Impact of deferred grazing and fertilizer on plant population density,ground cover and soil moisture of native pastures in steep hill country of southern Australia

The impact of deferred grazing (no defoliation of pastures for a period generally from spring to autumn) and fertilizer application on plant population density, ground cover and soil moisture in a hill pasture (annual grass dominated, with Australian native grasses being the major perennial species) were studied in a large‐scale field experiment from 2002 to 2006 in southern Australia. Three deferred grazing strategies were used: short‐term deferred grazing (no defoliation between October and January each year), long‐term deferred grazing (no defoliation from October to the autumn break, that is the first significant rainfall event of the winter growing season) and optimized deferred grazing (withholding time from grazing depends on morphological development of the plants). These treatments were applied with two fertilizer levels (nil fertilizer and 50 kg P ha^?1 plus lime) and two additional treatments [continuous grazing (control) and no grazing for year 1]. Deferred grazing increased (P < 0·05) perennial grass tiller density compared with the control. On average, the tiller density of the three deferred grazing treatments was 27–88% higher than the control. There was a negative (P < 0·01) relationship between perennial and annual grass tiller density. Fertilizer application increased (P < 0·05) legume plant density. The densities of annual grasses, legumes, onion grass (Romulea rosea) and broadleaf weeds varied between years, but perennial grass density and moss cover did not. The ground cover of the deferred grazing treatments in autumn was on average 27% higher than the control. Soil moisture differed between treatments at 15–30 cm depth, but not at 0–15 depth over autumn and winter. The results imply that deferred grazing can be an effective tool for rejuvenating degraded native pastures through increases in native grass tiller density and population and through improving farm productivity and sustainability.     

The effects of autumn closing date on sward leaf area index and herbage mass during the winter period

The provision of grass for early spring grazing in Ireland is critical for spring calving grass‐based milk production systems. This experiment investigated the effect of a range of autumn closing dates (CD), on herbage mass (kg DM ha^?1), leaf area index (LAI) and tiller density (m^?2) during winter and early spring. Thirty‐six grazing paddocks, closed from 23 September to 1 December 2007, were grouped to create five mean CD treatments – 29 September, 13 October, 27 October, 10 November, 24 November. Herbage mass, tiller density and LAI were measured every 3 weeks from 28 November 2007 to 20 February 2008; additionally, herbage mass was measured prior to initial spring grazing and tiller density was measured intermittently until September 2008. Delaying CD until November significantly (P < 0·05) reduced herbage mass (by approximately 500 kg DM ha^?1) and LAI (by approximately 0·86 units) in mid‐February. On average, 35% of herbage mass present on swards on 20 February was grown between 28 November and 30 January. LAI was positively correlated with herbage mass (R² = 0·78). Herbage mass increased by approximately 1000 kg DM ha^?1 as spring grazing was delayed from February to April. Tiller density increased from November to February, although it did fluctuate, and it was greatest in April (9930 m^?2). This experiment concludes that in the south of Ireland adequate herbage mass for grazing in early spring can be achieved by delaying closing to early mid‐October; swards required for grazing after mid‐March can be closed during November.     

Grazing management and tussock distribution in elephant grass

Soil occupation capacity via lateral expansion of tussocks in elephant grass (Pennisetum purpureum Schum.) may be associated with basal tillering. As grazing management alters the proportion of basal and aerial tillers in a tiller population, the hypothesis of this work was that grazing management affects tussock size and distribution with implications for plant population stability. The objective of this study was to evaluate the tiller population stability index, the proportion of basal and aerial tillers, tussock size, and the frequency of tussocks and bare ground in rotationally managed elephant grass cv. Napier. Treatments resulted from the combination of two post‐grazing heights (35 and 45 cm) and two pre‐grazing conditions (95% and maximum canopy light interception during regrowth – LI_0·95 and LI_Max) and were allocated to experimental units (850 m² paddocks) according to a 2 × 2 factorial arrangement in a randomized complete block design, with four replications. Measurements were taken from January 2011 to April 2012. The post‐grazing height treatments affected the tiller population stability index, but did not influence the pattern of tussock distribution. On the other hand, the different grazing frequencies (targets of LI pre‐grazing) altered the pattern of tussock distribution and the proportion of bare ground. In general, the tiller population stability index and frequency of tussocks were higher and the frequency of bare ground lower on swards managed with the LI_0·95 target relative to those managed with the LI_Max target, regardless of the post‐grazing height used, indicating a larger soil occupation capacity of plants under the more frequent defoliation regime. Such responses were associated with larger population of basal tillers and highlight the importance of tiller category and perennation pathway in defining patterns of plant growth and tussock distribution.     

