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1.
The hypothesis that dynamics of growth, branching of stolons and appearance of leaves are important for the persistence of white clover ( Trifolium repens ) in mixed swards was tested. The effect of cutting frequency and white clover cultivar on stolon and leaf dynamics was studied throughout the growing season in a field experiment. Mixtures of perennial ryegrass ( Lolium perenne ) and white clover cultivars with different leaf sizes, cvs. Alice, Gwenda and Retor, were evaluated for white clover persistence at two cutting frequencies. Stolon dynamics, stolon survival, leaf and node appearance rate, branching, flowering and stolon elongation rate were analysed and related to white clover content and yield.
There were clear seasonal fluctuations in stolon and leaf characteristics. Stolon elongation rate and appearance rates of nodes, leaves and branches declined in autumn. Temperature and irradiation explained a major part of the variation of stolon elongation rate and leaf appearance rate and 25% of the variation in stolon branching rate.
Significant and consistent differences in yield and botanical composition were found between mixtures. Mixtures with cv. Alice had the highest total and white clover yield and the highest white clover content, whereas mixtures with cv. Retor had the lowest yield and the lowest white clover content. Stolon elongation rate and stolon internode length were significantly higher in cv. Alice than in the other white clover cultivars, whereas cv. Retor had a significantly higher percentage of leaves with damage caused by insects and slugs than the other cultivars. Little support was found for the hypothesis that branching characteristics are a key component of competitive success in mixed pasture, as most measured branching characteristics were not associated with differences in white clover yield between cultivars and cutting regimes.  相似文献   

2.
Selective grazing of white clover (Trifolium repens) over grass species in temperate pastures results in reduced clover abundance and availability over time. Within sheep‐ and cattle‐grazed dryland (<800 mm annual rainfall) hill and high country areas of New Zealand, naturalized unsown annual clover species show greater persistence and abundance over sown clovers. With a view to understanding legume abundance in these areas, Merino sheep grazing preference was investigated for pure swards of naturalized species Trifolium dubium, T. glomeratum, T. arvense and T. striatum and commonly sown species T. repens and T. subterraneum. The Chesson–Manly preference index was used to explore the hypothesis that grazing preference differs between these species and changes as plants mature. Herbage offtake was quantified at vegetative (mid–late spring; November) and reproductive (early summer; December) stages of plant maturity. Significant preference distinctions between species (P < 0·05) occurred in December, with relative preference ranging from 0·248 for T. repens to 0·065 for T. dubium. Reduced relative preference for naturalized species was related to decreasing nutritive value from spring to summer, reflecting increased stem and flower sward content. Relative preference was negatively related to increasing acid detergent fibre and neutral detergent fibre and positively related to greater crude protein and dry‐matter digestibility. Naturalized annual clover species of lower grazing preference at reproductive maturity will benefit pasture sustainability via herbage and seed production and associated nitrogen‐fixation inputs.  相似文献   

3.
Single pugging events, which involve remoulding of the soil around the hooves of livestock during treading, of moderate or severe pugging intensity were imposed in plots in a long‐term white clover‐ryegrass pasture during spring, by using dairy cows at varying stocking rates (4·5 cows 100 m?2 for 1·5 or 2·5 h respectively). Changes in the growth and morphology of white clover were investigated over the following 12 months. Defoliation at approximately 3‐week intervals was carried out by mowing. Annual herbage production was reduced following moderate and severe pugging proportionately by 0·16 and 0·34 compared with the non‐pugged control treatment. The corresponding decreases in white clover production were 0·09 and 0·52 respectively. Annual perennial ryegrass production was reduced by 0·37 under severe pugging. Pugging had an immediate adverse effect on growth of white clover which persisted for up to 156 d, and coincided with a large decrease in the proportion of white clover in herbage over the same period (e.g. 0·40 vs. 0·12, in control and severely pugged treatments, respectively, on day 112). In comparison, recovery in ryegrass growth was apparent after 50 d in severely pugged treatments, indicating that white clover is more vulnerable to severe pugging than perennial ryegrass. Analysis of individual white clover plants extracted from turves (300 mm × 300 mm) showed that direct hoof damage, fragmentation and burial of stolons were the major factors which reduced white clover production, rather than the changes in soil physical properties measured. Morphological characteristics associated with plant size (e.g. stolon length, growing points, and leaf numbers) all decreased under pugging. The situation had reversed by late summer, with larger plants dominating pugged plots, and coincided with the recovery of the proportion of white clover in herbage. Strategic pasture management practices, such as restricted grazing and the use of stand‐off pads when soils are overly wet, are suggested as means of minimizing treading damage to pasture and reducing negative impacts on the growth and productivity of white clover.  相似文献   

