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1.
Six varieties of white clover, each grown with perennial ryegrass, four intervals between cuts and two levels of applied nitrogen in all combinations, were compared in a field experiment during the first 27 months after sowing. Information about yields, crop fractions, heights and ryegrass tillers has been presented in an earlier paper (Wilman and Asiegbu, 1982). The present paper is concerned with the more detailed studies of white clover, which help to explain the yield results and contribute to the understanding of the response of this species to management when grown in competition with grass. Increasing the interval between harvests increased the length of clover stolon per unit area of ground and increased stolon diameter, petiole length, weight per leaf and number of leaves harvested as a proportion of the number present in the sward while only slightly reducing the rate of leaf emergence, helping to explain the positive effect of increasing the interval on clover yield noted in the earlier paper. During regrowth, successive leaves had longer petioles and the length of individual petioles increased beyond the stage at which the leaflets were fully opened. Weight per leaf in clover increased considerably from April to June and declined to below the April value by October. It was shown that weight per leaf can be greatly increased by increasing the interval between harvests without reducing the number of leaves harvested per unit area per year. The stolon length measurements provided some support for the view that medium large-leaved varieties of white clover can with advantage be defoliated rather less frequently than small-leaved varieties. Stolon length was less adversely affected by applied N in the medium large- than in the small-leaved varieties. The small-leaved varieties had thinner stolons than the medium large-leaved varieties but about twice the stolon length when no N was applied, and a relatively high proportion of leaves which escaped defoliation. The application of N reduced stolon diameter, increased petiole length and had little or no effect on weight per clover leaf.  相似文献   

2.
Three experiments were conducted to determine the association between leaf number per tiller at defoliation, water‐soluble carbohydrate (WSC) concentration and herbage mass of juvenile ryegrass plants when grown in a Mediterranean environment. Seedlings of ryegrass were grown in nursery pots arranged side‐by‐side and located outside in the open‐air to simulate a mini‐sward in Experiments 1 and 2, and a mixture of annual ryegrass and subterranean clover (Trifolium subterraneum L.) was grown in a small plot field study in Experiment 3. Swards were defoliated mechanically with the onset of defoliation commencing within 28 d of germination. Frequency of defoliation ranged from one to nine leaves per tiller, whilst defoliation height ranged from 30 mm of pseudostem height that removed all leaf laminae in Experiment 1, to 50 mm of pseudostem height with some leaf laminae remaining post‐defoliation in Experiments 2 and 3. A positive relationship between herbage mass of ryegrass, WSC concentration and leaf number per tiller at defoliation was demonstrated in all experiments. In Experiment 1, the herbage mass of leaf, pseudostem and roots of tillers defoliated at one leaf per tiller was reduced to 0·10, 0·09 and 0·06 of those tillers defoliated less frequently at six leaves per tiller. However, the reduction in herbage mass from frequent defoliation was less severe in Experiment 2 and coincided with a 0·20 reduction in WSC concentration of pseudostem compared with 0·80 measured during Experiment 1. In Experiment 3, the highest harvested herbage mass of ryegrass occurred when defoliation was nine leaves per tiller. Although the harvested herbage from this sward contained senescent herbage, the in vitro dry‐matter digestibility of the harvested herbage did not differ significantly compared with the remaining treatments that had been defoliated more frequently. Leaf numbers of newly germinated ryegrass tillers in a Mediterranean environment were positively associated with WSC concentration of pseudostem and herbage mass. A minimum period of two to three leaf appearances was required to restore WSC concentrations to levels measured prior to defoliation thereby avoiding a significant reduction in herbage mass. However, maximum herbage mass of a mixed sward containing ryegrass and subterranean clover was achieved when defoliation was delayed to nine leaves per tiller.  相似文献   