Effects of long‐term grazing management on dandelion (Taraxacum officinale) in Agrostis capillaris grassland

Dandelion (Taraxacum officinale agg.) is a common forb species in grasslands in Europe. Although sometimes regarded as a valuable forage herb, it may become a weed, especially in arable land. There is limited information on the response of Taraxacum to long‐term grassland management practices. Therefore, we analysed cover and dry‐matter standing biomass of Taraxacum in a long‐term (1998–2012) grazing experiment on an Agrostis capillaris grassland. The following treatments were laid out on formerly abandoned grassland: (i) intensive grazing (IG); (ii) extensive grazing (EG); (iii) first cut followed by intensive grazing (ICG); (iv) first cut followed by extensive grazing (ECG); and (v) unmanaged grassland (U). During the first 10 years, all defoliation treatments (i–iv) supported the presence of Taraxacum, and the lowest proportion was recorded in the unmanaged treatment (U). During the final 7 years of the study, combined cutting and grazing promoted Taraxacum cover more than that of grazing only (ICG > IG > ECG > EG). Cover of Taraxacum was negatively affected by increasing sward height where Taraxacum plants had lower fitness. Due to the relatively strong relationship between percentage cover of Taraxacum and its dry‐matter biomass, percentage cover could be used as a simple method for the assessment of biomass of Taraxacum in a sward. Results are discussed in the context of adapting the management of A. capillaris grassland as a simple method for control of Taraxacum abundance, particularly in situations of extensification or abandonment.     

Reduced dairy grassland yields in Central Norway after a single springtime grazing event by pink‐footed geese

Populations of migratory geese overwintering in Europe have risen rapidly during recent decades, leading to increased pressure on available forage resources and more grazing on agricultural lands. Farmers throughout Europe have complained of yield losses due to goose grazing. In spring, the Svalbard‐breeding population of pink‐footed goose (Anser brachyrhynchus) migrates through specific staging sites in Norway, where the geese graze on dairy grasslands and other types of agricultural lands in the early growing season. Despite this, little is known of the impacts of goose grazing on hay biomass and quality in Norway. An experiment using exclosures to prevent goose grazing, and plots that were open for grazing, was established in Central Norway to test the effects of variable grazing intensity on dairy grassland yields. A single spring‐grazing event had severe negative impact at the site with the highest grazing intensity, leading to a 25% reduction in forage yield (milk feed units per hectare) as compared to ungrazed areas. The impacts on the sites with lower grazing intensity were more subtle. The overall reduction (across all sites) of biomass yield was 26%. Forage quality, in terms of milk feed units per kg, was not much affected. Grazing increased the proportion and diversity of weeds, as evidenced by a 49% increase of the Shannon biodiversity index, and there was a 1·3% decrease in the proportion of herbage biomass of sown species. Hence, we have confirmed farmer reports on yield losses, gaining an increased understanding of the overall farmer costs associated with goose grazing in this northern latitude region.     

Spring and autumn animal treading effects on pre‐grazing herbage mass and tiller density on two contrasting pasture types in Ireland

A perennial ryegrass (Lolium perenne L.)‐dominated sward on a well‐drained soil (Experiment 1) and a creeping bent (Agrostis stolonifera L.)‐dominated sward on a poorly drained soil (Experiment 2) were subjected to four treading treatments: control (C, no damage), light damage (L), moderate damage (M) or severe damage (S) to quantify the effects on herbage dry‐matter (DM) production and tiller density. In Experiment 1, treading damage was imposed in spring. In Experiment 2, one‐third of the site was damaged in autumn, one‐third in spring and one‐third in both spring and autumn. Both sites were rotationally grazed after treading treatments. Pre‐grazing herbage mass was measured eight times in Experiment 1 and seven times in Experiment 2 on each plot, and tiller density was assessed four times in each experiment. In Experiment 1, pre‐grazing herbage mass was reduced by 30% in S plots at the first harvest after damage, but cumulative pre‐grazing herbage DM production was not different between treatments (12·7 t DM ha^?1). In Experiment 2, annual cumulative pre‐grazing herbage mass was reduced by between 14 and 49%, depending on intensity of treading damage event and season when damage occurred. Tiller density was not affected by treatment in either experiment. A perennial ryegrass‐dominated sward on a well‐drained soil was resilient to heavy treading damage. A creeping bent‐dominated sward on poorly drained soil requires a more careful grazing management approach to avoid major losses in cumulative pre‐grazing herbage mass production during wet weather grazing events.     

