Differential growth response of Rytidosperma species (wallaby grass) to phosphorus application and its implications for grassland management

Rytidosperma species (formerly Austrodanthonia) are native grasses common in temperate grasslands of southern Australia. Nine Rytidosperma species, Lolium perenne and Bromus hordeaceus were grown as microswards in pots in a glasshouse, and their growth response to six levels of applied P was measured. Shoot yield differed up to twofold between the highest‐ and lowest‐yielding Rytidosperma species. Some Rytidosperma species were slow growing with minimal ability to respond to increased soil P availability. However, three species, Rytidosperma duttonianum, Rytidosperma racemosum and Rytidosperma richardsonii, had a similar shoot yield to L. perenne. Species that grew well at high P also grew well at low P, except B. hordeaceus, which was the lowest‐yielding species at low P, but had among the highest yields at high P. No species showed evidence of P toxicity. The species exhibited a range in critical external P requirement (i.e. amount of P applied for 90% maximum yield). Among the fast‐growing Rytidosperma species, R. richardsonii was notable because it had a low critical external P (16·3 mg P pot^?1) and high agronomic P‐use efficiency (94·1 g DW g^?1 P applied). In contrast, R. duttonianum had a higher critical external P requirement (22·4 mg P pot^?1) and lower agronomic P‐use efficiency (85 g DW g^?1 P applied). It was concluded that it is important to know which Rytidosperma species are present in a grassland to understand how it may respond to P fertilization. The results help to explain the diverse opinions expressed about the productivity of pastures containing Rytidosperma species.     

Hide and seek – Infection rates and alkaloid concentrations of Epichloë festucae var. lolii in Lolium perenne along a land‐use gradient in Germany

The common forage grass Lolium perenne has evolved with the systemic fungal endophyte Epichloë festucae var. lolii. The endophyte provides herbivore resistance to the grass due to defensive alkaloids, some of which are toxic to grazing livestock. In this field study, we determine whether distribution of the endophyte‐grass association changes along a land‐use intensity gradient on 87 managed grasslands in three German regions. Endophyte infections were detected in 66% of the studied sites and infection rates within infected sites ranged from 1% to 95%. Alkaloid concentrations of lolitrem B (vertebrate toxin) exceeded the toxicity thresholds in 50 (14%) of 351 infected plants and of peramine (invertebrate deterrent/toxin) in 12 (3%) of 351 plants. Infection rates and alkaloid concentrations were not significantly affected by land‐use intensity and region, but alkaloid concentrations were higher in summer compared to spring. We conclude that risks for livestock intoxication are currently low, as (i) average alkaloid concentrations per grassland were always below toxicity thresholds and as (ii) none of the grasslands was dominated by L. perenne. We suggest avoidance of grass monocultures in Europe to keep intoxication risks for livestock low; we also recommend regular examination of seeds and grasslands, as seed producers might accidentally distribute infected seeds, and as climate warming might further enhance the distribution of Epichloë endophytes in European grasslands.     

Annual forage legumes in dryland agricultural systems of the West Asia and North Africa Regions: research achievements and future perspective

Forage legumes are vitally important to animal production in the dryland farming systems of the Mediterranean region. Of the diverse forage‐legume species adapted to the Mediterranean climate, vetches, (Vicia spp.), chicklings (Lathyrus spp.), annual medics (Medicago spp), clovers (Trifolium spp.) and species of the Lupinus, Lotus, Onobrychis, Hedysarum and Ornithopus genera are considered to be the most agronomically important and economically valuable species for the region. Adoption of perennial self‐regenerating medic (Medicago spp.) has been limited because of technical difficulties, but annual vetch (Vicia spp.) has the greatest potential as a viable animal‐feed source and a rotation crop with cereals. Some forage legumes survive harsh conditions by their unique underground growth habit, for example, V. amphicarpa and Lathyrus ciliolatus. Efforts to improve forage legumes have been based on both management/cultural factors and breeding. Research based on several long‐term barley‐ and wheat‐based rotation trials has demonstrated the viability of forage legumes, especially vetch, in the region's improved farming system. An additional benefit to such legumes is the enhancement of soil quality, that is, soil fertility, soil organic matter and soil physical properties. Thus, the development of forage legumes is essential to agricultural sustainability in the Mediterranean region and in other dryland cereal‐growing areas of the world where grazing livestock is a dominant enterprise. To build upon the considerable research conducted on forages, intensified efforts are needed to develop locally adapted forage cultivars, to provide economic assessment of forages in cropping systems and to promote technology transfer at the farm and community level.     

