Sward Botanical Composition Research Articles

Positive effects of plant diversity on dry matter yield while maintaining a high level of forage digestibility in intensively managed grasslands across two contrasting environments

AbstractThe local abiotic and environmental conditions of a grass‐based farming system may influence the agricultural benefits of mixtures in comparison to pure stands. We investigated the effects of species identities and interactions between grass, legume, and herb species on dry matter yield and sward digestibility and explored how contrasting environments may affect these relationships. We established experimental plots across 11 mixtures and 4 monocultures of perennial ryegrass (Lolium perenne L.), chicory (Cichorium intybus L.), white clover (Trifolium repens L.), and red clover (Trifolium pratense L.) established at two seeding densities in two sites Brody and Szelejewo (Poland) and managed them over a 3‐year period. The two sites were close geographically and had similar climates, but differed in soil types (Luvisols and Cambisols, respectively). We confirmed that the annual DM yields were generally higher on Cambisols soil as compared to Luvisols soil; both individual species effects and species interaction strengths differed across the two contrasting environments. The predicted annual DM yield for the 4‐species mixtures in general gave comparable or higher yields compared to monocultures across the 3 years, with the mixtures giving around 10%–30% higher yields than the weighted average of the monocultures of the constituent species. Analysing the transgressive overyielding it turned out that there was no significant difference between the 4‐species mixtures and best performing monoculture. The benefits of species diversity in our study was greater on less productive site because we found larger overyielding of the 4‐species sward on the Luvisols soil than on the Cambisols soil. Additionally, the effect of mixtures composed by 4‐species increased the yield stability compared to monocultures in the 3‐year period of our study, particularly on Cambisols soil. Sward digestibility applied to average values did not differ much between sites with mixtures performing similarly to monocultures. The reason for that could have been the dynamics of sward botanical composition during study years shifted towards increased perennial ryegrass and decreased proportions of chicory in the sward as well as the observed phenomenon that the species in mixed swards progressed to successive growth stages more slowly than in pure sowing.

Feedlot growth performance and carcass characteristics of steers backgrounded on buffel grass or buffel-Desmanthus mixed pastures.

Feedlot performance and carcass characteristics of tropical beef steers backgrounded on buffel grass (Cenchrus ciliaris) only or buffel grass oversown with desmanthus (Desmanthus spp. ; 11.5% initial sward botanical composition) were evaluated. It was hypothesized that tropical beef cattle steers backgrounded on buffel grass only or buffel grass oversown with desmanthus with similar backgrounding growth performance will not differ in feedlot growth performance and carcass quality. Three hundred and twelve Bos indicus × Bos taurus tropical composite steers, 20–23 months old and weighing 413 ± 24 kg, previously backgrounded on buffel grass only or buffel-desmanthus mixed pastures for 147 days were finished on a concentrate diet in the feedlot for 110 days before slaughter. Buffel–desmanthus backgrounded steers had a slightly higher average daily gain (ADG; 1.8 kg/day) than the buffel grass backgrounded steers that had 1.7 kg/day ADG (p < 0.01). However, the final live weight and dry matter intake were not different (p ≥ 0.59). All the carcass traits measured were not different (p ≥ 0.18). Only 4% buffel grass and 8% buffel-desmanthus backgrounded steers fell short of the Meat Standards Australia (MSA) index, a level that is within the 4–9% reported for cattle produced in Queensland and slaughtered between July 2019 and June 2020. These findings indicate that desmanthus can be used to background beef cattle in northern Australia vertosol soil regions, where there is a paucity of adapted pasture legumes, with no negative impact on feedlot performance and carcass quality. The hypothesis that tropical beef cattle steers backgrounded on buffel grass only pastures or buffel grass oversown with desmanthus with similar backgrounding growth performance will have similar feedlot growth performance and carcass quality was accepted.

