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).     

Effects of harvesting perennial ryegrass at different levels of herbage mass on voluntary intake and in vivo digestibility in sheep

The production performance of herbage‐fed animals is affected by herbage voluntary dry‐matter intake (VDMI) and organic matter digestibility. The objective of this study was to determine the effect of herbage mass (HM) on in vivo herbage voluntary intake and digestibility in sheep. The three HM treatments were as follows: 1,100 kg dry matter (DM)/ha (low, L), 2,300 kg DM/ha (medium, M) and 3,700 kg DM/ha (high, H). The study was a Latin square design, repeated on two occasions in 2012: 24 May to 20 July (summer) and 21 July to 5 October (autumn). Twelve Texel wether sheep (individually housed) were offered fresh cut perennial ryegrass herbage for ad libitum consumption. Using the total faecal collection method, the digestibility of dry matter, organic matter, neutral detergent fibre and acid detergent fibre was determined. In summer, L had a similar VDMI to M and both had a higher VDMI than H. In autumn, L had a higher VDMI than both M and H. For dry‐matter digestibility and organic matter digestibility, there was no significant difference between L and M, which were both higher than H. For every 1% increase in neutral detergent fibre digestibility, VDMI increased by 0.03 kg. In the zero‐grazing scenario examined, offering low (1,100 kg DM/ha) HM swards enabled animals to achieve high intakes of highly digestible herbage, which should ensure high animal production performance.     

Effects of grazing and precipitation on herbage production,herbage nutritive value and performance of sheep in continental steppe

The present study highlights the effects of sheep grazing and precipitation on herbage and animal performance in a grazed steppe of Inner Mongolia. Experimental data were collected during grazing periods of four consecutive years (2005–2008), and effects were analysed across a gradient of seven grazing intensities. Variation in annual precipitation, reflected by the effect of ‘year’, was the major factor affecting herbage; i.e., the production and nutritive value of herbage increased with increasing precipitation. Herbage parameters were also affected by grazing intensity, as herbage production (HP) and herbage nutritive yields decreased, while herbage nutritive values increased with increasing grazing intensity. The grazing‐induced decrease in herbage nutritive yields suggests that decreases in HP offset the positive effect of grazing on the nutritive value. Liveweight gain (LWG) was predominantly affected by grazing intensity, as LWG per sheep and per ha decreased and increased, respectively, with increasing grazing intensity. However, responses varied among years: LWG per sheep was maximized by light grazing in the drought year and by moderate grazing the wet year. Our results showed that herbage shortage at high grazing intensities reduces LWG per sheep and thus diminishes responses in LWG per ha. Nevertheless, the highest grazing intensity provides highest animal production per ha in the short term; however, this is not sustainable in the mid‐ and long term because decreasing HP induces degradation processes. Based on our results, a reduction in grazing intensity that still provides 78% of the maximum LWG per ha meets the requirements of a sustainable grazing management.     

Red clover for silage: management impacts on herbage yield,nutritive value,ensilability and persistence,and relativity to perennial ryegrass

This 6‐year experiment quantified the impacts of management factors on red clover yield, persistence, nutritive value and ensilability, and compared these with perennial ryegrass receiving inorganic N fertilizer. Within a randomized complete block design, field plots were used to evaluate a 2 (cultivar, Merviot and Ruttinova) × 2 (alone and with perennial ryegrass) × 2 (0 and 50 kg fertilizer N ha^?1 in mid‐March) × 2 (harvest schedule) combination of the factors relating to red clover, and a 2 (harvest schedule) × 4 (0, 50, 100 and 150 kg N ha^?1 for each cut) combination of the factors relating to perennial ryegrass. The early and late harvest schedules both involved four cuts per year, but commenced a fortnight apart. Red clover treatments averaged 14 906 kg dry matter (DM) ha^?1 per year, whereas perennial ryegrass receiving 600 kg inorganic N fertilizer per year averaged 14 803 kg DM ha^?1 per year. There was no yield decline evident across years despite a decline in the proportion of red clover. The early harvest schedule and sowing ryegrass with red clover increased the herbage yield and digestibility. March application of fertilizer N to red clover treatments reduced the annual yield. Early harvest schedule increased and both fertilizer N and sowing with ryegrass decreased the proportion of red clover. Sowing with ryegrass improved the indices of ensilability, but reduced the crude protein content. Both red clover cultivars had similar performance characteristics. A selected red clover‐based treatment, considered to exhibit superior overall production characteristics, outyielded N‐fertilized perennial ryegrass in mid‐season. However, it had poorer digestibility and ensilability indices.     

