Competition between white clover (Trifolium repens L.) and subterranean clover (Trifolium subterraneum L.) in binary mixtures in the field

White clover, (cv. Haifa) and subterranean clover (cv. Seaton Park) were grown in binary replacement series mixtures in the field at proportions of 100:0, 90:10, 50:50. 10:90 and 0:100, and cut every four weeks over three growing seasons from 1985 to 1987 at Scone, New South Wales (NSW) (32°S).
Relatively low plant densities minimized competition in 1985, but in subsequent seasons Haifa and Seaton Park competed vigorously for the same resource;.; usually having relative crowding coefficients greater than 1.0, and relative yield totals greater than 1.0 in spring of 1986 and 1987, and autumn 1987. This over-yielding appeared to be due to some complementarity of leaf morphology and canopy architecture.
Haifa severely depressed seed production of Seaton Park in mixtures. Haifa regenerated as an annual in 1986, but as a perennial, from surviving stolons, in 1987 owing to lower maximum temperatures and better rainfall distribution in late summer and autumn of 1987.
It is concluded that white clover can survive severe competition from subterranean clover as a seedling, and if moisture allows, may severely depress seed production from subterranean clover, regardless of whether plants are annual or perennial in origin. Spatial separation may minimize competition in average years but competition effects may be severe in seasons with sufficient summer rainfall for perennation of white clover, and seasonal autumn rainfall for germination of subterranean clover.     

Influence of seed quality on seedling growth of white clover (Trifolium repens L.)

The influence of seed quality on seedling growth of white clover cv Makibashiro plants was examined in a controlled environment. The average dry matter (DM) yield of 70-day-old seedlings from a poor-quality seed lot was significantly less than that from a high-quality seed lot. In both seed lots, a linear relationship between the DM yield and time from sowing was observed. The slope of regression of DM yield against time from sowing for the poor-quality seed lot was less than the equivalent slope of the high-quality seed lot, suggesting that possible avenues for increased DM accumulation in a high-quality seed lot are somewhat indirect (time of emergence, uniform emergence etc.); a direct effect of seed quality on the photosynthetic ability of plant tissue seems less likely to occur. The root: shoot ratios declined in both groups of plants with increasing age. Seedlings from the high-quality seed lot reached a stable root:shoot ratio (equilibrium state) much earlier than those from the poor quality seed lot. The seed quality had no influence on the proportion of DM partitioned to various organs. The results of this study are discussed in relation to field establishment.     

Sclerotinia trifoliorum Erikss. on white clover (Trifolium repens L.)

Herbage dry-matter yields of sown plots of white clover were greatly reduced by a natural infection of clover rot ( Sclerotinia trifoliorum ), the extent of the reduction being related to the level of infection. Examination of seasonal yield patterns suggested that although the plants apparently recovered from the disease it re-exerted its influence later in the season. No effects on seed yield could be detected but effects on the development of inflorescences and the proportion of ripe heads surviving to harvest were noted. Marked differences between varietal types existed for some of the characters examined.     

Causes of low seed set in white clover (Trifolium repens L.)

A field experiment was conducted to clarify the factors responsible for poor seed set in four white clover ( Trifolium repens L.) cultivars. Although the mean number of ovules per floret was 5·18–5·29, the average number of seeds per floret was found to be only 1·23-1·82. A stainclearing technique was used to examine the cytoplasmic state of the embryo sac in intact, unfertilized, mature ovules and it was found that 28–33% of ovules per carpel were sterile. The abortion rate of fertilized ovules and immature seeds (7 days after pollination) ranged between 32 and 34%. Beyond this period, it was observed that only a very small proportion of the total seeds were lost. The observation of high pollen fertility and a high pollen load strongly suggests that poor pollination does not account for the reduced number of seeds per floret. A 'nutrient competition' hypothesis was proposed for high ovule sterility and post-fertilization abortion of developing seeds.     

Peduncle characteristics, inflorescence survival and reproductive growth of white clover (Trifolium repens L.)

