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1.
Tillage causes both vertical redistribution of weed seeds and changes in soil physical properties. These two factors are rarely distinguished in studies of the impact of tillage on seedling emergence or seed survival. In this study, seeds of Chenopodium album L., Amaranthus retroflexus L., and Abutilon theophrasti Medik, were planted at particular depths in pots of undisturbed or stirred soil to separate these effects. Emergence and survival data were analysed by non-linear regression to determine the nature of significant differences between treatments. Emergence increased with slight burial and then decreased exponentially at greater depths. Average emergence over all depths was generally greater in tilled sou than in unfilled soil, particularly for C. album and A. retroflexus . Seed survival approached a maximum with increasing depth. Average survival of seeds that did not produce emerged seedlings was greater in tilled soil than in untilled soil for C. album and A. retroflexus . Thus, tillage affects emergence and seed survival of weeds through changes in soil conditions independently of effects resulting from redistribution of seeds in the soil profile.  相似文献   

2.
Sonchus oleraceus (common sowthistle) is a dominant weed and has increased in prevalence in conservation cropping systems of the subtropical grain region of Australia. Four experiments were undertaken to define the environmental factors that favor its germination, emergence, and seed persistence. Seeds were germinated at constant temperatures between 5 and 35°C and water potentials between 0 and ?1.4 MPa. The maximum germination rate of 86–100% occurred at 0 and ?0.2 MPa, irrespective of the temperature when exposed to light (12 h photoperiod light/dark), but the germination rate was reduced by 72% without light. At water potentials of ?0.6 to ?0.8 MPa, the germination rate was reduced substantially by higher temperatures; no seed germinated at a water potential >?1.0 MPa. Emergence and seed persistence were measured over 30 months following seed burial at 0 (surface), 1, 2, 5, and 10 cm depths in large pots that were buried in a south‐eastern Queensland field. Seedlings emerged readily from the surface and 1 cm depth, with no emergence from below the 2 cm depth. The seedlings emerged during any season following rain but, predominantly, within 6 months of planting. Seed persistence was short‐term on the soil surface, with 2% of seeds remaining after 6 months, but it increased with the burial depth, with 12% remaining after 30 months at 10 cm. Thus, a minimal seed burial depth with reduced tillage and increased surface soil water with stubble retention has favored the proliferation of this weed in any season in a subtropical environment. However, diligent management without seed replenishment will greatly reduce this weed problem within a short period.  相似文献   

3.
Experiments to monitor weed seedling emergence from various soil depths were begun in 1989. Recently shed seeds were buried in either narrow bands at a range of depths in the soil or mixed evenly between the soil surface and each of these depths. Total emergence of Stellaria media (L.) Vill., Matricaria spp., Veronica persica Poiret, Veronica arvensis L. and Polygonum aviculare L., declined with increasing depth of burial. A similar pattern was observed for Chenopodium album L. with the exception of emergence from the surface layer. The reduction in emergence with increasing soil depth was greater for seeds in the narrow-banded treatments than for those in broad layers. A model was developed using the data from the narrow-banded treatments to predict emergence from distributions over broad layers. Predictions from the model closely agree with the data from the present broad-layer treatments and those from a similar experiment made in the 1960s. By including the effects of depth of seed burial on seedling emergence, this model could be combined with models that determine the effects of cultivation on seed distribution, and therefore improve precision of predictions of seedling emergence from the seedbank.  相似文献   