Effects of plant architecture and drought stress level on lucerne forage quality

Breeding for enhanced quality in lucerne (Medicago sativa) frequently involves selection for higher leaf‐to‐stem ratio, multifoliolate leaves or short‐internode stems. Three populations selected for such alternative morphologies and a reference cultivar were evaluated for forage yield, leaf‐to‐stem ratio and protein and fibre concentrations in leaves, stems and whole plants. Four managed environments were obtained by combining two stress levels (moderate or nil) with two sowing times. The population selected for high leaf‐to‐stem ratio, as well as the short‐internode population, had highest leaf‐to‐stem ratio (1.27) across six harvests in two non‐stress environments. The latter population had higher stem protein (12.9%) and lower stem neutral‐detergent fibre (NDF) concentration (58.7%) than other populations. The multifoliolate population had intermediate quality, showing low expression of the multifoliolate trait (14.0% across four environments), particularly under stress (10.5%). The autumn‐sown, fully irrigated environment had, on average, highest dry‐matter yield (4.19 t ha^?1) and lowest leaf‐to‐stem ratio (0.74). Drought‐stressed environments had lower plant NDF (?12.3% on average) and leaf protein (?9.7%), and higher stem protein (+8.6%) than fully irrigated environments. The results suggested that environmental effects might have greater impact on quality than genetic effects, even for a population set including material selected for quality‐driven morphology.     

Mice find endophyte‐infected seed of tall fescue unpalatable – implications for the aviation industry

Bird strike is a significant problem for the aviation industry, caused in part by the attractiveness of the grass surrounding airports to birds. Endophyte‐infected grasses such as Avanex^® have been shown to reduce bird populations at airports through the production of secondary metabolites. These metabolites are unpalatable to herbivorous, omnivorous and granivorous birds and are known to reduce insect densities, thereby making the sown areas less attractive to insectivorous birds. Raptors also provide a bird‐strike threat which could be reduced by controlling mouse populations around airports. In this study, the effect of endophyte‐infected seed on mouse feeding behaviour has been investigated. By performing a choice trial offering diets containing endophyte‐infected and endophyte‐free tall fescue seed, it was shown that endophyte‐infected seed was less palatable to mice (P < 0·001 in a 14‐d trial). Furthermore, when diet positions were reversed, mouse feeding behaviour was modified to again select endophyte‐free material (P < 0·001 over a further 14 d). This result shows that endophyte‐infected grasses could not only be used in the control of bird populations but they also have the potential to control mouse populations which in turn would decrease the number of raptors. This use of endophyte‐infected grasses in areas surrounding airport runways shows great promise for the aviation industry.     

Species interactions in a grassland mixture under low nitrogen fertilization and two cutting frequencies: 1. dry‐matter yield and dynamics of species composition

Four‐species mixtures and pure stands of perennial ryegrass, tall fescue, white clover and red clover were grown in three‐cut and five‐cut systems at Ås, southern Norway, at a low fertilization rate (100 kg N ha^?1 year^?1). Over a three‐year experiment, we found strong positive effects of species diversity on annual dry‐matter yield and yield stability under both cutting frequencies. The overyielding in mixtures relative to pure stands was highest in the five‐cut system and in the second year. Among the possible pairwise species interaction effects contributing to the diversity effect, the grass–grass interaction was the strongest, being significant in both cutting systems and in all years. The grass–legume interactions were sometimes significant, but no significant legume–legume interaction could be detected. Competitive relationships between species varied from year to year and also between cutting systems. Estimations based on species identity effects and pair‐specific interactions suggested that the optimal proportions of red clover, white clover, perennial ryegrass and tall fescue in seed mixtures would have been around 0·1, 0·2, 0·4 and 0·3 in the three‐cut system, and 0·1, 0·3, 0·3 and 0·3 in the five‐cut system.     

A simultaneous effect of selfing and Epichloë endophyte on forage,seed yield and turf characteristics of perennial ryegrass (Lolium perenne L.)

