Biomass production and nitrogen accumulation and remobilisation by Miscanthus × giganteus as influenced by nitrogen stocks in belowground organs

The nitrogen (N) requirement of dedicated crops for bioenergy production is a particularly significant issue, since N fertilisers are energy-intensive to make and have environmental impacts on the local level (NO₃ leaching) and global level (N₂O gas emissions). Nitrogen nutrition of Miscanthus × giganteus aboveground organs is assumed to be dependent on N stocks in belowground organs, but the precise quantities involved are unknown. A kinetic study was carried out on the effect of harvest date (early harvest in October or late harvest in February) and nitrogen fertilisation (0 or 120 kg N ha⁻¹) on aboveground and belowground biomass production and N accumulation in established crops. Apparent N fluxes within the crop and their variability were also studied.Aboveground biomass varied between 24 and 28 t DM ha⁻¹ in early harvest treatments, and between 19 and 21 t DM ha⁻¹ in late harvest treatments. Nitrogen fertilisation had no effect on crop yield in late harvest treatments, but enhanced crop yield in early harvest treatments due to lower belowground biomass nitrogen content. Spring remobilisation, i.e. nitrogen flux from belowground to aboveground biomass, varied between 36 and 175 kg N ha⁻¹, due to the variability of initial belowground nitrogen stocks in the different treatments. Autumn remobilisation, i.e. nitrogen flux from aboveground to belowground organs, varied between 107 and 145 kg N ha⁻¹ in late harvest treatments, and between 39 and 93 kg N ha⁻¹ in early harvest treatments. Autumn remobilisation for a given harvest date was linked to aboveground nitrogen accumulation in the different treatments. Nitrogen accumulation in aboveground biomass was shown to be dependent firstly on initial belowground biomass nitrogen stocks and secondly on nitrogen uptake by the whole crop.The study demonstrated the key role of belowground nitrogen stocks on aboveground biomass nitrogen requirements. Early harvest depletes belowground nitrogen stocks and thus increases the need for nitrogen fertiliser.     

Thirteen‐year variation in biomass allocation under climate change in an alpine Kobresia meadow,northern Qinghai–Tibetan Plateau

Alpine grassland ecosystems are thought to be the most sensitive ecosystems to climate change, yet the responses of their belowground biomass and potential climatic controls are poorly understood. Thirteen‐year (2004 ‐ 2016) time‐series of observational belowground biomass data and environmental factors were analysed in a humid alpine Kobresia meadow on the Northern Qinghai–Tibetan Plateau. Results showed that the mean air temperature increased by 0.44°C from 2004 to 2016, while annual precipitation remained relatively stable. The belowground biomass across all soil depths (0–10 cm, 10–20 cm, 20–40 cm) increased significantly, while aboveground biomass showed little change. The proportion of 0–10 cm belowground biomass decreased, whereas the other proportions both increased, which could be mostly attributed to variations in maximum air temperature. There was no significant relationship between aboveground biomass of plant functional groups and belowground biomass across all depths, indicating that the impact of maximum air temperature on belowground biomass should not be limited by aboveground biomass. The asymmetrical response of aboveground and belowground biomass under current climate fluctuations could provide new insights for the appropriate management of the alpine ecosystem.     

Performance and environmental effects of forage production on sandy soils. I. Impact of defoliation system and nitrogen input on performance and N balance of grassland

