Search

Multispecies swards, comprised of different plant functional groups have comparable production potential to high N input L. perenne swards at reduced N when legumes are included. However, information on the appropriate management of multispecies swards is limited. The effect of differing management practices on the herbage dry‐matter (DM) production and botanical composition of different sward types was investigated using a 3 × 2 × 2 factorial design plot experiment. The experiment consisted of three sward types: L. perenne‐only receiving (LP; 250 kg N ha−1 a−1); L. perenne‐Trifolium repens (LP‐TR); multispecies sward containing L. perenne, Phleum pratense, Trifolium repens, Trifolium pratense, Plantago lanceolata and Cichorium intybus (MSS). LP‐TR and MSS received 90 kg N ha−1 a−1. Harvesting of plot herbage took place every 21 or 28 days to a defoliation height of 4 or 6 cm, over two growing seasons (March to November 2020 and 2021 inclusive). Annual herbage produced by both LP and LP‐TR was not significantly affected by defoliation frequency. However, MSS produced 1923 kg DM ha−1 a−1 more herbage when harvested less frequently. Unsown species contributed significantly less to the herbage DM of MSS compared to LP and LP‐TR and remained similar in 2020 and 2021, whereas the contribution of unsown species to herbage DM increased in LP and LP‐TR from 2020 to 2021, with noxious species more associated with LP and LP‐TR than MSS. Results demonstrate the role of multispecies swards in improving the sustainability of grass‐based agricultural systems in an environment of reduced fertilizer inputs. [ABSTRACT FROM AUTHOR]

Background: In the Western Highlands of Cameroon (WHC), information on the nutritional value of fodder species consumed by ruminants is very limited. Methods: Through interviews with farmers and monitoring of animals on the range, information was obtained on the types of fodder resources consumed by the ruminants. Samples of each forage species were collected in 15 districts, mixed, chopped, and dried in a ventilated oven at 60°C, and then ground for chemical composition analysis. Results: Twenty‐two forage species were identified. Among these species, Vernonia amygdalina (29.43% ± 0.45% dry matter [DM]) and Pennisetum clandestinum (87.21% ± 1.33% DM) were, respectively, the highest in protein and neutral detergent fiber contents. Manihot esculenta was one of the most energy‐rich forages in terms of forage unit for lactation and forage unit for meat production. Hierarchical ascending classification revealed three main groups of forages, respectively, rich in crude fiber (Group 1), protein (Group 2), and energy (Group 3). Conclusions: The present study identified 22 forage species browsed by ruminants in WHC. Further studies should be carried out to determine the antinutritional factors and to evaluate their nutrient value using in vitro or in situ digestibility techniques. [ABSTRACT FROM AUTHOR]

Drought can induce phenotypic plasticity in a range of plant root and shoot traits. These traits have been shown to explain differences in root and shoot litter decomposability between species. However, it is unknown how drought‐induced plasticity of root and shoot traits alters their decomposability.To investigate this issue across a range of species, we grew a grass Lolium perenne, a forb Plantago lanceolata and a legume Trifolium repens common to European temperate grasslands and subjected them to a 5‐week moderate drought treatment. We compared morphological and chemical root and shoot traits of the droughted plants to well‐watered controls. We then conducted a decomposition assay of the senesced root and shoot material over 16 weeks, with mass loss measurements at five timepoints.Drought had significant and sometimes strong effects on morphological and chemical root and shoot traits of all three species, sometimes similar to differences between species and generally in line with a shift to a more resource‐conservative strategy. Drought also increased the labile litter fraction in roots of Lolium perenne, which was associated with a substantial increase in non‐structural carbohydrates. Drought decreased the labile litter fraction in shoots of Plantago lanceolata, but this could not be explained by the traits we measured. Drought effects on litter decomposability were weaker than on plant traits.Our results suggest that plant trait‐mediated effects of drought on litter decomposability can either increase or decrease vegetation feedbacks to climate change. They also show that drought‐induced plasticity in root and shoot traits does not automatically translate into equivalent changes in litter decomposability. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

Perennial ryegrass (PRG, Lolium perenne L.) breeding effort in New Zealand (NZ) has increased since c. 1990, resulting in greater functional trait diversity (e.g. heading date, ploidy, and associated Epichloë endophyte strain) in commercial products. This study quantified the variation, associations and interactions in dry matter (DM) yield, nutritive value and persistence‐related traits among commercial cultivar‐endophyte combinations released between 1973 and 2012, as a basis for assessing gains in value being delivered to the pasture‐based livestock industries. Twenty‐four or 28 combinations were compared over 3 years in two trials in each of two regions: Waikato in northern NZ (dryland), and Canterbury in central eastern South Island (irrigated). Cultivar‐endophyte combinations were sown in mixtures with white clover, and pastures were intensively grazed 8–11 times per year by dairy cows. Principal Component Analysis identified 4 distinct clusters for the DM yield variables and for metabolisable energy (ME) content in each of the four trials. A broadly‐adapted group of three late‐season flowering, AR37‐infected diploids with NZ and Spanish breeding backgrounds dominated the highest‐yielding clusters. Tetraploids dominated the high ME content clusters. Interactions with region were observed throughout the data set: the strongest of these was driven by endophyte strain effects in Waikato. High‐yielding cultivar‐endophyte combinations in these trials were also generally high‐yielding in the standard cultivar merit testing system operated in New Zealand, as interpreted via the DairyNZ Forage Value Index. However, alignment was poorer for medium‐ and lower‐yielding cultivar‐endophyte combinations. Several implications for forage evaluation methods and end‐user industries are identified. [ABSTRACT FROM AUTHOR]

The effect of soil environment on cultivars compatibility was evaluated in a cutting field experiment during two growing seasons. A factorial combination of four perennial ryegrass (Lolium perenne L.; PR) and three white clover (Trifolium repens L.; WC) cultivars were grown on deep (DSS) and shallow (SSS) soils under irrigated conditions. Measurements included herbage accumulation (HA), root attributes, leaf chlorophyll content, and interception of photosynthetic radiation. The PR–WC compatibility was affected by soil environment. In both soil sites and growing seasons, the WC + PR herbage accumulations were similar but with different PR and WC partial accumulation. In DSS, the partial PR HA was 22% less than that observed in SSS; the partial WC HA was almost twice in DSS relative to SSS. In SSS, the WC stolon growing point numbers, stolon length, and stolon biomass increased 60, 88, and 94% relative to DSS, respectively. In the same way, the mixed sward increased root biomass and root length density, which was considered as a mechanism for improving plant resources capture from the soil. At cultivar level, the PR–WC compatibility was affected mainly by WC cultivar, and the effect of PR cultivar was fairly weak. The medium‐leaved WC cultivar 'Will' showed the greatest compatibility with PR, particularly with cultivar 'Bealey'. These results are valuable when designing new management strategies for mixed sward production in marginal environments. Modern cultivars of PR have capacity for adapting to marginal environments; however, it is necessary to improve the competitive ability of WC to capture soil resources under marginal soil conditions. Core Ideas: Understanding compatibility of perennial ryegrass and white clover cultivars allows for optimized mixed sward herbage accumulation.Modern cultivars of perennial ryegrass have capacity for adapting to marginal environments.Mixed sward changes its phenotypic expression in marginal environments. [ABSTRACT FROM AUTHOR]