Fatty acid composition and nutritive value of twelve cultivars of perennial ryegrass

A comparison was made of the fatty acid composition and nutritive value of twelve cultivars of perennial ryegrass ( Lolium perenne L.) differing in heading date and ploidy level. The cultivars were sown in triplicate plots and three sequential cuts of herbage were taken at 20-d intervals during the late spring and early summer to describe the fatty acid composition and other measurements of nutritive value. Differences between cultivars were recorded for DM content ( P  <   0·01) and concentrations of gross energy, neutral-detergent fibre (NDF) and ash ( P  <   0·05). Diploid cultivars had a higher DM content and concentration of NDF ( P  <   0·01) than tetraploid cultivars whilst late-heading date cultivars had the lower NDF ( P  <   0·05), ADF and ash ( P  <   0·01) concentrations. There was variation between cultivars in fatty acid composition. Diploid cultivars had a higher concentration of C18:0 ( P  <   0·01) and C18:1 ( P  <   0·05) than tetraploid cultivars and late-heading date cultivars had the highest concentrations of total fatty acids, C16:0, C18:2 and C18:3 ( P  <   0·05). This was predominantly due to the cultivar Tyrella which is a diploid, late-heading cultivar. The study showed that some variation exists between perennial ryegrass cultivars in concentrations of polyunsaturated fatty acids, which may present opportunities to select for this trait, but further research on the developmental stages and degree of leafiness of cultivars is first required.     

Morphology and nutritive value of perennial ryegrass cultivars at different phenological stages

Eight perennial ryegrass cultivars (representing the variations in ploidy, heading date and water‐soluble carbohydrates concentration) were investigated for morphology and nutritive value at three phenological stages: pre‐heading vegetative, reproductive and post‐flowering vegetative stages. Chemical compositions and digestibility of morphological components (lamina, pseudostem and reproductive stem) from each perennial ryegrass cultivar were analysed in a split‐plot design. At the vegetative stages, perennial ryegrass cultivars differed significantly in the proportions of lamina and pseudostem. Tetraploid cultivars, Base and Bealey, always had the greatest lamina proportion (51.8% and 53.2% at the pre‐heading and post‐flowering vegetative stages respectively). At the reproductive stage, the emergence of seed heads diminished the differences in morphology among cultivars. Perennial ryegrass cultivars also had distinct nutritive value throughout three phenological stages. The high‐sugar cultivar, AberMagic, had high WSC concentrations (276, 227 and 90 g/kg DM at the pre‐heading vegetative, reproductive and post‐flowering vegetative stages respectively); the intermediate‐heading cultivars, Kamo and Commando, generally had a lower organic matter digestibility in dry matter than the late‐heading cultivars at the pre‐heading vegetative (70.7% vs. 74.4%) and reproductive stage (63.9% vs. 68.2%). However, although the morphological components were different in nutritive value consistently, the differences in morphology did not account for the variation in nutritive value among perennial ryegrass cultivars.     

Effects of shrub encroachment on herbage production and nutritive value in semi-arid Mediterranean grasslands

There is limited information on the effects of the increase in the density of shrubs on herbage production and nutritive value of natural grasslands in the Mediterranean region, currently facing major land use changes. Herbage production of drymatter (herbaceous fractions, of plant functional groups and by species), crude protein (CP), neutral‐detergent fibre (NDF), acid‐detergent fibre (ADF), acid‐detergent lignin (ADL) and hemicellulose concentrations and in vitro organic matter digestibility were determined at the time of peak of annual growth across four types of grassland vegetation each characterized by different shrub cover regimes. A sharp reduction in herbage production and a reduction in nutritive value were found as a result of the increase in shrub cover. These changes appeared to be closely related to the shift in plant functional groups detected as shrub density increased. Herbage production from grasses and legumes was found to be more sensitive to shrub cover changes than herbage production from forbs, whereas, as grassland types became denser, annual species were gradually replaced by perennials and C₄ grasses by C₃ ones. The impact of shrub encroachment on Mediterranean grasslands is discussed in relation to their use by livestock.     