Grassland and its management is central to the productivity of and nitrogen (N) losses from dairy farms in north‐west Europe. Botanical composition, production and N surplus of grassland were assessed during five consecutive years. The experiment consisted of all combinations of five defoliation systems: cutting‐only (CO), rotational grazing (GO), grazing + one (MSI) or two silage cuts (MSII) and simulated grazing (SG). Four mineral N fertilization rates (0–300 kg N ha^?1 year^?1) and two slurry levels (0 and 20 m³ slurry ha^?1 year^?1) were applied. Fertilizer N was more efficient in producing net energy (NEL) in grazing‐dominated, low white clover systems (GO and MSI systems: 70 and 88 MJ NEL kg^?1 N) than in white clover‐rich systems (MSII, CO and SG systems: ≤60 MJ NEL kg^?1 N). While sward productivity in system MSI was similar to that in system GO, system MSII benefited from increased N₂ fixation at low N rates. There were small differences in NEL concentrations of the herbage between defoliation systems. Crude protein concentration of the herbage increased with increasing N supply from fertilizer, excreta and N₂ fixation. N surpluses (?63 to +369 kg N ha^?1 year^?1) increased with increasing grazing intensity and increasing N fertilization rate. The average response in N surplus applied was 0·81, 0·59, 0·40, 0·33 and 0·24 kg N ha^?1 in systems GO, MSI, MSII, CO and SG respectively.     

Above and belowground litter decomposition of cover crops grazed at different intensities

Grazing cover crops may increase land-use efficiency while promoting sustainability. We investigated how grazing intensity affects cover crop litter quantity, quality, decomposition, and cotton (Gossypium hirsutum L.) N uptake. Cover crops were a mixture of rye (Secale cereale L.) and oat (Avena sativa L.) managed as follows: no grazing +34 kg N ha⁻¹ (NG34), no grazing +90 kg N ha⁻¹ (NG90), heavy grazing (HG), moderate grazing (MG), and light grazing (LG). Grazed treatments received 90 kg N ha⁻¹. After cover crop termination, above- and belowground litter was collected and incubated in situ for 0, 4, 8, 16, 32, 64, and 128 days, with cotton plants sampled on the same days to estimate N recovery and synchrony between N release from litter and uptake by cotton. By Day 128, only 13% of initial NG34 aboveground biomass had disappeared, whereas 42% of HG disappeared. Nitrogen retained in aboveground litter of HG was less than NG90 (27 vs. 60 kg N ha⁻¹), and aboveground final N stock (at Day 128) of HG was less than NG90 and LG (16, 47, and 41 kg N ha⁻¹, respectively). Belowground litter contributed 98 kg N ha⁻¹ versus 46 for aboveground. Belowground N disappearance from litter bags was greater from NG90 than NG34 (39 vs. 21 kg N ha⁻¹). Cotton N uptake by Day 128 was similar across treatments (191 kg N ha⁻¹). Grazing cover crops impact aboveground litter quantity, quality, and decomposition rates, and belowground litter plays an important role on the N cycling.     

Foliar N/P ratio and nutrient limitation to vegetation growth on Keerqin sandy grassland of North‐east China

To examine whether the critical leaf N/P ratios (of 14, 16) are valid to test nutrient limitation in the context of semi‐arid sandy grasslands, an experiment was conducted on a Keerqin sandy grassland in North‐east China to investigate the responses of plant biomass and nutrient concentrations to fertilization. Plant biomass production and leaf nutrient concentrations were measured after five consecutive years of fertilization with N (20 g N m^?2 year^?1) and/or P (10 g P₂O₅ m^?2 year^?1). Nitrogen fertilization increased the shoot biomass by twofold and consequently the shoot/root ratio, whereas P fertilization had little effect on either shoot biomass or shoot/root ratio. Leaf N/P ratio varied among species with an average of 5·6 in the control, while the mean leaf N/P ratio (7·5) under the N fertilization treatment remained below the threshold of 14. Our results suggest that the critical N/P ratio (14, 16) is not applicable as a test for nutrient limitations in the context of semi‐arid, sandy grassland.     