Ryegrass (Lolium perenne L.) is a putative turf and forage plant characterized as mainly outcrossing in which the extent of self‐fertilization and its consequences has not been investigated. In this study, selfed and half‐sib family seeds were obtained from ten clonally propagated ryegrass plants among which two were endophyte‐free (EF) and eight were endophyte‐infected (EI). Then, 20 seed populations plus two commercial varieties of Speedy and Vigor were sown and evaluated in a biennial experiment for their turf and forage characteristics. Selfing caused significant inbreeding depression for plant fresh and dry weight and leaf length and width in the first year for both EI and EF genotypes. In the second year, only leaf length remained depressed among these characters. Also, for the most growth, turf and reproductive traits, EI populations showed less depression. The presence of endophyte in self‐pollinated populations made an increasing effect for the number of seed per spike and days to heading, although seed weight was reduced. Some of the populations derived from self‐pollination and infected with fungal endophyte including S9 and S10 were even superior to the two commercial varieties in terms of both seed production and turf characteristics. However, for seed‐related characteristics including number of spikes per plant, seed weight and seed yield, EF populations including Speedy and Vigor were more reproductive than EI populations. It is concluded that selfing may increase the discrimination between EI and EF ryegrass plants because endophyte infection may mitigate the negative consequences of inbreeding depression in prone populations.     

Impact of ferulic acid esterase‐producing lactobacilli and fibrolytic enzymes on ensiling and digestion kinetics of mixed small‐grain silage

This study evaluated the effects of a ferulic acid esterase (FAE) and a non‐FAE‐producing inoculant applied alone or in combination with exogenous fibrolytic enzymes (EFE) on the fermentation and nutritive value of mixed grain (barley, oats and spring triticale) silage. The mixed crop was ensiled in laboratory mini‐silos either untreated (CON), or treated with a FAE inoculant (FAE), a non‐FAE inoculant (NFAE) or NFAE + EFE. Inoculated silages were lower (P < 0·01) in water‐soluble carbohydrate, whereas NFAE and NFAE + EFE silages had higher (P < 0·001) DM loss than other silages. FAE and NFAE silage had higher neutral detergent fibre (NDF), but were lower in NFAE + EFE than other silages (P < 0·001). Copy numbers of 16S rRNA associated with Lactobacillus buchneri were higher (P < 0·001) in NFAE and NFAE + EFE silages than in others, resulting in higher (P < 0·001) acetic acid in these silages. NFAE + EFE silage had lower (P < 0·001) in vitro gas production and NDF digestibility (NDFD) than other silages. FAE silage had higher (P < 0·01) in situNDFD than CON and NFAE + EFE silages. Inoculation of mixed small‐grain silage with NFAE‐producing inoculants combining EFE reduced NDFD.     

Morpho‐physiological variation of Poa alpina L. genetic resources from the Rhaetian Alps,Italy, grown in two altitude‐contrasting sites

Alpine bluegrass (Poa alpina L.) is common in mountain areas, where it represents a valuable forage resource and is widely used for ecological restoration of disturbed landscapes. This study assessed the variation of germplasm from the Rhaetian Alps, Italy. Both seed production and morphology were examined for potential use in restoration projects and for conservation and selection purposes of local genetic resources. The effects of the ex situ growing site were also assessed in two altitude‐contrasting sites. Individual populations harboured great phenotypic diversity for all traits, including seed yield, while variation among valleys of origin was less manifest. Noticeable site‐specific population yield responses were observed, suggesting that the environment adopted for seed production may steer the choice of materials to be multiplied. The longer vegetative period in the lowland site, combined with environment‐tailored agronomic practices, contributed to better plant growth, seed yield and survival compared to the mountain site, suggesting that seed production of this Alpine species could be feasible in a lowland environment when adequate inputs were provided. One valley (Valchiavenna) displayed high average levels of seed yield and plant vigour across growing sites, indicating its possible value as a source of germplasm suitable for resowing at high altitude.     

Determining the critical plant test potassium concentration for annual and Italian ryegrass on dairy pastures in south‐western Australia

Potassium fertilization in intensive grassland systems is particularly important on sandy soils with limited K storage capacity. A 3‐year plot experiment was conducted in south‐western Australia to determine the critical K concentration in herbage dry matter (DM) of annual and Italian ryegrass required to achieve 0.95 of the maximum yield, under best‐practice grassland management. A factorial design was employed with eight fertilizer K rates (range 0–360 kg ha^?1 year^?1) and two ryegrass species replicated four times, on a sandy soil site managed over 7 years to deplete mean soil Colwell K concentration to 42 mg/kg. Herbage was defoliated six times per year at the 3‐leaf stage of regrowth. Herbage DM yield, macronutrient and micronutrient concentrations were measured at each defoliation. Dry‐matter yield increased significantly (p < .001) with increasing levels of K fertilizer in all 3 years and the effect was curvilinear, while 0.95 of the maximum herbage DM yield was achieved at an annual K fertilizer application rate of 96, 96 and 79 kg/ha respectively. At these K fertilizer application levels, the mean K concentration of herbage DM over the 3 years was derived to be 11.4, 12.7 and 11.2 g/kg respectively. Sodium, magnesium and calcium concentrations of herbage DM all declined significantly (p < .001) as the K concentration increased. Grassland producers on sandy soils should target a K concentration in herbage DM of 16 g/kg for annual ryegrass and Italian ryegrass‐dominant swards to ensure K availability is not limiting herbage production.     