Dry matter (DM) production of multispecies swards compared to perennial ryegrass (Lolium perenne; PRG) swards under intensive grazing warrants investigation as it is relatively unknown. A 5 × 2 factorial experiment, with five sward types and two defoliation methods, was used to investigate the effect of grazing versus cutting on dry matter (DM) production of multispecies and PRG‐only swards. Five sward types were established namely: a PRG‐only sward, receiving 250 kg N ha−1 year−1 (PRG250), and a PRG‐only sward (PRG90), a two‐species sward with PRG and white clover (Trifolium repens; PRGWC), a six‐species sward (6S) and a nine‐species sward (9S), each receiving 90 kg N ha−1 year−1. Cutting plots measured 1.95 × 10 m and grazing plots measured 10 × 10 m. All plots were harvested concurrently every 21–30 days from April‐November for two years (2015 and 2016). A strip from the grazing plots was cut for DM yield determination prior to turning in cattle for grazing. There was an interaction between sward type and defoliation method (p < .01), whereby there was no effect of defoliation method on the PRG‐only swards, however, the annual DM production of PRGWC, 6S and 9S swards reduced under grazing compared to cutting (p < .001; on average 1,929 kg DM/ha lower). Multispecies swards had lower DM production under grazing compared to cutting, while the DM yield of PRG‐only swards was unaffected by defoliation method. [ABSTRACT FROM AUTHOR]

Increasing herbage dry‐matter (DM) production and utilization on‐farm improves efficiency and sustainability. The objective of this study was to investigate the effect of perennial ryegrass, Lolium perenne L., ploidy and white clover, Trifolium repens L., inclusion on herbage DM production and utilization in an intensive animal grazing system, with high nitrogen (N) inputs (250 kg N ha−1) and a high stocking rate (2.75 livestock units ha−1). The study was a 2 × 2 factorial design, consisting of diploid and tetraploid cultivars sown as grass‐only and grass‐white clover to give four sward treatments (diploid‐only, tetraploid‐only, diploid‐white clover, tetraploid‐white clover). These were evaluated at each grazing occasion (8–10 per year) for 3 years (2014–2016). Tetraploid‐white and grass‐white clover swards had a lower sward density (−9 and −8 kg DM cm−1, respectively) and perennial ryegrass tiller density (−820 and −1,436 tillers m−2, respectively) leading to lower postgrazing sward heights (−0.15 and −0.41 cm, respectively), and maintained a superior nutritive value when compared with diploid‐only and grass‐only swards respectively. White clover inclusion resulted in higher productivity characterized by increased herbage DM production (+1,468 kg DM ha−1), improved nutritive value and increased utilization across the three grazing seasons. Varying sward composition with perennial ryegrass ploidy led to improved nutritive value and favourable grazing characteristics in tetraploid swards. [ABSTRACT FROM AUTHOR]

Abstract: BACKGROUND: Including forage legumes in dairy systems can help address increasing environmental/economic concerns about perennial ryegrass monoculture pastures. This work investigated the effect of substituting fresh‐cut grass with increasing quantities of fresh‐cut white clover (WC) on milk fatty acid (FA) profile and transfer efficiency of dietary linoleic (LA) and α‐linolenic (ALNA) acids to milk fat. Three groups of three crossbred dairy cows were used in a 3 × 3 crossover design. Dietary treatments were 0 g kg−1 WC + 600 g kg−1 grass, 200 g kg−1 WC + 400 g kg−1 grass, and 400 g kg−1 WC + 200 g kg−1 grass. All treatments were supplemented with 400 g kg−1 concentrates on a dry matter basis. Cows had a 19‐day adaptation period to the experimental diet before a 6‐day measurement period in individual tie stalls. RESULTS: Increasing dietary WC did not affect dry matter intake, milk yield or milk concentrations of fat, protein or lactose. Milk polyunsaturated FA concentrations (total n‐3, total n‐6, LA and ALNA) and transfer efficiency of LA and ALNA were increased with increasing dietary WC supply. CONCLUSION: Inclusion of WC in pastures may increase concentrations of nutritionally beneficial FA, without influencing milk yield and basic composition, but any implications on human health cannot be drawn. © 2018 The Authors. Journal of the Science of Food and Agriculture published by JohnWiley & Sons Ltd on behalf of Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

The aim of this study was to determine the associative effects between fresh perennial ryegrass and fresh white clover on intake and digestion in sheep. Five proportions of ryegrass and white clover, ranging from 0 to 1 in 0·25 increments ( DM basis), were allocated to two groups of five sheep according to a replicated 5 × 5 Latin square design, and intake behaviour and digestive parameters including methane ( CH4) emissions were measured. Feeding behaviour was affected through increased forage intake when the proportion of white clover was increased, and there were positive associative effects on intake, eating time and eating rate during the main meals consumed immediately after feed was given. These effects seemed to be related to a greater motivation to eat, rather to more efficient digestion, as no difference on DM digestibility (average 766 g kg−1) was detected. There were no differences in CH4 yield (average 18·1 g kg−1 DM intake) among the treatments. The optimal proportion of white clover fed with ryegrass to optimize intake and digestion was between 0·25 and 0·50. These results indicate that mixing perennial ryegrass and white clover positively affects forage intake in sheep and their motivation to eat. [ABSTRACT FROM AUTHOR]

For pastures, root turnover can have an important influence on nutrient and carbon cycling, and plant performance. Turnover was calculated from mini-rhizotron observations for chicory ( Cichorium intybus), lucerne ( Medicago sativa), perennial ryegrass ( Lolium perenne) and white clover ( Trifolium repens) grown in the Manawatu, New Zealand. The species were combined factorially with four earthworm species treatments and a no-earthworm control. Split plots compared the effects of not cutting and cutting the shoots at intervals. Observations were made c. 18 days apart for 2.5 years. This article concentrates on differences between plant species in root turnover in the whole soil profile to 40 cm depth. At this scale, earthworm effects were generally small and short lived. For ryegrass and white clover, root length and mass were linearly related ( R2 = 0.82-0.99). For chicory and lucerne, the relationships were poorer ( R2 = 0.38-0.77), so for those species length turnover may be a poor indicator of mass turnover. Standing root length, total growth and death generally decreased in the sequence ryegrass > lucerne > chicory = white clover. In length terms, scaled turnover (growth divided by average standing root length) generally followed the sequence lucerne > white clover > perennial ryegrass = chicory. Across species the scaled turnover rate averaged 3.4 per year or 0.9% per day. Cutting shoots reduced standing root length, growth and death, but increased scaled turnover. These results indicate fast and prolonged root turnover. For ryegrass and white clover, at least there is need to reappraise how to measure and model shoot : root ratios, dry matter production and carbon cycling. [ABSTRACT FROM AUTHOR]