Reintroduction of grazing management after deforestation of formerly abandoned grassland and its effect on early vegetation changes in the Western Carpathians (Slovakia)

Although the process of reforestation of grassland has been widely studied in Europe, little is known about the effect of deforestation on grassland development. Thus, the specific objective of this study was to evaluate early changes in plant species composition, functional group, yield and biomass quality after deforestation of long‐term abandoned pastures. The experiment was established immediately after deforestation on sparse herbaceous vegetation (mean initial cover 27%) with the following treatments: grazing management only (G0), cutting and grazing aftermath (CG), grazing after seeding of grassland mixture (GS), grazing after a burning treatment in which branches were burned after deforestation (GB) and unmanaged control (U). Very rapid recovery of bare ground by germination and/or sprouting of grassland species was similar under all types of grazing management. Total plant species richness increased in all managed treatments except GB. Similarities according to redundancy analyses in plant species composition were found among G0, CG and GB treatments, especially for forbs with correlated rosette or creeping growth. The woody species, tall grasses and tall forbs had higher abundance in the U treatment. The restoration of grassland following deforestation of formerly reforested grassland area by grazing management was a relatively fast process, and swards were created after 3 years. The highest biomass yield was observed under treatments GS and GB. Forage quality of all managed treatments was sufficient for the demands of beef cattle grazing. However, for subsequent grassland preservation, some type of grazing management is necessary to prevent reforestation, which can occur immediately after deforestation in unmanaged places.     

Effect of different grazing management systems on the herbage mass and pasture height of a Nardus stricta grassland in western Scotland, United Kingdom

The aims of this study were to examine the effect of three grazing treatments (year‐round stocking rates of 0·8 ewes ha^?1, 0·5 ewes ha^?1 and 0·5 ewes ha^?1 plus grazing cattle in summer), imposed for 4 years, on the herbage mass and surface height of a Nardus stricta‐dominated grassland in western Scotland and to obtain estimates of annual productivity of this grassland. Nardus stricta‐dominated grassland comprised proportionately 0·20 of the grazing area. Stocking rate of sheep had no significant effect on the herbage mass of the grassland in the first 2 years of the experiment, although mean summer pasture heights were significantly higher under the lower stocking rate of sheep. The pasture on the treatment with cattle grazing in summer had a significantly lower herbage mass and lower surface height than the two sheep‐only grazing treatments. Year‐to‐year variation in the herbage mass and surface height of herbage in summer was greater than the effect of treatments. Despite changes in surface height, the structural diversity of the grasslands was not increased by the treatments. The annual production of vascular plant material ranged from 417 g DM m^?2 in 1994 to 628 g DM m^?2 in 1996.     

Effect of sward height and vertical distribution of clover on performance of cashmere goats in autumn

To investigate the effect of sward height on liveweight change in goats grazing grass/white clover swards, an experiment was conducted from mid-August to mid-November with groups of non-lactating female cashmere goats that continuously grazed perennial ryegrass (Lolium perenne)/white clover (Trifolium repens) swards. Three replicated different sward height treatments — 10–8 cm (high), 7–5 cm (medium) and 5–3 cm (low) — were used to examine the effects on the competitive ability of grass and clover components within the sward canopy and their effect on liveweight. The pasture after grazing by goats had relatively higher ryegrass leaf (+0·26, high; +0·32, medium; and +0·18, low) and lower dead ryegrass proportions (?0·28, high; ?0·23, medium; and ?0·18, low) than at the beginning of the experiment, whereas the white clover fraction in the sward remained constant (+0·04, high; ?0·02, medium; and +0·03, low). Higher proportions of the white clover leaf lamina and petiole were found near the top of the sward canopy and were negatively correlated with the rate of liveweight gain by goats (P < 0·05). Goats gained 50·2 g Live weight (LW) d^?1 on the tallest treatment (high) but lost 0·01 and 42·3 g LW d^?1 on the medium and low sward height treatments respectively (s.e.d. 13·21, P < 0·001). Liveweight changes that occurred between sampling periods were also correlated (_R2= 0·858, P < 0·001) with changes in the mean sward height and proportion of white clover lamina-petiole at the sward surface in relation to the proportion found within the whole sward. These results suggest that goat liveweight gains would be increased if another species was introduced to reduce the white clover proportion in the surface horizon.     