3.
A factorial pot-experiment was carried out to investigate the effect of burial of stolons (stolons unburied or buried to a depth of 0·5–1 cm at day 0), with and without defoliation (plants uncut or all unfolded laminae removed at weekly intervals) on the growth of two varieties of white clover (cv. Kent or cv. Milkanova) harvested on three dates (14 d, 28 d and 42 d after burial). The soil used was a 3:2:1 mixture of clay loam:peat:sand, and there were three replicates of each variety for each treatment at each harvest date. Burial of stolons in the absence of defoliation had no effect on stolon extension, leaf appearance, or the concentration of water-soluble carbohydrate in the stolons. The number of axillary buds developing (new branches plus flowers) was increased on the new surface-growing tips of primary stolons but was reduced on branch (i.e. secondary) stolons. The proportion of branches to flowers was largely unaffected by burial. Defoliation caused substantial reductions in the concentration of water-soluble carbohydrates in stolons and stolon extension growth, a reduction in number of axillary buds developing, and in the proportion of buds which were floral, but had only a small effect in reducing leaf appearance. The combination of stolon burial and defoliation resulted in the death of secondary stolons; 42% of all secondary stolons had died by day 42, and stolon extension, leaf appearance and numbers of axillary buds developing on secondary stolons were severely reduced. The numbers of axillary buds developing on primary stolons was increased owing to more buds developing on the resurfaced stolon tips, but the increase was inadequate to compensate for the reduced growth, and death of secondary stolons. Differences between clover varieties in response to treatments were small. In general, the smaller variety, cv. Kent, was more adversely affected by burial than the larger variety, cv. Milkanova. A variety x defoliation interaction occurred for senescence of leaves; petiole senescence of cut leaves was reduced or similar to that of intact leaves for cv. Kent, but was increased for cv. Milkanova. The results are discussed in relation to treatment effects on carbon sources and sinks, and in relation to climate-soil interactions.  相似文献   

4.
Leaves of different ages were removed 7 times between June and October. Each defoliation was timed to match the appearance of successive leaves on each tiller. The removal of leaves at progressively younger stages reduced total production above ground, but the most severe treatment, the removal of all expanded leaves repeatedly, still produced about 75% as much as the least severely defoliated sward. Clipping with shears 3 times reduced yield as much as removing all expanded leaves 7 times. A crop allowed to grow untouched apparently produced more than any defoliated treatment, but this may have been an artefact.
The lower production following increasingly drastic defoliation was not associated with reduced concentrations of nitrogen or potassium in the foliage removed, or in the crop left behind. The total quantity of these elements recovered in the crop was greatest in those treatments where least dry matter was produced. Explanations for the results depend on the capacity of swards of predominantly young leaves to assimilate carbon more rapidly than those containing old and senescent tissue.  相似文献   

5.
Single plants of white clover (Trifolium repens) were subjected either to two intensities of overall defoliation or to severe defoliation of different parts of the plant. Measurements were made of growth in terms of leaf size, petiole length, internode length and other parameters, and compared with those of undefoliated plants. The results show that, while growth of all parts of the plant was reduced by severe overall defoliation, partial defoliation affected various parts of the plant differently according to which leaves were removed. The results are interpreted in terms of the acropetal movement of assimilates from alternative sources in response to defoliation. The probable effects of this on yield and its relevance to grazing management of newly seeded clover are discussed.  相似文献   

6.
The effects of different defoliation regimes on the growth and development of three contrasting white clover cultivars (S184, Menna and Alice) were assessed in three experiments in the glasshouse. Experiment 1, with clover growing on its own, investigated the effects of three times of onset × two intensities of defoliation. In Experiment 2, clover was grown with grass and there were two times of onset × two heights × two frequencies of defoliation. Experiment 3, also with grass, investigated the effects of changing defoliation frequency at different intervals from sowing. All clover cultivars responded similarly to the various treatments and there were no interactions between time of onset and subsequent defoliation regimes in Experiments 1 and 2. Without competition from grass (Experiment 1), defoliating early at the three leaf-stage of clover decreased the number of growing points by 32% and stolon weights and lengths by 50% compared with delaying defoliation until the nine leaf-stage. Maintaining one compared with two leaves per growing point had similar effects. Over 17 weeks undefoliated seedlings produced ten times more stolon than early defoliated or intensively defoliated seedlings. In competition with grass (Experiment 2) delaying defoliation significantly decreased all aspects of stolon growth. Seedlings growing in swards defoliated frequently and closely had most growing points whereas those defoliated infrequently had least. Stolon lengths and weights were larger for seedlings growing in swards defoliated frequently than for those defoliated infrequently at both heights of cutting. Mean weight of stolon per unit length was greater when swards were defoliated at 6 cm than at 2 cm height. Changing defoliation from every 2 weeks to every week (Experiment 3) decreased stolon growth slightly when the change was made early but increased it when the change was made late, although similar amounts of stolon were produced by seedlings continuously defoliated throughout every week and every 2 weeks. The results are discussed in relation to the seedlings' leaf complements and growth habit; the over-riding influence of grass competition is highlighted. The possibility of devising optimal defoliation strategies and the need to test these in the field are also outlined.  相似文献   