Effect of grazing management on herbage protein concentration,milk production and nitrogen excretion of dairy cows in mid‐lactation

The objective of this experiment was to use diurnal and temporal changes in herbage composition to create two pasture diets with contrasting ratios of water‐soluble carbohydrate (WSC) and crude protein (CP) and compare milk production and nitrogen‐use efficiency (NUE) of dairy cows. A grazing experiment using thirty‐six mid‐lactation Friesian x Jersey cows was conducted in late spring in Canterbury, New Zealand. Cows were offered mixed perennial ryegrass and white clover pastures either in the morning after a short 19‐day regrowth interval (SR AM) or in the afternoon after a long 35‐day regrowth interval (LR PM). Pasture treatments resulted in lower pasture mass and greater herbage CP concentration (187 vs. 171 g kg^?1 DM) in the SR AM compared with the LR PM but did not affect WSC (169 g kg^?1 DM) or the ratio of WSC/CP (1·0 g g^?1). Cows had similar apparent DM (17·5 kg DM cow^?1 d^?1) and N (501 g N cow^?1 d^?1) intake for both treatments. Compared with SR AM cows, LR PM cows had lower milk (18·5 vs. 21·2 kg cow^?1 d^?1), milk protein (0·69 vs. 0·81 kg cow^?1 d^?1) and milk solids (1·72 and 1·89 kg cow^?1 d^?1) yield. Urinary N concentration was increased in SR AM, but estimated N excretion and NUE for milk were similar for both treatments. Further studies are required to determine the effect of feeding times on diurnal variation in urine volume and N concentration under grazing to predict urination events with highest leaching risk.     

Seed dormancy and dormancy‐breaking methods in Leymus chinensis (Trin.) Tzvel. (Poaceae)

Leymus chinensis (Trin.) Tzvel. is a perennial grass with high productivity and forage value; however, poor stand establishment, often due to seed dormancy, limits its widespread use for forage production. To investigate the mechanism of seed dormancy and to develop effective methods of improving germination, the contribution of each part of the caryopsis to dormancy was investigated, and a number of single or combined dormancy‐breaking pre‐treatments were conducted using three seed lots. The palea, lemma, pericarp/testa, and endosperm all contributed to seed dormancy. The contribution of each part to dormancy was 23·4%, lemma; 6·2%, palea; 28·4%, pericarp/testa; and 42·0%, endosperm. Hull (palea and lemma) removal, pericarp/testa piercing, and soaking in distilled water or 30% sodium hydroxide (NaOH) significantly decreased the percentage of dormant seeds (i.e. increased germination). Treating hull‐removed and pericarp/testa‐pierced seeds with gibberellic acid (GA₃) also significantly decreased the percentage of dormant seeds. Compared with each of the single pre‐treatments, the combined pre‐treatment of pre‐soaking in water for 1 d, then 30% NaOH for 60 min and treating with 300 μm GA₃ resulted in the highest germination (89%); and seed viability was 91%.     

Historical land use by domestic grazing revealed by the soil seed bank: a case study from a natural semi‐arid grassland of NW Patagonia

Livestock can affect the soil seed bank through various mechanisms associated with changes in vegetation. We sampled vegetation and seed banks of Patagonian grasslands, in areas with different historical use by grazing (exclosure, moderate use and high use) to evaluate to what extent changes in vegetation are reflected in the seed bank. We also evaluated the effect of historical grazing on horizontal spatial seed distribution by sampling under shrubs and in between plant gaps. We focused the study on functional groups, and on the palatable Poa ligularis, an indicator of grassland status. In general, the proportional changes in composition and abundance of functional groups produced in grazed sectors (relative to each exclosure) were bigger for the seed bank than for the aboveground vegetation. Impacts on seed bank were led by a decrease (moderate use), or total disappearance (high use) of perennial grasses, results clearly reflected by P. ligularis. Although shrubs were represented in vegetation, they were undetected in the seed bank through germination, probably due to the lack of the conditions required for breaking seed dormancy. Intensive grazing produced homogenization in seed spatial distribution. Our work revealed a poor contribution of the seed bank to vegetation regeneration at increasing historical use by grazing. We recommend sampling the seed bank when monitoring the conservation status of grasslands to obtain consistent management guidelines.     