The use of pasture reflectance characteristics and arbuscular mycorrhizal root colonization to predict pasture characteristics of tallgrass prairie grazed by cattle and bison

An experiment was conducted to evaluate the potential for using arbuscular mycorrhizal fungal (AMF) root colonization and pasture reflectance characteristics as indicators of changes in tallgrass prairie vegetation resulting from differences in grazing history. The experiment was conducted within the context of a separate long‐term experiment in which eight 4·9‐ha pastures were grazed by either bison or cattle for nine consecutive years. Two separate ungrazed pastures were selected for comparison with grazed areas on the basis of similarity in burning regime, vegetation, soil and topographic characteristics. Four 45 m‐long transects were located in the upland sites within each pasture, and four plots were clipped to ground level along each transect. Reflectance readings were taken with a hand‐held radiometer at each sampling location and a soil core was collected within each plot for analysis of AMF root colonization. Reflectance readings at sixteen different wavelengths were used directly as inputs during multiple regression development or were transformed into each of three vegetation indices (normalized difference vegetation index, soil‐adjusted vegetation index and wide‐dynamic‐range vegetation index) and used in simple linear regressions. Ungrazed pastures were characterized by higher (P < 0·01) grass biomass, total biomass and canopy height than grazed pastures, but had a lower proportional abundance of forbs (P < 0·01) and amounts of forb biomass (P = 0·04). Species of herbivore did not significantly influence above‐ground characteristics that were measured. In general, AMF root colonization was relatively small and was not significantly affected by treatment and, accordingly, the variation was insufficient to test its potential as an indicator of grazing effects on vegetation or its potential relationship with pasture reflectance. Multiple regression equations based on individual wavelength reflectance values explained significantly more of the variation in above‐ground vegetation characteristics than did simple regressions using vegetation indices as predictor variables (r² values from 0·36 to 0·46 vs. 0·11 to 0·27) and have the potential to predict above‐ground vegetation characteristics in heterogeneous rangelands.     

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.     

Effect of structure of a tropical pasture on ingestive behaviour, digestibility of diet and daily intake by grazing cattle

The effect of the structure of a tropical pasture, based on Dichanthium spp., on the ingestive behaviour, in vivo digestibility of the diet and herbage intake by eight Creole tethered heifers was studied. Two levels of nitrogen fertilizer (0 and 50 kg ha^?1) were applied to plots after each grazing cycle and there were 28 d between each of the three grazing cycles. Four heifers grazed individual subplots daily on each plot for 14 d in each of the successive grazing cycles. Simultaneous measurements of bite depth, bite mass, biting rate, short‐term intake rate and daily grazing time were made in two 4‐d periods at the end of each 14‐d period. The in vivo organic matter digestibility (OMD) and daily herbage organic matter intake (OMI, expressed on a kg LW^0·75 basis) were also measured at the same times. Relationships among pasture characteristics and ingestive behaviour were similar to those reported in other short‐term studies: pasture height was highly correlated with bite depth, bite mass and biting rate (r = 0·91, r =0·79 and r = ?0·68, respectively, P < 0·001). Pasture variables had lower correlations with grazing time and short‐term intake rate than with bite depth, bite mass and biting rate. Pasture structure was more highly correlated with OMD than OMI: leaf mass and length and also the extended tiller length were highly correlated with OMD (r = 0·77, r = 0·76 and r = 0·72, respectively, P < 0·001) whereas the crude protein concentration of the herbage was correlated with OMI and digestible OMI (r = 0·50 and r = 0·69, respectively, P < 0·001). Ingestive behaviour variables, as well as OMD, were correlated more with pasture characteristics than was OMI.     

