yield, particularly from late July onwards, was shown in a second field experiment during 1979 and 1980 using a 3-cut management. It was estimated that to produce a 20% reduction in grass growth in July-August and October, R. obtusifolius ground covers of 30% and 20% respectively were needed. Sixty per cent of the total herbage harvested in 1980 consisted of R. obtusifolius. These results indicate the damage that can be caused by this species and suggest that control measures should be taken before early summer.