4.
A New Zealand selection of marsh birdsfoot trefoil proved more productive than white clover when oversown on wet upland pasture in the west of Scotland and exposed to close grazing during 1966–70. A number of introductions were assessed simultaneously at lowland and upland sites as spaced aggregate clumps in 1970–71 and showed variations in growth habit and time of flowering. These collections out-yielded clover control varieties at the upland site during both harvest years, Chilean material being the most promising in terms of DM yield and recovery after defoliation. Three New Zealand selections were compared with local material in two new experiments sown on the same day at the same sites and in a spaced-clump experiment at the upland site. Establishment was adversely affected by prolonged dry weather after sowing, but at the lowland site, probably aided by the germination of hard seed, the plants developed sufficiently to allow DM yields to be determined. The induced tetraploid variety Grasslands Maku was high in seedling vigour and subsequently yielded well at both trial sites, whereas normal diploid varieties established less rapidly, yet produced similar DM yields in the second harvest year. The species clearly shows promise as an oversown legume for improving livestock feed in wet upland pastures.  相似文献   

5.
Two experiments are described in which the effect of grazing or defoliating mixed swards at different times over winter and spring on clover content and development was investigated. In the first experiment swards were grazed with sheep (to about 3 cm) for a short period in (a) November, (b) November, January and March, (c) March or (d) not at all, in three consecutive years. All swards were grazed intermittently during the grazing season with cattle and cut for silage once each year. Each plot received either 0 or 50 kg N ha?1 in March. The effect of N fertilizer was to reduce clover content in each summer and clover growing point density in the third year. In two of the three years, treatments involving grazing in March had lower subsequent net annual herbage accumulation compared with the other two treatments and higher clover content in summer of the third year. Reduction in growing point density in all plots during the grazing season was associated with cattle grazing when conditions were wet, suggesting that stolon burial was implicated. Grazing with sheep in November, January and March resulted in significantly more visible (when counted in situ) clover growing points in April in year 2 and more total growing points (counted after dissection of turves) in the third year than the November grazed and ungrazed treatments which had, on occasions, higher grass tiller density. In a microplot experiment, high herbage mass standing over winter was associated with lower potential photosynthesis per unit clover lamina area and lower growing point density in March. Cutting herbage in March to 2-3 cm resulted in higher clover content and higher growing point number per unit stolon length. The latter was significantly correlated with total irradiance and red: far red at the canopy base. Potential photosynthesis of clover was not affected by cutting in March. It is concluded that growing point density can be increased by grazing or cutting during winter or spring. However, in order for these new stolons to contribute to clover yield during the summer, they have to be maintained until then by ensuring that competition from grass is minimized by keeping the sward short in winter and spring and avoiding the burial of stolons during grazing.  相似文献   