Effect of drought on biomass allocation in two invasive and two native grass species dominating the mixed‐grass prairie

Control of exotic plant species invading the native prairie relies on our understanding of the eco‐physiological mechanisms responsible for the spread of these species as they compete with native plants for soil resources. We used a greenhouse pot experiment to study vegetative biomass allocation in response to drought stress in two exotic grass species, Kentucky bluegrass (Poa pratensis L.) and smooth brome (Bromus inermis Leyss), and two native species, western wheatgrass (Pascopyrum smithii (Rydb.) A. Löve) and green needlegrass (Stipa viridula Trin.). The experiment was conducted over 3 months in 2010 and again in 2011 in a factorial design of four species and two drought treatments. The proportional data of biomass allocation to shoots, roots, rhizomes and crowns (shoot base) of grass seedlings were analysed by both the nonparametric Mann–Whitney U‐test on the original data and one‐way anova on the arcsine‐transformed data. Our data suggest a clear distinction between the two invasive and two native species in potential competitiveness in soil resource use, with the two exotic species having higher biomass allocation to roots than the two native species and the native species having a higher biomass allocation to crowns than the two exotic species. It is interesting to note that the strongly rhizomatous smooth brome did not produce rhizomes in the first season's growth, regardless of the water stress level. The effect of drought stress on biomass allocation manifested itself more on rhizomes or crowns than on roots or shoots of the four studied grass species, with the effects species‐specific in nature.     

Effects of soil bulk density and strength on seedling growth of annual ryegrass and tall fescue in controlled environment

Grasses sown with minimal tillage commonly exhibit slower establishment and lower herbage yield than those sown into a conventionally tilled seedbed. Some of the difference in performance may be attributed to differences in bulk density between tilled and untilled ground. It is not known if performance rankings of grass cultivars established in clean‐tilled ground remain valid in more compacted soil characteristic of no‐till seeding. Seedlings of five cultivars of Italian ryegrass (Lolium multiflorum Lam.) [IRG] and five cultivars of tall fescue [Festuca arundinacea Schreb. also known as Lolium arundinaceum Schreb. (Darbysh.)] [TF] were grown in pots of Coyle or Stephenville series soils (sandy loam and loamy sand respectively) packed to 0·75, 0·88 or 1·00 of maximum packing densities, established as 1·47 and 1·68 g cm^?3 for Coyle and Stephenville soil respectively. Leaf appearance was measured until seedling harvest at 540 growing degree days after emergence. Increased bulk density decreased leaf appearance rates, reduced final leaf and tiller numbers and aerial and root biomass at harvest in both IRG and TF. Among cultivars within species, there was no difference (P > 0·05) in response to measured parameters to change in bulk density. Seedling growth and development of IRG were consistently greater than that of TF but showed greater reduction in response to increased soil bulk density. Soil strength provided a better indicator of likely seedling response to soil compaction than bulk density. The results suggest that cultivar rankings obtained under conventional tillage are likely to be valid with no‐till planting.     

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.     

The effects of treading by dairy cows on soil properties and herbage production for three white clover‐based grazing systems on a clay loam soil

White clover can reduce fertilizer‐N requirements, improve sward nutritive value and increase environmental sustainability of grazed grasslands. Results of previous experiments in glasshouse conditions and on mown plots have suggested that white clover may be more susceptible than perennial ryegrass to treading damage on wet soils. However, this phenomenon has not been investigated under actual grazing conditions. This experiment examined the effects of treading on clover content, herbage production and soil properties within three clover‐based grazing systems on a wet soil in Ireland for 1 year. Treading resulted in soil compaction, as evidenced by increased soil bulk density (P < 0·001) and reductions in the proportion of large (air‐filled) soil pores (P < 0·001). Treading reduced annual herbage production of both grass and white clover by similar amounts 0·59 and 0·45 t ha^?1 respectively (P < 0·001). Treading reduced the sward clover content in June (P < 0·01) but had no effect on annual clover content, clover stolon mass or clover content at the end of the experiment. Therefore, there was little evidence that white clover is more susceptible to treading damage than perennial ryegrass under grazing conditions on wet soils.     