4.
Flaxleaf fleabane ( Conyza bonariensis [L.] Cronquist) is a difficult-to-control weed in dryland minimum tillage farming systems in the northern grains region of Australia. Experiments under field and controlled environments were conducted to study the seed germination, emergence, and persistence of C. bonariensis . The base, optimum, and maximum temperatures for seedling germination were estimated at 4.2, 20, and 35°C, respectively, with light stimulating germination. The soil types and burial depths had significant effects on seed persistence and emergence. The persistence pattern showed an initial rapid drop, followed by a slow but steady decline over time. After 3 years of burial, there were ≈ 7.5%, 9.7%, and 1.3% viable seeds at 10, 5, and 0–2 cm soil depths, respectively. Conyza bonariensis predominantly emerged from the soil surface or from the burial depth of 0.5 cm. Very few seeds emerged from a depth of 1 cm and none emerged from ≥ 2 cm. The emergence was greater in lighter soils. On-farm monitoring of the field emergence over time in a light sandy loam soil showed that 99% emergence occurred in late autumn, early and late winter, and a small fraction of 1% emerged in mid-spring. The predominant emergence from the soil surface suggests that the fleabane problem is a result of weed species shift toward the minimum tillage systems that provide moist conditions for better emergence compared to conventional tillage systems. The seed longevity of at least 3 years in the soil and the prolonged emergence patterns between autumn and spring have posed great difficulties for the long-term management of C. bonariensis .  相似文献   

5.
NAVIE  PANETTA  MCFADYEN  & ADKINS 《Weed Research》1998,38(5):335-341
Parthenium hysterophorus L. seeds were buried at a depth of 5 cm for periods of 2–24 months to determine their longevity. The majority (73.7%) of these seeds were still viable after 24 months of burial. The remainder could not be recovered (18.0%) or were no longer viable (8.3%). There was a log-linear decline in persistence of germinable seeds over time, which indicated a constant rate of loss and a half-life of about 6 years. Seedling emergence from surface-sown seeds was also studied. Although there was considerable rainfall (31 mm), seedlings did not emerge during the first month of this experiment. In the succeeding 3 months, there was substantial seedling emergence after rainfall, and 51.4% of seeds had germinated by the end of the fourth month. After 5 months had passed, further seedling emergence was not detected, and intact seeds could not be located. These findings suggest that seed incorporation into the soil is important to the long-term persistence of P . hysterophorus seeds. In an initial test of germination, unburied seeds from the same seed lot exhibited a degree of innate dormancy, and this may explain the delayed germination observed in the surface-sown seeds. In the seed burial and recovery experiment, innate dormancy was lost after 2 months of burial in the field, although in situ germination of buried seed remained low for at least 24 months. Therefore, it appears that more than one dormancy mechanism may contribute to the persistence of P. hysterophorus seeds.  相似文献   

6.
The longevity of buried Rottboellia cochinchinensis (Lour.) W.D. Clayton seed represents a major survival mechanism for the weed, enabling the persistence of a continuing source of weed seeds in crop land. The pattern of seed persistence and depletion of R. cochinchinensis in cultivated maize soils was investigated by means of (1) studies on the effect of depth and duration of burial on the viability of the weed seeds, (2) quantitative estimation of the seed population and viability in cultivated fields, and (3) the periodicity of emergence and effects of cultivation on seed germination both in the field and in the greenhouse. The results indicated that the mode of persistence was innate (8.5%) and enforced (35%) dormancy after 1 year of burial, and that the persistency component of the seed population on cultivated soils ranged from 40.60%. The weed was able to remain viable at depths of 45 cm, indicating an excellent mechanism of escaping the effects of most soil-applied herbicides, and it was shown that tillage increases the depletion rate of the weed seed reserve by 32% per year.  相似文献   

7.
Seed dormancy and persistence in the soil seedbank play a key role in timing of germination and seedling emergence of weeds; thus, knowledge of these traits is required for effective weed management. We investigated seed dormancy and seed persistence on/in soil of Chenopodium hybridum, an annual invasive weed in north‐western China. Fresh seeds are physiologically dormant. Sulphuric acid scarification, mechanical scarification and cold stratification significantly increased germination percentages, whereas dry storage and treatments with plant growth regulators or nitrate had no effect. Dormancy was alleviated by piercing the seed coat but not the pericarp. Pre‐treatment of seeds collected in 2012 and 2013 with sulphuric acid for 30 min increased germination from 0% to 66% and 62% respectively. Effect of cold stratification on seed germination varied with soil moisture content (MC) and duration of treatment; seeds stratified in soil with 12% MC for 2 months germinated to 39%. Burial duration, burial depth and their interaction had significant effects on seed dormancy and seed viability. Dormancy in fresh seeds was released from October to February, and seeds re‐entered dormancy in April. Seed viability decreased with time for seeds on the soil surface and for those buried at a depth of 5 cm, and 39% and 10%, respectively, were viable after 22 months. Thus, C. hybridum can form at least a short‐lived persistent soil seedbank.  相似文献   

