Clover Swards Research Articles

Mixed-species grazing management to improve sustainability and biodiversity.

Mixed-grazing systems occur when two or more large herbivores graze together. Body size and anatomical differences between animal species are reflected in differences in their selected diet and foraging behaviour, which can bring about opportunities for complementary pasture use. The extent to which niche separation occurs within farming systems depends on the degree of sward heterogeneity and the scale of the resource available, with cultivated swards generally offering comparatively little occasion for selective grazing, in comparison to native pastures. However, even then there are opportunities for mixed grazing to benefit productivity. A range of studies have shown that if sheep are grazed together with cattle on simple grass/white clover swards, the performance of the sheep is improved in comparison to sheep-only grazing, leading to a higher total output per unit area. Semi-natural vegetation communities offer much more opportunity for selective grazing as they are generally more botanically and structurally diverse. Examples are given of the impact of losing large and small grazers from grazed ecosystems in marginal areas. Loss of cattle grazing from the uplands of Wales has been instrumental in the spread of invasive hill grass species linked to the loss of heathland habitats of international conservation importance. Conversely, the loss of sheep and goats from common lands in the Cantabrian Mountains has led to the progressive expansion of woody vegetation, again at the expense of heathlands. Such examples highlight the role that mixed grazing can play in promoting economic and environmental sustainability, particularly in marginal areas.

Nitrogen and white clover impacts on the management of perennial ryegrass–clover swards for grazing cattle

SUMMARYPerennial ryegrass and white clover (WC) have been shown to form compatible mixtures for pasture production under temperate climates. The inclusion of WC has the potential to enhance the performance of grass swards, but the extent of the improvement under contrasting grazing management strategies is unclear. Grazing rotation and fertilizer nitrogen (N) use have been identified as two major factors that can influence the performance of grass–clover swards. The objective of the current study was to examine the effect of differing grazing rotation lengths and the level of N application on the dry matter (DM) yield performance of grass–clover and grass-only swards as well as on WC productivity and persistency under animal grazing. Swards were managed by N application and grazing rotation length: High-N swards were managed on a 21-day grazing rotation (Man 1) and low-N swards were managed on a 30-day grazing rotation (Man 2). The four treatments were: 250 kg N/ha without WC (HN−C), 250 kg N/ha with WC (HN+C), 100 kg N/ha N without WC (LN−C) and 100 kg N/ha with WC (LN+C). There was a significant management × WC interaction over the 3 years for annual DM yield. The LN−C swards produced lower DM yield (−1917 kg DM/ha) than the swards of the other three treatments (11 167 kg DM/ha). Management had a significant effect on annual DM yield with Man 1 swards yielding 801 kg DM/ha more than Man 2 swards (10 288 kg DM/ha). The inclusion of WC yielded significantly more annual DM yield (+1009 kg DM/ha) than grass-only swards. Notably, LN+C produced the same annual total DM yield as swards under High N and a 21-day grazing rotation. Total WC DM yield and proportion across the year was altered significantly by management. Higher N fertilized swards at shorter grazing intervals had a lower WC DM yield (−1544 kg DM/ha) and proportion (−0·13). Dry matter yield of WC with low N application can be similar to that at high N levels if rotation length is used as a mechanism to determine grazing timing. Variations in WC productivity into the final year of the experiment indicate that persistence of significant contributions to DM yield by WC under low N at longer grazing intervals remains unclear after 3 years.

Evidence for soil carbon enhancement through deeper mouldboard ploughing at pasture renovation on a Typic Fragiaqualf

Permanent pastures require periodic renewal (cultivation and resowing) to maintain their productive potential, which involves a short-term carbon (C) loss. Normal cultivation (ploughing or discing) often involves only the top 10–15 cm, or less, of pasture soils. A regrassing field trial with ryegrass plus white clover swards was established in 2011 to assess the effect of deeper ploughing (25 cm) on C storage in an imperfectly drained soil (Tokomaru silt loam). The site was core sampled (0–30 cm depth) 2 and 4 years (i.e. in 2013 and 2015 respectively) after cultivation and regrassing (soil inversion treatment) to assess changes in soil C content at different depths. At both times, an adjacent uncultivated ryegrass paddock (undisturbed pasture treatment) under similar grazing intensity was also sampled and C stocks were compared. Profiles of cultivated soils (soil inversion) showed higher (P < 0.01) C stocks than the adjacent permanent pasture at the nominal 15–25 and 25–30 cm depths and significantly lower (P < 0.01) C stocks in the topsoil (nominal 0–5 cm depth) for both years sampled (2013, 2015). These findings imply that the differences (inversion – pasture) were consistent 4 years after cultivation and deep ploughing at pasture renewal had resulted in an overall increase in soil C mass to approximately 30 cm of ~18% (13.9 Mg C ha–1; equivalent soil mass 3701 Mg soil ha–1) compared with not undertaking the regrassing. This gain in soil C may be temporary, but in a period of 4 years it has significantly increased the net residence time of C in soil related to soil inversion.

