Genetic diversity in perennial ryegrass and white clover among old Dutch grasslands as compared to cultivars and nature reserves

To support conservation policies for old Dutch grasslands that are still in agricultural use, morphological variation and AFLP-based (amplified fragment length polymorphism-based) genetic diversity was studied in perennial ryegrass and white clover populations and compared with the diversity in reference varieties. In addition, AFLP variation was also studied in grasslands located in nature reserves. From principal component analysis (PCA), it appeared that date of ear emergence in perennial ryegrass and characters related to plant vigour in white clover were the main morphological characters separating the reference varieties from the old Dutch grassland populations, and some of the grassland populations from each other. In both species, intrapopulation variation was lower for the reference varieties. Lower heterogeneity within the reference varieties was also found in the AFLP analysis. All common AFLP's observed in old Dutch grasslands could also be found in the reference varieties and nature reserves. Only a small number of low-frequency alleles found in old Dutch grasslands were absent from the other two groups. However, band frequencies of markers could vary considerably between populations, which may have been caused by selection. Analysis of the AFLP data by PCA distinguished the majority of reference varieties from the old Dutch grasslands, and showed genetic differentiation only between some grasslands. Comparison of old Dutch grasslands with grasslands in nature reserves indicated that basically the same range of genetic variation is covered by the two groups. Our study indicates that the Netherlands harbour a more or less continuous population for major parts of the diversity of perennial ryegrass and white clover. It was concluded that no specific conservation measures are presently needed to maintain genetic diversity of perennial ryegrass and white clover occurring in old Dutch grasslands.     

Grass species and their fungal symbionts affect subsequent forage growth

Persistence of forage grasses is enhanced through the deliberate and selective use of symbiotic fungal endophytes that confer benefits, particularly pest resistance. However, they have also been implicated in reduced plant community diversity as a result of directly or indirectly enhancing competitive ability. A relatively underexplored mechanism by which endophytes might influence pasture plant composition is by altering the biotic or abiotic soil conditions. To examine the soil conditioning effects of forage grass species and their fungal symbionts we tested the responses of three pasture plants, perennial ryegrass, prairie grass, and white clover in nine different soils that had been conditioned by monocultures of endophyte-containing (E+), or endophyte-free (E?), perennial ryegrass, tall fescue, or meadow fescue. Conditioning grass species had little effect on the responses of perennial ryegrass and prairie grass regardless of E+ or E? treatments. In contrast, conditioning species had a strong effect on the response of white clover, resulting in reduced biomass when grown in perennial ryegrass conditioned soils. The presence of endophyte also had significant growth consequences for white clover, but was either positive or negative depending on the conditioning grass species. In comparison to their respective E? treatments, E+ tall and meadow fescue conditioned soils resulted in reduced biomass of white clover, whereas E+ perennial ryegrass conditioned soils resulted in increased biomass of white clover. Among the conditioning strains (AR1, AR37, NEA2, WE) of E+ perennial ryegrass, white clover showed significantly different responses, but all responses were positive in comparison to the E? treatment. By examining the effects of several grass species and endophyte strains, we were able to determine the relative importance of grass species vs. fungal symbiont on soil conditioning. Overall, the conditioning effect of grass species was stronger than the effects associated with endophyte, particularly with regard to the response of white clover. We conclude that both grass species and their fungal endophytes can influence pasture plant community composition through plant–soil feedback.     

混播草地不同种群再生性的研究

在不同刈割频率和时间尺度下 ,对混播草地多年生黑麦草 (Lolium perenne)分蘖数和叶片生长、白三叶 (Trifoliumrepens)分枝数和匍匐茎生长及不同种群年产量和组分进行了连续 3年的监测研究 .结果表明 ,刈割能刺激黑麦草叶片、白三叶匍匐茎生长和分枝数发生 ,保持混播草地黑麦草和白三叶的适宜比和稳定共存 ,提高草地年生产力 ,但不同刈割频率和刈割时间对其影响差异不显著 (P >0 .0 5 ) .黑麦草叶片生长对 6月刈割效果比 8月明显 ,而白三叶匍匐茎生长则与之相反 ,黑麦草产量主要取决于叶片生长 ,白三叶产量主要取决于匍匐茎分枝数 .刈割的黑麦草、白三叶产量组分比分别为 5 0 %、15 % ,比试验前约低 10 %、5 % ,而CK为 39%、6 % .     