8.
Seed germination and seedling establishment are critical stages in plant life history, and both processes may be affected when buried under soil. Our aim was to investigate the effects of soil burial on the germination and seedling establishment of invasive Prosopis juliflora (Fabaceae). We studied the effects of burial, from soil surface to 4?cm deep, under greenhouse conditions and the effects of seed-storing in burial conditions at two depths (5 and 20?cm) and two storing periods (during 6 and 12?months) in field conditions. Soil burial limited the germination and the establishment of P. juliflora, which did not germinate at soil depths deeper than 3?cm. Some seedlings coming from seeds germinated at 2?cm, and every seedling at the soil surface and at 3?cm deep died. In contrast, survivorship of emerged seedlings was close to 90% between 0.5 and 2?cm depth. Seedlings developed the longest shoots at 1?cm deep, indicating that P. juliflora was able to get advantage at a moderate soil depth. Un-embedded seeds survived buried in the soil for months; however, their germination and the emerged seedling survivorship decreased after burial for 12?months.  相似文献   

9.
Common ragweed (Ambrosia artemisiifolia L.) is one of the annual plants that were described recently as invasive weeds in Europe. This species is described as an invasive plant that produces seeds that are highly variable. Its production of variably sized seeds is regarded as promoting its spread in different environments. Experiments were carried out to determine the influence of the seed weight and temperature on germination and the influence of the seed weight and burial depth on seedling emergence. The seeds were divided into a number of classes of weight and the seed weight effect on germination was evaluated by Petri dish assays. In another experiment, the seeds were buried at different depths in a clay soil/sand mix to estimate the burial effect on germination and seedling emergence. The germination level of A. artemisiifolia was high overall, between 76.8% and 94.2%. The seed germination was modified by temperature but it was not influenced by the seed weight. The amounts of germination and seedling emergence were greater for the seeds on the soil surface and decreased with an increasing burial depth, from 2 to 8 cm. No germination or emergence was observed for the seeds that were buried at 10 and 12 cm. The lightest seeds were more sensitive to burial. A greater level of seedling emergence for those seeds that were placed near the soil surface could explain the success of this species in open habitats, where the probability of deeper burial is low. After high seed production, the management of A. artemisiifolia in fields could be partly achieved through soil tillage, burying seeds below 10 cm, and not carrying out deep soil tillage the following year.  相似文献   

10.
Studies were made of seedling emergence of three phenotypes of Avena fatua L. with dif ferent coloured lemmas (fA, fB, fC) originally collected from one site. Each phenotype was grown under the same conditions in 1975 and the resulting seed buried 25 mm deep in soil im mediately after collection. The soil was either left uncultivated (all phenotypes) or cultivated monthly (phenotype fA only). Seedling emergence was assessed weekly and the number of remaining viable seeds was determined at the end of three years. Seeds of different lines of A. fatua (fA phenotypes) obtained from separate locations were grown under the same conditions in 1983, buried and seedling emergence moni tored for 85 months. Without cultivation, overall emergence (mean of three phenotypes) in successive autumns and springs was 9%, 18%, 9%, 33%, < 1%, 14% and <1%. A further 3% of viable seeds were recovered at the end of the experiment. Periodicity of emergence was the same for all phenotypes. Actual numbers of seedlings emerging in each of the periods varied between phenotypes. Total emergence of seed from the inner zone of panicles was significantly less than that from the outer zone, although there was little difference between the two zones in each of the natural emergence periods. Cultivation increased emergence, particularly from secondary seed in the first spring after burial, but did not changes its periodicity. By the second spring seed numbers had declined, and seedling counts were similar from cultivated and non-cultivated soil. No viable seed remained in the cultivated soil after three years. Emergence from the two lines of fA was very different. Seedling emergence occurred after hot dry con ditions, or in warm periods immediately after periods of chilling, particularly those below 4°C.  相似文献   