There is increasing interest in tall fescue ( Festuca arundinacea Schreb.) in Western Europe and elsewhere, mainly because of its better drought resistance and yield potential compared with perennial ryegrass ( Lolium perenne L.). Important drawbacks of tall fescue, compared with perennial ryegrass, are its lower digestibility and voluntary intake. Mixtures of both species might combine the advantages of each, and species interactions may eventually lead to transgressive overyielding. We compared the agronomic performance of tall fescue, perennial ryegrass and tall fescue-perennial ryegrass mixtures, as pure-grass swards or in association with white clover ( Trifolium repens L.). Tall fescue-perennial ryegrass mixtures differed in the proportion and ploidy of the perennial ryegrass component. Yield, feed quality and botanical composition were measured in the 3 years after the sowing year. We found significant effects of ploidy of the ryegrass variety and of the proportion of ryegrass in the initial seed mixture on the botanical composition of the swards. Nevertheless, all swards were dominated by tall fescue at the end of the experiment. No overyielding of the mixtures compared with that of single-species swards was found, but feed quality was intermediate between that of the single-species swards. Mixed swards had better drought resistance than L. perenne and higher feeding quality than F. arundinacea swards. [ABSTRACT FROM AUTHOR]

Nitrous oxide (N2O) emissions are subject to intra- and interannual variation due to changes in weather and management. This creates significant uncertainties when quantifying estimates of annual N2O emissions from grazed grasslands. Despite these uncertainties, the majority of studies are short-term in nature (<1 year) and as a consequence, there is a lack of data on interannual variation in N2O emissions. The objectives of this study were to (i) quantify annual N2O emissions and (ii) assess the causes of interannual variation in emissions from grazed perennial ryegrass/white clover grassland. Nitrous oxide emissions were measured from fertilized and grazed perennial ryegrass/white clover grassland (WC) and from perennial ryegrass plots that were not grazed and did not receive N input (GB), over 4 years from 2008 to 2012 in Ireland (52°51'N, 08°21'W). The annual N2O-N emissions (kg ha-1; mean ± SE) ranged from 4.4 ± 0.2 to 34.4 ± 5.5 from WC and from 1.7 ± 0.8 to 6.3 ± 1.2 from GB. Interannual variation in N2O emissions was attributed to differences in annual rainfall, monthly (December) soil temperatures and variation in N input. Such substantial interannual variation in N2O emissions highlights the need for long-term studies of emissions from managed pastoral systems. [ABSTRACT FROM AUTHOR]

Increasing plant species diversity in grasslands may improve productivity and stability of yields. In a field experiment, we investigated the herbage dry-matter ( DM) yield and crude protein content of two-species swards of perennial ryegrass-white clover ( Lolium perenne L.- Trifolium repens L.) and three-species swards of ryegrass-white clover with red clover ( Trifolium pratense L.). Five different managements represented cutting, grazing and combinations thereof, with different slurry fertilization treatments in 1- to 4-year-old swards. The three-species mixture out-yielded the two-species mixture in years 1 and 2. Across all 4 years, yields were 8-10% higher in cut swards. Inclusion of red clover increased the yields of clover across the 4 years by 51% without fertilizer and by 90% when fertilized. Responses to slurry fertilization were similar in both mixtures and were mainly independent of sward age. There was a complementary effect over the season and across managements. Red clover dominated in the first and third cuts; white clover dominated in the second and fourth cuts. Red clover dominated in cut swards and white clover in grazed swards. Future prospects of the inclusion of red clover in sown swards are discussed. These may include higher nitrogen-use efficiency in ruminants, increased soil fertility and improved sward flexibility to cope with changing managements. The findings also suggest positive yield effects of alternating between cutting and grazing within the season or between years. [ABSTRACT FROM AUTHOR]

The benefits of white clover ( Trifolium repens L.) in pastures are widely recognized. However, white clover is perceived as being unreliable due to its typically low content and spatial and temporal variability in mixed (grass-legume) pastures. One solution to increase the clover proportion and quality of herbage available to grazing animals may be to spatially separate clover from grass within the same field. In a field experiment, perennial ryegrass ( Lolium perenne L.) and white clover were sown as a mixture and compared with alternating strips of ryegrass and clover (at 1·5 and 3 m widths), or in adjacent monocultures (strips of 18 m width within a 36-m-wide field). Pastures were stocked by ewes and lambs for three 10-month grazing periods. Over the 3 years of the experiment, spatial separation of grass and clover, compared with a grass-clover mixture, increased clover herbage production, although its proportion in the sward declined through time (0·49-0·54 vs 0·34 in the mixture in the first year, 0·28-0·33 vs 0·15 in the second year and 0·03-0·18 vs 0·01 in the third year). Total herbage production in the growing season in the spatially separated treatments decreased from 11384 kg DM ha−1 in the first year to 8150 kg DM ha−1 in the third year. Crude protein concentration of clover and grass components in the 18-m adjacent monoculture treatment was greater than the mixture treatment for both clover (310 vs 280 g kg−1 DM) and grass (200 vs 180 g kg−1 DM). There was no clear benefit in liveweight gain beyond the first year in response to spatially separating grass and clover into monocultures within the same field. [ABSTRACT FROM AUTHOR]

In change-over trials, mid-lactation dairy cows were fed concentrate-supplemented, isonitrogenous and isofibrous perennial ryegrass-legume silage diets that satisfied energy requirements but were suboptimal with respect to metabolizable protein supply. Legumes were either birdsfoot trefoil with low levels of condensed tannins (typical for hemiboreal conditions), or white clover. Averaged over two experimental years, birdsfoot trefoil-based silage resulted in lower digestibility ( P < 0·001) of dry matter (50 g kg−1), organic matter (52 g kg−1), neutral detergent fibre (120 g kg−1) and nitrogen (24 g kg−1) and lower rumen total volatile fatty acid concentration (7 m m; P = 0·009). Milk protein yield was 36 g d−1 higher with birdsfoot trefoil silage ( P = 0·002), while raw milk yield tended to be 0·8 kg d−1 higher ( P = 0·06). Rumen ammonia concentration was similar between diets, but milk urea concentration ( P < 0·001), urinary urea excretion ( P = 0·002) and faecal- N proportion ( P = 0·001) were higher with birdsfoot trefoil silage. The results suggest that grass-birdsfoot trefoil silage produced in hemiboreal areas exhibits a protein-sparing effect in dairy rations, despite a low condensed tannin content that is further diluted by companion grasses and ration concentrate proportion. [ABSTRACT FROM AUTHOR]