7.
The frequency and severity of defoliation of individual grass tillers and clover plant units was studied in Lolium perenne-Trifolium repens swards grazed by sheep at stocking rates ranging from 25 to 55 sheep ha-1 and either receiving no N fertilizer or 200 kg N ha-1. On average, sheep at the highest stocking rate defoliated individual tillers once every 4·2 d compared with once every 9·2 d at the lowest stocking rate with the removal of 58% and 47% of the leaf length of each tiller leaf at these stocking rates. Clover plant units were defoliated once every 4·2 d at the highest stocking rate and once every 7·2 d at the lowest stocking rate with the removal of 51% of its leaves and 12% of its stolon at the high stocking rate and 42% and 4% respectively at the low stocking rate. Differences in frequency and severity of defoliation between N fertilizer treatments were smaller than between stocking rates. Grass tillers and clover plant units were both defoliated less frequently and less severely in swards fertilized with N, though the difference in defoliation frequency between fertilizer treatments decreased as stocking rate increased. Defoliation frequency was related to the length of grass leaf per tiller or number of clover leaves per plant unit, and to the number of these tillers and the herbage on offer.  相似文献   

8.
The effects of application of sodium fertilizer on the turnover and defoliation of leaf tissue were investigated in a perennial ryegrass (Lolium perenne) pasture grazed by dairy cows. Eight plots were allocated to treatments either with or without sodium fertilizer, with the former receiving 32 kg Na ha–1 applied in five applications of NaNO3 over the grazing season. An equivalent amount of nitrogen was given to the controls as ammonium nitrate, the application of which was reduced in the sodium treatment to equate nitrogen fertilizer applications for the two treatments. In nine periods between April and September, marked tillers were recorded to measure leaf turnover, leaf lamina growth and specific leaf weight and, when combined with tiller density measurements, gave an estimate of herbage flux for the sward. The defoliation and net growth of the marked tillers were monitored at 3-day intervals and the data were combined with tiller density and specific leaf weight data to determine the intake of the expanding, penultimate and oldest live leaf laminae. Sodium fertilizer application did not affect the rate at which leaves appeared, but it retarded their rate of disappearance. The extension rate and the specific weight of green laminae were both increased by sodium fertilizer application and therefore the net gravimetric growth rate was increased. Tiller density was not affected by sodium fertilizer application and hence the estimated herbage growth and net herbage flux were increased by sodium fertilizer application. Application of sodium fertilizer did not affect lamina length, and in both treatments the penultimate laminae were approximately twice as long as expanding and oldest live laminae. Defoliation frequency decreased from the expanding to the oldest live laminae in the control treatment without sodium. Sodium fertilizer application increased the frequency of defoliation of the oldest live leaf and also increased the length of the expanding leaf that was defoliated. For penultimate leaf laminae sodium fertilizer application reduced the defoliation frequency and length of foliage grazed. The dry-matter (DM) intake of the oldest live laminae was increased by the application of sodium fertilizer. It is concluded that sodium fertilizer application increases net herbage growth both by increased extension rate of leaf laminae and specific leaf weight and by delayed laminae senescence, and that it increases herbage DM intake by increasing the defoliation frequency of the oldest live leaf laminae.  相似文献   

9.
Mixtures of perennial ryegrass ( Lolium perenne L.) and white clover ( Trifolium repens L.) sown in alternate rows or in a thoroughly mixed matrix were grazed by sheep, either continuously or during short grazing tests, and were used to investigate the influence of the vertical and horizontal components of the sward structure on defoliation by sheep.
In an experiment under continuous grazing, the defoliation intensity was greater for white clover compared with perennial ryegrass leaves (0·80 and 0·58 respectively). In spring, perennial ryegrass leaves were more defoliated than white clover leaves, whereas the reverse was observed in summer. The ratio of the proportion of white clover to perennial ryegrass leaves grazed was negatively correlated with the difference between the surface height of the perennial ryegrass and white clover rows in spring. In both spring and summer, white clover leaves of the same extended leaf length had a higher proportion of them grazed than perennial ryegrass leaves.
In another experiment, during short grazing tests with perennial ryegrass–white clover swards that were grazed at the same sward surface height and at the same white clover content as in the previous experiment, there were no significant differences in the proportion of white clover and perennial ryegrass leaves grazed between strips of the two species and thoroughly mixed structures. The proportion of white clover leaves grazed was higher than that of perennial ryegrass leaves.
These results show that the differential defoliation by sheep of perennial ryegrass and white clover leaves varies according to their vertical distribution in the mixed canopy, but is little affected by their horizontal distribution. Even small differences in sward surface height between mixed perennial ryegrass and white clover can affect diet selection by sheep to a rather large extent.  相似文献   