Field indicators of leaf nutritive value for perennial ryegrass and tall fescue pastures under different growing and management conditions

Field indicators of forage nutritive value could help farmers with rapid management decisions to optimize timing and intensity of grazing and meet objectives regarding animal nutrition. The objective of this research was to evaluate the likely relationships among leaf blade nutritive value, herbage mass and leaf stage of pasture regrowth under different growing seasons and residual sward heights. Experiments were performed on perennial ryegrass (Lolium perenne L.) and tall fescue (Festuca arundinacea Schreb.) pastures during spring and summer of 2016. In both pastures, three residual sward height treatments (3, 6 and 12 cm) were imposed on plots arranged in a split plot design, replicated in three blocks. Sward plots were harvested 5–6 times at intervals spaced 7–10 days apart to measure herbage mass, plant morphology, neutral detergent fibre (NDF), and the 24-hr in vitro digestibility of NDF (NDFD) and dry matter (DMD) of leaf blades. Pastures showed strong (R²: .62 to .70), but variable, negative relationships between NDFD and herbage mass that varied with the rate at which pasture grew in each season of experimentation. Although there was a consistent NDFD decline as leaf stage of regrowth progressed (R²: .75 to .97), the NDFD also decreased as residual sward height increased, most notably in tall fescue. Additionally, findings indicate that the greater leaf length plasticity of tall fescue compared to residual sward heights may offer opportunities to manage both post- and pre-grazing targets to achieve tall fescue forages with a similar high nutritive value as perennial ryegrass. However, the evaluation of this hypothesis at the farm level and its impacts on animal intake and performance warrants further careful investigations.     

Effects of perennial ryegrass (Lolium perenne L.) cultivars on herbage production, nutritional quality and herbage intake of grazing dairy cows

Four perennial ryegrass (Lolium perenne L.) cultivars were compared for differences in herbage production, nutritive value and herbage intake of dry matter (DM) during the summers of 2002 and 2003. Two paddocks were sown with pure stands of four cultivars in a randomized block design with three replicates. Each plot was subdivided into fourteen subplots (22 m × 6 m) which were grazed by one cow during 24 h. Twelve lactating dairy cows were assigned to one cultivar for a period of 2 weeks in a 4 × 4 Latin square experimental design; the experiment lasted 8 weeks in each year. Sward structure (sward surface height, DM yield, green leaf mass, bulk density and tiller density) and morphological characteristics were measured. The ash, neutral‐detergent fibre, acid‐detergent lignin, crude protein and water‐soluble carbohydrate concentrations, and in vitro digestibility of the herbage were measured. The sward was also examined for infestation by crown rust (Puccinia coronata f. sp. lolii). Herbage intake of dairy cows was estimated using the n‐alkane technique. Cultivar differences for all sward structural characteristics were found except for bulk density and tiller density in 2003. Cultivars differed for proportions of pseudostem, stem (in 2003 only) and dead material. The chemical composition of the herbage was different among cultivars, with the water‐soluble carbohydrate concentration showing large variation (>0·35). Cultivars differed in susceptibility to crown rust. Herbage intake differed among cultivars in 2002 (>2 kg DM) but not in 2003. Herbage intake was positively associated with sward height, DM yield and green leaf mass. Canopy morphology did not affect herbage intake. Crown rust affected herbage intake negatively. It was concluded that options for breeders to select for higher intake were limited. High‐yielding cultivars and cultivars highly resistant to crown rust were positively related with a high herbage intake.     