Performance of five pasture-based dairy systems with increasing levels of nitrogen fertiliser and associated stocking rates

ABSTRACTA farm systems experiment comparing five pasture-based dairy systems was conducted in south-western Australia over 4 years on an annual ryegrass:subterranean clover sward. Fertiliser N inputs (0, 0.5, 1, 1.5 and 2 kg N ha−1 day−1) and stocking rate (SR; 1.25, 1.50, 1.75, 2.0 and 2.25 milking cows ha−1) increased concurrently for each treatment (F1–F5, respectively). By design, milk yield per cow did not differ between treatments; therefore, the response was measured in terms of changes in herbage dry matter (DM) utilisation and nutritive characteristics, as well as differences in feed input and imported forage required. Total annual pasture utilisation (t DM ha−1) increased from treatment F1–F3 (5.1, 5.9 and 7.3 t DM−1 ha−1, respectively), but responses beyond treatment F3 were not significant. Mean total N response efficiency was 9, 13, 8 and 7 kg DM per kg applied N for F2–F5, respectively, while mean marginal N response efficiency was 9, 17, −2 and 3 kg DM per kg applied N for F2–F5, respectively. The most efficient use of N fertiliser was achieved on treatment F3, where annual pasture utilisation levels in excess of 7 t DM ha−1 yr−1 were consistently demonstrated under the management strategies outlined, substantially greater than the local industry average.

Digestibility and clover proportion determine milk production when silages of different grass and clover species are fed to dairy cows

This study examined how silages of different grass and clover species affect dry matter (DM) intake, milk production, and eating behavior in dairy cows. The primary growth of perennial ryegrass (early and late harvested), festulolium, tall fescue, red clover, and white clover swards were cut, wilted, and ensiled without additives. Thirty-six Danish Holstein cows were fed ad libitum with total mixed rations containing 70% forage on DM basis in an incomplete Latin square design. The forage source was either 1 of the 6 pure silages or late perennial ryegrass silage mixed (50:50 on DM basis) with either red clover or white clover silage. Intake of DM, milk yield, and milk lactose concentration were higher, whereas milk fat and protein concentrations were lower when cows were fed clover compared with grass. No differences in DM intake and milk composition were detected between cows fed red clover and white clover, but white clover resulted in higher milk yield than red clover. Lower body weight, probably caused by lower rumen fill, in cows fed pure white clover compared with the other treatments indicated that intake was regulated physiologically instead of physically. Cows fed early perennial ryegrass, which had the highest silage organic matter digestibility (OMD), did not produce the expected amount of energy-corrected milk (ECM) compared with the other treatments based on the amount of OM digested in the gastrointestinal tract, but the reason was unclear. Across all other grass species, ECM was related to OMD. Inclusion of 50% clover in the diet increased ECM with 2.3 kg/d, and the response to OMD was comparable to the response for the grass silages. In situ fiber degradation profile parameters indicated that fiber in festulolium differed compared with fiber in the other grass species and resembled fiber in clover. Drinking and eating behavior differed markedly in cows fed pure white clover compared with the other treatments. Water intake per drinking bout was comparable among treatments, but cows fed pure white clover had higher drinking bout duration and reduced drinking rate. Additionally, meal size was smaller for cows fed pure white clover compared with the other treatments, for which meal size was similar. In conclusion, differences in ECM between different grass species can be explained by differences in OMD, and at a given OMD level inclusion of clover in the diet increased ECM.