Use of white clover as an alternative to nitrogen fertiliser for dairy pastures in nitrate vulnerable zones in the UK: productivity, environmental impact and economic considerations

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.     

Effects of coexistence on the performance of white clover-perennial ryegrass mixtures

Summary Yields from five white clover/perennial ryegrass mixtures, each based on coexisting components, were compared with those produced by ten mixtures whose constituents had no previous history of coexistence. The former group consisted of five paired clover/ryegrass populations, four collected from natural pastures and one from a sown pasture, whilst the latter group comprised the same five clover populations grown in turn with each of two ryegrass companions.In the first harvest year, when artificial fertilizer plus soil mineralization supplied most of the nitrogen to this experiment, the grasses were generally favoured at the expense of the clovers. Although those mixtures based on coexisting populations had significantly lower yields the clover within these mixtures made a significantly higher contribution to their productivity. This advantage was retained into the second harvest year when it was accompanied by a correlated response in the grasses, which by then may have become dependent upon the clover for their nitrogen supply. Consequently, by the end of the second harvest year those mixtures based on coexisting populations yielded over 20% more on average, due mainly to improved early season growth. Despite considerable differences in productivity, all five clover populations gave their highest yields when grown with their matching grass.     

The Influence of Frequent Defoliation and of Drought on Nitrogen and Sulphur in the Roots of Perennial Ryegrass and White Clover

Frequent defoliation and drought, imposed individually overa period of 60 days, both reduced substantially the root weightsof white clover grown in the field, while causing no reductionin the root weights of perennial ryegrass. Concentrations ofN and S in the root organic matter of the clover were reducedby between 14 and 25 per cent by both treatments, but with theryegrass concentrations were not reduced. Perennial ryegrass, white clover, roots, nitrogen, sulphur, defoliation, drought     

Sitona weevils (Coleoptera: Curculionidae) as agents for rapid transfer of nitrogen from white clover (Trifolium repens L.) to perennial ryegrass (Lolium perenne L.)

The effects of root feeding by larvae of Sitona hispidulus (F.) (a common weevil pest of white clover) on the rate of transfer of nitrogen between plants of white clover (Trifolium repens L.) and perennial ryegrass (Lolium perenne L.) were investigated using a nutrient slant board technique. Clover plants, labelled with ¹⁵N were grown adjacent to ryegrass plants and were either infested with Sitona larvae or not infested. Ryegrass plants associated with the infested clover plants had a significantly higher dry matter yield and nitrogen content (75% and 74% respectively) than the uninvested plants, after 33 days exposure to insect herbivory. It was concluded that root feeding insects could play an important role in the cycling of nitrogen in grass/clover swards.     

Water deficit and plant competition effects on growth and water-use efficiency of white clover ( Trifolium repens,L.) and ryegrass (Lolium perenne,L.)

The combined effects of soil water deficit and above and below ground interspecific plant competition on the growth, water-use efficiency (WUE), and measured carbon isotopic composition (δ¹³C) values of white clover and ryegrass were studied. White clover and ryegrass were grown in specially designed crates 1) individually; 2) in shoot competition; or 3) in shoot + root competition and either well-watered or at a moderate or severe soil water deficit. The effects of shoot + root competition on shoot dry matter growth were substantial and benefited both white clover and ryegrass when well-watered or at a moderate soil water deficit, while severely reducing white clover shoot dry matter growth at severe soil water deficit. Plant competition did not affect the WUE of white clover or ryegrass. As soil water deficit increased, the WUE of white clover did not change whereas the WUE of ryegrass increased and was greater than that of white clover. This was attributed to the lower leaf water conductance of ryegrass which conserved water and maintained growth longer compared to white clover. A stronger correlation existed between soil water deficit and measured δ¹³C values for ryegrass at each plant competition level (P<0.001) than existed for white clover (individual: P<0.01; shoot + root: P<0.001; shoot: P<0.10). Unlike white clover, the relationship between measured δ¹³C values and shoot dry matter growth indicated that C assimilation for ryegrass was dependent on type of plant competition. That WUE remained constant for white clover while measured δ¹³C values increased as soil water deficit increased, suggests that the role below ground respiration rate played in determining δ¹³C values increased. The WUE of white clover appears to be independent of the nature of the competition between plants and the soil water deficit level at which it is grown, whereas for ryegrass, the addition of root competition to shoot competition should lead to increases in its WUE. This revised version was published online in June 2006 with corrections to the Cover Date.     