Simple Assessment of Temperate Grassland Suitability as Habitat for Three Insect Taxa

We propose a set of indicators to evaluate how grazing by livestock and grassland management can help preserve biodiversity in the insect communities of grassland ecosystems. These indicators can be calculated for any grassland for which management and botanical composition are known, and they do not require advanced knowledge on conservation biology and entomology. Based on the scientific literature and expert interviews, each indicator combines pressure (i.e., 16 management classes) and state variables (i.e., sward botanical composition and several of the plant functional characteristics) to assess the effects on butterfly, bumblebee, and grasshopper abundance and species richness. Each indicator was based on a multicriteria decision tree with fuzzy partitioning to account for uncertainty in the threshold values between different alternatives. The output validation of indicators was performed by comparing decision tree output with standardized measurements from 10 surveys across France, Germany, Switzerland, Wales, and Italy. The prediction of grassland suitability for butterflies was more accurate for butterfly species richness (P &amp;lt; 0.05) than for butterfly abundance (P = 0.10), as even under standardized transect counts, recorders will observe disproportionately more individuals when it is sunny and warm. The sensitivity of the butterfly species richness indicator was then tested using an independent dataset of 395 French grasslands. There were significant differences in predicted species richness (χ215 = 121.16; P &amp;lt; 0.05) among the 16 management classes, and they were ranked consistently in spite of very parsimonious assumptions in the decision tree. The prediction of grassland suitability was good for bumblebee abundance (P &amp;lt; 0.05) and species richness (P &amp;lt; 0.01). This prediction was also successful for grasshopper abundance (P &amp;lt; 0.05) and species richness (P = 0.05), all outliers coming from a highly diverse grassland community located on shallow soil in the Italian survey. This set of indicators can thus provide a cost-effective evaluation of temperate grassland suitability as habitat for three insect taxa. These indicators have more relevance than general insect species richness, and their application does not require any entomological skill. The indicators can help stakeholders to make adequate decisions for insect conservation in grassland ecosystems, but do not have direct applicability to higher conservation value taxa or species.

УСТОЙЧИВОСТЬ КЛЕВЕРА ПОЛЗУЧЕГО (TRIFOLIUM REPENS L.) В СЕЯНЫХ ТРАВОСТОЯХ В ЗАВИСИМОСТИ ОТ ИХ СОСТАВА, КРАТНОСТИ СКАШИВАНИЯ И АЗОТНЫХ УДОБРЕНИЙ

The authors carried out studies at the experimental field station of Russian State Agrarian University – Moscow Timiryazev Agricultural Academy in 2008–2020. The study aimed to determine the resistance of white clover in mixtures with various types of grasses with two- and three-cut clipping treatments. In the experiment with four to five-component mixtures, the proportion of white clover reached 36–53% in the botanical composition of swards with the content of perennial ryegrass in the fourth year of life. It did not exceed 22–23% in the mixtures with cock’s foot. With the application of nitrogen fertilizers at a dose of N180, the clover content in the second year of swards was only 1–27%. With the aging of the swards, the proportion of clover in the harvest decreased. In the ninth year of life, its amount in swards with the content of perennial ryegrass without nitrogen application decreased to 13–24%, and in agrophytocenoses with cock’s foot and with nitrogen application to 0–14%. The cock’s foot dominated in the four-component grass mixtures, but during the overwintering of 2015–2016, cock’s foot and perennial ryegrass almost entirely dropped out of agrophytocenoses. Tall fescue was a more resistant species. The yield of grass mixtures composed of grass varieties of Russian selection amounted to 4.16–5.52 t/ha of dry weight on average for eight years, and from varieties of Dutch selection, the yield equaled 4.07–5.24 t/ha. There were no significant differences in yield between grass-legume mixtures based on perennial ryegrass and cock’s foot. With the introduction of nitrogen in a dose of N180 on grass/legume herbage, the yield increased by only 31%, and the return on fertilizers by yield increases was low, making up 4.6–8.9 kg of dry matter per 1 kg of nitrogen. The aftereffect of nitrogen fertilizers on the yield of grass-legume mixtures without the additional introduction of phosphorus and potassium was insufficiently effective. In long-term three-component swards, used from the 14th to the 24th years of life, white clover was more stable in the composition of agrophytocenoses after three-fold mowing than with two-mowing. In years with favorable atmospheric moisture conditions, the proportion of white clover in two and three mows reached 20.1–34.7 and 2.2–24.3%, respectively, and with a moisture deficit, it decreased to 0–9%. For 26 years of growing grasses, there was a significant increase in soil acidity – pHKCl decreased from 6.3 to 4.91–5.36, which negatively affected the resistance of clover as the herbage was aging.