6.
An established sward of binary mixtures of meadow fescue (Festuca pratensis) and white clover (Trifolium repens) (either AberHerald, Grasslands Huia or Sandra) was subjected to (A) no further defoliation, (B) a defoliation in late September or (C) a defoliation in late October after four harvests had been taken during the grazing season. About a tonne of dry matter (DM) was removed by the autumn defoliations. There were two levels of nitrogen application in spring, either 0 or 90 kg ha?1. The development of grass and clover morphology and population sizes from early autumn until the first harvest the following year was followed by regular sampling of the above-ground material. Stolons were analysed for total non-structural carbohydrates (TNCs), and the temperature at stolon level was continuously recorded. There were no interactions between autumn defoliation, clover cultivar or nitrogen treatments on any of the parameters studied. White clover growing-point numbers and stolon morphological characteristics were reduced in size during the winter and did not recover during the spring. A defoliation in late September resulted in the greatest reduction, whereas there were no differences between the other two treatments. The grass tiller population increased from early autumn until the last sampling occasion in May, but both autumn defoliations resulted in a smaller increase. Defoliation in late September had the greatest impact. The TNC content of white clover stolons fell from about 350 g kg?1 to 150 g kg?1 DM from late autumn until late April. There were small differences between the treatments, but a defoliation in late September resulted in a significantly lower level in late autumn. The temperature amplitude at stolon level was consistently greater in plots defoliated in late September. Total DM harvested in spring was 4367, 2564 and 3536 kg ha?1, of which 388, 352 and 460 kg ha?1 was white clover, from treatments A, B and C respectively. It is concluded that an autumn defoliation may affect the overwintering of white clover negatively, but that the effect on the grass may be even more detrimental.  相似文献   

7.
Three experiments designed to investigate different facets of autumn management on white clover stolon development are described. The effects of defoliation interval (2, 4, 6 and 8 weeks during 16 weeks from 27 July) were investigated. The shortest interval resulted in the shortest length of stolon material per unit area but cutting interval had no effect on growing point density nor on hardiness of stolon tips evaluated in October, December and January.
Chemical grass suppressants were employed to reduce grass biomass during winter in two experiments to evaluate the influence of grass on white clover development. One experiment involved varying grass tiller density by spraying a perennial ryegrass/white clover sward in October with three rates of three chemical suppressants (Clout, Kerb and Checkmate). Although tiller and clover growing point density were inversely related in January, the overall relationship was not strong.
Clout at l·5kg a.i. ha−1 was sprayed in October on one of two subplots in each of twelve grazed grass/white clover plots that had been maintained at 7 or 9 cm from July to October then grazed to 3–4 cm with sheep. Sward height had no effect on clover population density but the shorter sward had a greater mean node number per secondary stolon branch. By March, suppressing grass resulted in more than double the stolon population density, a higher proportion of plants with tertiary and quaternary branches, and on marked stolons, five times more branches and 60% higher dry matter (DM) produced during winter but with shorter petioles compared with clover in untreated plots.
It is concluded that white clover has the capacity to branch during a mild winter and as stolon branch numbers can suffer a net loss as a result of the presence of the grass canopy, management that controls grass growth during winter should aid over-wintering and improve persistence of white clover.  相似文献   

8.
White clover ( Trifolium repens ) is a valuable pasture component that is frequently present in insufficient quantity for optimal animal nutrition. Several methods of reintroducing white clover into a permanent pasture without conventional tillage were investigated. Three seeders (Hunter, Vredo and a conventional seed drill), two white clover cultivars (Sacramento, and Sonja), two pasture pre-treatments (a hard spring grazing or grazing plus light harrowing) and two defoliation regimes (grazing or mowing) were used to determine optimal seedling establishment conditions. Defoliation treatments were used as a method of investigating pasture improvement experiments. Measurements were taken to determine proportion of white clover present and total herbage mass.
Plots renovated using a Hunter drill had the highest white clover content in the months immediately after renovation. Subsequently pre-treatment method appeared to have no significant effect on herbage mass or species composition. The proportion of white clover in plots sown with the cultivar Sacramento was frequently higher than that in plots sown with the cultivar Sonja, but, overall, herbage production of cultivars was not different.
Mowed plots had higher herbage production and tended towards a greater white clover content than grazed plots. Compaction of the surface to a depth of 10 cm in the grazed plots may have been a factor in the observed difference in herbage production. Regardless of management, within two years white clover content was similar among all treatments, including controls.  相似文献   