Control of Elymus repens by rhizome fragmentation and repeated mowing in a newly established white clover sward

SummaryControl of perennial weeds, such as Elymus repens, generally requires herbicides or intensive tillage. Alternative methods, such as mowing and competition from subsidiary crops, provide less efficient control. Fragmenting the rhizomes, with minimal soil disturbance and damage to the main crop, could potentially increase the efficacy and consistency of such control methods. This study's aim was to investigate whether fragmenting the rhizomes and mowing enhance the control of E. repens in a white clover sward. Six field experiments were conducted in 2012 and 2013 in Uppsala, Sweden, and Ås, Norway. The effect of cutting slits in the soil using a flat spade in a 10 × 10 cm or 20 × 20 cm grid and the effect of repeated mowing were investigated. Treatments were performed either during summer in a spring‐sown white clover sward (three experiments) or during autumn, post‐cereal harvest, in an under‐sown white clover sward (three experiments). When performed in autumn, rhizome fragmentation and mowing reduced E. repens shoot biomass, but not rhizome biomass or shoot number. In contrast, when performed in early summer, rhizome fragmentation also reduced the E. repens rhizome biomass by up to 60%, and repeated mowing reduced it by up to 95%. The combination of the two factors appeared to be additive. Seasonal differences in treatment effects may be due to rhizomes having fewer stored resources in spring than in early autumn. We conclude that rhizome fragmentation in a growing white clover sward could reduce the amount of E. repens rhizomes and that repeated mowing is an effective control method, but that great seasonal variation exists.

Identification of operational performance attributes for pasture measuring devices

Abstract Farmers have expressed difficulty determining the performance of precision farming devices both before and after purchase. The aim of this study was to develop guidelines for operational performance of pasture measuring devices using a Delphi survey method with 25 dairy pasture management specialists. The eight important attributes of devices for use on dairy farms, as identified by survey respondents were: the device is easy to use; weekly data are available during high pasture growth periods; data are available within 24 hours of measurement; data are accurate; data are collected quickly; data are easily uploaded into third party software; the device is easy to maintain; and the device has been/can be calibrated for ryegrass/ clover swards. The attributes identified through this process provide measurement device developers with a design guide. The results also provide farmers with a list of attributes to consider when investing in pasture measuring devices or services. Keywords: pasture measurement, technology development, precision grazing, Delphi survey

Herbage production, botanical composition and survival of perennial ryegrass- and tall fescue-based swards in simple and diverse species mixtures in a dryland environment

Species diversity in grazed swards can improve sward DM production and stability when compared with traditional, simple binary perennial grass–clover combinations. In dairying regions faced with frequent seasonal soil moisture deficit, and environmental and economic incentives to lessen reliance on inputs (nitrogen fertiliser and irrigation) to overcome this, DM production from the traditional perennial ryegrass–clover swards can be reduced. Mitigating reduced DM production and feed deficits in the absence of inputs could potentially be achieved through increasing sward species diversity through the inclusion of additional forage species that are more productive at key times of the season when perennial ryegrass–clover swards commonly have reduced growth (i.e. summer). A 4-year, grazed small-plot experiment was conducted to evaluate sward DM production, species composition and sward survival of perennial ryegrass- and tall fescue-based swards with varying species compositions. The experimental design was a 2 × 6 factorial of two grasses, perennial ryegrass (PR) or tall fescue (TF), sown with white clover in six species combinations, as follows: no additional species (Control); with red clover (RedCl); lucerne (Luc); chicory and plantain (Herb); timothy and prairie grass (Grass); or a mix of all additional species (Mix). Mean annual DM production over the 4 years was greater (P < 0.05) from PR than from TF swards (13.4 vs. 12.9 t DM/ha/year), owing to superior DM production in 2 of the 4 years, largely during winter and autumn. The addition of other species to tall fescue-based swards did not improve annual or seasonal DM production. Increases in DM production (P < 0.05) were observed from PR-based swards sown with Grass, Herb or Mix in Year 3, when summer rainfall was 37% below the average (0.8–1.3 t DM/ha/year), but this effect was not seen in the following year when rainfall was even lower. Total sown-species content varied over the study period and was greater in PR-based than in TF-based swards (83 vs 70%, P < 0.01). Including additional species had varied effects on sown-species content; when differences were observed, it was greater sown-species content in the Herb and Mix than in the Control swards. However, by the end of the study, there was no observed improvement of sward survival with increased diversity. The findings of the present study suggested that there was no consistent advantage to increasing species diversity in PR- or TF-based swards on DM production or sward survival in dryland grazed dairy swards.