Season‐long, mixed stocking of a cool‐temperate pasture

AbstractMixed‐species grazing offers a means to diversify livestock production systems for cool‐temperate regions typified by the Appalachian plateau of the USA. Our objective was to determine how mixed grazing influenced herbage and animal production, and sward botanical composition of three grazing systems including cattle and sheep. Three replicated systems were as follows: (A) cattle only with winter grazing; (B) cattle and sheep with winter grazing; and (C) cattle and sheep without winter grazing. Herbage mass and growth rate differed by grazing period; system C had the lowest growth rate and showed an interaction of system and grazing period. The proportion of grass in the sward differed by period, and the legume component was influenced by an interaction of system and period. Forbs and dead were influenced by period and sampling location. Herbage crude protein was not influenced by treatment. Herbage fiber components and lignin were consistently higher during the second grazing period. Steers performed similarly in all systems, but total gains varied with year. Lambs in the system without a winter grazing component were heavier than lambs in the system with a winter grazing component. Live weight gains were modest. Lamb fecal egg count was higher in the system with a winter grazing component; however, the fecal egg count per gram was relatively low throughout the experiment. Animal productivity differed with year and tended to be slightly greater for the system without a winter grazing component. Our findings suggest that livestock production systems that included mixed‐species grazing and extended‐season grazing practices contributed to desirable changes in botanical composition and improved herbage productivity patterns, especially in years with ample precipitation. The practices could be used to drive pasture composition by modifying relative abundance of various plant functional groups.

Behavioral patterns of (co-)grazing cattle and sheep on swards differing in plant diversity

Both botanical composition and the presence of additional grazer species may modify the grazing efficiency and ingestive behavior of ruminants. However, at present, potential effects of interactions between sward diversity and presence of multiple animal species on the grazing behavior of cattle and sheep are poorly understood. The objective of this study was to evaluate the effect of mono- or co-grazing of sheep and cattle, as well as the influence of sward botanical composition (either diverse or grass-dominated swards) on animal behavior patterns in a fully factorial design (α=0.05). Sixteen core animals (two mono-grazing animals per species on two sward types, plus two co-grazing animals per species on two sward types) were observed simultaneously. The main behavior (grazing, walking, ruminating/resting) of core animals per paddock was recorded repeatedly in scan samplings every ten minutes from 6 to 22h on twelve observation periods distributed over the grazing seasons of 2009 and 2010. Four daylight quarters of four hours each were differentiated within one observation period. Additionally, bites per minute, bites per step and steps per minute were observed 15 times per core animal on each observation date. Behavioral observations showed that cattle decreased the time allocated to grazing in the presence of sheep (co-grazing management; P≤0.036) and ruminated/rested longer (P≤0.023). However, sward botanical composition had no effect on cattle behavior (P≥0.05). In contrast, sward botanical composition impacted sheep behavior to a greater degree than mono- or co-grazing management (P≤0.05). Both cattle and sheep had a tendency to spend more time grazing and less time ruminating/resting towards the end of the day. In cattle, longer grazing periods were followed by longer ruminating/resting times, whereas sheep varied less in their time spent grazing or ruminating throughout the day. Sheep and cattle responded differently in their grazing behavior to vegetation composition and grazing management showing a potential of the livestock to adapt to a broad range of conditions. The behavior data suggests that livestock performance might gain from co-grazing management. Cattle and sheep behavior should be considered in planning future directions for grassland management and productivity.

Effects of sward botanical composition on nitrogen and potassium leaching in cut grassland

The leaching of nutrients in regions where annual precipitation considerably exceeds evaporation needs to be minimised. Our objective was to study the dependence of leached nitrogen and potassium on botanical composition of grassland sward. Mini-lysimeters filled with loamy sand were embedded in three swards (a mixture of three grass species, grasses mixed with white clover and grasses mixed with lucerne). Annual nitrogen application rates (0, 60, 120 and 180 kg ha -1 ) in conjunction with three fertilizers (mineral fertilizer, cattle slurry and sewage sludge) were applied. The nitrogen and potassium leaching was measured monthly during three years. We concluded that nitrogen and potassium leaching are affected by sward botanical composition. The leaching of both elements was the lowest from grass-clover sward.