Performance of cultivated perennial grass mixtures under different grazing intensities in the alpine region of the Qinghai-Tibetan Plateau

In 1998, seeds of four cultivated native perennial grasses, Bromus inermis (B), Clinelymus nutans (C), Elymus nutans (E) and Agropyron cristatum (A), were sown as mixtures with different seed rates in three combinations (B + C, B + E + A and B + E + C + A) in a field study in the north‐eastern part of the Qinghai‐Tibetan Plateau, China. A grazing experiment was conducted in 2000 to investigate the performance of these grass mixtures at leaf, plant and sward scales under different grazing intensities (GI). Four GIs, expressed as the proportion of herbage consumed by Tibetan lambs in relation to the available biomass (IP), were applied in the summer: no grazing, and 0·30, 0·50 and 0·70 of IP. Tiller numbers of the grasses increased and leaf photosynthetic rate, sward leaf area index (LAI) and herbage mass declined with increase in GI. No effect of GI on specific leaf area was observed. Interactions between GI and grass mixtures on the dynamics of species composition, swards’ LAI and herbage mass were found. Large fluctuations in species composition with different GIs showed the poor species compatibility and sward persistence of these grass mixtures under high GI by sheep.     

Cattle and sheep grazing effects on soil organisms, fertility and compaction in a smooth-stalked meadowgrass-dominant white clover sward

This experiment was carried out to improve understanding of sward and soil responses to cattle and/or sheep rotational grazing of low-input (no N fertilizer), natural swards dominated by smooth-stalked meadowgrass (Poa pratensis) syn. Kentucky bluegrass and based on white clover (Trifolium repens). Treatments during two grazing seasons (1989–90) were: cattle grazing alone (C); cattle grazing followed by topping (CT); cattle grazing followed by sheep grazing (CS); and sheep grazing alone (S), Mean target pre- and post-grazing herbage masses were 2200 and 1100 kg dry matter (DM) ha^?1. Plants in sheep-grazed swards regrew more quickly and accumulated more herbage (8·28 compared to 5·35 t DM ha^?1 for cattle-grazed swards, unadjusted for rejected area) than in other treatments. After 2 years, soil in sheep-grazed areas contained 0·25% N, 5·7 kg available P ha^?1, and 379 kg K ha^?1, compared to an average of 0·19, 3·9, and 179 respectively for the same soil nutrients in cattle-grazed treatments. Besides differences in manure distribution and sward rejection, differences in soil compaction among treatments also may have affected soil organisms and thus plant growth. After 2 years, soil bulk densities (g cc^?1) were 1·37, 1·37, 1·27, and 1·12; soil penetrometer measurements (kg cm sec^?1 sec^?1) to 20-cm soil depth were 9·8, 9·3, 9·5, and 6·7; soil nematodes per 100 g of soil were: 5333, 8705, 2810, and 15208; soil rotifers per 100 g soil were: 288, 242, 715, and 33; and earthworms m^?2 (and their biomass (g m^?2)) were 262 (205), 157 (162), 344 (409), and 294 (343) for C, CT, CS, and S treatments, respectively.     

Re‐evaluation of the liming‐fertilization interaction in grasslands on poor and acid soils

The effect of surface liming on herbage production in permanent grasslands is rather uncertain. To better understand the effect of liming on the grassland, a study was made with a field experiment and a pot experiment with soil from the same field. In the field, the effects of liming and NPK fertilization on the production and composition of the vegetation were studied. In pots, the effects of liming and phosphate fertilization on different grass species were analysed. The effect of NPK fertilization (+3·96 t ha^?1) on the production of the original grassland was greater than that of liming (+0·68 t ha^?1), which was only observed (P < 0·05) on the unfertilized plots. Liming increased the total number of species and the proportion of dicotyledons. After replacing the semi‐natural community with Dactylis glomerata L., the effects of liming (+2·37 t ha^?1) and fertilization (+6·52 t ha^?1) were increased. These results, together with those of the pot trial, show the important role of phosphorus in the fertilization effect, and are interpreted as a protective effect of P against aluminium toxicity.     