Tolerance of Three Clovers (Trifoliumspp.) to Common Herbicides

Clover inclusion may increase the sustainability of certain low-maintenance turfgrasses. However, selective weed control within mixed turfgrass–clover swards proves problematic because of clover susceptibility to herbicides. Research was conducted to identify common turf herbicides that are tolerated by threeTrifoliumspecies, including white clover, ball clover, and small hop clover, within low-maintenance turfgrass. Leaf and flower density, as well as plant height, were measured 4 wk after treatment as indicators of clover response to 14 herbicides. The threeTrifoliumspp. were moderately tolerant of bentazon (< 35% decrease in leaf density, height, or flowering). Simazine was well tolerated by white clover (< 5% decrease in all response variables), yet moderate injury to ball clover and small hop clover was observed (> 32% decrease in leaf density and > 27% decrease in flower density). Pronamide was well tolerated by white and ball clovers, with no effect on measured response variables; however, pronamide decreased small hop clover height and flower density (38 and 42%, respectively). Imazethapyr and imazamox were moderately well tolerated by white clover and small hop clover (< 39% decrease by all response variables), yet ball clover may be more susceptible to these herbicides than was anticipated based on previously reported tolerance. The herbicides 2,4-DB, halosulfuron, and metribuzin were well tolerated by white clover, with no effect on measured response variables; however, results suggest ball and small hop clovers were less tolerant. Clopyralid, 2,4-D, glyphosate, imazaquin, metsulfuron-methyl, and nicosulfuron resulted in varying degrees of injury across clover species and response variables, but, in general, these herbicides may not be viable options when attempting to maintain any of the three clover species tested. Further research is needed to quantify long-term effects of herbicide application on sward composition and clover succession.

Comparison of ingrowth core and sequential soil core methods for estimating belowground net primary production in grass–clover swards

AbstractEstimation of belowground net primary production (BNPP) is crucial for prediction of grassland soil organic carbon sequestration, but there are high coefficients of variation (CV) among methods of estimation. We compared accuracy and precision of two variations of the traditional soil core method and three of the ingrowth core method, over 2 years on grass–white clover swards in Germany. The ingrowth core method (5‐ to 9‐week ingrowth period) provided the most accurate BNPP estimate (471 g m−2) with the highest precision (CV: 31%), whereas the two soil core approaches resulted in underestimation and high error. Comparing results with other grassland studies, we found that reliability of the ingrowth core method was influenced by ingrowth period and sward rooting pattern related to grass phenological stages, while the precision was determined by ingrowth period and grassland productivity. We therefore recommend using the ingrowth core method for managed grasslands where belowground productivity is relatively high and installation disturbance is likely to be negligible. Using a 6‐ to 8‐week ingrowth period, the method delivers reliable and feasible BNPP estimates for temperate managed grasslands which can be applied to long‐term soil carbon budget simulation. Results from our work and other studies also indicated that standing root biomass masks seasonal pattern of rooting due to synchrony between root birth and death. The soil core method is likely to lead to underestimates and higher errors than the ingrowth core methods and thus should be avoided.

A Comparison between Conventional Tilled and Bicropped Winter Wheat Grown in Monoculture over Four Years

<p>A four year experiment was conducted at a site in the south-east of Ireland in which medium and high input conventional winter wheat production systems were compared to no input and low input systems in which winter wheat was direct drilled into an understory of white clover. Whole crop and grain yields from all systems were strongly related to external input levels, yields from bicropped treatments were poor. Nitrogen uptake and grain yields from the conventional treatments declined during the course of the study whereas nitrogen uptake and yields from bicropped treatments were more stable. Fertiliser N application significantly depressed biological production efficiency and altered biomass partitioning. The proportion of biomass partitioned to the stem decreased with fertiliser N, differences between treatments persisted until final harvest. Although the clover sward was still present in the fourth year, this component of the bicrop was gradually replaced by weeds as the experiment progressed in spite of several attempts to control weeds. It is suggested that further research is needed to identify a clover management strategy which ensures the persistence of the white clover sward and allows it to enrich soil fertility in such a way as to be of benefit to the accompanying wheat crop.</p>

Spatial and Temporal Abundance of Interacting Populations of White Clover and Grass Species as Assessed by Image Analyses

The dataset comprises detailed mappings of two communities of interacting populations of white clover (Trifolium repens L.) and grass species under differing experimental treatments over 4-5 years. Information from digital photographs acquired two times per season has been processed into gridded data and documents the temporal and spatial dynamics of the species that followed from a wide range of spatial configurations that arose during the study period. The data contribute a unique basis for validation and further development of previously published models for the dynamics and population oscillations in grass-white clover swards. They will be well suited for estimating parameters in spatially explicit versions of these models, like neighborhood based models that incorporate both the dispersal and the local nature of plant-plant interactions.