Field experiments were carried out in four harvest years to compare the peduncle characteristics and reproductive growth of the small-leaved white clover ( Trifolium repens L.) cv. AberDale, selected for long and strong peduncles, with other varieties bred in the Institute of Grassland and Environmental Research (IGER). The peduncles of cv. AberDale were of larger diameter and had a greater fresh and dry weight than those of other varieties. There were also differences in structure as the peduncles of cv. AberDale had more pronounced ridges and furrows than those of cv, Menna.
Inflorescences of cv. AberDale and other varieties were tagged when in full bloom throughout the flowering period in each of the four harvest years. Generally, more inflorescences of cv. AberDale remained intact until harvest, particularly from the early tagging dates. Although there were seasonal differences, at harvest in each of the 4 years, cv. AberDale had more inflorescences and seeds per floret and a greater potential seed yield than the other varieties.
The basis of peduncle strength and effect on reproductive growth is discussed, and the implications for improving the seed yield potential of white clover varieties is considered.     

Quantification of cyanogenic glycosides in white clover (Trifolium repens L.) from horse pastures in relation to equine grass sickness

As a preliminary step in testing the hypothesis that ingestion of cyanogenic glycosides in white clover (Trifolium repens L.) may be one of the risk factors for equine grass sickness (EGS, or equine dysautonomia), the cyanogen content of clover leaves collected from fields (n = 16) soon after an occurrence of EGS was compared with that of (i) control white clover samples (n = 10) collected from the same fields out of the disease period and (ii) control clover samples (n = 54) collected sequentially from three control fields. Clover samples from EGS fields were highly cyanogenic, with a median cyanide potential of 497 (range 307–1786) mg kg dry matter^?1. Furthermore, clover collected from EGS fields soon after an occurrence of EGS had significantly higher concentrations of the cyanogenic glycosides linamarin and lotaustralin than control samples. While these findings indicate that horses grazing EGS fields may ingest significant quantities of cyanogenic glycosides, the design of the study does not facilitate investigation of any potential association between cyanogens and EGS. Further study is therefore required to determine whether cyanogens are a risk factor for EGS or whether these findings simply reflect variations in plant metabolism unrelated to disease pathogenesis.     

The effect of some invertebrate species on the growth of white clover (Trifolium repens L.) in the lahoratory

In laboratory experiments to clarify earlier field observations, Sitona lepidus larvae caused significant damage to established clover plants at infestations of approximately 1–2 per plant. When eggs were placed on the soil, cultivars of differing cyanogenic capacity were damaged equally. The plants did not recover when larval feeding ended.
Leatherjackets, slugs and 'lucerne flea' fed most on the least cyanogenic cultivars, even where no choice was offered. Plants ultimately recovered from damage by leatherjackets. Deroceras reticulatum caused more damage than did Arion fasciatus. The proportion of leaves damaged by lucerne fiea was highest in the least cyanogenic eultivar but also tended to increase in the most cyanogenic cultivar, confirming a field observation. At high population densities lucerne flea was capable of killing some seedlings but was not tested against established plants.     

Changes during growth in the nutritive value of components of berseem clover (Trifolium alexandrinum L.) under different cutting treatments in a Mediterranean region