9.
Five white clover populations of Swiss origin and three bred varieties were grown in binary mixtures with two perennial ryegrass varieties, Aurora and S23. The seasonal yields of clover and grass plus clover were measured under a cutting regime during the second and third years after establishment. A series of destructive detailed sward measurements was made during the late autumn to spring period preceding each harvest year. In this way changes in the amounts of stolon, leaf plus petiole and numbers of growing points were monitored during the winter.
There were large differences in clover yield between populations in both years. These were evident from the first (spring) harvest in each year. Higher-yielding clovers in spring tended to produce higher annual clover yields. No grass × clover interaction was evident at any harvest. Large differences between clovers were also apparent in the morphological characteristics measured, with the Swiss material generally having greater amounts of stolon, leaf plus petiole and numbers of growing points present in early spring. It is proposed that these factors contribute to the high spring yield in the Swiss populations. Loss of stolon length over each winter was less in the Swiss material, indicating that its good spring growth was not obtained at the expense of winter hardiness. Annual clover yield was found to be significantly positively correlated with the amount of stolon present in spring, exemplifying the importance of stolon survival over the winter.  相似文献   

10.
Plants of two contrasting white clover varieties (cv. Aberystwyth S184 and Olwen) were planted in the field in spring in each of 2 years at four densities (9, 25, 49 and 100 plants m−2) in 1-m2 plots. The effect of plant density on stolon growth and development and the components of seed yield was subsequently measured.
Stolon growth and development was influenced by plant density, variety and year. At low plant densities both white clover varieties produced longer primary stolons than at higher densities. Plant density, however, had no significant effect on the number of inflorescences at harvest. At the high stolon densities there were significantly fewer reproductive nodes per primary stolon than at the lower plant densities. Plant density did not significantly affect any other seed yield components, but the number of inflorescences at harvest, florets per inflorescence, seed set per floret and 1000-seed weight were all significantly influenced by both variety and year.
The relationship between the vegetative and reproductive growth of white clover is discussed in relation to plant density, variety and climate and the possible role of defoliation managements on inflorescence development.  相似文献   

11.
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.  相似文献   

12.
Five pasture treatments: (1) controlled grazing, (2) controlled grazing + lime, (3) controlled grazing + lime + phosphate, (4) controlled grazing + lime + phosphate + oversown white clover and (5) controlled grazing + lime + phosphate + oversown white clover + oversown perennial ryegrass were applied to three semi-natural hill grassland communities. The communities were those dominated by Agrostis/Festuca, Molinia and Nardus. The proportion of Nardus at the Nardus-dominant site was substantially reduced by herbicide before treatments were applied. All treatments were grazed simultaneously by mature wether sheep on three occasions each year. There were two grazing periods each of 4 weeks duration between mid-May and mid-August with a further grazing period of 3 weeks starting mid-October. During each grazing period stock numbers were set so that a residual herbage mass of 560 kg DM ha ?1 remained at the end of the grazing period. Measurements of net herbage accumulation (NHA) were made annually over a period of 13 years at each site. The green:dead ratio of grasses, species composition of the pasture and the pH of the soil were measured at intervals during the experiment. Estimates of mean annual NHA ranged from 3860 kg DM ha?1 for treatment 1 (controlled grazing) to 5170 kg DM ha?1 for treatment 5 (oversown white clover and perennial ryegrass). The application of lime and phosphate increased annual NHA by 300–350 kg DM ha?1 with a further increase of around 400 kg DM ha?1 when white clover was sown. Increases in NHA between year 1 and year 13 ranged from 30% for treatment 1 to around 55% for treatment 5. Although there was no difference in the mean NHA between sites, the herbage from the Agrostis/Festuca site contained a higher proportion of green grass and white clover than that from the other sites. The highest levels of green grass and white clover were found on the oversown treatments at each site. The grazing pressure exerted produced relatively little change in the botanical composition at the Agrostis/Festuca site. At the Molinia-dominant site the Molinia was largely replaced by Nardus during the first 6 years and Nardus also increased in cover at the Nardus site. Application of lime and phosphate generally increased the proportion of Poa pratensis, Festuca rubra and Agrotis tenuis but did not halt the spread of Nardus at the Molinia and Nardus sites. White clover and perennial ryegrass were successfully introduced by oversowing and proportions remained high throughout the 13 years. The cover by bryophyte spp. increased at all sites with the greatest increases occurring in each case on the less comprehensive pasture treatments. These results suggest that on Agrostis/Festuca-dominant pastures herbage biomass production can be increased with relatively low-cost pasture treatments while maintaining Species diversity. However, Nardus and Molinia dominant pastures are likely to require more comprehensive pasture treatments involving sown grasses and white clover to provide herbage of acceptable quality and avoid an increase in Nardus and bryophytes in the sward. With a regime of episodic summer grazing and the addition of fertilizers oversown pastures can be maintained over long periods of time.  相似文献   