Mixtures of clovers with plantain and chicory improve lamb production performance compared to a ryegrass–white clover sward in the late spring and early summer period

AbstractA research programme was undertaken over two consecutive years with the purpose of studying the effect of herb–clover swards on lamb production performance year‐round. The focus of this study was on two consecutive late spring and early summer periods (2011, 2012). In each year, three sward treatments were compared on grazed paddocks with 40 lambs ha−1: (i) grass–clover mixture (perennial ryegrass [Lolium perenne L.] and white clover [Trifolium repens]); (ii) plantain–clover mixture (plantain [Plantago lanceolata], white clover and red clover [Trifolium pratense]); and (iii) chicory–plantain–clover mixture (plantain, chicory [Cichorium intybus L.] and white and red clovers). Lambs were weighed at 2‐week intervals, and carcass weights and GR tissue depth measurements were obtained at slaughter. In both years, lambs on treatments (ii) and (iii) had greater (P < 0·05) final live weight, liveweight gain, carcass weight, dressing‐out percentage and GR tissue depth measurements, and lower feed conversion ratio compared to lambs on treatment (i). Lamb production was similar in treatments (ii) and (iii) (P > 0·05) in each year. Therefore, during the late spring and early summer period, herb–clover mixture swards were found to be a superior option to perennial ryegrass–white clover for finishing lambs.

The influence of season on lambs' feeding preference for plantain, chicory and red clover

The objective of the three studies reported here was to examine the grazing preference and diet selection of lambs for plantain (Plantago laceolata), chicory (Cichorium intybus L.) and red clover (Trifolium pratense) compared with New Zealand’s conventional ryegrass (Lolium perenne) pasture. Study One investigated the diet selection of lambs for 7 days at the beginning of March, using transects with tagged plants on a mixed plantain, chicory and red clover sward. Study Two was an outdoor preference experiment conducted in both March and May by observation of lambs on adjacent monocultures of plantain, chicory and red clover. Study Three was an indoor feeding trial that aimed to determine the intake rate and relative preference of weaned lambs for two herbages (chicory and plantain), two legumes (lucerne and red clover) and ryegrass pasture, in both spring (November) and summer (March). Study One determined that when grazing the mixed sward for a period of 7 days, the mean day that lambs commenced grazing red clover, chicory and plantain was Day 1.6 ± 0.1, 4.8 ± 0.2 and 6.2 ± 0.2, respectively, with significant (P < 0.05) differences between all species. In relation to preference as observed in Study Two, more lambs (P < 0.05) were seen to be grazing red clover at any time, and more lambs were grazing chicory (P < 0.05) than plantain. There was, also an interaction of season with preference, with plantain becoming more acceptable (P < 0.05) to the lambs in May (late autumn) versus March (early autumn). In Study Three, the term ‘preference’ refers to the natural logarithm of the ratio of amounts eaten between the forage being tested and the alternative forage offered simultaneously. This was established in triplicate by offering pairs of all the plant species side by side to individually penned lambs. The results indicated that plantain was consumed at a similar rate (P > 0.05) to that of ryegrass, whereas red clover and chicory had higher voluntary feed intakes, likely due to lower fibre content. The intake rate of chicory was greater in summer than spring and may be related to increased palatability due to the increased water-soluble carbohydrate content of chicory in summer. Regardless of season, average preference for red clover was always higher (P < 0.05) than that of chicory, plantain and ryegrass. Plantain was considerably less preferred in summer than spring. Differences in diet selection and preference may offer a unique opportunity to manipulate utilisation of pastures using a diverse range of plant species.