Sward botanical composition and sward quality affect the foraging behaviour of free-range laying hens

In a two-year experiment, we investigated the influence of sward plant species composition (sward type), stocking duration and state of sward degradation on the foraging behaviour of chickens. Laying hens (ISA Warren) were pastured on 15 sward types including 14 monocultures of grassland plant species (nine grasses and five forb species) and one mixed sward of the 14 species for three levels of stocking duration (one, two and three days). The behavioural traits pecking plants, ground pecking and scratching were recorded by scan sampling. Sward type had a significant effect on scratching, plant pecking, and total sward-directed pecking (plant and ground pecking together) in the grass swards (p<0.01), and on ground pecking in the forb swards (p<0.05). With prolonged stocking, the frequency of ground pecking significantly increased, whereas that of scratching, plant pecking and total sward-directed pecking significantly decreased. There was a significant stocking duration×sward type interaction for all of the observed behaviours (p<0.01). The tested sward types differed strongly with respect to the extent of degradation resulting from the fixed levels of stocking duration. Sward degradation as measured by percentage ground cover of green leaves or stolons and stems had a significant effect on ground, plant and total sward-directed pecking in forb swards (p<0.001). Considering the observation of other studies that the presence of vegetation and a good use of the run benefit animal welfare by reducing the incidence of feather and injurious pecking, the results of this study may be relevant for the design and management of swards for laying hens outdoor runs and for a welfare-oriented optimization of husbandry systems.

Dynamics of sward condition and botanical composition in mixed pastures of marandugrass, forage peanut and tropical kudzu

This study was carried out to evaluate the dynamics of sward condition and botanical composition of a mixed pasture of marandugrass (Brachiaria brizantha cv. Marandu), forage peanut (Arachis pintoi cv. Mandobi) and tropical kudzu (Pueraria phaseoloides), rotationally stocked at four daily forage allowance levels (6.6, 10.3, 14.3 and 17.9% of live weight). Sward condition was characterized in each stocking cycle by measuring pre- and post-grazing sward height, forage mass and percentage of bare ground. Botanical composition (grass, forage peanut, tropical kudzu and weeds) was evaluated before each stocking period. Swards under smaller forage allowances presented lower height, forage mass and ground cover. This condition favored the growth of forage peanut, which constituted 21.1, 15.2, 8.4 and 3.8% of forage mass in the last quarter of the experimental period, from the lowest to the highest forage allowance, respectively. Tropical kudzu was sensitive to all forage allowance levels and its percentage in the botanical composition was strongly reduced along the experimental period, especially during the dry season (July to September). Forage peanut cv. Mandobi and marandugrass form a more balanced mixture when pre-grazing sward height is maintained shorter than 45 cm. Tropical kudzu is intolerant to intensive grazing management systems when associated to marandugrass.

Green biorefinery (GBR) scenarios for a two-cut silage system: Investigating the impacts of sward botanical composition, N fertilisation rate and biomass availability on GBR profitability and price offered to farmers

Abstract In Ireland, grass is a readily available bioresource. It has previously been established that Green biorefinery (GBR) could become a potential use of Irish grasslands, and a blueprint for a sustainable GBR industry in Ireland has been developed. The objective of this paper is to use scenario analysis to investigate the sensitivity of the profitability of the GBR blueprint to variations in grass quantity and quality as a function of botanical composition, fertiliser application, and biomass availability. As an outcome of these scenario analyses, the price the GBR can offer to farmers above their production costs (€ t −1 dry matter) was calculated. Results of the scenario analyses determined that GBR systems located in a catchment area of permanent pasture ( Lolium perenne > 60%) with annual grass yields in the range of 9–12 t dry matter (DM) ha −1 , and supplied with grass biomass with a fibre content of 500–555 g kg −1 DM and a protein content of 110–130 g kg −1 DM, were viable. The most profitable scenarios were generated when nitrogen fertiliser application was greater than 90 kg ha −1 a −1 . Biomass availability of less than 30% resulted in reduced profitability and for some scenarios resulted in a loss for both the GBR and farmer due to increased transport costs. Within the scenario assumptions of this study, grass feedstock was valued at €4–€56 t −1 dry matter above production costs. However, this value depended on the yields and biomass availability of the GBR catchment area.

An evaluation of the effects of extended grazing pasture with ewe lambs on sward botanical composition

An evaluation of the effects of extended grazing pasture with ewe lambs on sward botanical composition

Botanical composition, production and nutrient status of an originally Lolium perenne-dominant cut grass sward receiving long-term manure applications