13.
Appropriate pre-sowing methods for the introduction of improved forage legume and grass germplasm are an important issue for hill pasture improvement in New Zealand. A pastoral fallow, which involves not defoliating pasture for a period generally from late spring/early summer to autumn, could create a potentially favourable environment for introducing improved germplasm. A field study was conducted on two aspects (shady and sunny) of moist, low-fertility hill country with or without added fertilizer (phosphorus and sulphur) in the southern North Island of New Zealand, to investigate the changes in plant population density and sward structure during a full or partial pastoral fallow, compared with a rotationally grazed pasture. A 7-month (October to May) pastoral fallow dramatically decreased the densities of grass tillers by 72% (P < 0·01), white clover (Trifolium repens L.) growing points by 87% (P < 0·01) and other species by 87% (P < 0·05). The decline in tiller density by pastoral fallow was enhanced on the shady aspect. Fertilizer application increased white clover growing-point density on the shady aspect (P < 0·05) and grass tiller density on the sunny aspect (P < 0·05). Decreased plant density during pastoral fallowing was attributed to aboveground biomass accumulation, which altered sward structure, leading to interplant competition and mortality by self-thinning and completion of the life cycle of some matured plants. The plant size-density relationship during pastoral fallowing in this mixed-species sward followed the serf-thinning rule, particularly when the calculation was based on all plant species rather than grass alone. There was no significant (P > 0·05) difference in final plant population density between the 7-month pastoral fallow and a shorter term (October to December) pastoral fallow. It is concluded that pastoral fallowing effectively reduced the plant population density and altered sward structure of a hill pasture. Such changes create a more favourable environment for the introduction of improved forage species.  相似文献   

14.
A method for measuring the growth, senescence and defoliation fluxes in a mixture consisting of alternate rows of perennial ryegrass (Lolium perenne) and white clover (Trifolium repens) was used to calculate the actual and potential efficiencies of grass and clover utilization under continuous sheep grazing. White clover contributed relatively more to the growth than to the herbage mass of the mixture and its relative growth rate was usually significantly greater than that of its companion grass. The primary reason for the greater potential efficiency of herbage use of the white clover component was, however, its lower rate of senescence. Greater potential efficiency was not reflected in a greater actual efficiency because the contribution of white clover to the total herbage removed was always smaller than its contribution to the growth flux of the mixture. Despite the commonly assumed sheep preference for white clover, the legume was usually the least defoliated species, presumably because of the lower surface height of white clover compared with grass, which resulted in a lower vertical availability of white clover, thereby restricting its defoliation rate. The positive net herbage accumulation observed with white clover at a constant sward surface height occurred partly through stolon and bud development and partly through the growth of undefoliated leaves from axillary growing points and contributed to a net herbage accumulation per unit dry weight in white clover greater than that in ryegrass. This resulted in an increase in the white clover content of the sward, which was observed independently by destructive measurements.  相似文献   