Grassland responses to grazing disturbance: plant diversity changes with grazing intensity in a desert steppe

This study quantifies the impact of four different grazing regimes (heavy, moderate, light and ungrazed) on the vegetation dynamics of rangeland ecosystems along the southern boundary area of the Mu Us Desert, China. As the grazing intensities decreased, the soil quality, canopy cover, height, density, above‐ and below‐ground biomass, litter, root/shoot ratio and native plant (Aneurolepidium dasystachys) and grass abundances significantly increased; the above‐ground biomass of grasses increased, but the above‐ground biomass of forbs decreased. Ungrazed grassland has significantly improved from grasslands experiencing three other levels of grazing pressure, especially in the grassland biomass. Species richness increased as the grazing intensity decreased in the grazing grasslands, but peak species richness appeared under moderate and light grazing against lower productivity. Grazing exclusion causes desirable transitions in plant communities of desert steppe rangelands. Therefore, appropriate and efficient grazing exclusion is an available way to counteract local grassland degradation and promote rangeland sustainability.     

The effect of early spring grazing and dairy cow grazing intensity on particulate phosphorus losses in surface run‐off

A four‐treatment (UG‐UG, UG‐G, LG‐G and HG‐G) experiment (involving sixteen plots: 3·0 × 7·0 m) examined the effect of early spring grazing intensity on particulate phosphorus (PP) losses in surface run‐off. Ten dairy cows fitted with manure collection ‘bags’ grazed during two short‐term grazing events, Grazing‐1 (23 February) and Grazing‐2 (6 April). During Grazing‐1, two treatments remained ungrazed (UG‐), while treatments LG‐ and HG‐ were lightly grazed and heavily grazed respectively. At Grazing‐2, three treatments were grazed to a similar intensity (‐G), while one remained ungrazed (‐UG). Run‐off was generated at two and 16 days after Grazing‐1 and Grazing‐2 using rainfall simulators (40 mm h^?1) and analysed for a range of P fractions. Grazing had no effect on either dissolved reactive phosphorus (DRP) concentrations or dissolved unreactive P concentrations (mean, 0·15 and 0·16 mg L^?1 respectively) in run‐off. However, PP concentrations increased (P < 0·05) following Grazing‐1 (0·39, 0·53 and 0·72 mg L^?1 with UG‐, LG‐ and HG‐ respectively, Day‐2 Rainfall event), with these effects still evident following Grazing‐2, especially with HG‐G (3·25 mg L^?1). The risk of PP loss in run‐off can be substantially reduced by removing cows from pastures before significant damage to the soil takes place.     

Regrowth patterns of elephant grass (Pennisetum purpureum Schum) subjected to strategies of intermittent stocking management

The morphogenetic responses of individual tillers and the composition of tiller populations throughout regrowth in response to all combinations of two post‐grazing heights (35 and 45 cm) and two pre‐grazing conditions (95% and maximum canopy light interception during regrowth – LI_95% and LI_Max) were studied in swards of elephant grass (Pennisetum purpureum Schum. cv. Napier) from November 2011 to April 2012. Swards were subjected to the same treatments from January 2011 until measurements began, to enable them to adapt to the defoliation regimes. Treatments were allocated to experimental units (850 m² paddocks) according to a 2 × 2 factorial arrangement in a randomized complete block design, with four replications. The total number of tillers (basal + aerial) was similar for both LI pre‐grazing targets. However, there was a change in the preferential growth pathway used by plants characterized by modification in the proportion of tiller classes in plant population. Swards managed with the LI_Max target had a smaller population density of basal tillers and used the recruitment of aerial tillers as the main growth pathway. Although effective for maintaining stable rates of leaf elongation and senescence, such a strategy resulted in greater tiller death. Additionally, stem elongation, a consequence of the competition for light under those circumstances, resulted in differences in sward herbage mass and morphological composition with potential implications for herbage feeding value.     