Effects of long-term applications (50, 100 and 200 m3 ha−1y−1) of pig and cow slurries on yield, botanical composition and nutrient content of herbage of an original perennial ryegrass sward were assessed in a three-cut silage system and compared with unamended and fertilized controls in the 36th year of the experiment. Cow slurry at 50 m3 ha−1 produced similar annual herbage DM yield to 200 kg ha−1 fertilizer N in 2006, whereas about 100 m3 ha−1 pig slurry were required to produce a similar amount of DM. The highest slurry application rate significantly influenced sward botanical composition without depressing DM yield. The principal invading species were creeping bent and meadow grasses (similar to findings at a previous assessment in 1981) except in the unamended control (which were common bent and Yorkshire fog). Perennial ryegrass remained a main species in plots receiving fertilizer (31 % annual DM yield) and low slurry rates (38 %) but declined to 3 % annual DM yield at the highest slurry rate where the ability of ryegrass to utilize slurry N and P may have been affected by chemically or physically induced deficiencies of other nutrients (e.g. Ca) or direct physical effects such as smothering.

Adaptation and evaluation of the integrated farm system model to simulate temperate multiple-species pastures

Whole-farm simulation provides a tool for predicting the effects of farm management strategies on farm productivity and profitability. One such model, the Integrated Farm System Model (IFSM), was modified to allow representation of up to four forage species coexisting in a pasture mixture. The model was calibrated to simulate net herbage accumulation (NHA) observed during six periods of a 2002 experiment in a 3-species pasture in Pennsylvania, USA, composed of orchardgrass ( Dactylis glomerata L.), white clover ( Trifolium repens L.), and chicory ( Cichorium intybus L.). The model also predicted sward botanical composition, total annual NHA, crude protein (CP), and neutral detergent fiber (NDF). Sensitivity analysis showed that predictions of NHA were most sensitive to both chicory and orchardgrass specific leaf area and partitioning of photosynthate to the shoot, as well as chicory photosynthetic efficiency. The model was evaluated against data from the same 3-species pasture in 2003 as well as a 2-species pasture (lacking chicory) from the same experiment in 2002 and 2003. Predictions of total annual NHA in 2- and 3-species pastures were within ±18% of observed values, though predictions of within-season NHA were less accurate. Predictions of botanical composition tended to remain within ±15% of observed values by species. Predictions of within-season CP and NDF concentrations in the whole sward tended to remain within ±22% and ±15%, respectively. Given the generality and realism required of IFSM, the degree of precision in the modified pasture submodel is acceptable for achieving IFSM’s primary goal of comparing the effects of different management scenarios on forage productivity and the long-term profitability and environmental impact of farms.

Nitrate leaching and bread-making quality of spring wheat following cultivation of different grasslands

The influence of sward botanical composition and ley age on grassland residual effects, quality of spring wheat and subsequent nitrate leaching was investigated. Grazed grasslands of different age (1, 2 and 8 production years) and composition (unfertilised grass-clover and fertilised perennial ryegrass) were ploughed and followed by spring wheat and spring barley. For reference, an adjacent field without grassland history but with the same crop sequence in 2002–2003 was treated with increasing quantities of N fertiliser. Yields and N uptake of spring wheat following grasslands always exceeded those of the reference plots with a history of cereal production. The nitrogen fertiliser replacement values of grass-clover and ryegrass were 59–100 and 72–121 kg ha−1, respectively, with the highest values representing the 8-year-old leys. Grain yield and N uptake increased while those for straw decreased with increasing ley age. There were no effects of previous grassland type (grass-clover/ryegrass) on content of protein, starch and gluten, but grassland age significantly influenced protein (P < 0.05) and gluten (P < 0.01) contents. It is suggested that N mineralisation following the ploughing of older grass leys occurred later than when following the first year ley. The protein and gluten contents of wheat following unfertilised grass-clover corresponded to those following cereals given 125–150 kg N ha−1, but the rheological properties of the gluten were different to what could be achieved using equivalent quantities of mineral fertiliser. Probably, the slow release of N from decomposition of old grassland gave a better synchrony between N release and plant demand. Nitrate leaching in year 1 after ploughing was significantly influenced by type of grassland (P < 0.001) with 10 and 29 kg N ha−1 leached from grass-clover and ryegrass, respectively. Nitrate leaching following ploughing of 1-year-old leys averaged 11 kg N ha−1 which was significantly lower than the 24 kg N ha−1 following 2- or 8-year-old leys. The flow-weighted mean nitrate concentration decreased from 8.5 mg N l−1 in year 1 after grassland cultivation to 4.5 mg N l−1 in year 2. More N was released following ploughing of ryegrass swards and from grasslands of increasing age, but differences were moderate compared to the estimated N-surplus. This indicates that when organic matter in grasslands is partially decomposed and readily mineralisable N used, the remaining organic N is released only very slowly.