A series of laboratory experiments was carried out with the main objective of contributing to the development of biosafety testing methods for transgenic plants or plants produced by other novel technologies. The adult stage of a New Zealand native weevil, Nicaeana cervina (Broun) (Coleoptera: Curculionidae: Entiminae), was used as a test insect as this has become well-adapted to introduced pasture species, feeding on both ryegrass [ Lolium perenne L. (Poaceae)] and white clover [ Trifolium repens L. (Fabaceae)]. Ryegrass plants used in experiments were infected with strains of the symbiotic endophytic fungi Neotyphodium lolii (Latch, M.J. Chr. & Samuels) and Epichloe festucae Leuchtm., Schardl & M.R. Siegel and included a transgenic endophyte, which was modified to eliminate production of the insect deterrent, peramine. Nicaeana cervina was exposed to these endophyte-infected plants along with endophyte-free ryegrass. Weevils were also exposed to white clover with high or low levels of cyanogens, and to white clover selections bred conventionally to contain high or low levels of crude protein. These bioassays were carried out sometimes over a series of time intervals, and weevil survival, feeding, and reproductive performance variables were measured. Nicaeana cervina survival was generally high, although feeding and oviposition were variable between experiments despite high replication in some cases. A summary of significant differences obtained across all experiments suggested that data on the proportion of weevils feeding and amounts of leaf material consumed were more often significantly different than treatment effects on survival or reproductive performance. A positive relationship between the proportion of weevils feeding and those ovipositing was found, suggesting that a 50% reduction in feeding would result in a 28% reduction in the proportion of weevils ovipositing. Power analysis using the range of values recorded for the variables measured indicated that for proportions of weevils surviving, feeding, or fecund, about 35–42 replicates would be required for a 40% difference in values. For measures of leaf consumption and numbers of eggs per female, fewer replicates were required for 95% power when these values were at the higher end of the range than when they were at the lower end of the observed range. The usefulness of the case study test insect and risk assessment protocols used for biosafety testing are discussed. [ABSTRACT FROM AUTHOR]

Perennial ryegrass and perennial ryegrass/white clover permanent dairy pastures are compared with respect to productivity, environmental impact and financial costs in nitrate vulnerable zones (NVZ) in the UK. With appropriate management, and utilisation of recommended perennial ryegrass and white clover cultivars, white clover is likely to stabilise at around 20% of total dry matter production in a mixed pasture. Plant dry matter production and milk production from a perennial ryegrass/white clover pasture are likely to be similar to that from a perennial ryegrass pasture receiving 200 kg N ha−1 annum−1 and around 70% of that obtained with perennial ryegrass supplied with 350–400 kg N ha−1 annum−1. Nitrate, phosphorus and methane losses from the system and decreases in biodiversity relative to a grazed indigenous sward are likely to be similar for a perennial ryegrass/white clover pasture and a perennial ryegrass pasture receiving 200 kg N ha−1 annum−1: nitrate leachate from both systems is likely to comply with European legislation. Greenhouse gas emissions resulting from nitrogen (N) fertiliser production would be avoided with the perennial ryegrass/white clover pasture. Within NVZ stocking rate restrictions, white clover can provide the N required by a pasture at a lower financial cost than that incurred by the application of N fertiliser. [ABSTRACT FROM AUTHOR]

Nitrogen (N), accumulating in stubble, stolons and roots, is an important component in N balances in perennial ryegrass–white clover swards, and the effects of cutting frequency on the biomass of above- and below-harvest height were studied during two consecutive years. Total dry matter (DM) and total N production, and N2 fixation, were measured at two cutting frequencies imposed in the summers of two years either by cutting infrequently at monthly intervals to simulate mowing or by frequent cutting at weekly intervals to simulate grazing. Total DM production harvested was in the range of 3000–7000 kg DM ha−1 with lower DM production associated with the frequent cutting treatment, and it was significantly affected by the different weather conditions in the two years. The higher cutting frequency also reduced the biomass below harvest height but the different weather conditions between years had less effect on stubble and, in particular, biomass of roots. The biomass of roots of white clover was significantly lower than that of roots of perennial ryegrass and remained at a relatively constant level (200–500 kg DM ha−1) throughout the experiment, whereas the biomass of perennial ryegrass roots increased from 2400 kg DM ha−1 in the year of establishment to 10 200 kg DM ha−1 in the infrequent cutting treatment and 6650 kg DM ha−1 in the frequent cutting treatment by the end of the experiment, giving shoot:root ratios of 4·7–16·6 and 0·5–1·6 for white clover and perennial ryegrass respectively. Annual N2 fixation was in the range of 28–214 kg N ha−1, and the proportion of N fixed in stolons and roots was on average 0·28. However, as weather conditions affect the harvested DM production and the shoot:root ratio, care must be taken when estimating total N2 fixation based on an assumed or fixed shoot:root ratio. [ABSTRACT FROM AUTHOR]

There is a need to evaluate grass varieties under grazing management to allow selection of varieties to increase animal performance. However, the evaluation of animal performance under grazing with each variety is arduous and time-consuming. An alternative is to describe the preference by grazing animals when given a choice of different varieties. Indeed, there is some indications that preference is related to variety characteristics such as leaf content or digestibility, characteristics having also an impact on the level of intake of this variety. However, preference for grass varieties, when sown alone, may not reflect agricultural practice as grasses often occur in mixed swards, associated with white clover. So, the aim of the present work was to determine whether, under grazing management, cattle expressed selections when given a choice of mixed swards in which different perennial ryegrass varieties were grown in association with a common white clover variety at two levels of fertilizer application (60 or 160 kg N ha−1 annum−1). The preference for perennial ryegrass varietyper sewas then assessed after taking white clover content into consideration. The results show that there were significant differences in preference for perennial ryegrass varieties,per se, even for varieties with the same heading date and ploidy. The effect of white clover cover on sward selection was more marked in swards which received the higher level of nitrogen fertilizer application which may have been related to a more variable white clover content between swards. This suggests that, under low nitrogen fertilizer application, differences in perennial ryegrass varieties preference can be determined in the same experiments as are used to determine ryegrass varieties persistence in association to white clover. Nevertheless, before such‘variety preference’ tests can be applied in practice, a validation of the possible correlation between‘variety preference’ and‘variety intake’ will be necessary. [ABSTRACT FROM AUTHOR]