11.
Changes in the numbers of Avena fatua seed, incorporated into soil, were monitored in four successive spring barley crops which were harvested early for silage to prevent seed shedding. In the first year there were four times as many seedlings after tine cultivation compared with ploughing, but this was reversed in the second year as re-ploughing brought up dormant seeds and gave more seedlings than tine cultivation. Only 11–14% of the sown seeds produced seedlings during the 4 years. When the seeds were first buried to 25 cm by ploughing, and the barley was direct drilled without cultivation, only 0.4% emerged as seedlings. Few viable seeds remained in the soil after 4 years whether the soil was cultivated annually or not but seed numbers decreased more rapidly with tine cultivation than with ploughing. A few of the deeply buried seeds persisted where the land was direct drilled without cultivation.  相似文献   

12.
P K JENSEN 《Weed Research》2009,49(6):592-601
Persistence of seeds of the four winter annual grass species, Alopecurus myosuroides , Bromus sterilis , Bromus hordeaceus and Vulpia myuros , were studied under field conditions. The studies also included the two dicotyledon species, Tripleurospermum inodorum and Galium aparine . Seed samples were stored in the field at different depths in the plough layer for a year. Following germination, seedling emergence was taken as an indicator of field persistence. In a supplementary investigation, seed samples were placed on the soil surface or buried at 2 cm for a month and then tested for viability. Persistence of the two Bromus species was very short, irrespective of depth and duration of burial. Persistence of the other species was positively correlated with incorporation of seeds to a few centimetres depth. Increasing the depth of incorporation below 2 cm had a variable influence on persistence. Persistence of seeds placed directly on the soil surface was short, whether they were left there for a year or a month. Whether seeds at the soil surface were left uncovered or covered with chopped straw had limited influence on seed persistence. However, straw cover significantly increased persistence of A. myosuroides seeds and there was the same tendency with T. inodorum .  相似文献   

13.
Anoda cristata is a troublesome annual broad-leaved weed in summer crops in the rolling Pampa in Argentina; seeds are the only source of regeneration of this species. Seed persistence or depletion is the result of survival and loss processes, including predation. The objective of this study was to determine survival at two burial depths in undisturbed soil and predation rates of A. cristata seeds in soyabean crops in different rotations and tillage systems. Survival was discontinuous and decreased to 25% after 35 months, after which no further reduction in survival was observed to the end of the experiment at 96 months. No differences in seed survival between seeds placed on the soil surface and buried 5 cm below the soil surface were found at 80 months, but at later times survival was lower for seeds placed on the soil surface. Predation rates ranged between 0.3% day−1 and 6.7% day−1. Of the models tested, a polynomial regression of the rate of predation with time gave the best representation of seed predation. From January to July, predation was higher in non-tillage plots in the wheat/soyabean rotation. There was no significant difference in predation rates between tillage systems in the soyabean monoculture and no difference between planting densities. Higher crop residue levels in non-tillage plots in the wheat/soyabean rotation was the dominant factor influencing seed predation, probably because such habitat favours the presence of seed predators.  相似文献   