Regrowth Interval Influences Productivity, Botanical Composition, and Nutritive Value of Old World Bluestem and Perennial Ryegrass Swards

Botanical composition of pasture in much of the Appalachian Region varies as weather patterns interacting with abiotic and biotic factors create conditions allowing a range of plant species to occupy temporal and spatial gaps in the stand. Field‐grown old world bluestem [Bothriochloa caucasia (Trin.) C.E. Hubb.] or perennial ryegrass (Lolium perenne L.) were defoliated at fixed time intervals (1‐, 2‐, or 4‐wk for old world bluestem and 2‐, 4‐, or 6‐wk intervals for perennial ryegrass). Herbage mass, sward botanical composition, and estimates of nutritive value were determined. White clover (Trifolium repens L.), black medic (Medicago lupulina L), and various common forbs and grasses volunteered in all stands. Old world bluestem yields ranged from 3.38 Mg ha−1 (1‐wk regrowth interval in 2002) to 9.42 Mg ha−1 (4‐wk regrowth interval in 2000). Perennial ryegrass yield increased with increasing regrowth interval in 2002, ranging from 3.16 to 7.29 Mg ha−1. The longest regrowth interval did not necessarily lead to the greatest productivity. Old world bluestem swards clipped at 4‐wk intervals decreased 60% by the third growing season, whereas perennial ryegrass swards clipped at 6‐wk intervals increased by 37%. The proportion of encroaching species increased substantially in perennial ryegrass but not old world bluestem swards by 2002, suggesting that combined effects of repeated defoliation and weather influenced sward composition and productivity. Choice of plant resource, timing and intensity of defoliation, and very likely nutrient inputs coinciding with requirements of sown species could influence sward composition and help manage diversity to sustain productivity.

Spatial and structural uniformity of lowland agricultural grassland in England: a context for low biodiversity

AbstractThe contention that agricultural grassland within the UK is spatially and structurally uniform across wide differences in livestock farming intensity is examined. Total nitrogen (N) input was used as a surrogate for management intensity. Farms with average annual N inputs of &gt;200 kg ha−1 were categorized as highly intensive, those with N inputs of 50–200 kg N ha−1 as moderately intensive and those with inputs of &lt;50 kg N ha−1 were categorized as extensive. Four farms within each management category were selected in two discrete regions: one in south‐west England, typifying a landscape dominated by agricultural grassland, the other in south‐east England with a more mixed‐farming landscape. Specific N input and management data, and sward botanical composition and structure, were obtained on four fields per farm. The south‐west region had a higher proportion of farms with dairy cattle than in the south‐east England region. The average N input and stocking rates were higher within the intensive‐management category farms in south‐west England than in south‐east England. Old permanent grasslands contained variable amounts of sown species, such as Lolium perenne, and were dominated by a few (generally &lt;5) non‐sown grass species. Grassland that received &gt;75 kg N ha −1 year−1 contained &lt;7 plant species and &lt;3 forb species m−2. Grassland communities with &gt;12 plant species and &gt;5 forb species m−2 were only found in study fields that received &lt;50 kg N ha−1 year−1. Grasslands with &gt;10 forb species m−2 were found only in sites receiving &lt;15 kg N ha−1. Of importance at a landscape scale was ubiquity of species‐poor and similar grassland plant communities across the management intensity range within and between livestock farms. Grassland in the extensive management category was similar in structure in terms of sward height and/or sward density to more intensively managed grasslands. This study revealed, albeit in two lowland sample regions in the UK, the ubiquity of grass‐dominated, species‐poor and structurally uniform grasslands, irrespective of apparently broad differences in farming intensity. The consequences of this spatial uniformity on grassland biodiversity are likely to be profound.