The nutritive value of berseem clover (Trifolium alexandrinum L.) may be influenced by changes in the nutrient concentrations of morphological fractions as a consequence of cutting treatment. The aim of this study was to evaluate the effects of different cutting treatments on the nutritive value of herbage and leaf and stem components in two Mediterranean berseem genotypes during growth in order to develop management approaches for harvesting forage with a high nutritive value. Spring growth of genotypes of Egyptian (cv. Giza 10) and Italian (cv. Sacromonte) origins was harvested in each of 2 years beginning 196 days after sowing and thereafter every 6 days (twelve harvests in total) to measure dry matter (DM) yield and nutritive value. Cutting treatments were initiated at sixth internode elongation (A) and early flowering (B) and there was an uncut control treatment (C). In vitro digestibility of organic matter (IVOMD) and crude protein (CP) concentration were determined for leaf, stem and total forage of each cultivar at each harvest. For both cultivars, in the uncut treatment (C), DM yield increased linearly to a maximum of 14 800 kg ha^?1, on average, by 250 days after planting, the same time at which stem DM accumulation peaked, whereas the nutritive value, in terms of IVOMD and CP concentration, declined with age, coinciding with a reduction in leaf:stem ratio (LSR) from 1·00 to 0·30. Plant parts differed (P < 0·01) in nutritive value with stems being of lower nutritive value than leaves, in the two cutting treatments. There were strong positive correlations between LSR and herbage IVOMD and CP concentration, in both cutting treatments, indicating that, during growth, part of the changes in IVOMD and CP concentration of berseem clover plants was due primarily to the changes in the LSR. Defoliation induced a considerable reduction in DM yield, but an increase in the LSR and a small increase in nutritive value. Plants cut at the sixth internode elongation (A) showed a small proportional decrease (0·19) in total DM yield, but higher LSR values and similar or higher IVOMD and CP concentration than initiating cutting at early flower (B). Delaying defoliation to the early flowering stage (B) increased the proportion of stems and, therefore, decreased nutritive value. Therefore, harvest management in which cuts are applied at the stage of sixth internode elongation appears to be the most favourable for obtaining relatively high yields of forage with high nutritive value in berseem clover grown in Mediterranean regions.     

Influence of boron on seed yield and seed quality of organic white clover (Trifolium repens L.)

The effects of boron (B) application on flower development, nectar production, germination and seed yield were investigated in organic seed crops of white clover grown in soils with <1 mg B kg^?1. Application techniques of a liquid B product were studied in two field experiments in 2009–2011. Three rates of B application to the soil at sowing and three rates of B as a foliar application in the harvest year were compared with untreated control plots. None of the B treatments had a significant effect on seed yield, relative to the control. In one experiment, with a dense crop stand, the results indicated a small (10%) yield increase with B applied to the soil. Seed germination and B concentration of shoots, roots and seeds were unaffected by B application, although the soil concentration increased. In seeds with an average B concentration of 22 mg kg^?1, 73% germinated as normal seedlings and 14% were assessed as hard seeds; corresponding values for seeds with an average B concentration of 17 mg kg^?1 were 60 and 38% respectively. The results indicate the need for further studies of factors determining B uptake in white clover .     

Preliminary trials using a white clover (Trifolium repens L.) understorey to supply the nitrogen requirements of a cereal crop

A method of growing cereals with no input of N fertilizer was tested. Two experiments are reported in which white clover ( Trifolium repens L.) was used to supply the nitrogen requirements of the cereal. Spring barley, spring oats and winter barley were direct drilled into an established clover crop and grown with the legume as an understorey. The yield of whole crop cereal, for ensilage, and yield of cereal grain were similar to those grown by traditional methods. In the first experiment, clover survived adequately to be used again, but in the second experiment it was killed by a very high slug population. A method of slug control by mob stocking with sheep is discussed. Where clover survived, no weed, insect or disease problems were encountered. The technique offers a possible method of reducing the environmental problems arising from the use of nitrogen fertilizers.     

The relationships between stolon characteristics, winter survival and annual yields in white clover (Trifolium repens L.)

Five white clover populations of Swiss origin and three bred varieties were grown in binary mixtures with two perennial ryegrass varieties, Aurora and S23. The seasonal yields of clover and grass plus clover were measured under a cutting regime during the second and third years after establishment. A series of destructive detailed sward measurements was made during the late autumn to spring period preceding each harvest year. In this way changes in the amounts of stolon, leaf plus petiole and numbers of growing points were monitored during the winter.
There were large differences in clover yield between populations in both years. These were evident from the first (spring) harvest in each year. Higher-yielding clovers in spring tended to produce higher annual clover yields. No grass × clover interaction was evident at any harvest. Large differences between clovers were also apparent in the morphological characteristics measured, with the Swiss material generally having greater amounts of stolon, leaf plus petiole and numbers of growing points present in early spring. It is proposed that these factors contribute to the high spring yield in the Swiss populations. Loss of stolon length over each winter was less in the Swiss material, indicating that its good spring growth was not obtained at the expense of winter hardiness. Annual clover yield was found to be significantly positively correlated with the amount of stolon present in spring, exemplifying the importance of stolon survival over the winter.     