15.
Four experiments were established in 1981–84 to investigate the effect of defoliation treatments on white clover varieties when grown with S23 perennial ryegrass. Treatments included a cutting only regime, as used in National List trials, and grazing systems simulating as near as possible those used on farms.
Differential effects of cutting and continuous sheep stocking on white clover varieties, together with significant variety × defoliation interactions, illustrated the importance of the grazing animal in the evaluation of white clover. Differential effects of cattle and sheep grazing were also evident. Cattle grazing was less detrimental to white clover than was sheep grazing, i.e. cattle were not selective, and less stolon was removed. In general, with both cattle and sheep grazing the larger the clover leaf size the greater the loss in stolons, which in turn decreased persistency. The results illustrate how alternating cutting, sheep grazing and cattle grazing managements can be used to maintain optimum clover/grass balance.
Successful clover/grass swards depend on the retention of clover, yet avoiding clover dominance. The difference in N transfer between clover varieties, especially those within the same leaf category, and the extra grass produced without fertilizer N, emphasized the importance of varietal choice. Breeding programmes have been concerned with the selection of larger-leaved, long-petioled varieties for growing in competition with grass in the presence of fertilizer N. However, the present results showed that, under continuous sheep stocking, increase in leaf size does not increase clover yield or persistency.
The results presented emphasize the importance of the grazing animal in the evaluation of white clover varieties and indicate that yield of clover dry matter should not be the major criterion for selection of varieties for farm systems.  相似文献   

16.
Six dryland pastures were established at Lincoln University, Canterbury, New Zealand, in February 2002. Production and persistence of cocksfoot pastures established with subterranean, balansa, white or Caucasian clovers, and a perennial ryegrass‐white clover control and a lucerne monoculture were monitored for nine years. Total annual dry‐matter (10.0–18·5 t DM ha?1) and sown legume yields from the lucerne monoculture exceeded those from the grass‐based pastures in all but one year. The lowest lucerne yield (10 t ha?1 yr?1) occurred in Year 4, when spring snow caused ungrazed lucerne to lodge and senesce. Cocksfoot with subterranean clover was the most productive grass‐based pasture. Yields were 8·7–13·0 t DM ha?1 annually. Subterranean clover yields were 2·4–3·7 t ha?1 in six of the nine years which represented 26–32% of total annual production. In all cocksfoot‐based pastures, the contribution of sown pasture components decreased at a rate equivalent to 3·3 ± 0·05% per year (R2 = 0·83) and sown components accounted for 65% of total yield in Year 9. In contrast, sown components represented only 13% of total yield in the ryegrass‐white clover pastures in Year 9, and their contribution declined at 10·1 ± 0·9% per year (R2 = 0·94). By Year 9, 79% of the 6.6 t ha?1 produced from the ryegrass‐white clover pasture was from unsown species and 7% was dead material. For maximum production and persistence, dryland farmers on 450–780 mm yr?1 rainfall should grow lucerne or cocksfoot‐subterranean clover pastures in preference to ryegrass and white clover. Inclusion of white clover as a secondary legume component to sub clover would offer opportunities to respond to unpredictable summer rainfall after sub clover has set seed.  相似文献   