14.
Studies were conducted to investigate seed longevity, seedling emergence and seed production of the weed Phalaris minor in wheat in northern India. The longevity of P. minor seeds buried in bags in the field was often limited to less than 1 year, although many seeds buried at 30 cm depth in a rice–wheat rotation remained viable for longer. The application of direct seeding in wheat reduced the seedling emergence rate of P. minor , when compared with conventional ploughing and sowing. However, a larger P. minor seedbank in the upper soil layer in plots under direct seeding partly reversed this positive effect in one of the two studies. Besides differences in relative distribution of weed seeds through the soil profile, it was likely that other factors such as reduced soil disturbance and soil characteristics associated with the application of direct seeding were also involved in regulating the emergence rate. Mature P. minor plants in wheat were found to invest a stable part (27%) of their aboveground biomass in seed, so that total seed weight was strongly linearly correlated with the aboveground biomass of the mother plant. Individual seed weight, however, was little affected by the weight of the mother plant.  相似文献   

15.
Lithospermum arvense is an increasing annual weed in winter crops of the semiarid region of southern Argentina under low impact tillage systems, an agricultural practice that has become popular in recent years. Seed distribution in the soil profile under conventional tillage will change when reduced tillage is implemented, thus affecting the germination microenvironment. The effect of seed burial depth and soil water regime on field germination, enforced dormancy, innate dormancy and seed decay was studied in relation to burial time in a field experiment. In addition, the effect of burial depth on seed germination and seedling emergence was examined under laboratory controlled conditions. Field germination of buried seed ranged from 55% to 65% for shallow (2 cm) and from 5% to 30% for greater depths (20 cm). Enforced dormancy levels were significantly higher among deeper seeds. The amount of innate dormant seeds was reduced to <10% after a year of burial. Lithospermum arvense seedbanks can be classified as short-term persistent. Germination in the laboratory was unaffected by burial depth, while seedling emergence reduction was adequately described by a sigmoidal model. Results indicate that agricultural practices that accumulate L. arvense seeds near the soil surface enhance seedling recruitment.  相似文献   

16.
A mathematical model has been developed for the prediction of the population dynamics of Oryza sativa L. var. sylvatica . The input variables included in the model were the seedbank composition; the number of panicles per plant and seeds per panicle; the rate of shattering; the seed longevity and the number of weed seeds contained in the sown grain; the type of soil tillage (ploughing, minimum and No tillage); the weed control efficacy; and the predation. The output variables were the number of seedlings that emerged from different depths and the seedbank evolution. The model relies on probability matrices that predict the vertical movement of the seeds after different soil tillage practices. Sensitivity analysis showed that the weed control efficacy and number of grains per panicle were the parameters that had the highest influence on the development of the weed population. The model evaluation was carried out by comparing the predicted with the observed seedling emergence at different seedbank values and under different soil tillage conditions. The model performance showed a tendency to overestimate seedling densities. The agreement between the estimated and experimental data was closely related to the accuracy of the input values of the seed distribution along the soil profile.  相似文献   

17.
This study aimed to determine whether seedling herbivory by the field cricket, Teleogryllus emma (Ohmachi et Matsuura), promoted the mortality of Italian ryegrass (Lolium multiflorum Lam.), a non‐native grass weed in Japan, whether the impact of seedling herbivory differed depending on the depth of seedling emergence and the influence of cricket density on seedling mortality. First, the seedlings at emergence depths of 0, 1 and 2 cm were exposed to the cricket for 2 days in plastic cups and the amount of seedling mortality by herbivory was calculated. The level of mortality of 60 seedlings that emerged from seeds on the soil surface was 92.4%, significantly higher than that of the seedlings that emerged from seeds at depths of 1 cm (10.8%) and 2 cm (9.6%). Second, the seedlings at the emergence depths of 0 and 1 cm were exposed to the crickets at four different densities (zero, one, two and three individuals per 5700 cm2) for 5 days in plastic containers and the amount of seedling mortality by herbivory was calculated. The level of mortality by herbivory of the seedlings that emerged from 100 seeds on the soil surface was higher (33.3–61.3%) than that of the seedlings that emerged from seeds at a depth of 1 cm (4.7–13.1%) in the containers with one‐to‐three crickets. The level of seedling mortality tended to increase with an increasing cricket density. These results suggest that seedling herbivory by crickets is an important factor in weed mortality, particularly in no‐till fields and in field margins, where the seeds are more prevalent near the soil surface.  相似文献   