Evaluation of seed production potential in white clover (Trifolium repens L. varietal improvement programmes

The components of actual and potential seed yield were examined in field experiments on a wide range of varieties of white clover (Trifolium repens L.). The factors affecting seed yield under conditions typical of management regimes used in the production of commercial seed crops were assessed in two experiments. In the first, carried out on spaced plants, considerable diferences are shown between six varieties across the range of leaf sizes in the distribution and profuseness of inflorescence production through the flowering season. In the second, carried out in plots, typical on-farm criteria were used to choose a single harvest date. Significant variation was found between varieties, including representatives of different leaf size categories, for seed yield components that include number of inflorescences m^?2, number of florets per inflorescence and harvestable seed weight. Large-leaved varieties tended to produce more seeds per floret and higher seed weights per inflorescence, whereas small-leaved varieties gave the highest number of inflorescences ^?2. However, the small-leaved variety AderDale, selected for strong peduncles, was exceptional, giving high values for all seed yield components. The impact of weather conditions on many seed yield components (e.g. total number of inflorescences) was demonstrated by the differences between the 2 years of the experiment. However, other characterstics, e.g. number of florets per inflorescence and number of seeds per floret, did not vary between years. Deviations from potential seed yield were assessed fromthe perspective of commerical seed production. The implications of these results for the production of white clover varieties with increased seed yields under UK conditions are discussed.     

Thresholds of economic damage by clover seed weevil (Apion fulvipes Geoff.) and lesser clover leaf weevil (Hypera nigrirostris Fab.) on white clover (Trifolium repens L.) seed crops

Severe reductions in the seed yield of white clover can occur because of feeding by the white clover seed weevil Apion fulvipes and the lesser clover leaf weevil Hypera nigrirostris which together can reduce the seed yield by more than 0·50. From 2002 to 2006 five field experiments were carried out to investigate the relationship between the density of these two weevil species and seed yield of white clover. Damage caused by the weevils was calculated as the difference in the number of weevils and the difference in seed yield between the average of insecticide‐treated and untreated plots. Loss of seed yield was expressed as a proportion of the seed yield in insecticide‐treated plots, which allowed for a comparison between years as yields in insecticide‐treated plots varied. A multiple regression approach was chosen in which proportional loss in seed yield was the response variable and the weevils A. fulvipes and H. nigrirostris were the independent variables. Data obtained from the experiments were used to construct the following threshold model of economic damage:      

Variation in HCN potential among cultivars of white clover (Trifolium repens)

The hydrogen cyanide potential (HCNp) of 17 cultivars of white clover were compared. With inadequate phosphorus supply, HCNp ranged from 24 mg kg DM⁻¹ for cv Lucky to approximately 640 mg kg DM⁻¹ for cv Huia and from 6 to 322 mg kg DM⁻¹ for the same cultivars, with adequate phosphorus. The four North American cultivars examined had notably lower HCNp than all European or Australasian cultivars except cv Clarence.     

The interactive effects of phosphorus, potassium, lime and molybdenum on the growth and morphology of white clover (Trifolium repens L.) at establishment

The effects of simultaneously varying P, K, lime and Mo supplies on the growth and shoot morphology of white clover ( Trifolium repens ) at establishment were investigated in a factorially designed glasshouse experiment. Phosphorus and lime applications had almost identical, additive, effects on dry-matter (DM) production, and it was clear that the benefit of both treatments lay in the resultant improvements in plant available P. The adverse effects of P deficiency on young plants resulted, immediately, in a large decrease in stolon branch numbers, but only when the deficiency became acute did similar declines in the dimensions of leaves and petioles occur. It was suggested that this preferential maintenance of leaf and petiole expansion processes under moderate P deficiency, by enabling white clover to retain favourable upper canopy positions, could be an ecological adaptation to maximize its chances of survival in mixed grass–clover swards. Unlike P, K had little effect on clover growth or shoot morphology. However, there was some evidence that plants suffering from acute K deficiency preferentially partitioned resources to organs associated with exploratory growth, i.e. to stolons, at the expense of the plant's photosynthetic capability. Molybdenum application had no effect on DM production or shoot morphology, but did improve the N status of shoots, presumably by enhancing N₂ fixation. It was concluded that the survival of white clover in swards at establishment is critically dependent on P supply, and that one of the main benefits of liming is the resultant improvement in P availability.     