Effect of grazing severity on perennial ryegrass herbage production and sward structural characteristics throughout an entire grazing season

The objective of this study, which was part of a larger grazing‐systems experiment, was to investigate the cumulative impact of three levels of grazing intensity on sward production, utilization and structural characteristics. Pastures were grazed by rotational stocking with Holstein–Friesian dairy cows from 10 February to 18 November 2009. Target post‐grazing heights were 4·5 to 5 cm (high; H), 4 to 4·5 cm (intermediate; I) and 3·5 to 4 cm (low; L). Detailed sward measurement were undertaken on 0·08 of each farmlet area. There were no significant treatment differences in herbage accumulated or in herbage harvested [mean 11·3 and 11·2 t dry matter (DM) ha^?1 respectively]. Above the 3·5 cm horizon, H, I and L swards had 0·56, 0·62 and 0·67 of DM as leaf and 0·30, 0·23 and 0·21 of DM as stem respectively. As grazing severity increased, tiller density of grass species other than perennial ryegrass (PRG) decreased (from 3,350 to 2,780 and to 1771 tillers m^?2 for H, I and L paddocks respectively) and the rejected area decreased (from 0·27 to 0·20 and to 0·10 for H, I and L paddocks respectively). These results indicate the importance of grazing management practice on sward structure and quality and endorse the concept of increased grazing severity as a strategy to maintain high‐quality grass throughout the grazing season. The findings are presented in the context of the need for intensive dairy production systems to provide greater quantities of high‐quality pasture over an extended grazing season, in response to policy changes with the abolition of EU milk quotas.     

Diet selection of dry and lactating beef cows grazing extensive pastures in late autumn

The diet selection, made by twelve dry and twelve lactating spring‐calving Salers beef cows at the end of the grazing season on an extensively grazed natural mountain pasture in central France, was compared. Sward structure, selection bites, daily grazing time and digestibility of the diet were measured in mid‐October (P₁) and mid‐November (P₂). Live weights were measured twice monthly throughout the experiment. Daily milk production was assessed in the week before the grazing behaviour measurements. Lactating cows grazed more selectively than dry cows: they took more bites on green patches (0·20 vs. 0·13 of total bites, P < 0·01; Jacob's selectivity index: 0·13 vs. ?0·25, P < 0·001), which is consistent with the higher overall nitrogen concentration in faeces (18·1 vs. 17·3 g kg^?1 DM, P < 0·05). Lactating cows tended to slightly increase their daily grazing time compared with dry cows (on average 9·9 vs. 9·5 h, P = 0·07) and grazed faster in mid‐November (74 vs. 69 bites min^?1, P < 0·05). The lactating cows lost more live weight (?24 vs. ?12 kg cow^?1, P < 0·05) between P₁ and P₂. A positive correlation was found between consumption of green patches by lactating cows and their daily milk production in P₂ (r = 0·574, P = 0·05), whereas no correlation occurred between individual milk production and liveweight loss. Dry cows were less selective, which supports management practices that promote the use of cows with low requirements on extensively grazed pastures in late season.     

Ingestion and excretion of nitrogen and phosphorus by beef cattle under contrasting grazing intensities

There is increased global interest in the environmental impacts of farming, including the need to prevent the contamination of soil, water and air with excessive amounts of nitrogen (N) and phosphorus (P) in grazed systems. Reduction in grazing intensity has frequently been recommended to meet biodiversity and production goals in sustainable grazing systems. The objective of this experiment was to measure N and P ingestion and excretion by beef cattle grazing semi‐natural pastures at two grazing intensities (Moderate or Lenient). The cattle grazing at Moderate grazing intensity had significantly more defaecations each day than those grazing at Lenient intensity (9·5 vs. 7·5) and tended to have more urinations (7·0 vs. 5·8). For the Moderate and Lenient treatments, respectively, 113 vs. 76 g N d^?1 was excreted compared with 136 vs. 94 g N d^?1 ingested; 12 vs. 8 g P d^?1 was excreted compared with 13 vs. 10 g P d^?1 ingested and urine N comprised 0·51 and 0·52 of the total N excreted each day. In improved, intensively managed grassland systems, urine N comprises a much higher proportion (approximately 0·70–0·85) of the daily total N excreted. The lower level found here is likely to impact on potential volatilization, denitrification and leaching losses, and these aspects should be examined further to see the extent to which semi‐improved grasslands containing increased plant diversity compared with improved grasslands can deliver higher resource protection, as well as enhanced grassland faunal diversity and abundance.     