10.
An examination was made of the effects of different spring treatments on the growth of white clover in a ryegrass/white clover sward. Plots were either cut once (in February, March or April) or twice (in February and April) or left uncut. Nitrogen was applied to half of the plots in each instance. The clover was sampled at intervals of approximately 3 weeks from February to June to determine numbers of leaves and growing points and weights of plant parts. Rates of leaf appearance were also observed and estimates were made of total herbage mass from ground-level cuts.
Percentages of white clover in the herbage were higher in unfertilized than in fertilized plots and in defoliated than in undefoliated plots. The percentage increases that followed defoliation were usually maintained into later regrowth, showing that clover content was not automatically reduced as herbage mass increased. Increases in growing points were recorded after the beginning of April in defoliated unfertilized plots but not in undefoliated fertilized plots or in plots fertilized and defoliated twice during the spring period, in which numbers fell substantially.
Inverse relationships were found between rates of leaf appearance, or the number of green leaves retained per stolon, and herbage mass, whereas heights of clover and grass leaves and the percentage of dry matter allocated to petiole rather than leaf in the clover increased with increasing herbage mass.
We suggest that the observed differences between spring treatments in clover percentage result primarily from their differential effects on the formation and death of tillers and growing points in the early stages of regrowth.  相似文献   

11.
Previous results with red clover ( Trifolium pratense ) leaflets, leaf petioles and stems indicated that the epidermis continued to impose a barrier to water loss at low water contents. Further experiments with red clover leaf petioles and stems suggest that cuticular wax is the epidermal component concerned and that treatments which remove or merely modify this will also increase drying rate. However, when treatments to reduce epidermal resistance were applied to pseudostems and flowering stems of Italian ryegrass ( Lolium multiflorum ) the initial increase in drying rate produced was not sustained at low water contents. The pseudostems consisted of three layers of leaf material rolled one within the other and the true flowering stems were surrounded by one leaf sheath. Their pattern of response to treatments suggested that these affected only the outer sheath, which produced an initial acceleration in drying rate, but that this was not sustained after the outer sheath was dry because the lower untreated layers dried in a similar way to untreated controls.
The results suggest the possibility of devising practical treatments to increase drying rate at low water contents with crops containing a high proportion of leaf or stem not surrounded by leaf sheath. Devising such treatments for crops with a high proportion of grass pseudostem or flowering stem surrounded by leaf sheath will be considerably more difficult.  相似文献   

12.
The effects of simultaneously varying P, K, lime and Mo supplies on the growth and shoot morphology of white clover ( Trifolium repens ) at establishment were investigated in a factorially designed glasshouse experiment. Phosphorus and lime applications had almost identical, additive, effects on dry-matter (DM) production, and it was clear that the benefit of both treatments lay in the resultant improvements in plant available P. The adverse effects of P deficiency on young plants resulted, immediately, in a large decrease in stolon branch numbers, but only when the deficiency became acute did similar declines in the dimensions of leaves and petioles occur. It was suggested that this preferential maintenance of leaf and petiole expansion processes under moderate P deficiency, by enabling white clover to retain favourable upper canopy positions, could be an ecological adaptation to maximize its chances of survival in mixed grass–clover swards. Unlike P, K had little effect on clover growth or shoot morphology. However, there was some evidence that plants suffering from acute K deficiency preferentially partitioned resources to organs associated with exploratory growth, i.e. to stolons, at the expense of the plant's photosynthetic capability. Molybdenum application had no effect on DM production or shoot morphology, but did improve the N status of shoots, presumably by enhancing N2 fixation. It was concluded that the survival of white clover in swards at establishment is critically dependent on P supply, and that one of the main benefits of liming is the resultant improvement in P availability.  相似文献   