Comparisons of biological nitrogen fixation in association with white clover (Trifolium repens L.) under four fertiliser nitrogen inputs as measured using two 15N techniques

The objectives of this study were to compare techniques for measuring biological nitrogen fixation (BNF) and to assess how fertiliser N input affects the balance between BNF and sustainable herbage production on perennial ryegrass (Lolium perenne L.)/white clover (Trifolium repens L.) grassland. Biological N fixation and herbage production by white clover based grassland was measured in 2011 and 2012 under four nominal annual fertiliser N inputs: 0 (0N), 86 (86N), 140 (140N) and 280 kg ha−1 (280N). Biological N fixation was measured using the 15N isotope dilution and 15N natural abundance techniques under all fertiliser N inputs and also using the nitrogen difference technique under 0N. The two 15N techniques produced similar annual estimates of above-ground BNF across the range of fertiliser N inputs. Fertiliser N input resulted in higher herbage dry matter yield, but reduced annual BNF which averaged 80, 64, 66 and 47 kg ha−1 on 0N, 86N, 140N and 280N, respectively, across both techniques and years. The two 15N techniques were comparable in estimating BNF. Intermediate fertiliser N inputs achieved a balance between minimising detrimental impact on BNF and potential N loss while producing more herbage DM yield than clover swards receiving no fertiliser N.

White Clover Inclusion within a Bermudagrass Lawn: Effects of Supplemental Nitrogen on Botanical Composition and Nitrogen Cycling

ABSTRACTWhite clover (Trifolium repens L.) inclusion is a proposed means of increasing the sustainability of low‐maintenance turfgrass scenarios due to its ability to biologically fix N and transfer it to associated grasses. Little is known about white clover N contribution to maintained warm‐season turfgrass swards. A 3‐yr study was conducted to evaluate the effects of white clover inclusion within a hybrid bermudagrass [Cynodon dactylon (L.) Pers. × C. transvaalensis Burtt Davy] lawn. Supplemental N (0, 0.5, 1, 2, 4, and 8 g N m−2) was applied monthly, from April to August, to test the effects of supplemental N on biomass composition, N fixation, and N transfer. Mixed grass plus clover swards yielded higher clipping biomass than grass‐alone swards, which was evidence of enhanced bermudagrass growth due to biological N fixation. Likewise, grass biomass of mixed swards was increased relative to that of grass‐alone swards at supplemental N rates ≤10 g N m−2 yr−1 but was decreased at higher supplemental N rates. Nitrogen fixation was estimated to be 6.6 g m−2 yr−1 during the 3‐yr study, with an apparent increase in fixation as years progressed. Results indicate that N fixation was suppressed at the lower and upper extremes of supplemental N rates. Nitrogen transfer to the associated bermudagrass sward was estimated to be 24% during the latter 2 yr of the study. These results offer evidence of white clover utility when included within maintained warm‐season turfgrass scenarios.

Grazing alternative herbages in lactation increases the liveweight of both ewe lambs and their progeny at weaning

Breeding ewe lambs is a management tool that can be used to increase farm profit. However, there are potential negative impacts on the liveweight of progeny at weaning and the liveweight of the ewe lamb at the following breeding. A potential method of minimising these impacts is through the provision of quality herbages such as lucerne or a herb mix containing chicory, plantain, and red and white clover. The aim of this 2-year study was to examine the impact of offering ewe lambs either a traditional ryegrass and white clover pasture (Pasture), Herb-mix or Lucerne throughout the lambing period and in lactation. During lactation in both years of the study, ewe lambs offered the Herb-mix or Lucerne treatments were heavier (P < 0.05) than those offered Pasture. In addition, progeny of ewe lambs offered the Herb-mix or Lucerne treatment were also heavier (P < 0.05) in lactation than those born onto ryegrass white clover. Interestingly, in one of the 2 years, the ewes and their progeny on the Lucerne treatment were heavier (P < 0.05) in lactation than those in the Herb-mix treatment. Combined, these results indicated that offering either Herb-mix or Lucerne increases the performance of the young dam and her progeny above that found on a ryegrass and white clover sward.

Effects of a winter or spring sowing date on soil nitrogen utilisation and yield of barley following a forage crop of red clover, lucerne or hybrid ryegrass