Fertilisation, seed mixtures and supplementary feeding for annual legume–grass–cereal pastures in organic milk production systems

Two field trials were carried out in North Karelia during 1999 in order to evaluate annual legume–grass–cereal mixtures for grazing cows within an organic milk production system. For all mixtures, Italian ryegrass ( Lolium multiforum Lam.) was used as the source of grass and barley ( Hordeum vulgare L.) was used as the cereal component. The effect of compost fertilisation (0 and 25 t ha −1) and legume in four mixtures (common vetch ( Vicia sativa L.), hairy vetch ( Vicia villosa Roth.), Persian clover ( Trifolium resupinatum L.) and a mixture of Persian and white clover ( Trifolium repens L.) based) on botanical composition, herbage mass (HM), nutritive value and postgrazing sward height (SH), were studied in Experiment 1. Experiment 2 assessed the effects of two legume based mixtures (common and hairy vetch or Persian and white clover) and two concentrate feeding regimens (once or twice daily) on milk production. In both experiments, herbage nutritive value was relatively constant during the entire grazing season, despite major changes in sward botanical composition. Compost application had no effect on pregrazing botanical composition, but stimulated increases in both pre- ( P=0.056) and postgrazing ( P<0.05) HM and postgrazing SH ( P<0.05). Use of hairy vetch resulted in higher mean pregrazing HM ( P<0.05) and a greater proportion of legumes in grazed swards ( P<0.05) than common vetch. Neither compost nor seed mixture influenced pre- minus postgrazing HM ( P>0.05). In spite of lower digestibility and sugar content, milk production was similar ( P>0.05) for cows grazing vetch compared with clover based swards. At the end of grazing season, high proportions of clover in the sward were associated with an increased incidence of bloat. Concentrate feeding regimen had no effect on animal performance ( P>0.05).

The liveweight gain of Limousin × Friesian heifers grazing perennial ryegrass/white clover swards of different clover content and the effects of their grazing on sward botanical composition

An experiment was carried out in 1992 and 1993 to examine the effect of white clover content of perennial ryegrass/white clover swards on the performance of Limousin × Friesian heifers. Swards with low (L), medium (M) and high (H) white clover contents were established and managed by continuous variable stocking. A compressed sward height of 5·5 cm was maintained using a buffer fence to vary plot areas, with herbage surplus to grazing requirements cut, removed and yields measured. The mean white clover proportions for treatments L, M and H were 0·02, 0·19 and 0·18 in 1992 and 0·13, 0·16 and 0·31 in 1993 respectively. White clover contents of the swards reached a maximum in August and September, and differences between treatments diminished. There was no significant difference between treatments in the content of white clover in the swards in autumn 1993.Liveweight gains of heifers increased asymptotically with increasing white clover content of the sward. Below a white clover herbage mass of 300 kg DM ha–1, there was little effect on liveweight gain, which was 0·70 kg day–1 over the grazing season. Between 400 and 450 kg DM ha–1 white clover, liveweight gains were 0·85–0·90 kg day–1. While clover content of the sward did not significantly affect utilized metabolizable energy output; the mean output over the grazing season in the two years from liveweight gain and herbage yield was 78 GJ ha–1. It is suggested that, using this grazing system, white clover reached an equilibrium with a mean herbage mass of about 400 kg DM ha–1 over the grazing season.

Influence of sward botanical composition on performance of cool temperate grassland under contrasting nitrogen fertilization regimes

Eight field experiments, which tested the effects of lime, phosphorus (P), and two rates of nitrogen (N) on a range of permanent grassland swards in Northern Ireland (NI), were re‐examined to investigate the influence of sward botanical composition on aerial dry matter (DM) productivity under ‘low’ and ‘high’ levels of ? input. The aim of the investigation was to verify results previously obtained using ‘pure’ single‐species swards, which suggested that secondary grasses are more productive than perennial ryegrass at low levels of ? input (i.e., < 100 kg ? ha‐1 a‐1)#lb The swards used in the investigation varied considerably in botanical composition, but were largely dominated by three main species: perennial ryegrass (Lolium perenne L.), creeping bent (Agrostis stolonifera L.), and rough stalked meadow grass (Poa trivialis L.), all of which were characteristic of fertile habitats. The results confirmed that under reduced ? input management, swards dominated by these secondary grasses are capable of out‐performing those in which perennial ryegrass is a major component. The superior (aerial) productivity of the secondary grasses was attributed to their ability to conserve resources and maintain high shoot‐to‐root ratios under ‘moderate’ ? stress conditions.

Tissue Turnover Within Grass-Clover Mixed Swards Grazed by Sheep. Methodology for Calculating Growth, Senescence and Intake Fluxes

1. 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 grazing 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 'botanical 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. For vegetative tillers and elongated clover growing points, both estimates were highly correlated with no significant bias. 6. Although this method is labour intensive, it yields reliable estimates of the growth, intake and senescence fluxes, at three different levels (square metre, population unit and plant part). Hence, a better understanding of the impacts of herbivory on the grass-legume balance in a grazed mixture can be gained.