The influence of the radiation environment around the node on morphogenesis and growth of white clover (Trifolium repens)

The growth of clonally propagated clover plants ( Trifolium repens ) in the glasshouse was compared with their growth under canopies of Tropaeolum peregonium with or without supplementation from red light emitting diodes (LEDs) directed at the youngest node bearing a fully expanded leaf. The T. peregonium was grown over a net support so that its roots did not meet those of the clover. A similar experiment was set up in a permanent grassland using canopy shade from various grass species ( Holcus lanatus, Lolium perenne and Agrostis stolonifera ) with and without supplementation. The LEDs increased the ratio of red to far red radiation (R/FR) received by the treated node with no apparent increase in photosynthetically active radiation (PAR) during the day.
The morphogenetic effects of canopy shading (notably fewer branched nodes and less well-developed branches) were largely removed by supplementation so that the supplemented plants came to resemble those grown in full daylight, particularly in the glasshouse experiments. The results highlight the Importance of the radiation environment at the base of the canopy in the morphogenetic responses of plants to putative competition, and the data are consistent with the hypothesis that responses are communicated acropetally along the stolon.     

Patterns of nodal rooting in Trifolium repens (L.) and correlations with stages in the development of axillary buds

Forty per cent of while clover nodes had roots when a pasture was rotationally grazed by sheep compared with 29% when grazed continuously by set stocking. Nodal roots were most frequent during spring and least frequent during summer. About 5% of nodes had a root primordium which had not developed but was still viable. A high proportion of nodal roots (66%) occurred within 10 nodes of the apex. Root presence was highly correlated with the establishment and survival of branches but was less closely related to branch initiation or the viability of axillary buds. It is suggested that the association between nodal roots and branches is strongest when resources are limited, and that root survival at a node is enhanced by the presence of a branch originating at the same node.     

Performance and quality of tall fescue (Festuca arundinacea Schreb.) and perennial ryegrass (Lolium perenne L.) and mixtures of both species grown with or without white clover (Trifolium repens L.) under cutting management

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.     

Forage quality of white clover (Trifolium repens L.) × Caucasian clover (T. ambiguum M. Bieb.) hybrids and their grass companion when grown over three harvest years

Interspecific hybrids between white clover (Trifolium repens L.) and Caucasian clover (Trifolium ambiguum M. Bieb.) have been developed to introgress the rhizomatous growth habit into white clover, to increase persistence and drought tolerance. The forage quality of T. repens, T. ambiguum and the backcross 1 (BC1) and backcross 2 (BC2) hybrids and companion grass, when grown in mixtures with an intermediate perennial ryegrass (Lolium perenne L.) under a cutting‐only management, was measured. In vitro dry‐matter digestibility (DMD), water‐soluble carbohydrate (WSC) and crude protein (CP) concentrations of the legume and grass fractions were measured throughout the growing season over three harvest years. Trifolium repens had a lower WSC but a higher CP concentration than the perennial ryegrass companion in all harvest years and at all cuts. The legume fractions from the BC1 and BC2 hybrid plots had a higher WSC and a lower CP concentration but an in vitro DMD value comparable with white clover throughout the growing season and in each harvest year. The grass fractions from the mixtures with the backcross hybrids had a higher WSC and a lower CP concentration than the grass fraction from the T. repens plots, in all harvest years and throughout the growing season. No difference in in vitro DMD between parental species and backcross hybrids was observed. The implications of these results for the development of these hybrids and animal performance are discussed.     

Nitrogen metabolism and milk production in dairy cows fed semi‐restricted amounts of ryegrass–legume silage with birdsfoot trefoil (Lotus corniculatus L.) or white clover (Trifolium repens L.)

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 mm ; 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.