Single pugging events, which involve remoulding of the soil around the hooves of livestock during treading, of moderate or severe pugging intensity were imposed in plots in a long-term white clover-ryegrass pasture during spring, by using dairy cows at varying stocking rates (4·5 cows 100 m−2 for 1·5 or 2·5 h respectively). Changes in the growth and morphology of white clover were investigated over the following 12 months. Defoliation at approximately 3-week intervals was carried out by mowing. Annual herbage production was reduced following moderate and severe pugging proportionately by 0·16 and 0·34 compared with the non-pugged control treatment. The corresponding decreases in white clover production were 0·09 and 0·52 respectively. Annual perennial ryegrass production was reduced by 0·37 under severe pugging. Pugging had an immediate adverse effect on growth of white clover which persisted for up to 156 d, and coincided with a large decrease in the proportion of white clover in herbage over the same period (e.g. 0·40 vs. 0·12, in control and severely pugged treatments, respectively, on day 112). In comparison, recovery in ryegrass growth was apparent after 50 d in severely pugged treatments, indicating that white clover is more vulnerable to severe pugging than perennial ryegrass. Analysis of individual white clover plants extracted from turves (300 mm × 300 mm) showed that direct hoof damage, fragmentation and burial of stolons were the major factors which reduced white clover production, rather than the changes in soil physical properties measured. Morphological characteristics associated with plant size (e.g. stolon length, growing points, and leaf numbers) all decreased under pugging. The situation had reversed by late summer, with larger plants dominating pugged plots, and coincided with the recovery of the proportion of white clover in herbage. Strategic pasture management practices, such as restricted grazing and the use of stand-off pads when soils are overly wet, are suggested as means of minimizing treading damage to pasture and reducing negative impacts on the growth and productivity of white clover. [ABSTRACT FROM AUTHOR]

Abstract Two experiments were carried out to evaluate the performance of blends of three white clover (Trifolium repens L.) varieties in comparison with the component varieties and three other varieties sown individually in a mixture with perennial ryegrass (Lolium perenne L.). The plots were grazed rotationally in Experiment 1 by cattle and sheep and in Experiment 2 by sheep alone. In both experiments, the blend was composed of three medium-leaved varieties (AberDai, AberVantage and AberHerald), but with different relative contributions of the three varieties in the two experiments. Dry matter (DM) yields of white clover and perennial ryegrass were assessed in replicate plots for two years (1999 and 2000) after the establishment year. In Experiment 1, there was no significant difference between the DM yields of white clover or perennial ryegrass in either year. The decline in DM yield of white clover between years that was observed for some varieties was not found for the blend. In Experiment 2, significant differences were found in DM yields of white clover in both years. In 1999, AberDai had the highest DM yield. In 2000, AberHerald and AberVantage had the highest DM yields, and AberDai showed a decline in DM yield that was mirrored by the mean for all the white clover varieties. In both experiments, the blend did not show significantly higher DM yield than one or more of its components; indeed, in Experiment 2, it was significantly lower yielding than AberDai in 1999. However, where one component of the blend declined in DM yield between years, this was compensated for by an increase in the yield of another component. These preliminary findings suggest that the yield stability of blends may give them a potential role in agricultural practice. [ABSTRACT FROM AUTHOR]

Three replicate paddocks, each of 0·235 ha, containing adjacent monocultures of perennial ryegrass or white clover [50:50 by ground area, 6 cm sward surface height (SSH) at start of experiment] were continuously stocked with three yearling and four mature non-lactating, non-pregnant Scottish halfbred ewes for 12 weeks. Herbage intake, grazing behaviour and dietary selection were measured on seven occasions. Clover SSH declined rapidly over the first 5 weeks then stabilized at 1·2–1·6 cm, whereas perennial ryegrass SSH rose slightly initially, then declined gradually. Animals initially included proportionately c . 0·6 white clover in their diet but, by the end of the experiment, this had fallen to 0·3. Total daily herbage intake declined over the 12 weeks from 1·8 kg dry matter (DM) day–1 at the start to 1·0 kg DM day–1 . Total grazing time increased from 561 min day–1 to 649 min day–1 at the end of the experiment. The results suggest that, despite overall herbage depletion and a greater depletion of white clover than perennial ryegrass as a result of the initial partial preference for white clover, the animals traded-off a reduced total intake and an increased grazing time in an attempt to maintain their initial preferred dietary composition. [ABSTRACT FROM AUTHOR]

AbstractTwo medium leaf size varieties of white clover (Trifolium repens L.) were grown in mixture with a range of grass species and varieties in a field experiment conducted over 4 years. The clovers were grown singly or as a blend in swards with a tetraploid perennial ryegrass (Lolium perenne L.), a diploid Italian ryegrass (Lolium multiflorum L.) or tetraploid hybrids between these two species (Lolium x boucheanum Kunth). These grasses were also grown in monoculture. Swards were managed in a regime involving two periods of sheep grazing, two periods of cattle grazing and a silage cut in the same year for 4 years. The objectives of this experiment were 3-fold: (1) to examine the yield and persistency of white clover in highly productive systems with modern perennial, hybrid and Italian ryegrasses; (2) to compare the performance of white clover varieties grown singly in mixture with grasses with their performance together as a blend, and (3) to examine the persistency of new Italian ryegrass varieties, exemplified by AberComo. The clover content of the sward remained high throughout the experiment, with a mean of 31 % overall. Differences in clover yield between plots were largely attributable to the effects of companion grasses. Total yields were very similar in plots containing different clover varieties and in plots where these varieties had been grown singly or as a blend. Grass yields in mixture were greater than those in monoculture but showed similar relative rankings. The diploid Italian ryegrass variety AberComo showed an unexpectedly high yield in the 4th year of the experiment. The implications of these results for strategies for productive, sustainable agriculture using modern white clover and ryegrass varieties are discussed. [ABSTRACT FROM AUTHOR]

Non-pregnant, non-lactating ewes grazed adjacent monocultures of white clover and perennial ryegrass with three sward surface height (SSH) combinations [6 cm white clover: 6 cm perennial ryegrass (c6g6), 3 cm white clover: 6 cm perennial ryegrass (c3g6), 3 cm white clover: 9 cm perennial ryegrass (c3g9)] at two stocking densities (21·3 or 29·8 ewes ha–1). Immediately prior to the experiment, all ewes grazed a c6g6 sward. Grazing time on each plant species was recorded during daylight over two 48 h-test periods. Subsequently, herbage intake rates for each species at each SSH were measured allowing intakes of each species to be calculated. For the first 24 h of both test periods (D1), ewes on treatment c3g6 spent less time grazing white clover than those on treatment c6g6 (228 vs. 362 min) and more time grazing perennial ryegrass (360 vs. 182 min). Total grazing time on treatment c3g6 was more than on treatment c6g6 (587 vs. 544 min) but the difference was not significant. Perennial ryegrass intake was higher (895 vs. 452 g), and white clover intake (814 vs. 1687 g), total intake (1719 vs. 2140 g) and proportion of white clover in the diet (0·460 vs. 0·794) were lower for treatment c3g6 than treatment c6g6. There were no significant differences in total grazing time, grazing time on either species, proportion of grazing time on white clover or proportion of white clover in the diet between treatment c3g6 and treatment c3g9. However, the higher intake rate of perennial ryegrass in treatment c3g9 led to higher perennial ryegrass and total intakes. For the second 24 h of both test periods (D2), ewes on treatment c3g6 again spent more time grazing perennial ryegrass than on treatment c6g6 (270 vs. 161 min) but time spent grazing white clover was similar (318 vs. 308 min). Total grazing time was significantly higher on treatment c3g6 than on treatment c6g6 (588 vs. 469 min) but proportion of grazing time on white clover was similar... [ABSTRACT FROM AUTHOR]