Measurement of above-ground plant biomass, forage availability and grazing impact by combining satellite image processing and field survey in a dry area of north-eastern Syria

Field survey and satellite image processing methods were used to estimate the total available forage over an area of 95 034 ha in north‐eastern Syria, and to assess grazing impact on the area. The above‐ground plant biomass was measured by a quadrat method at three sites in each of eight vegetation classes. Available forage was measured by excluding woody parts of shrubs from the whole aerial plant parts. The total above‐ground plant biomass and available forage were estimated by extrapolating the measured point data to the whole target area using classified vegetation data by satellite image processing. Grazing impact was assessed by calculating the differences between the total available forage at the end of growing season and the end of dry season. The values for the estimated total available forage (s.e. of mean) in the area were 55 628 000 (12 920 000) kg DM and 30 007 000 (2 437 000) kg DM at the end of growing season and dry season respectively. Although the area of the cereal fields covered only 0·315 of the area, about 0·69 and 0·82 of the available forage existed in the harvested cereal fields at the ends of growing season and dry season respectively. The integration of cereal fields and rangeland is a normal land use system for livestock management in the area. The higher cover of herbaceous vegetation types showed higher grazing impacts which reduced the total available forage at the end of the growing season by 0·817 (0·199) at the end of the dry season. Although these dense herbaceous vegetation types could possibly produce more available forage, they would incur more intensive grazing impact. On the contrary, lighter grazing impact would occur with a higher cover of shrub vegetation types. The importance of maintaining plant cover over the rangeland area to protect the land against soil erosion is stressed.     

A comprehensive study of plant density consequences on nitrogen uptake dynamics of maize plants from vegetative to reproductive stages

Nitrogen (N) use efficiency (NUE), defined as grain produced per unit of fertilizer N applied, is difficult to predict for specific maize (Zea mays L.) genotypes and environments because of possible significant interactions between different management practices (e.g., plant density and N fertilization rate or timing). The main research objective of this study was to utilize a quantitative framework to better understand the physiological mechanisms that govern N dynamics in maize plants at varying plant densities and N rates. Paired near-isogenic hybrids [i.e., with/without transgenic corn rootworm (Diabrotica sp.) resistance] were grown at two locations to investigate the individual and interacting effects of plant density (low—54,000; medium—79,000; and high—104,000 pl ha⁻¹) and sidedress N fertilization rate (low—0; medium—165; and high—330 kg N ha⁻¹) on maize NUE and associated physiological responses. Total aboveground biomass (per unit area basis) was fractionated and both dry matter and N uptake were measured at four developmental stages (V14, R1, R3 and R6). Both plant density and N rate affected growth parameters and grain yield in this study, but hybrid effects were negligible. As expected, total aboveground biomass and N content were highly correlated at the V14 stage. However, biomass gain was not the only factor driving vegetative N uptake, for although N-fertilized maize exhibited higher shoot N concentrations than N-unfertilized maize, the former and latter had similar total aboveground biomass at V14. At the R1 stage, both plant density and N rate strongly impacted the ratio of total aboveground N content to green leaf area index (LAI), with the ratio declining with increases in plant density and decreases in N rate. Higher plant densities substantially increased pre-silking N uptake, but had relatively minor impact on post-silking N uptake for hybrids at both locations. Treatment differences for grain yield were more strongly associated with differences in R6 total biomass than in harvest index (HI) (for which values never exceeded 0.54). Total aboveground biomass accumulated between R1 and R6 rose with increasing plant density and N rate, a phenomenon that was positively associated with greater crop growth rate (CGR) and nitrogen uptake rate (NUR) during the critical period bracketing silking. Average NUE was similar at both locations. Higher plant densities increased NUE for both medium and high N rates, but only when plant density positively influenced both the N recovery efficiency (NRE) and N internal efficiency (NIE) of maize plants. Thus plant density-driven increases in N uptake by shoot and/or ear components were not enough, by themselves, to increase NUE.     