Effects of defoliation on whole‐plant maize characteristics as forage and energy crop

Hail affects yield and quality of maize crops, and consequences also depend on the growth stage at which the injury occurred. Whole‐plant maize (WPM) silage is often used within the same farm for cattle feeding and biogas production. The present study aimed to verify the effects of hail damage, simulated by artificial defoliation, on yield and chemical and nutritional features, as well as on biochemical methane potential (BMP) of maize forage. In a randomized block design with three replicates, four defoliation levels (0%, 33%, 66% and 100% of leaf area removal respectively) have been applied at either the V12 (12th leaf), R1 (silking) or R3 (milk) stages for two consecutive years. WPM yield, chemical and nutritional features, and BMP were measured. Dry‐matter (DM) yield per hectare was progressively reduced (p < 0.001) with increasing levels of defoliation and with application at V12 in comparison with R1 or R3 (1.26 vs. 1.39 and 1.46 kg ha^?1 for V12 vs. R1 and R3; p < 0.003). Nutritive value and BMP per unit of product were less altered than dry‐matter yield per hectare by defoliation. Anticipating defoliation reduced net energy for lactation (5.26 vs. 5.46 MJ kg^?1 DM for V12 and R3 respectively; p = 0.02). Total defoliation resulted in an accumulation of nitrates (NO₃) compared to the other treatments (3.98 vs. 1.53 g NO₃ kg^?1 DM; p < 0.001). BMP was mainly reduced by early and complete defoliation. Equations were developed to estimate the effects of defoliation on yield, composition, and nutritive and energetic values of WPM.     

Mild peroxyformic acid fractionation of Miscanthus × giganteus bark. Behaviour and structural characterization of lignin

Miscanthus × giganteus bark was subjected to mild fractionation with peroxyformic acid by a two stage process. A factorial experimental design was used to study and quantify the effect of the variables (formic acid concentration (80-90%), hydrogen peroxide concentration (0.2-0.4%), temperature of the first stage (60-80 °C), and treatment time of the second stage (60-120 min)) on the main parameters of fractionation: pulp yield, remaining lignin and total polysaccharides in pulp. The dependence of lignin precipitation rate on hydrogen peroxide concentration in liquor was also studied. Hydrogen peroxide concentrations inferior to 0.5% seems to be suitable to recover high percentages of lignin. The isolated lignin was analysed by 2D-HSQC, ¹³C- and ³¹P NMR spectroscopy, FTIR spectroscopy, size-exclusion chromatography and chemical analysis. The most important chemical modifications taken place in the lignin during the fractionation were identified: β-O-4′ cleavage and hydrolysis of LC-bond structures. The C9-formula was also determined: C₉H_6.81O_2.90(OCH₃)_0.68(COOH)_0.07(OH^Ph)_0.38(OH^Al)_0.33.     

In vitro rumen methane output of grasses and grass silages differing in fermentation characteristics using the gas‐production technique (GPT)

The chemical composition of silage consumed by cattle can influence the subsequent rumen microbial fermentation patterns and methane (CH₄) emissions. The objectives of this study were to (i) evaluate the effect of ensilage on the in vitro rumen methane output of perennial ryegrass and (ii) relate the silage fermentation characteristics of grass silages with in vitro rumen methanogenesis. Three pre‐harvest herbage‐conditioning treatments and seven silage‐additive treatments were used in a laboratory‐scale silo experiment to produce a diversity of silage fermentation characteristics. Ensilage reduced (P < 0·01) the in vitro rumen CH₄ output (mL CH₄ g^?1 dry matter (DM) disappeared). This reflected differences in the direction of rumen fermentation (lower acetic (P < 0·05) and higher propionic (P < 0·001) acid proportions in volatile fatty acids) rather than major changes in the extent of in vitro rumen fermentation (i.e. mmol VFA g^?1 DM). The magnitude of the decrease in CH₄ output (mL g^?1 DM incubated) owing to ensilage increased as the extent of silage fermentation, and in particular the lactic acid concentration, increased. In contrast, among silages with relatively similar extents of silage fermentation (i.e. total fermentation products), an increase in the proportion of lactic acid in silage fermentation products led to a more extensive in vitro rumen fermentation and thus to a greater CH₄ output (mL g^?1 DM).     