The period of leaf expansion in white clover (Trifolium repens) grown with perennial ryegrass (Lolium perenne) in mixed swards and the relationship between the period of leaf expansion and leaf appearance rate were examined in a field experiment in The Netherlands in which two cutting frequencies (low and high) and three white clover cultivars (Alice, Retor and Gwenda) were used. A significant positive correlation existed between the period of leaf expansion and leaf appearance rate under a low frequency of cutting, indicating that a longer cutting interval might allow the expression of cultivar and environmental differences in both leaf expansion and leaf appearance rate. In most cases, frequent cutting tended to shorten the period of leaf expansion, which may be an important cause of lower dry-matter yield in the high frequency of cutting treatment. The large-leaved cv. Alice had a significantly longer period of leaf expansion than the other cultivars under frequent cutting in autumn. This might partly account for the mixtures with Alice having a greater proportion of white clover than the mixtures with Retor and Gwenda in autumn. Some of the variation between low- and high-frequency cutting treatments in the period of leaf expansion could be explained by mean and minimum temperatures (38% and 15% respectively). [ABSTRACT FROM AUTHOR]

The selection by sheep (six Coopworth ewe hoggets, 44·3 ± 4·6 kg live weight) and goats (six Saanen/Anglo-Nubian yearling males, 38·1 ± 3·8 kg live weight) for perennial ryegrass (Lolium perenne) and white clover (Trifolium repens) and for sward height was measured in two experiments involving paired turves. Pairs of turves with herbage of differing height and of either the same or different plant species were offered. One sward (fixed height species, FHS) was always offered at 130 mm and the other (variable height species, VHS) at 130, 90 or 50 mm. Turves (450 mm × 220 mm) were cut to a soil depth of 100–150 mm from areas of perennial ryegrass and white clover regrown to the desired height after previously being cut to 30 mm. Each turf in a pair was weighed (±1 g) before and after grazing by penned animals maintained on a barley-based pelleted diet. The number of prehending bites taken from each turf was recorded over a grazing period (128 ± 12 s). Bite mass, bite rate and intake rate were calculated. As the sward height of the VHS turf declined, an increasing proportion of the diet was selected from the 130 mm turf. When averaged over all height contrasts, both animal species selected a higher proportion (0·776 ± 0·026) of their diet from 130-mm white clover than from 130-mm perennial ryegrass (0·591 ± 0·018) turves. On average, goats selected a higher proportion (0·721 ± 0·022) of their dry-matter (DM) intake from the 130-mm turf than sheep (0·646 ± 0·019), but the effect was not consistent. In contrasts with perennial ryegrass as the VHS (and both perennial ryegrass and white clover as FHS), the proportion of the diet selected from the 130-mm turf was very similar for both animal species. However, with white clover as the VHS (and both perennial ryegrass and white clover as FHS), goats selected a higher proportion of their intake from the 130-mm... [ABSTRACT FROM AUTHOR]

In a field experiment carried out over 3 years, the nitrate content of herbage from perennial ryegrass (Lolium perenne) swards increased exponentially with nitrogen application rate, but herbage nitrate content appeared to reach potentially dangerous concentrations only when nitrogen application rates were greater than those needed to stimulate dry-matter production. Thus, on average over all the harvests, maximum yield could be obtained with annual application rates of 400 kg N ha–1 (six applications of 67 kg N ha–1) for perennial ryegrass and 300 kg N ha–1 (six applications of 50 kg N ha–1) for perennial ryegrass/white clover (Trifolium repens) swards, whereas the mean nitrate concentrations were 3340 and 2929 mg NO3 kg–1 dry matter (DM) respectively. Nitrate content, however, varied considerably from harvest to harvest, reaching maxima of 9345 mg NO3 kg–1 DM at 400 kg N ha–1 for perennial ryegrass and 6255 mg NO3 kg–1 DM at 300 kg N ha–1 for perennial ryegrass/white clover. The nitrate content of herbage from perennial ryegrass/white clover swards was always greater than that of perennial ryegrass swards receiving the same rate of nitrogen application, even though in the herbage from the mixed sward the nitrate content of white clover was usually less than half that of the perennial ryegrass component. The physical environment did not have a clearly interpretable effect on nitrate content, although herbage harvested in May had a much lower nitrate content than that harvested at any other time of the season. It was not possible to find a single multiple regression equation relating herbage nitrate content to nitrogen application and to other environmental variables that explained more than 60% of the variance in herbage nitrate, but it is suggested that, by reducing the later-season nitrogen applications from 67 to 50 and finally to 33 kg N ha–1 for perennial ryegrass and from 50 to 33 kg N ha–1 for perennial ryegrass/white clover, it would be possible to achieve over 90% of the maximum yield while reducing average nitrate content to <40% of that at maximum yield, with no samples containing more than 2300 mg NO3 kg –1 DM. [ABSTRACT FROM AUTHOR]

The severity of damage by certain invertebrate species to white clover (Trifolium repens) leaves on the main stolons of plants grown in mixed perennial ryegrass/white clover swards was examined in a field experiment in the Netherlands in which two cutting frequencies (high and low) and three white clover cultivars (Retor, Alice and Gwenda) were used. The damage to the leaves was described in terms of the numbers of damaged leaves and the extent of that damage (slight <20%, moderate 20–50% and heavy >50%). The relationships between leaf damage and sward characteristics (white clover content, above-ground biomass and sward height) were evaluated throughout the growing season. Over the whole experimental period, 23·7% and 27·4% of the total number of leaves produced per stolon were damaged by slugs and weevils in the low- and high-frequency cutting treatments respectively. High-frequency cutting increased the number of leaves in the total leaf damage and moderate leaf damage categories by 21·4% and 34·8%, respectively, compared with the low-frequency cutting. The cv. Retor (medium-leaved) experienced the most severe damage by invertebrates. It had much higher leaf damage than cvs Alice (large-leaved) and Gwenda (small-leaved) at either cutting frequency, both in the total number of damaged leaves and in the different damage categories. Differences among cultivars in the number of damaged leaves and relative leaf damage occurred primarily in spring, late summer and autumn, but did not differ during the early- and mid-summer months. This study indicates that variations in leaf damage among clover cultivars were associated with differences in measured sward characteristics. Both the number of damaged leaves and the relative leaf damage were strongly negatively correlated with white clover content and biomass in spring, late summer and autumn under each cutting treatment. White clover content and biomass explained 65%, 59% and 50% of the variation in the number of damaged leaves in spring, late summer and autumn, respectively, and 58%, 57% and 45% of the variation in relative leaf damage in these three periods. Thus, sward characteristics may play a role in regulating the severity of invertebrate damage to clover leaves in addition to the primary effects of HCN. [ABSTRACT FROM AUTHOR]