How does grazing intensity influence the diversity of plants and insects in a species‐rich upland grassland on basalt soils?

The effect of stocking rate on the species richness, abundance and functional diversity of vascular plants, butterflies and grasshoppers was examined in a semi‐natural upland pasture in central France. Over a 5‐year period, 3·6‐ha plots were continuously grazed by Charolais heifers at 1·4 (High stocking rate), 1·0 (Intermediate) and 0·6 (Low) livestock units (LU) ha^?1. To evaluate botanical diversity, percentage cover of all plant species was estimated in late July in ten fixed 1 m × 1 m quadrats per plot. Butterflies were counted on three occasions between late June and early August along three fixed 50‐m‐long transects per plot using the ‘Pollard walk’, with grasshoppers being recorded on two occasions along the same transects. Diversity patterns of the three taxa were affected by stocking rate. For plants, species abundance changed more than species number. Abundance of forbs became higher under the Low compared with the High stocking rate. Stress‐tolerant grasses were also more abundant in plots grazed at the Low stocking rate, while an opposite trend was observed for competitive grasses. Butterflies consistently responded to alterations in vegetation composition, especially to the dynamics of nectar plants. The species richness of grasshoppers also increased in plots at the Low stocking rate. The Low and Intermediate stocking rates were suitable for providing a high diversity of the three taxonomic groups. The results suggested that at least butterfly diversity would peak in vegetation taller than that of vascular plants.     

Selection by sheep and goats for perennial ryegrass and white clover offered over a range of sward height contrasts

The selection by sheep (six Coopworth ewe hoggets, 44·3 ± 4·6 kg live weight) and goats (six Saanen/Anglo‐Nubian yearling males, 38·1 ± 3·8 kg live weight) for perennial ryegrass (Lolium perenne) and white clover (Trifolium repens) and for sward height was measured in two experiments involving paired turves. Pairs of turves with herbage of differing height and of either the same or different plant species were offered. One sward (fixed height species, FHS) was always offered at 130 mm and the other (variable height species, VHS) at 130, 90 or 50 mm. Turves (450 mm × 220 mm) were cut to a soil depth of 100–150 mm from areas of perennial ryegrass and white clover regrown to the desired height after previously being cut to 30 mm. Each turf in a pair was weighed (±1 g) before and after grazing by penned animals maintained on a barley‐based pelleted diet. The number of prehending bites taken from each turf was recorded over a grazing period (128 ± 12 s). Bite mass, bite rate and intake rate were calculated. As the sward height of the VHS turf declined, an increasing proportion of the diet was selected from the 130 mm turf. When averaged over all height contrasts, both animal species selected a higher proportion (0·776 ± 0·026) of their diet from 130‐mm white clover than from 130‐mm perennial ryegrass (0·591 ± 0·018) turves. On average, goats selected a higher proportion (0·721 ± 0·022) of their dry‐matter (DM) intake from the 130‐mm turf than sheep (0·646 ± 0·019), but the effect was not consistent. In contrasts with perennial ryegrass as the VHS (and both perennial ryegrass and white clover as FHS), the proportion of the diet selected from the 130‐mm turf was very similar for both animal species. However, with white clover as the VHS (and both perennial ryegrass and white clover as FHS), goats selected a higher proportion of their intake from the 130‐mm turf to the extent that in the 130‐mm perennial ryegrass/50‐mm white clover contrast sheep showed as strong selection for 50‐mm white clover as goats did for 130‐mm perennial ryegrass. This lesser selection of goats for white clover as its height in a sward declines is likely to contribute to the higher white clover content observed in swards grazed by goats. Bite mass was greater on white clover (246 ± 5 mg DM bite^–1) than on perennial ryegrass (173 ± 5 mg DM bite^–1) and was greater for goats (255 ± 6 mg DM bite^–1) than for sheep (195 ± 5 mg DM bite^–1). Bite rate was greater on perennial ryegrass (45·9 ± 1·0 bites min^–1) than on white clover (39·9 ± 1·0 bites min^–1) and was greater for sheep (45·5 ± 1·1 bites min^–1) than for goats (42·5 ± 1·1 bites min^–1). Apparent intake rate by both sheep and goats was lower (mean, 5·0 ± 0·29 g DM min^–1) on 130 mm perennial ryegrass/white clover than on 130 mm perennial ryegrass/perennial ryegrass (7·0 ± 0·27 g DM min^–1), but was higher (9·62 ± 0·29 g DM min^–1) on 130‐mm white clover/perennial ryegrass than on 130‐mm white clover/white clover (8·2 ± 0·29 g DM min^–1) combinations.     