17.
This study estimates the relative contributions of environment and farm management strategies in influencing soil faunal assemblages and attempts to identify the species with potential to affect sustainability of intensive grazing management systems in the north‐eastern USA. It arises because of the change from confinement feeding of dairy cattle, consequent upon concerns about negative environmental effects, the rising costs for machinery and housing, and reduced profit margins, together with the absence of data from which the consequences of such change on the soil fauna may be predicted. Macro‐invertebrates were sampled in soil from seventy‐eight grazed pastures on twenty‐one dairy farms in Pennsylvania, USA, in the spring of 1994. On five of these farms, macro‐invertebrates were sampled (four pastures per farm) in the spring, summer and autumn seasons of 1994, 1995 and 1996. In 1997, macro‐invertebrates were sampled in soil during spring, summer and autumn from (four pastures per farm) on three farms in New York, and during spring and summer on three farms in Vermont. Species richness ranged from two to twelve species (mean 6·4) per pasture site in Pennsylvania and five to eighteen species (mean 10·7) in New York and Vermont. The communities were dominated at most sites by earthworms. Earthworms were correlated with soil basal and substrate‐induced respiration/carbon ratio, and soil moisture, but were negatively correlated with cows per hectare and herbage biomass in Pennsylvania. Sitona larvae were recorded at nineteen of the twenty‐one farms during the spring of 1994 across Pennsylvania and occurred at populations >5 m?2 in 68% of the sampled pastures. Sitona larvae were less abundant in New York and Vermont. Elaterid larvae comprised a complex of seven species of which Aeolus melillus (Say) and Melanotus communis (Gyllenhal) comprised 35% and 39%, respectively, of the elaterids collected in Pennsylvania. Agriotes mancus (Say) and Ctenicera destructor (Brown) comprised 41% and 26%, respectively, of four species collected in New York and Vermont. Scarabaeid larvae, comprising a complex of eight species, were detected at only 27% of the seventy‐eight pastures sampled in spring 1994 in Pennsylvania. Five species were collected in ten of the twelve New York pastures and four species in nine of the twelve Vermont pastures. Populations of scarabaeid larvae averaged <25 m?2 in all three states, except in three Pennsylvania pastures in spring 1994. Detrended canonical correspondence analysis (DCCA) showed pasture standing biomass, legume diversity, pre‐winter stubble height, white clover pasture content, and soil phosphorus levels influenced numbers of invertebrate species more than climatic factors, such as temperature, rainfall, altitude, latitude and seasonal water table. DCCA also showed most pastures to be close to the average of environmental factors. The extremely low density of herbivorous macro‐invertebrates in soil and the absence of pest outbreaks may indicate a stable soil ecosystem.  相似文献   

18.
Pasture legumes that persist under challenging agroecological conditions are crucial to ensure high lamb growth rates in dryland pastures. Pasture and lamb production from binary and diverse mixtures (Mix) of tall fescue (TF) with white clover (Whc), balansa clover (Bc), subterranean clover (Sc) and birdsfoot trefoil (Bft) were compared in a summer‐dry hill site in Corvallis, Oregon over a two‐year period. In 2018, all pasture combinations provided similar lamb liveweight gains (LWG, mean 177 g/day) in the first half of spring. Lambs in TF‐Bc and TF‐Mix pastures grew 31 to 41 g/day faster than those grazing TF‐Sc, TF‐Whc and TF‐Bft in the second half of spring (p < .05). Overall, TF‐Bc and TF‐Mix had higher (p < .05) legume contents (32% and 37% respectively) compared to other pasture combinations. In spring 2019, lambs that grazed the TF‐Mix and TF‐Whc pastures had higher LWG than those on other pastures (p < .05). The superior lamb growth rates were associated with the higher legume content and pasture quality maintained into the late spring period. Overall, the legume content of all pastures decreased over the course of the two‐year trial, with the decline being substantial for balansa clover. The present study confirmed that a high legume content of pastures leads to greater lamb growth rates. Total annual yields of pastures that had greater legume contents were superior to others (p < .05). Thus, a combination of self‐regenerating annual clovers with perennial legumes in pasture mixtures may ensure a higher legume content and longer persistence in dryland hill pastures.  相似文献   