Comparison of the performance of dairy cows offered kale,swedes and perennial ryegrass herbage in situ and perennial ryegrass silage fed indoors in late pregnancy during winter in Ireland

The effects on the performance of dairy cows offered kale, swedes, and perennial ryegrass in situ and perennial ryegrass silage fed indoors to dairy cows pre‐partum during winter in Ireland was examined. Eighty‐eight spring‐calving dairy cows were randomly assigned to one of four offered treatments; (i) 8 kg of dry matter (DM) of kale leaf and stem + 4 kg DM of perennial ryegrass silage (treatment K), (ii) 8 kg DM of the root and leaf of swedes + 4 kg DM of perennial ryegrass silage (treatment S), (iii) 12 kg DM of perennial ryegrass herbage (treatment G) offered in situ and (iv) perennial ryegrass silage offered ad libitum indoors (treatment ID). Cows on treatments K, S and ID had a greater (P < 0·001) increase in body condition score (0·20, 0·14 and 0·50 units respectively) pre‐partum than cows on treatment G which lost 0·22 units. Pre‐partum treatment had no effect on variables of milk production in the following lactation. In the first 100 d of lactation, cows on treatment G pre‐partum had a lower milk fat concentration (35·6 g kg^?1) compared with cows on treatments S and ID (38·3 and 39·3 g kg^?1 respectively). There was no effect of treatment on the intervals between parturition and first insemination (mean 74·6 d) and conception (mean 96·1 d). The results suggest that offering kale and swedes to dairy cows pre‐partum resulted in a similar lactation performance to dairy cows grazing a perennial ryegrass sward or offered perennial ryegrass silage indoors.     

The influence of weather factors on the drying rate of cut perennial ryegrass herbage under controlled conditions

The rates of drying of cut perennial ryegrass (Lolium perenne L.) herbage over short periods of time were measured in four experiments in a controlled environment room. Standard weights of 33·7 g grass dry matter (DM) were placed in half the area of wire‐mesh trays (0·5 m long × 0·3 m wide × 0·07 m high with 11‐mm‐square mesh) which, so as to simulate conditions in a swath, were supported on wooden frames within dark plastic boxes 25 mm above 35‐mm‐thick wet sponges. The trays of grass in the controlled environment room were weighed hourly for 7 h, drying rate being assessed by the change in grass fresh weight. Light was supplied from 400‐W mercury vapour lamps, while an air conditioning unit within the controlled environment room allowed control of vapour pressure deficit (VPD). Only one particular VPD could be created on any one day and resource limitations restricted the study to one replicate per day. The first experiment correlated drying rates under the mercury vapour lamps with drying rates in the open air under sunshine over 3 d. This work showed that a distance of 200 mm between the tray and lamps equated to 1081 W m^–2, 400 mm to 432 W m^–2 and 600 mm to 281 W m^–2. Experiment 2, conducted with previously frozen grass, was a 4 × 4 factorial design with light intensity and VPD as factors. The third experiment (Experiment 3) compared the drying rate of freshly cut grass with grass that had previously been frozen in a 2 × 2 × 2 factorial design with the two grasses, two light intensities and two wind speeds as factors. The final experiment (Experiment 4) was a 3 × 2 × 2 factorial design with light intensity, VPD and wind speed as factors. A wind of approximately 3 m s^–1 was simulated using a 22‐mm, 30 W fan set in a fixed position 600 mm from each tray plus grass. Fresh grass was cut each morning of the experiment. There were six replicates of each treatment. The effect of the three radiation intensities on grass DM concentration in Experiment 2 was highly significant (P < 0·001). VPD had less effect (P < 0·05). Results from Experiment 3 showed that previously frozen material dried much more rapidly than fresh grass and as a result would not simulate actual grass drying in the field. Consequently in Experiment 2 fresh grass was used as opposed to previously frozen material. In Experiment 4, light intensity had the greatest influence on grass drying followed by VPD and wind speed. However, the influence of wind speed was variable. A wind speed of ≈3 m s^–1 increased the rate of water loss from grass with a low initial DM concentration (<160 g kg^–1) receiving low levels of solar radiation (281 W m^–2), while at higher initial DM concentrations (>210 g kg^–1) and higher solar radiation levels (432 W m^–2) the effect of wind was to slow grass drying. The results from Experiments 2 and 4 also indicated that high levels of either wind (3 m s^–1) or VPD (>6 mbars), when associated with low levels of solar radiation, resulted in large increases in grass DM concentration. However, these extreme weather conditions are unlikely to occur in practice.     