Assessment of genetic diversity in cultivars of white clover (Trifolium repens L.) detected by SSR polymorphisms.

White clover (Trifolium repens L.) is an important temperate pasture legume that plays a key role as a companion to grass species, such as perennial ryegrass (Lolium perenne L.). Due to the outbreeding nature of white clover, cultivars are highly heterogeneous. Genetic diversity was assessed using 16 elite cultivars from Europe, North and South America, Australia, and New Zealand. Fifteen simple sequence repeat markers that detect single, codominant polymorphic genetic loci were selected for the study. The genetic relationships among individuals were compared using phenetic clustering, and those among cultivars were compared using nonmetric multidimensional scaling. Intrapopula tion variability exceeded interpopulation variability, with substantial overlap among populations and weak interpopula tion differentiation. No obvious or significant differentiation was observed on the basis of morphology or geographic origin of the cultivars. The number of parental genotypes used to derive each cultivar was not a major determinant of genome-wide genetic diversity. The outcomes of this assessment of genetic variation in elite white clover germplasm pools have important implications for the feasibility of molecular marker-based cultivar discrimination, and will be used to assist the design of linkage disequilibrium mapping strategies for marker-trait association.     

Regrowth and Nutrient Composition of Different Plant Organs in Grass-clover Canopies as Affected by Phosphorus and Potassium Availability

Regrowth after cutting and the distribution of nitrogen (N),phosphorus (P) and potassium (K) in different plant organs ofwhite clover and perennial ryegrass growing in pure or mixedswards were investigated under field conditions in a soil witha low-to-moderate availability of P and K. In all treatments,white clover constituted more than 70% of the above-ground biomassin the mixed swards. The petioles were the dominant pool ofdry matter throughout regrowth and contained the greatest amountsof N, P and K. Increased supply of P and K increased the growthof ryegrass, but not that of white clover in the mixed swards.The increased competition from ryegrass led to a decline inthe yield of white clover laminae as well as in the N contentper unit of dry matter in laminae, petioles and stolons. TheP content of all white clover organs also declined followingP application to the mixed swards, whereas K application increasedtheir K contents. In the pure swards of ryegrass and white clover,yields and contents of N, P and K in the dry matter were eithernot affected or increased following P and K application. Itwas concluded that commonly-used defoliation heights may remove80% or more of the nutrient and dry matter pools located inthe petioles but the remaining quantities of dry matter andnutrients in the petioles will normally exceed the correspondingquantities in the stolons. Copyright 2001 Annals of Botany Company Coexistence, competition, phosphorus, potassium, regrowth, ryegrass, white clover     

Root turnover in pasture species: chicory,lucerne, perennial ryegrass and white clover

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.     

Yield and persistency of contrasting white clover populations grown in pure swards and in mixed swards with S.23 perennial ryegrass

Ten contrasting white clover populations were grown as spaced plants, in pure clover swards and in mixed swards with S.23 perennial ryegrass. Four of the populations were also tested for tolerance of low temperatures. In the establishment year, the autumn yields of populations were correlated with leaf size. However, during the severe winter which followed, populations with large leaves, particularly those of Mediterranean origin, suffered extensive stolon kill. This winter damage reduced the spring yields and total annual yields of populations with large leaves, so that leaf size and total annual yield were not correlated in the year after sowing. Stolon kill was positively correlated with autumn growth activity as measured by leaflet size and stolon internode length in October. Stolon kill during winter was correlated with cold tolerance of naturally-hardened stolon apices, assessed in artificial cold tests.     