Effects of nitrogen fertilization and cutting intensity on the agronomic performance of warm‐season grasses

Responses of grasses to N fertilization are affected by cutting intensity although little is known regarding the interactions of these factors in warm‐season grasses. Pre‐cutting canopy height, herbage accumulation and changes in the nutritive value of warm‐season grasses in response to four different management strategies were assessed from October 2011 to September 2014. Treatments included two cutting intensities (70 vs. 50% depletion of canopy height set by 95% light interception), two N fertilization levels (zero vs. 300 kg N ha^?1 year^?1) and six perennial C₄ grass species (Axonopus catharinensis; Cynodon spp. hybrid Tifton 85; Hemarthria altissima cv. Flórida; Megathyrsus maximus cv. Aruana; Paspalum notatum cv. Pensacola; and Urochloa brizantha cv. Marandu) grown in monoculture in a factorial experimental design. Canopy height varied among grass species, cutting intensity and N treatments, mainly among seasons, indicating that more than one management target (i.e. canopy height) existed throughout the plant growth cycle for each species. The largest herbage accumulation occurred in the N fertilization treatments for most species, regardless of cutting intensity. Nitrogen fertilization and 50% depletion of canopy height increased the leaf proportion and decreased the neutral detergent fibre content. Overall, N fertilization had a stronger positive impact than cutting intensity on the acid detergent fibre content, dry‐matter digestibility and crude protein content, but the magnitudes of the responses were species‐specific.     

Potential of Cistus ladanifer L. (rockrose) in small ruminant diets – effect of season and plant age on chemical composition,in vitro digestibility and antioxidant activity

Shrubs can provide an important contribution to the fodder resources for small ruminants in Mediterranean areas, but there is limited information on their feed value, including secondary metabolites and their seasonal differences. This study evaluated the effect of seasonal variation in chemical composition, in vitro digestibility and antioxidant activity of the aerial parts of plants of Cistus ladanifer of two age groups [young plants vs. older ones (2–6 years old)]. Aerial parts of C. ladanifer plants of both age groups were characterized by moderate cell‐wall content [321–410 g NDF kg^?1 dry matter (DM)], high levels of phenolic compounds (55·1–106 g gallic acid equivalents per kg DM) and condensed tannins (CT) (32·1–161 g kg^?1 DM), low protein content (55–100 g kg^?1 DM) and low digestibility (249–315 g of digestible organic matter per kg DM). During autumn and winter, C. ladanifer showed higher protein levels and lower cell‐wall content than in the other seasons. The highest values of phenolic compounds, CT and antioxidant activity were achieved during summer. Young plants showed higher levels of phenolic compounds during spring, summer and winter, and higher CT contents in summer (more than 54 g kg^?1 DM) compared to old plants. Aerial parts of C. ladanifer of both age groups may be used as a component of ruminant nutrition, but only as a supplement and associated with other feeding resources to complement its nutritional imbalances.     

Effects of sheep stocking on the plant community and agricultural characteristics of upland Anthoxanthum odoratum–Geranium sylvaticum meadow in northern England

In the UK, upland hay meadows (Anthoxanthum odoratum–Geranium sylvaticum grassland) with high plant biodiversity are rare and confined to submontane areas of northern England. We report results from a 5‐year experiment to test suggestions that recent biodiversity declines were attributable to increased sheep‐stocking density and a longer spring stocking period, thus delaying the shut up date for the growth of the hay crop. Longer stocking periods and higher stocking densities decreased the forage mass at 8 July, but they increased herbage N content and digestibility, reduced plant species diversity and reduced populations and seed production of Rhinanthus minor. Compared with unstocked swards, the similarity of the vegetation to Anthoxanthum odoratum–Geranium sylvaticum grassland was reduced by 16·9% when stocking with sheep continued until 27 May each year, and by 8·3% when sward heights were maintained at 3 cm compared with 5 cm. Increased mean sward height and height of R. minor were positively correlated with accumulated temperatures. Results support suggestions that recent reductions in the nature value of these grasslands might be a consequence of high stocking densities persisting until later in the spring, carried out during a 1‐year period with warmer temperatures.