Effects of continuous or rotational grazing of two perennial ryegrass varieties on the chemical composition of the herbage and the performance of finishing lambs

Plant breeding has developed perennial ryegrass varieties with increased concentrations of water‐soluble carbohydrates (WSCs) compared with conventional varieties. Water‐soluble carbohydrates are major metabolic and storage components in ryegrass. Therefore, if perennial ryegrass herbage is allowed to grow to greater heights it should contain higher water‐soluble carbohydrates concentrations, for example as under rotational grazing rather than continuous grazing by livestock. This study investigated this hypothesis and measured the performance of lambs grazed rotationally and continuously. Replicated plots of the variety AberDart (bred to express high WSC concentrations) or the variety Fennema were grazed by a core group of ten male Cheviot lambs for 10 weeks. Lambs were weighed and replicate forage samples were taken every 7 d. Concentrations of WSC in AberDart herbage were significantly (P < 0·05), but not substantially, higher than those in Fennema herbage. Rotational grazing did not increase the differential in WSC concentration between the AberDart and Fennema varieties. However, there was a tendency (P = 0·07) for lambs rotationally grazing the AberDart swards to have a higher final live weight than lambs grazing the Fennema swards. Overall, lamb performance was increased when either perennial ryegrass variety was rotationally rather than continuously grazed (P < 0·001).     

Effects of autumn and spring defoliation management on the dry‐matter yield and herbage quality of perennial ryegrass swards throughout the year

A small‐plot experiment was conducted in south‐west Ireland to investigate (i) the effects of pre‐closing regrowth interval and closing date on dry‐matter (DM) yield and sward structural and composition characteristics, during the autumn–winter and spring opening periods, and (ii) subsequent carryover effects. The study used a randomized block design with a factorial arrangement of treatments (4 closing dates × 2 opening dates) with a split plot (two pre‐closing regrowth intervals). The long pre‐closing (LPC) interval began on 9 August, and the short pre‐closing interval (SPC) started on 15 September. The autumn closing dates were as follows: 1 October (CD1), 15 October (CD2), 1 November (CD3) and 14 November (CD4). Plots were defoliated again on 1 February (EOD) or 1 March (LOD). On the LPC treatment, herbage yield increased from CD1 (2463 kg DM ha^?1) to CD3 (3185 kg DM ha^?1). On the SPC treatment, herbage yield was similar for CD3 and CD4, indicating a ceiling in herbage accumulation. For each 1‐d delay in closing date between CD1 and CD4, the opening herbage yield was reduced by 10 kg DM ha^?1. Herbage quality decreased as the closing date was delayed; DMD and CP decreased by 0·06 and 12 g kg DM^?1, respectively, between CD1 and CD4. The EOD resulted in increased leaf and decreased dead proportions over the LOD treatments. A balance between autumn CD and spring OD needs to be achieved to ensure a sufficient supply of high‐quality grass in spring.     

Efficiencies of ryegrass and white clover herbage utilization in mixtures continuously grazed by sheep

A method for measuring the growth, senescence and defoliation fluxes in a mixture consisting of alternate rows of perennial ryegrass (Lolium perenne) and white clover (Trifolium repens) was used to calculate the actual and potential efficiencies of grass and clover utilization under continuous sheep grazing. White clover contributed relatively more to the growth than to the herbage mass of the mixture and its relative growth rate was usually significantly greater than that of its companion grass. The primary reason for the greater potential efficiency of herbage use of the white clover component was, however, its lower rate of senescence. Greater potential efficiency was not reflected in a greater actual efficiency because the contribution of white clover to the total herbage removed was always smaller than its contribution to the growth flux of the mixture. Despite the commonly assumed sheep preference for white clover, the legume was usually the least defoliated species, presumably because of the lower surface height of white clover compared with grass, which resulted in a lower vertical availability of white clover, thereby restricting its defoliation rate. The positive net herbage accumulation observed with white clover at a constant sward surface height occurred partly through stolon and bud development and partly through the growth of undefoliated leaves from axillary growing points and contributed to a net herbage accumulation per unit dry weight in white clover greater than that in ryegrass. This resulted in an increase in the white clover content of the sward, which was observed independently by destructive measurements.     