19.
Seven cultivars of white clover (Trifolium repens L.) (Kent, S184, Huia, Menna, Donna, Alice and Nesta) and a commercial mixture, ‘Ensign’, were strip-seeded into an upland perennial rye-grass (Lolium perenne L.) sward in late June 1986. Swards were first grazed by sheep, either on 5/6 August (early) or on 19/20 August (late) and then every 14–21 days (frequently) or 28–42 days (infrequently) during 1986, followed by a common grazing regime in 1987. During April to mid-June 1988 the swards received either a moderate amount of nitrogen or none and were cut frequently or once only in mid-June. Growth of individual seedlings was assessed before and after grazing during 1986 and stolon accumulation and distribution and sward colonization were assessed during 1987 and 1988. All cultivars emerged rapidly and satisfactorily and there were no consistent significant differences in the overall dry matter accumulation per seedling during establishment. During the first autumn the proportion of the aboveground biomass removed during grazing was smallest in Kent (c. 20%) and largest in Nesta (c. 40%). Kent and S184 produced most leaves and stolons and the greatest length of stolons per seedling and per individual stolon, and Nesta and Alice the fewest leaves and stolons and shortest stolons. Seedlings grazed early had heavier and longer stolons than those grazed late; those grazed frequently had more leaves, stolons and growing points than those grazed infrequently, especially following early grazing. During 1987 Kent and S184 had consistently the largest number of stolon growing points, and weight and length of stolons per unit area; these two cultivars and Nesta also colonized the sward more rapidly than the other cultivars. All cultivars contributed substantially and similarly to herbage production in late September. There were no residual effects of the 1986 treatments after the summer of 1987. During 1988 additions of nitrogen fertilizer at 100 kg N ha-1 or allowing the herbage to remain undefoliated between mid-April and mid-June both independently halved the number of stolon growing points per unit area; together they reduced it by 80%. Nitrogen also, on average, halved stolon weights but less so in Nesta, Alice and Huia and more so in all other cultivars. Infrequent defoliation greatly decreased stolon weights in Kent and S184 but had no significant effects on the other cultivars. Sward colonization was almost complete by June and entirely so by October for all cultivars in all treatments. Implications of the results for the after-management of strip-seeded white clover are discussed.  相似文献   

20.
Two experiments, each lasting approximately 12 months, were carried out at North Wyke, Devon, in 1982-83 (A) and 1983-84 (B), to investigate various sward managements following oversowing of white clover (Trifolium repens, cv. Grasslands Huia) at 4 kg ha-1 with a Hunter Rotary Strip-Seeder in June or July into the stubble of a permanent grass sward following conservation. Experimental managements comprised cutting, grazing with wether sheep or grass suppression by herbicide, as appropriate, in late summer/autumn (Phase I), winter (Phase II) and spring/early summer (Phase III). During Phase I, there was no differential effect on clover stolon development of lenient grazing at approximately 4-weekly intervals or topping at the same frequency to a similar height. Early in Phase II of Experiment A, grazed paddocks became so badly poached that no differences occurred between grazing either to early January or throughout the winter. Under drier conditions in Phase II of Experiment B, continuous grazing at either five (L) or ten (H) sheep ha-1 had no immediate effect on clover stolon development, but in a silage cut in June, paddocks formerly stocked at the lower rate yielded 40% more DM than those at the higher rate. Experiment A compared the use of a grass-suppressing herbicide, propyzamide, applied at 0.6 kg a.i. ha-1 in either October or February; in Experiment B it was applied in October. Prophyzamide applied at either time in Experiment A increased the clover content of herbage regrowing after the end of the experimental period from 16% to 36% (s.e.d. ± 3.9). In Experiment B, October application raised the clover contents of herbage cut in June 1984 from 10% (H) and 17% (L) to 32% (s.e.d.±5.9), and stolon lengths per m2 at the end of the summer period from 33 (H) and 56 (L) to 86m (s.e.d. ± 11.7). However, the effect of spraying propyzamide on subsequent herbage yields was erratic, and appeared to depend on the incidence of frost after application. In Phase III of Experiment A, continuous grazing was compared with a silage cut in June. At the end of the experiment there were 31 m m-2 of clover stolon in silaged areas compared with only 2.5 m m-2 following grazing (s.e.d.±6.6). Clover content and herbage yields were also significantly higher following conservation. In Experiment B in the same period, rotational grazing with a 14- or 35-day recovery interval was compared with a silage cut in June, with or without 100 kg N ha-1 applied in March. Application of N to the conservation treatment reduced clover stolon length per unit area, and in the regrowth in the post-experimental period the conservation treatment without N had the largest clover content (31% compared with 16-23% for other treatments, s.e.d. ± 3.6)  相似文献   

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