Competition of Leymus chinensis and Bromus inermis in response to gap size and neighbouring root exclusion

A two‐year small‐plot field experiment was carried out to investigate the competitive relationship between seedlings of two important forage grasses, Leymus chinensis and Bromus inermis, under three levels of gap size (distance between seedlings and their neighbours) of 10, 20 and 40 cm in diameter, with neighbouring roots present or absent. Seeds of the two species were sown into artificially created gaps, in either monoculture or mixtures at equal rates. Results indicated that gap size had significant effects on seedling emergence, seedling survival and the growth performance of the two species, grown alone or in a mixture. Excluding the roots of neighbouring plants enhanced all the measured attributes and had significant effects on both the number of inflorescences and the biomass of B. inermis and on the biomass of L. chinensis. The performance of the two species differed significantly, both alone and in mixtures, with B. inermis outperforming L. chinensis consistently. The number of inflorescences of B. inermis was 2·6‐fold higher than L. chinensis when grown in a mixture, and L. chinensis displayed a large and significant reduction in biomass when grown in a mixture with B. inermis (5·7 g plot^?1) as compared with a monoculture (25·9 g plot^?1). The relative yield (RY) for B. inermis exceeded 0·5, but for L. chinensis, it was below 0·5 in all treatments, and aggressivity (A) in all treatments was above 0. In addition, the relative competition intensity (RCI) of B. inermis was less than that of L. chinensis in all treatments, both separately and when averaged across treatments. We conclude that B. inermis is a superior competitor to L. chinensis in gaps, whereas the performance of L. chinensis was greatly suppressed in mixtures. This indicated that under similar conditions, B. inermis outcompetes L. chinensis during early growth stages. The results have practical implications for the restoration and revegetation of grasslands in northern China.     

Effects of date of autumn closing and timing of winter grazing on herbage production in winter and spring

Growth of grass herbage in Ireland is highly seasonal with little or no net growth from November to February. As a result, feed demand exceeds grass supply during late autumn, winter and early spring. At low stocking rates [≤2 livestock units (LU) ha^?1], there is potential to defer some of the herbage grown in autumn to support winter grazing. This study examined the effects of four autumn‐closing dates and four winter‐grazing dates in successive years on the accumulation of herbage mass and on tiller density in winter and subsequent herbage production at two sites in Ireland, one in the south and one in the north‐east. Closing swards from grazing in early and mid‐September (north‐east and south of Ireland respectively) provided swards with >2 t DM ha^?1 and a proportion of green leaf >0·65–0·70 of the herbage mass above 4 cm, with a crude protein (CP) concentration of >230 g kg^?1 DM and dry matter digestibility (DMD) of >0·700. The effects of autumn‐closing date and winter‐grazing date on herbage production in the subsequent year varied between the two sites. There was no significant effect of autumn‐closing date in the north‐eastern site whereas in the south earlier autumn closing reduced the herbage mass in late March by up to 0·34 t DM ha^?1 and delaying winter grazing reduced the herbage mass in late March by up to 0·85 t DM ha^?1. The effects of later grazing dates in winter on herbage mass continued into the summer at the southern site, reducing the herbage mass for the period from late March to July by up to 2 t DM ha^?1. The effects of imposing treatments in successive years did not follow a consistent pattern and year‐to‐year variation was most likely linked to meteorological conditions.     

The implications of controlling grazed sward height for the operation and productivity of upland sheep systems in the UK: 7. Sustainability of white clover in grass/clover swards with reduced levels of fertilizer nitrogen