An experiment tested the hypothesis that the yield and nitrogen content of a spring-cultivated barley (Hordeum vulgare) crop (cv. Riviera) would be higher than for a winter-cultivated barley crop (cv. Pearl) when following 3-year-old swards of either red clover (Trifolium pratense), lucerne (Medicago sativa) or hybrid ryegrass (Lolium hybridicum) maintained and harvested for silage. Four replicate, 15m×15m plots of red clover, lucerne, hybrid ryegrass receiving 250kgNha−1annum−1 (250-N HRG) or hybrid ryegrass receiving 0Nha−1annum−1 (Zero-N HRG) were sown on 2 September 2002. On 13 October 2004 and 17 March 2005, half of each plot was ploughed and sown with either winter or spring barley, respectively. Barley was harvested as whole-crop at the dough stage. Soil samples were collected from all plots in autumn 2004, spring 2005 and autumn 2005 for soil mineral N (SMN) analyses and ceramic cups were used to assess nitrate leaching from red clover plots. The grain DM yield of barley was higher when cultivating winter barley compared with spring barley when sown following Zero-N ryegrass (P<0.05), whereas the grain DM yield was higher when cultivating spring barley compared with winter barley when sown following legumes (P<0.05). In autumn 2005, following harvest of the barley crops, SMN and soil nitrate-N was higher in soils cultivated the previous autumn compared with soils cultivated in spring 2005 (P<0.001). SMN was higher (P<0.05) in red clover plots than Zero-N HRG plots, but there were no differences in SMN among the other treatments (P>0.05). The total N leached from red clover plots was higher from winter-cultivated barley plots (57kgNha−1) compared with spring cultivated barley plots (35kgNha−1) (P<0.01). Overall, the results showed that the best practice to optimise the recovery of SMN by a subsequent cereal crop following legumes in this study was to cultivate and sow barley in spring rather than in autumn whereas, when sowing cereals after ryegrass, the best use of SMN was obtained when cereals were sown in the autumn compared with the spring.

A spatially explicit population model of the effect of spatial scale of heterogeneity in grass–clover grazing systems

SUMMARYThe benefits of using white clover (Trifolium repensL.) as a source of nitrogen (N) and nutritious feed in pasture grazed by ruminant livestock have been widely recognized. However, clover is considered inadequate and unreliable as the main source of N input, since its abundance in pasture is patchy, low (typically &lt;0·20) and shows great year-to-year variation. This is thought to be due to the metabolic costs of N fixation, competition with grass, the preference for clover by grazing animals and patchy dung and urine deposition. One solution suggested by a number of authors is to increase the heterogeneity within the pasture by spatially separating clover from grass. This method of pasture management, in order to sustain higher clover content in both the sward and diet of grazing animals, would remove inter-specific competition and equalize grazing pressure, allowing clover to grow unimpeded in greater abundance than previously observed. An existing spatially explicit grass–clover simulation model, developed to investigate the intrinsic spatial and temporal variability within mixed grass–clover swards, was modified and then used to examine the impact of spatial separation on the content, variability and patchiness of clover in pasture. The results show that spatial separation increases both the content and spatial aggregation of clover and reduces year-to-year variation compared with a mixed pasture that fluctuates around a lower mean. The same model was also used to examine the impact of spatial separation across a range of spatial scales, from narrow strips to complete separation, as a means of managing the concerns over disruption to the N cycle within the pasture. The present study shows the importance of the initial sowing arrangement of plant species in sustaining a high content of clover within a pasture in the short term, to at least 20 years depending on the scale of separation, and demonstrates that the spatial separation of clover from grass within a grazed pasture may overcome some of the limitations associated with the use of clover in conventional grass–clover pastures. Results are discussed in terms of benefits to both herbage dry matter production and animal performance.

The effects of simulated summer‐to‐winter grazing management on herbage production in a grass–clover sward

AbstractThe effects of summer‐to‐winter simulated grazing management factors, namely defoliation interval (INT: 21, 42, 56 or 84 d), defoliation height (DH: 2·7, 3·6, 5·3 or 6·0 cm) and final defoliation date (FIN: 23 September, 4 November or 16 December) on herbage production in a grass–clover sward were studied. Treatments were imposed between July and December 2008, with all plots under common management in the following March to June 2009. The 42‐d INT achieved the highest (P &lt; 0·001) total herbage yield at 11·00 t DM ha−1. Shorter (21 d) and longer (56–84 d) intervals reduced annual clover herbage yield and biological nitrogen fixation estimates. Lowering DH from 6·0 to 2·7 cm in the summer‐to‐winter period increased sward clover content and clover herbage yield through to the following June, 6 months after treatments ended. Delaying FIN from 23 September to 16 December had no significant effect on annual clover, grass or total herbage yield. Spring–summer clover herbage yield was positively correlated with spring–summer clover stolon mass (R2 = 0·54, P &lt; 0·001) and, to a lesser extent, light penetration through the sward in the previous winter (R2 = 0·16, P &lt; 0·05). A 42‐d INT with low DH (2·7–3·5 cm) is therefore recommended for grass–clover swards.