13.
White clover swards were grown in a freely ventilated glasshouse during August and September 1979. The uninterrupted growth of these swards, which were grown in Perlite with either nitrate or biologically fixed nitrogen, was studied from 5 weeks after sowing until peak dry weights of the live sward components occurred. The dry weight of leaf laminae, petioles, stolons, roots, nodules and dead material was determined weekly together with live leaf numbers and leaf lamina area. The pattern of dry matter accumulation of the yield components of the swards (live leaf laminae plus petioles) was characterized by an initial period of more or less exponential growth up to 6 weeks from sowing dominated by leaf lamina development. This was followed by a linear phase, when petiole weight increased rapidly and a final slowing down period terminated by peak yields of live DM 12 weeks after sowing.
The weight of stolons, roots and nodules increased slowly during the period dominated by leaf lamina growth compared with the rapid increase thereafter, which resulted in a two- to three-fold increase in the weight of stolons, roots and nodules by the time the weights peaked. It is assumed that after the leaf area index of the sward had reached a plateau there was a limit to the assimilate supply to the sward components at a stage when they were all apparently competing for photosynthates. There was a progressive slowing down in the rate of dry matter accumu-  相似文献   

14.
An apparatus is described which enables excised pieces of plant material lo be weighed al frequent intervals as they dry in controlled conditions of temperature, humidity and air-speed. The effect of removing the epidermis on the drying rate of red clover ( Trifolium pratense ) leaflets, leaf petioles and stems is examined. Initially this treatment caused a very large increase in the drying rate of leaflets. Although the effect declined as water content fell, leaflets from which the epidermis had been removed still dried more rapidly than the controls at a water content equivalent to 50% of the dry weight. Removing the epidermis had a greater effect on the drying rate of leaf petioles and stems at low water contents than it did on the drying rate of leaflets.
Slow drying at low water contents is a major factor responsible for the undesirably long periods for which hay may lie in the field. Slow drying occurs even though swath microclimate becomes more favourable for drying as water content falls. The results presented here suggest that treatments which reduce cuticular resistance have the potential to reduce field drying time.  相似文献   

15.
Establishing Kura clover (Trifolium ambiguum) in mixtures with grass species is challenging, because slow growth of clover seedlings results in low competitive ability. This study examined establishment success by altering time of seeding of the grass component to reduce competition with Kura clover seedlings. Two trials, one of Kura clover–meadow bromegrass (Bromus biebersteinii) and the other Kura clover–orchardgrass (Dactylis glomerata) mixtures were planted in Edmonton, Alberta. Grasses were seeded at the same time as the clover, or introduced when the clover reached one true leaf or three true leaves, in the autumn of the planting year or the following spring. Species composition varied significantly between treatments. When sown at the same time, Kura clover contributed 31 and 14% of yield in the establishment year when sown with meadow bromegrass and orchard grass, respectively. Delaying grass sowing until Kura clover had one or three leaves gave a higher percentage of Kura clover compared with planting at the same time. Autumn and spring grass sowing resulted in stands of 78 and 80% clover with meadow bromegrass, and 74 and 67% clover with orchardgrass. Altering the competitive advantage of the grass species to produce a more balanced mixture was successfully achieved by delaying seeding of the grass relative to Kura clover. A long interval before introducing the grass (autumn or following spring), was not successful as established Kura clover seedlings have an increased competitive ability.  相似文献   