18.
A study on changes in the seed bank size of a glyphosate ( N -(phosphonomethyl)glycine)-resistant (R) Eleusine indica biotype was carried out on a naturally occurring infestation of a young oil palm plantation. The total number of shed seeds collected was 53% of the predicted potential total number of seeds produced by the plants. Ametryn ( N -ethyl- N' -(methylethyl)-6-(methylthio)-1,3,5-triazine-2, 4-diamine) was found to be able to control the R seed population in the soil. The periodicity of seedling emergence was influenced by rainfall subsequent to the 1 month period of seed shedding. Seed burial at 2, 10 and 20 cm depths showed that 39, 33 and 79%, respectively, of viable seed persisted in the soil after 2 years. Seeds in the state of enforced dormancy played an important role in maintaining the seed population throughout the 2 year period of burial in the soil.  相似文献   

19.
Seed germination, seedling emergence, and the morphological characteristics of juvenile seedlings of Commelina benghalensis L. were observed. For aerial seeds collected in September and October, seedling emergence peaked in April and June for large seeds and from June to August for small seeds, whereas seedling emergence for large seeds collected in November showed peaks in March and April under natural rainfall conditions, and in April and June under irrigation conditions. Seedlings from small seeds emerged intermittently over a longer period from April to August under both conditions. Aerial seeds of C. benghalensis germinated on wet filter paper on the second day after seeding (DAS) for large seeds and the fourth DAS for small seeds. The germination percentage for large seeds was higher than that for small seeds by the 14th DAS. The germination percentage for large aerial seeds showed no significant difference between light and dark conditions. However, the percentage for small aerial seeds was higher under light than under dark conditions. Seedlings from large aerial seeds emerged on the third DAS at 0–50 mm soil depths. The percentage of emergence at 0 and 1 mm soil depths increased until the 30th DAS, whereas those at soil depths of 5–50 mm showed no change after the 9th DAS. There was no emergence at a soil depth of 100 mm. Seedlings from small aerial seeds emerged on the 6th DAS at 0–1 mm soil depths, with the percentage increasing until the 30th DAS. Although seedlings at 5 and 10 mm soil depths also emerged on the 6th DAS, there was no change in the percentage after the 12th DAS. There was no emergence at soil depths of 20–100 mm. The hypocotyl and taenia (part of the cotyledon connected to the seed) in juvenile seedlings that emerged from soil depths of 50 mm were longer than those in seedlings emerging from a soil depth of 1 mm.  相似文献   

20.
Diversified cropping systems can have high soil microbial biomass and thus strong potential to reduce the weed seedbank through seed decay. This study, conducted in Iowa, USA, evaluated the hypothesis that weed seed decay is higher in a diversified 4‐year maize–soyabean–oat/lucerne–lucerne cropping system than in a conventional 2‐year maize–soyabean rotation. Mesh bags filled with either Setaria faberi or Abutilon theophrasti seeds and soil were buried at two depths in the maize phase of the two cropping systems and sampled over a 3‐year period. Setaria faberi seed decay was consistently greater at 2 cm than at 20 cm burial depth and was higher in the more diverse rotation than in the conventional rotation in 1 year. Abutilon theophrasti seeds decayed very little in comparison with seeds of S. faberi. Separate laboratory and field experiments confirmed differences in germination and seed decay among the seed lots evaluated each year. Fusarium, Pythium, Alternaria, Cladosporium and Trichoderma were the most abundant genera colonising seeds of both species. A glasshouse experiment determined a relationship between Pythium ultimum and S. faberi seed decay. Possible differences in seed susceptibility to decay indicate the need to evaluate weed seedbank dynamics in different cropping systems when evaluating overall population dynamics and formulating weed management strategies.  相似文献   

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