Effect of agrochemical applied at sowing on seedling emergence and herbage yield of perennial ryegrass and white clover

Plots of white clover ( Trifolium repens ) and perennial ryegrass ( Lolium perenne ) white clover were sown with and without fungicide seed treatment, seed treatment with Cytozyme (a proprietary growth-promoting agent) and pesticide granules (carbofuran or carbosulfan) mixed with the seed. Sowings were made in April/May at Hurley (1986 and 1987), Dorchester (1987) and Bronydd Mawr (1987). Only treatments containing pesticide significantly improved seedling emergence or herbage yield in the 1986 sowing. In 1987, pesticide greatly increased seedling emergence of ryegrass and clover at Hurley and Dorchester, but had no effect at Bronydd Mawr. At Hurley, herbage yield and the proportion of clover were more than doubled for up to a year, by chemical treatment after sowing in 1986.
Populations of plant parasitic nematodes were recorded at all sites and it is suggested that at Hurley and Dorchester seedlings with nematode damage were unable to survive the dry soil conditions that prevailed. In a subsequent pot experiment, pesticide granules controlled root endoparasitic nematodes and significantly increased seedling emergence of white clover in dry soil but had no effect in moist soil.     

The effect of a high-magnesium perennial ryegrass variety on the magnesium status of sheep

An early-heading variety of perennial ryegrass (Ramore) bred for high magnesium (Mg) content was compared with an early control variety (Frances) for its ability to increase Mg intake, Mg utilization and blood Mg concentration in sheep, and so reduce the incidence of hypomagnesaemic tetany. Swards of the two varieties were established and each was grazed by ewes suckling twin lambs from turn-out to weaning and thereafter by dry ewes. In early and late season herbage from a proportion of each sward was cut daily and fed fresh to ewes housed indoors in metabolism crates. Under grazing conditions herbage from Ramore swards had, over the 1992 and 1993 grazing seasons, a higher Mg concentration than Frances (2.35 g kg^?1 vs. 2.18 g kg^?1; s.e.m. 0.019, P< 0.001). During the spring period there was a higher (P 0.001, s.e.m. 0.0074) Mg concentration in the blood of ewes grazing Ramore (0.854 m mol 1^?l) swards compared with those grazing Frances (0.793 m mol 1 ^?1) whereas during the autumn period blood Mg concentrations were higher in ewes grazing Frances. Ewe and lamb liveweight gains, recorded in 1992 only, were higher on Ramore swards than on Frances swards, although the difference was not significant. Indoor feeding studies showed that Mg intake was significantly higher (P< 0.001, s.e.m. 0.026) in ewes offered Ramore (1.98 g d^?1) herbage compared with those offered Frances (1.74 g d^?1) herbage with no significant difference in dry-matter intake between the two varieties. Apparent availability and retention of Mg were higher for animals fed Ramore during the spring feeding periods than those fed Frances, but during the autumn feeding periods the reverse was true. Under indoor feeding conditions, variety had no significant effect on blood Mg concentrations. It was concluded that under grazing conditions a high Mg variety could provide an effective means of reducing the incidence of hypomagnesaemic tetany.     

Genotype × environment interactions for herbage yield of perennial ryegrass sward plots in Ireland

Perennial ryegrass (Lolium perenne L.) is by far the most widely sown grass species in Ireland. Genotype × environment (G × E) interactions are a frequent occurrence in herbage yield evaluations. The objectives were to determine (i) the nature and relative magnitudes of the pertinent G × E interaction variance components for dry matter yield of perennial ryegrass sward plots in Ireland and (ii) the optimal allocation of replicates, locations and years in a testing programme. Sixteen perennial ryegrass cultivars were sown at six locations throughout Ireland between 2000 and 2004. Plots from each sowing were harvested for 2 consecutive years under a simulated mixed grazing and conservation management programme. The largest component of the G × E variance was generally genotype × location × year emphasizing the need for evaluation of genotypes across locations and years to adequately characterize genotypes for differences in yield. Relative differences among genotypes from year to year and location to location were due mainly to changes in genotype rankings. Weather was estimated to have a greater effect on annual variation in herbage yield than age of stand. The optimum allocation of resources for a testing programme was estimated at four replicates per location, and either two locations and 3 sowing years or three locations and 2 sowing years with 2 harvest years for each sowing year. The most appropriate option depends on the relative importance of time vs. financial resources.     