Asymmetric relationship between grasses and forbs: results from a field experiment under nutrient limitation

We compared the role of grasses and forbs in managed grassland under nutrient‐poor conditions via the experimental removal of one of these two species groups and an evaluation of the removal effects over a 5‐year chronosequence (beginning 4 years after removal start), focusing on above‐ground biomass and community composition. There was evidence for the complementarity of grasses and forbs, as shown by better relative performance of both groups in the mixture, measured as the proportional deviation of their above‐ground biomass from that predicted using single‐group plots. Relative performance of forbs was better than that of grasses and did not change significantly throughout the experiment. Relative performance of grasses decreased, reaching a minimum value of 0·03, but then increased to 0·71, in parallel with increasing legume proportion in the above‐ground biomass (from 0·9 to 5·1%). The botanical composition of the grass group did not respond to forb removal. Among the forbs, subordinate species sensitive to light competition became more abundant after removal of grasses; the forb species richness increased on average by 1·6 species per plot. Our results show that the composition and diversity of the forb group is affected by the presence of grasses, and the presence of forbs in a grassland community assures higher temporal stability in above‐ground production. Under increasing depletion of soil nutrients, the grasses derive substantial benefits from the presence of legume species and possibly also from the other forb species. The study supports the need for realistic, long‐term experiments to better understand plant community dynamics.     

Effects of livestock breed and rearing experience on foraging behaviour of yearling beef cattle grazing unimproved grasslands

The relative importance of breed versus rearing experience on the grazing behaviour and diet selection of beef cattle when grazing unimproved grassland was examined over 4 years. Suckler‐reared calves of a traditional (T) breed (North Devon) or a commercial (C) breed (Simmental × Hereford Friesian) were cross‐fostered and then reared either extensively (E) on unimproved grassland or intensively (I) on agriculturally improved fertilized grassland. As yearlings, the four groups of calves (Traditional breed + Extensive rearing (TE); Traditional breed + Intensive rearing (TI); Commercial breed + Extensive rearing (CE) and Commercial breed + Intensive rearing (CI)) grazed unimproved grassland dominated by Molinia caerulea, for 2 months, and foraging behaviour was studied in a test phase. There was a breed effect on total (bites + chews; TJM) jaw movement rate (T, 78·2 vs. C, 76·5 min^?1; F prob. = 0·041) during grazing and on the proportion of bites taken from plant communities with sward height ≥6 cm (T, 0·83 vs. C, 0·76; F prob. = 0·018). Rearing experience affected TJM rate in the first year in July (E, 80·0 vs. I, 76·8 min^?1; F prob. = 0·015) and August (E, 78·5 vs. I, 75·5 min^?1; F prob. = 0·046). The intensively reared animals grew less well on average during the test phase than those that had previous experience of the unimproved grassland as calves with their mothers (E, 0·16 vs. I, 0·09 kg day^?1; F prob. = 0·033). Our findings indicate that the rearing experience of livestock appears to be as important as the breed when designing grazing managements for nature conservation areas.