Preference of dairy cows for ryegrass, white clover and red clover, and its effects on nutrient supply and milk quality

Two experiments were conducted with 30 dairy cows each, to study the preference for fresh (Experiment 1) and ensiled (Experiment 2) ryegrass, white and red clover. Both experiments consisted of three choice diets with white or red clover or both, offered with ryegrass, and two diets with ryegrass mixed with white or red clover (40% clover). Cows consumed diets with 37.7% fresh white and 45.9% red clover, and no preference was observed when the cows were offered all three forages. By contrast, cows preferred white and red clover silage (73.0 and 69.2%, respectively) over ryegrass silage (of lower nutritive quality). When offered three forages, cows preferred white (59.8%) over red clover (17.5%) and ryegrass (22.7%). Choice diets resulted in diets similar (fresh forages) or higher in nutrient content and digestibility (silages). Treatments did not affect feed intake and performance. Choices compared to mixed diets with red clover silage were preferable regarding the fatty acid composition of the milk fat. Obviously, only large differences in nutrient and energy concentration facilitate preferences for clovers over ryegrass, which could, depending on clover type, be beneficial in terms of the milk's fatty acid composition.     

The Effect of Temperature on Photosynthesis of Ryegrass and White Clover Leaves

The rate of photosynthesis of leaves of perennial ryegrass (Loliumperenne L.) and white clover (Trifollum pratense L.) grown atdifferent temperatures was measured at a range of temperatures.There was a small effect of the temperature at which a leafhad grown on its photosynthetic rate, but a large effect ofmeasurement temperature, especially in bright light, where photosyntheticrates at 15°C were about twice those at 5°C. It appearsthat temperature could affect sward photosynthesis in the field.Ryegrass and clover had similar photosynthetic rates which respondedsimilarly to temperature. Lolium perenne L., ryegrass, Trifolium pratense L., white clover, photosynthesis, temperature, irradiance     

The response of white clover (Trifolium repens L.) seedlings to spring root temperatures: The relative roles of the plant and the Rhizobium bacteria

Three experiments are reported which examine the relative roles of host and Rhizobium genotypes as factors limiting clover (Trifolium repens L.) growth at low soil temperatures.In the first experiment un-nodulated clover and perennial ryegrass (Lolium perenne L.) were grown with non-limiting nitrate at root temperatures of 8, 10 and 12°C. The ryegrass had substantially better relative growth rates (RGR) than the clover with the biggest difference occurring at 8°C. Alterations in growth rate with temperature were more marked in clover than in ryegrass but the latter still produced several times more dry matter than clover at each temperature.In the subsequent experiments clover nodulated with different strains of rhizobia was grown with and without non-limiting additions of nitrate at root temperatures of 9, 12 and 15°C. Plants receiving nitrate generally produced more dry matter than those dependent upon Rhizobium for nitrogen but differences in yield between these treatments did not alter with temperature. This suggests that limitations imposed by nitrogen fixation are similar at both high and low temperatures. Indeed, there was some evidence that nitrogen limitations were rather more pronounced at the highest temperature. The first experiment clearly demonstrated that the clover genotype makes particularly poor use of nitrate at low root temperatures when compared to its common companion perennial ryegrass.It can be concluded that improvements in spring growth of clover will rest largely with alterations to the plant genotype and its ability to use combined nitrogen for growth at lower temperatures rather than with changes in rhizobia or any symbiotic characters.     