Effects of pasture age on the genotype and phenotype of perennial ryegrass

Limited persistence of perennial ryegrass (Lolium perenne L.) in dairy pastures is a significant issue in parts of New Zealand. The contribution of plant genetic background to this problem is not well understood. Temporal changes were investigated in genotypic and phenotypic composition of two perennial ryegrass cultivars (Nui SE and Alto AR37, older and newer cultivars respectively) sown as fields plots at three locations. Samples from survivor populations collected annually over 6 years from each location were established in a field nursery, analysed by simple sequence repeat (SSR) markers and assessed for vigour, leaf morphology and tiller number. SSR-based estimates of the statistic G′_ST indicated no significant (p > .05) genetic differentiation between survivor populations and plants grown from remnant seed (ex-seed) after 5 years, and no significant change (p > .05) in within-population genetic diversity for either cultivar at any location. SSR analysis of endophytic fungus (Epichloë festucae var. lolii) type revealed only limited ingress of off-type ryegrass volunteers into plots at two locations. Vigour scores of survivor plants were not significantly (p > .05) different among plants collected from different locations and ex-seed plants. Leaves on ex-seed plants were longer (p < .001) than those on the survivor plants after four but not 6 years and may reflect a short-term response to climatic conditions experienced in the field nursery. Our results suggest that the reported poor ryegrass persistence is not driven by changes in population genetic structure and that the sown cultivars survived and remained true to type.     

Effect of humic substances on nutrient uptake by herbage and on production and nutritive value of herbage from sown grass pastures

The effect of humic substances on the nutrient uptake, herbage production and nutritive value of herbage from sown grass pastures was studied in six field experiments. Commercial humic substances were applied in combination with mineral fertilizer or slurry, either as a solution (HF liquid; 8·3 kg humic substances ha⁻¹) or incorporated into the mineral fertilizer (HF incorporated; 3·6 to 6·4 kg humic substances ha⁻¹). A series of cuts, ranging from two to five cuts, was taken during the growing season. The general response in herbage production to application of humic substances was an increase in herbage mass of dry matter (DM) at the first cut although this was only significant in two experiments for the HF incorporated treatment. Total herbage production of DM over the growing season, however, was similar for treatments with or without application of humic substances. The overall effect of HF incorporated and HF liquid on the herbage mass of DM at the first cut across the experiments was calculated using a meta-analysis technique and it was shown that there was a significant proportional increase of 0·14 ( P  <   0·05) with the HF incorporated treatment and a non-significant increase of 0·08 with the HF liquid treatment compared to the control treatment. The nutritive value of the herbage at the first cut was similar across all treatments. In general nitrogen, phosphorus and potassium uptake at the first grass cut was higher after application of humic substances but only in one experiment was this increase statistically significant.     

Effect of grazing severity on perennial ryegrass herbage production and sward structural characteristics throughout an entire grazing season

The objective of this study, which was part of a larger grazing‐systems experiment, was to investigate the cumulative impact of three levels of grazing intensity on sward production, utilization and structural characteristics. Pastures were grazed by rotational stocking with Holstein–Friesian dairy cows from 10 February to 18 November 2009. Target post‐grazing heights were 4·5 to 5 cm (high; H), 4 to 4·5 cm (intermediate; I) and 3·5 to 4 cm (low; L). Detailed sward measurement were undertaken on 0·08 of each farmlet area. There were no significant treatment differences in herbage accumulated or in herbage harvested [mean 11·3 and 11·2 t dry matter (DM) ha^?1 respectively]. Above the 3·5 cm horizon, H, I and L swards had 0·56, 0·62 and 0·67 of DM as leaf and 0·30, 0·23 and 0·21 of DM as stem respectively. As grazing severity increased, tiller density of grass species other than perennial ryegrass (PRG) decreased (from 3,350 to 2,780 and to 1771 tillers m^?2 for H, I and L paddocks respectively) and the rejected area decreased (from 0·27 to 0·20 and to 0·10 for H, I and L paddocks respectively). These results indicate the importance of grazing management practice on sward structure and quality and endorse the concept of increased grazing severity as a strategy to maintain high‐quality grass throughout the grazing season. The findings are presented in the context of the need for intensive dairy production systems to provide greater quantities of high‐quality pasture over an extended grazing season, in response to policy changes with the abolition of EU milk quotas.