16.
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   

17.
Turnover rates of grass laminae and clover leaf tissue were estimated over a range of intervals within three periods each year in the second to fourth years (1983-85) of a trial involving swards continuously grazed by steers and receiving either 60 kg N ha-1 in spring (60N) or 360 kg N ha?1 throughout the year (360N). Within the 60N swards initial stocking rates at turnout were low (60N LS) at 7-2 steers ha?1 and high (60N HS) at 90 steers ha?1 in 1983, and in 1984 and 1985 corresponding rates were 10-8 and 13-5 ha?1. The 360N swards were initially stocked at turnout at 96 (360N LS) and 120 (360N HS) steers ha?1. Stocking rates were reduced by 33% in midsummer except for 60N in 1984 and 1985 when they were reduced by 50%. Meaned over 3 years, 360N HS had lower herbage mass than 60N LS. Tiller density in 360N was almost 50% higher than in 60N and clover growing point density was only one quarter that of 60N with the 60N LS having lower clover densities than 60N HS in 1985. Generally, leaf extension rate per tiller was higher in 360N than 60N and, when significant, 60N LS had higher senescence rates per tiller than 360N HS. Rate of increase in new clover lamina tissue per stolon was not affected by treatments, whereas in 1983 LS had higher senescence rates of clover laminae than HS. Petiole growth per stolon was higher in LS than HS in 1983 and 1984, the mean over these years for 360N HS being 77% that of 60N LS. Petiole senescence per stolon was lower in 360N HS than 60N LS only in 1983. When comparing 60N HS and 360N LS (representing similar levels of grazing intensity, having similar herbage mass) the gross growth of leaf material in the former was 75% of the latter, in contrast to 57% for net growth. Clover contributed 18% to the estimated growth of leaves compared to a mean of 7% in herbage mass. Taking inflorescence and pseudostem into account in 1984 and 1985,60N HS had 7% clover in standing herbage and 14% in net growth. Therefore, the contribution of clover to growth is considerably higher than its presence in herbage mass would suggest in continuously grazed swards. It is concluded that low-N swards, owing to their lower tiller density and slower grass leaf extension rate, will be less efficiently grazed than swards at higher N levels at a given herbage mass, but the presence of clover will partly offset that disadvantage.  相似文献   

18.
Two experiments investigating the effects of simulated continuous defoliation on white clover development and senescence are described. Stolons growing in boxes in a glasshouse were defoliated repeatedly by hand to simulate different intensities of continuous grazing by sheep. The experiments continued in both instances until eleven leaves had been produced on stolons in the most favourable treatment.
It was found that leaf dry matter production was reduced in proportion to the leaf complement of the stolon. Reduction of the leaf complement from two leaves to one leaf led to a reduction in subsidiary branch production of about 25% and an increase in percentage dead stolon from 33 to 44%, If no fully expanded leaves were retained branch production fell to 40% or less of that observed when two leaves were retained.
Stolons growing in swards continuously grazed by sheep usually have a green leaf complement varying between zero and two leaves per growing point. The consequences of maintaining different leaf complements in this range are discussed in the light of the current experiments.  相似文献   

19.
李雪梅  朱长甫 《大豆科学》1996,15(3):228-234
本文研究了摘英、摘心和去叶处理对不同生长习性不大豆根瘤固氮酶活性的影响，结果表明，摘荚处理对无限型大豆固氮酶活性（ＡＲＡ）无明显影响，而使有限型和亚有限大豆的ＡＲＡ明显降低。摘心和去叶处理使三种生长习性大豆ＡＲＡ降低；摘英、摘心和去叶处理使三种生长习性大豆根瘤中酰脲含量增加；去叶处理使有限型大豆幼茎中酰脲含量明显增加，但对无限型和亚有限型大豆影响不大。摘英处理使有限型和亚有限型大豆幼茎中酰脲含量明  相似文献   

20.
The effects of different spring defoliation managements on potential harvestable seed yield and seed yield components of three contrasting white clover cultivars were assessed. The small-leaved cv. S184 produced more but smaller inflorescences than the large-leaved cv. Olwen and Menna, a medium-leaved cultivar. Cultivar Olwen, however, produced more ripe and brown (nearly ripe) inflorescences with more florets, seeds per floret and a higher seed yield per ten inflorescences than the other cultivars. Potential harvestable seed yield and individual seed yield components were only influenced by defoliation after bud emergence, as defoliation before bud emergence had no effect on seed yield components. Defoliation after bud emergence had a similar effect on all cultivars: the number of ripe inflorescences was unaffected by defoliation but the number of brown and therefore harvestable (ripe + brown) inflorescences was highest following defoliation three weeks after bud emergence. Florets per inflorescence, seed per floret, 1000 seed weight, seed yield per ten inflorescences and potential harvestable seed yield were not influenced by defoliation after bud emergence. Season had a significant effect on seed yield components and influenced the effect of defoliation treatments, emphasizing the importance of climate in white clover seed production. The results are discussed in relation to the spring defoliation of white clover seed crops, harvesting techniques and the provision of guidelines for optimizing seed yield.  相似文献   

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