Nitrogen contribution from the soil for herbage growth

Summary and conclusions 1. Possible sources of free nitrogen are enumerated and evaluation has been attempted in respect of a West of Scotland soil.2. The total annual contribution of nitrogen to the soil from all free sources could be of the order 100–120 lb N per acre (=101–130 kg N per ha).3. Assuming that two thirds of this is harvestable in grassland then 66–80 lb N may be expected in the absence of added fertilizer nitrogen.4. The observed value for the nitrogen uptake by the grass component in a mixed sward (perennial ryegrass and white clover) in its third year (1965) amounted to 66 lb/N/acre.5. The uptake of nitrogen by perennial ryegrass grown alone without added fertilizer amounted to 89 and 65 lb in 1964 and 1965 respectively. These results corroborate the values for estimated nitrogen contribution outlined in (3) above and also agree well with the experimental findings of (4).6. Since the amount of nitrogen in the grass monoculture was similar to that obtained by the grass when grown in association with clover (1965 Data) it would therefore indicate that white clover did not materially affect the nitrogen uptake by perennial ryegrass.     

Feeding Preferences in Greylag Geese and the Effect of Activated Charcoal

ABSTRACT Greylag geese (Anser anser) can cause serious damage to agricultural fields near wetlands that are attractive for resting and nesting but not for feeding. Alternative plantings or spraying fields may prevent goose damage. We randomly designed 64 plots in spring 2004 and prepared plantings of white clover (Trifolium repens), white clover with perennial ryegrass (Lolium perenne; mixture), fertilized perennial ryegrass (grass), or unfertilized perennial ryegrass. We measured goose-dropping densities in plots as a measure of feeding preference in autumn 2004 (7 weeks), spring 2005 (6 weeks), and autumn 2005 (7 weeks) following removal of a protective fence and vegetation sampling for content analysis in 2004. We also sprayed activated charcoal (20 kg/ha) in a suspension on 32 plots (8/planting) to deter geese in autumn 2004 only. In a second experiment we examined pairs of greylag geese in cages for preferences between grass treated with or without activated charcoal. Charcoal did not deter geese in either experiment. However, dropping density averaged highest for clover (1.01/m²), followed by the mixture (0.65/m²), then fertilized (0.23/m²) and unfertilized grass (0.16/m²). Preferences were consistent in all 3 experimental periods. Fertilized grass reached 31.8 cm in height on average in spring, whereas clover measured 15.4 cm. Crude protein and water-soluble carbohydrate content (g/kg dry matter) was 294 and 49, respectively, in white clover and 183 and 139, respectively, in fertilized grass. We found a positive partial correlation independent of vegetation type between dropping densities and crude protein and a negative correlation with water-soluble carbohydrate content. Thus, to prevent grazing damage to agricultural fields, we recommend planting white clover, strongly preferred by feeding geese, in areas (fallow agricultural or nonagricultural) adjacent to their habitat and not in agricultural fields under production.     

Temporal dynamics of spread of four viruses within mixed species perennial pastures