Persistence of white clover (Trifolium repens) in mixtures was studied in a long-term experiment. Mixtures of two cultivars of perennial ryegrass (Lolium perenne) with contrasting growth habits and three white clover cultivars differing in leaf size were sown in 1991 and evaluated at two cutting frequencies. During 1995 and 1996 mixtures with large-leaved white clover cv. Alice had the highest dry-matter (DM) content, clover and N yield, and the highest white clover content, and mixtures with medium-leaved Retor the lowest, whereas mixtures with small-leaved Gwenda yielded most grass DM. In 1995 averaged over cutting treatments and mixtures, the mixtures yielded 11·8 t DM ha-1 with a white clover content of 0·6; the apparent N fixation was 393 kg N ha-1. In 1996 these values declined to 8·5 t DM ha-1, 0·48 white clover and 236 kg N ha-1. There was no significant effect of cutting frequency on DM yield or white clover content, whereas the effects of grass cultivar were not consistent. In spring there was a peak in the DM production of the mixtures, coinciding with a peak in production of the grass component. However, in summer and autumn the seasonal pattern of DM production of the mixtures was similar to that of the white clover component. Both cultivars of perennial ryegrass showed the same seasonal response, but the seasonal growth pattern of white clover differed slightly between clover cultivars and cutting treatments. In later years only one cutting frequency was imposed, and no yield measurements were taken. White clover was judged to have performed well during 1997; the clover content in September was very high (0·76), whereas in October 1998 it was 0·45. Mixtures with Alice contained most white clover. Despite fluctuations in white clover content during 1991–98, all clover cultivars had persisted 7 years after sowing, irrespective of companion grass cultivar, at both cutting... [ABSTRACT FROM AUTHOR]

The effect of defoliation interval on growth patterns of contrasting perennial ryegrass (Lolium perenne)–white clover (Trifolium repens) mixtures was studied. The dynamics of increase in leaf area, light interception and dry-matter (DM) production were measured within successive regrowth periods. No N fertilizer was applied. During 1995 six mixtures were cut eight (F1) or six times (F2) at a stubble height of 5 cm. The stubble composition was stable throughout the growing season: after harvest about 50 g DM m-2 (with a white clover proportion of 0·52) was present with a leaf area index (LAI) of 0·5 (0·38 white clover). The percentage of intercepted radiation after cutting was 20–30% and increased during 3 weeks to about 95%. The relative growth rate of leaf area and DM was higher for white clover than for perennial ryegrass, with the proportion of clover in the LAI and DM increasing during each regrowth period. Mixtures with large-leaved white clover cv. Alice had a lower initial clover content after harvest, but a more rapid increase in clover LAI and DM than mixtures with the smaller leaved cvs Gwenda or Retor. Alice had the highest total and clover LAI and DM at harvest. Cutting frequency affected the change in white clover–perennial ryegrass ratio during regrowth. This was significantly higher in mixtures with Alice than in mixtures with Gwenda, but only under less frequent cutting (F2). In spring there was a mean white clover proportion of about 0·55 in the LAI and 0·45 in the total harvested DM. In summer the white clover proportion in the LAI and DM increased to 0·70–0·75. There was a decline during autumn, especially in F2 and in the mixtures with the small-leaved white clover cv. Gwenda and the medium-leaved cv. Retor. In contrast, grass DM and LAI declined from spring to summer. The decline in clover LAI in autumn was similar in Alice and Gwenda at frequent cutting (F1), but... [ABSTRACT FROM AUTHOR]

Pure stands of Trifolium repens L. N.Z. Huia and Lolium perenne L. S32 and mixtures of various densities and frequencies were treated with sulphuric acid solutions of pH 2.5, 3.5 and 5.6. The species yield was recorded over live sequential harvests. Multifactorial response equations were used to describe the behavior of the species yield as a function of acidity and the density of both species. Predictions, made through these models, showed that the response of yield of these species to simulated acid rain treatments varied greatly depending on the planting density, the time of harvesting and on whether the plants were growing in monoculture or in mixture. This suggests that it is not sufficient to consider the effects of experimentally applied acid rain on single individuals or low density stands, since the results obtained will not reflect the response in a close canopy sward. [ABSTRACT FROM AUTHOR]

Shoot concentrations of Se associated with a 10% reduction in dry matter yield were established for perennial ryegrass (Lolium perenne L.) and white clover (Trifolium repens L.) grown in sand culture. Selenite-treated plants had lower shoot concentrations of Se than those treated with selenate; the critical toxic values associated with a 10% reduction in growth were 48 and 320 µg Se g-1 dry matter shoots for ryegrass plants, and 160 and 330 µ Se g-1 dry matter shoots for white clover plants, respectively. Differences in the mode of absorption of selenite and selenate, and in the distribution and chemical form of Sc found in the plant after absorption, probably account for this disparity in toxicity. While both selenate and selenite increased the Se concentration in the tissues of the plants to high levels, a greater proportion of the absorbed Se was transported to the shoots of the selenate-treated plants than of those treated with selenite. Increasing supplies of selenate were associated with a reduction in chlorophyll content. Contrary to the concept of a common uptake mechanism in the roots for selenate and sulphate, increasing supplies of selenate had a synergistic effect on S concentrations in the shoots rather than the expected antagonistic effect. [ABSTRACT FROM AUTHOR]

In six experiments Lolium perenne L. and Plantago lanceolata L. were grown together in pots. Two experiments also included L. perenne alone, P. lanceolata alone, or L. perenne + Trifolium repens L. In five of the experiments prior sterilization of the soil followed by reinoculation was used to obtain two treatments, one having plants infected with vesicular-arbuscular mycorrhiza, the other non-mycorrhizal. The shoots of some plants in each pot ('donors') were injected with 32P. After a week these shoots were removed, and after a further week the remaining plants ('receivers') were harvested and their 32P content determined. In all experiments and species-combinations there was some 32P transfer to the shoots of both mycorrhizal and non-mycorrhizal receiver plants. The amount of transfer in mycorrhizal treatments was 2 to 8-fold greater than in non-mycorrhizal treatments, except in one experiment where mycorrhizal infection was very low. There was no clear difference between the different species combinations in the amount by which phosphorus transfer was enhanced by mycorrhizas. These results show that mycorrhizas can increase phosphorus transport between plants, but do not show whether there is direct transport from one root to another via interconnecting hyphae or whether the phosphorus must leave the donor root before being taken up by mycorrhizal hyphae. [ABSTRACT FROM AUTHOR]