The sustainability of white clover in grass/clover swards of an upland sheep system, which included silage making, was studied over 5 years for four nitrogen fertilizer rates [0 (N₀), 50 (N₅₀), 100 (N₁₀₀) and 150 (N₁₅₀) kg N ha^?1]. A common stocking rate of 6 ewes ha^?1 was used at all rates of N fertilizer with additional stocking rates at the N₀ fertilizer rate of 4 ewes ha^?1 and at the N₁₅₀ fertilizer rate of 10 ewes ha^?1. Grazed sward height was controlled, for ewes with their lambs, from spring until weaning in late summer by adjusting the proportions of the total area to be grazed in response to changes in herbage growth; surplus pasture areas were harvested for silage. Thereafter sward height was controlled on separate areas for ewes and weaned lambs. Areas of pasture continuously grazed in one year were used to make silage in the next year. For treatments N₀ and N₁₅₀, white clover stolon densities (s.e.m.) were 7670 (205·4) and 2296 (99·8) cm m^?2, growing point densities were 4459 (148·9) and 1584 (76·0) m^?2 and growing point densities per unit length of stolon were 0·71 (0·015) and 0·67 (0·026) cm^?1 respectively, while grass tiller densities were 13 765 (209·1) and 18 825 (269·9) m^?2 for treatments N₀ and N₁₅₀ respectively. White clover stolon density increased over the first year from 780 (91·7) cm m^?2 and was maintained thereafter until year 5, reaching 8234 (814·3) and 2787 (570·8) cm m^?2 for treatments N₀ and N₁₅₀ respectively. Growing point density of white clover increased on treatment N₀ from 705 (123·1) m^?2 to 2734 (260·7) m^?2 in year 5 and it returned to the initial level on treatment N₁₅₀ having peaked in the intermediate years. Stolon density of white clover was maintained when the management involved the annual interchange of continuously grazed and ensiled areas. The non‐grazing period during ensiling reduced grass tiller density during the late spring and summer, when white clover has the most competitive advantage in relation to grass. The increase in stolon length of white clover in this period appears to compensate for the loss of stolon during periods when the sward is grazed and over winter when white clover is at a competitive disadvantage in relation to grass. The implications for the management of sheep systems and the sustainability of white clover are discussed.     

Effects of method, rate and timing of slurry application to grassland on the preference by cattle for treated and untreated areas of pasture

Two experiments were conducted in the UK to investigate preference by cattle for areas of pasture treated or untreated with dairy cow slurry. Experiment 1 examined the effects of method and rate of slurry applied to a grass pasture in March (Spring); Experiment 2 examined the effects of method and timing of slurry application after cutting for silage in June (Summer). In both experiments, beef steers grazed grassland plots that had been treated with slurry on one half only of the plots for 4 weeks. Slurry was applied by shallow injection (I), trailing shoe (T) or conventional surface broadcasting (S) techniques. In Experiment 1, slurry was applied at 40 m³ ha^?1 (HI) or 20 m³ ha^?1 (LO) 21 d before grazing commenced; in Experiment 2, slurry was applied at 20 m³ ha^?1 either 32 d (E) or 10 d (L) before grazing commenced. Sward height was measured and animal behaviour was recorded during 8 × 24 h measurement periods in each experiment. Preference for slurry‐treated or untreated swards was indicated by a comparison of post‐grazing sward height on each sward and the proportion of total grazing time spent on the slurry‐treated swards. In Experiment 1, a smaller proportion of grazing time was spent on slurry‐treated areas of swards compared with untreated areas of swards on all treatments, but the proportion of time spent grazing the slurry‐treated sward was greater on method T than on methods I or S (0·28, 0·31 and 0·39 for methods S, I and T, respectively, s.e.d. = 0·035, P < 0·05). Steers showed no preference between slurry‐treated and untreated swards by 49, 45 and 44 d after slurry application for methods S, I and T respectively. Differences between HI and LO were not significant (P > 0·05). In Experiment 2, aversion to slurry‐treated swards compared with untreated swards was less for treatment E than for L, with a greater proportion of both residence and grazing time spent on the slurry‐treated sward of treatment E than L (0·43 and 0·28, respectively, for residence time, s.e.d. = 0·025, P < 0·001, and 0·47 and 0·30, respectively, for grazing time, s.e.d. = 0·021, P < 0·001). Significant differences were shown between the methods of slurry application for treatment E, with a greater proportion of grazing time spent on the slurry‐treated swards of methods I and T than method S (0·40, 0·52 and 0·49 for S, I and T, respectively, s.e.d. = 0·032, P < 0·001), and a greater difference between post‐grazing heights on slurry‐treated and untreated swards for method S than for I or T (30, 12 and 15 mm, respectively, s.e.d. = 4·8, P < 0·001). For treatment L, differences in the proportion of time spent grazing on slurry‐treated swards compared with untreated swards were not significant between treatments (0·26, 0·34 and 0·31 for methods S, I and T, respectively, s.e.d. = 0·040, P > 0·05) and indifference between slurry‐treated and untreated swards was achieved 77, 60 and 58 d after slurry spreading for methods S, I and T respectively. These results show that, when slurry is applied to pasture in a grazing rotation, the adverse effects on grazing behaviour associated with conventional surface broadcasting may be overcome by the use of novel slurry application techniques.