Six mixed species, perennial pastures at two locations, A (four pastures) and B (two pastures), were sampled at regular intervals over periods of 10 to 22 months. The predominant plant species present were white clover (Trifolium repens), perennial ryegrass (Lolium perenne) and kikuyu grass (Pennisetum clandestinum). To determine the extent to which incidences of viruses transmitted in different ways change in the same pastures over time, samples of each plant species were taken at random on every visit and tested for virus presence. To help identify factors that might explain changes in virus incidence, records were also made of aphid presence, pasture management practices, grazing regimes, sward height and the relative proportions of different plant species within the swards. Samples of white clover were tested for presence of Alfalfa mosaic virus (AMV) and White clover mosaic virus (WCMV), ryegrass for Barley yellow dwarf virus (BYDV) and Ryegrass mosaic virus (RyMV), and kikuyu grass for BYDV and potyvirus infection. AMV and WCMV were detected in white clover, and BYDV and RyMV in ryegrass at both locations but often with wide incidence fluctuations for the individual viruses. AMV incidences in white clover ranged from 0% to 19% at A, and from 27% to 100% at B. WCMV incidences in white clover fluctuated between 9% and 46% at B, but never exceeded 1% at A. RyMV incidences in ryegrass fluctuated between 3% and 34% at A, and 19% and 73% at B. BYDV incidences in ryegrass ranged from 0% to 6% at A and 4% to 17% at B. In kikuyu grass, an unknown potyvirus and BYDV were detected twice (1% incidence) and once (4% incidence) respectively at B, and the unknown potyvirus only once (2% infection) at A. During repeated trapping of aphids in four pastures (two each at A and B), numbers of aphids caught varied widely between trapping dates and between individual pastures on the same trapping date. The species caught were Acyrthosiphon kondoi, A. pisum, Aphis craccivora, Rhopalosiphum padi and Therioaphis trifolii. Except in summer, when only T. trifolii was caught, A. craccivora was the most abundant. The trends in incidence for each virus within each pasture were compared with those from the other pastures sampled over identical periods to determine whether there was any commonality. For RyMV in ryegrass, overall incidence trends within the different pastures at both locations resembled each other during the same sampling periods. Within pastures at the same location there was commonality in incidence trends for RyMV and BYDV in ryegrass, but with AMV in white clover periods of similarity were rare even when pastures were adjacent and managed identically. Unravelling the individual effects of alterations in season, vector numbers, mowing, intermittent heavy grazing and pasture species composition on virus incidence proved difficult due to complex interactions between these and other factors influencing new spread or declining virus occurrence.     

Influence of arbuscular mycorrhiza on clover and ryegrass grown together in a soil spiked with polycyclic aromatic hydrocarbons

 The effect of arbuscular mycorrhiza (AM) on white clover and ryegrass grown together in a soil spiked with polycyclic aromatic hydrocarbons (PAH) was assessed in a pot experiment. The soil was spiked with 500 mg kg^–1 anthracene, 500 mg kg^–1 chrysene and 50 mg kg^–1 dibenz(a,h)anthracene, representing common PAH compounds with three, four and five aromatic rings, respectively. Three treatments and two harvest times (8 and 16 weeks) were imposed on plants grown in spiked soil: no mycorrhizal inoculation, mycorrhizal inoculation (Glomus mosseae P2, BEG 69) and mycorrhizal inoculation and surfactant addition (Triton X-100). Pots without PAH were also included as a control of plant growth and mycorrhizal colonization as affected by PAH additions. The competitive ability of clover vis-à-vis ryegrass regarding shoot and root growth was enhanced by AM, but reduced by PAH and the added surfactant. This was reflected by mycorrhizal root colonization which was moderate for clover (20–40% of total root length) and very low for ryegrass (0.5–5% of total root length). Colonization of either plant was similar in spiked soil with and without the added surfactant, but the PAH reduced colonization of clover to half that in non-spiked soil. P uptake was maintained in mycorrhizal clover when PAH were added, but was reduced in non-mycorrhizal clover and in mycorrhizal clover that received surfactant. Similar effects were not observed on ryegrass. These results are discussed in the context of the natural attenuation of organic pollutants in soils. Accepted: 12 June 2000     

The Effect of Nitrogenous Fertilizer on the Photosynthesis and Growth of White Clover/Perennial Ryegrass Swards

The application of nitrogenous fertilizer in March to a whiteclover (cv. Blanca) and perennial ryegrass (cv. S23) sward resultedin a rapid suppression of the clover, relative to clover ina treatment given no added nitrogen. Thereafter, the cloverin both treatments grew more rapidly than the grass and itsproportion of the total leaf area in the mixture increased,as the leaf area index rose to 8. After a second applicationof N in early July, clover was not suppressed to the same extentas in the first growth period. Overall, the photosynthetic capacities of newly expanded cloverlaminae were similar in the two treatments. Clover laminae hadhigher photosynthetic capacities than grass, even in the grass-dominant+ N treatment. Lamina area, petiole length, and the number of live leaves perstolon were similar in the two treatments, indicating that thedifferences in total leaf area were due to the presence of fewerstolon growing points in the + N treatment. Trifolium repens L., white clover, Lolium perenne L., perennial ryegrass, nitrogen, leaf area index, photosynthesis, growth