The effect of long-term carbon dioxide enrichment on competition for nutrients and light in a ryegrass/clover association were determined for simulated swards of perennial ryegrass (Lolikum perenne L. cv. parcour) and white clover (Trifolium repens L. cv. Karina), which were grown as monocultures and in three mixtures (25/75, 50/50, 75/25), according to the replacement design, at tow levels of nitrogen (N) supply (no additional N and 200 kg N ha-1) and at season-long ambient (380 ppm) and elevated (670 ppm) CO2 concentrations in open- top chamebers. Stands were cut foru times, at about monthly intervals, to a height of 5 cm. Plant material was separated into different species, fresh and dry weights were determined and the content of macroelements (N, P, K, S, Mg) in both species was measued. In addition, plant height of both species at harves dats and during several regrowth periods was monitored. Results indicate that both species made demand on different resources and profited from growht in a mixed sward. CO2- related yield increase amounted to 16-42% for white clover whera the effect of high CO2 on rygrass yield ranged between -33% and +9% dependign on N supply, mixture and year. As a result the contribution of white clover to total yield in mixed swards was singifcantly enhanced by CO2 enrichment at many harvests in both N supply treaements. Without additional N supply, shoot competition for lighr was intensified by CO2 enrichment to the disadvantage of ryegrass, since clover petriles grew longer and ryegrass was shorter at elevated CO2. With N fertilization, no marked effect of CO2 enrichment on interspecific competition could be observed. [ABSTRACT FROM AUTHOR]

The aim of this study was to investigate whether symbiotic nitrogen fixation in white clover nodules limits nitrogen supply and hence clover growth by repeated defoliation at two cutting heights. Other possible factors governing symbiotic nitrogen fixation in the field were also elucidated. Using 15N, a 2-year field experiment including white clover (Trifolium repens L. cv. Ladino) and perennial ryegrass (Lolium perenne L. cv. Bastion) in monocultures and in mixtures was conducted in Eschikon, Switzerland. The effect of two cutting heights (4 cm and 10 cm above ground level) on the performance of symbiotic nitrogen fixation of white clover in the different sward-types was investigated. After each harvest, the plots were fertilized with 3 g N m-2 (equivalent to 30 kg N ha-1 cut-1 or 210 kg N ha-1 year-1). In both years, white clover grown in a mixture with grass received a significantly higher percentage of nitrogen from symbiotic fixation compared with clover grown in monoculture. This phenomenon is attributed to the strong competitiveness of ryegrass in soil nitrogen uptake. Consequently, white clover in the clover--ryegrass mixture was more dependent on symbiotic nitrogen fixation than that grown in monoculture. The cutting height did not preferentially influence symbiotic nitrogen fixation, as opposed to the uptake of mineral nitrogen from the soil. From this finding it is suggested that symbiotic nitrogen fixation did not limit the supply of nitrogen to clover and hence its growth. It is proposed that symbiotic nitrogen fixation in white clover is regulated by the demand for nitrogen rather than by the availability of carbohydrate reserves in the stolons. Symbiotic nitrogen fixation should thus be looked upon as an integrated plant growth factor and not as an isolated phenomenon. [ABSTRACT FROM AUTHOR]

Analysis of a half diallel cross among four white clover cultivars, grown as monocultures and in mixtures (duocultures) with two separate perennial ryegrass cultivars, confirmed that for stolon and leaf number a higher proportion of the genetic variance in duocultures was non-additive. For canopy height and dry weight, however, this proportion was less affected by inter-specific competition. An additive-dominance model of gene action sufficed for all four characters in monocultures, but in duocultures epistasis was just one of the factors complicating the genetic picture. This, coupled with short-term reversals in the direction of dominance, merely illustrates the complexity of breeding white clover cultivars, Possible future developments in the breeding of white clover are discussed in the light of these results. [ABSTRACT FROM AUTHOR]

A diallel cross amongst four contrasting white clover varieties was used provide genetic information on those characters which affect the productivity of white clover-perennial ryegrass mixtures when grown under a cutting-only management regime. Generally speaking those characters recorded on the clover families and in mixtures exhibited highly significant additive and non-additive genetic effects, though for some characters the latter could not be ascribed solely to dominance effects. For two of the clover characters, stolon and leaf number, the generic picture was radically altered in mixtures by the effects of inter specific competition. Pseudogeneric effects were also detected for the grass characters, but it was suggested that the two ryegrass varieties used here were exhibiting phenotypic plasticity. As a group the tour intra-varietal crosses performed significantly better than the six inter-varietal crosses for all clover and mixture characters. Only one of the inter-varietal crosses had significantly positive specific combining ability effects or most characters and that was between the two long established varieties "S. 184" and "S. 100." The implications of these results for the breeding of white clover varieties for use in mixtures are briefly discussed. [ABSTRACT FROM AUTHOR]

(1) Several features of the physiology of leaf expansion and the turnover and fate of leaves of two contrasting forage species were studied under continuous grazing to identify the mechanisms that control the relative performance of these species in a mixture. For this swards of perennial rye-grass and white clover were maintained at three intensities of continuous grazing by sheep (sward surface height of 3.6 and 9 cm) and a heavily fertilized grass sward was maintained at 6cm. (2) Grass and clover leaves appeared on average at a similar rate, but grass leaves appeared more slowly in the swards than in the short ones. In clover, leaf appearance was unaffected by grazing intensity but in the tall swards the leaves took longer to complete their expansion. (3) Growing clover leaves escaped grazing by appearing and expanding close to the soil surface, but once expanded near the top of the canopy, they were soon grazed, often in their entirety. Grass leaves were grazed earlier, often while they were still growing, but defoliation was only partial. This and a difference in the pattern of leaf unfolding, led to differences between grass and clove in the age structure of the leaf area in the canopy. (4) Grass and clover also differed in their degree of investment in lamina. Ungrazed youngest expanded units of clover had a smaller proportion of lamina to total weight than grass when the total size of the unit was large (e.g. under lenient grazing). But clover had a greater specific leaf area than grass in all cases. (5) These findings explain how clover had an advantage over grass during summer grazing and increased its proportion in the mixture. [ABSTRACT FROM AUTHOR]

I. A sustainable, low-input land use might be achieved by the use of grazed grass- legume mixtures. However, maintaining the species balance has proven to be difficult, especially as grating provides differential defoliation and regrowth. Since changes in the sward botanical composition can be ascribed to species differences in growth, senescence or intake, a method that yields independent estimates of these three fluxes for both components of a grazed grass-legume mixture is needed. 2. The objective of this paper is to present and assess such a detailed tissue turnover method based on non-destructive measurements of individually marked population units. This method was applied during two spring and summer growing seasons to a ryegrass-clover mixture continuously or rotationally grazed by sheep and is assessed using these experimental results. 3. Defoliation was measured on grazed population units (i.e. grass tillers; elongated and axillary shoot growing points of clover) To calculate the growth rate. of defoliated leaves, a sample of ungrazed leaves of each defoliation status (with or without previous defoliation) was used. Additionally, for clover, a sample of ungrazed leaves of each 'botanicaI number' was also required. The mean extension rates of leaves that underwent defoliation during an observed period. and of leaves that did not, was not significantly different during the preceding period. 4. The estimates of the mixture growth flux varied by less than 10 and 17% when the mean values of the gravimetric coefficients and of the density of the population units. respectively, were increased by one standard deviation. The net recruitment of new population units led to an underestimation of the growth flux by 8 and 5% with grass and clover, respectively. 5. The method was partially validated, by comparing independent estimates of the mean dry-weight of the population units based either on tissue turnover or on destructive measurements. [ABSTRACT FROM AUTHOR]