Mutual influence of forests and pastures on the seedbanks in the Eastern Amazon

The objective of this study was to compare the floristic composition and species diversity existing in the seedbanks of forests and pastures. The seedbanks were sampled in three forest and three pastures areas in a community of smallholder farmers, in Pará state, Brazil. Seedling emergence in a glasshouse was used to quantify and identify the seeds. The total densities and diversity of the seedbanks were not significantly different among the pastures and forests, but the floristic composition was different. The herbaceous species predominated in both the pastures and the forests, but in the forest the abundance of shrub and tree was higher than herb. The seed density of several pioneer woody species was higher in the forests and the density of several herbaceous species was greater in the pastures. The influence of the forest species on the pastures and of the pastures species on the forests is a result of the initial process of human occupation and illustrates a dynamic that can lead to both the conservation of forest species and the spread of weed species. Actions should be carried out to avoid disturbance in the forests and improve biodiversity preservation in rural areas.     

Fates of Setaria faberi and Abutilon theophrasti seeds in three crop rotation systems

Weed seeds in and on the soil are the primary cause of weed infestations in arable fields. Previous studies have documented reductions in weed seedbanks due to cropping system diversification through extended rotation sequences, but the impacts of different rotation systems on additions to and losses from weed seedbanks remain poorly understood. We conducted an experiment in Iowa, USA, to determine the fates of Setaria faberi and Abutilon theophrasti seeds in 2‐, 3‐ and 4‐year crop rotation systems when seed additions to the soil seedbank were restricted to a single pulse at the initiation of the study. Over the course of the experiment, seedlings were removed as they emerged and prevented from producing new seeds. After 41 months, seed population densities dropped >85% for S. faberi and >65% for A. theophrasti, but differences between rotation systems in the magnitude of seedbank reductions were not detected. Most of the reductions in seedbank densities took place from autumn through early spring in the first 5 months following seed deposition, before seedling emergence occurred, suggesting that seed predation and/or seed decay was important. For S. faberi, total cumulative seedling emergence and total seed mortality did not differ between rotation systems. In contrast, for A. theophrasti, seedling emergence was 71% lower and seed mortality was 83% greater in the 3‐ and 4‐year rotation systems than in the 2‐year system. Results of this study indicate that for certain weed species, such as A. theophrasti, crop rotation systems can strongly affect life‐history processes associated with soil seedbanks.     

Effects of soil and crop management practices and pedo‐hydrological conditions on the seedbank size of Galinsoga spp. in organic vegetable fields

Galinsoga quadriradiata and Galinsoga parviflora are very troublesome weeds in many organic vegetable crops in Europe. A very straightforward method to keep Galinsoga infestations under control is by targeting the Galinsoga seedbank. To identify cropping systems able to reduce the seedbank size in vegetable‐based cropping systems, the relationships between the seedbank size of Galinsoga species and prevailing soil/crop management practices and pedo‐hydrological conditions were investigated. Hereto, the seedbank of the 0–20 cm topsoil layer was sampled in 50 organic vegetable fields and analysed according to the seedling emergence method. Field history data were collected for the past 5 years, and physical, chemical and microbial soil quality was determined. Galinsoga quadriradiata was the most frequent and abundant Galinsoga species in the weed seedbank. The genus Galinsoga was present in 90% of the soil weed seedbanks of organic vegetable fields but displayed wide variation in abundance. Smallest Galinsoga seedbanks were found in fields that were predominantly tilled with non‐inversion implements or rotationally ploughed, and continuously cropped with competitive crops during the entire growing season (April 15‐November 15). Contrary to G. quadriradiata, seedbank size of G. parviflora was closely related to soil organic carbon content and sand fraction. Remarkably, soils with a low level of easily plant‐available phosphorus and concomitant high activity of arbuscular mycorrhizae had smaller G. quadriradiata seedbanks. To reduce Galinsoga infestations, fields should preferably be tilled without soil inversion, fertilised with organic amendments with low content of readily plant‐available phosphorus and cropped with competitive crops all season long.     

Soil seedbanks in slash‐and‐burn rice fields of northern Laos

Crops in shifting cultivation fields often suffer from severe weed infestation when long fallow periods are replaced by short fallow periods. The soil seedbank as a source of weed infestation was studied in four fields that differed in their last fallow duration. The effect of burning was analysed by comparing adjacent pre‐burn and post‐burn samples (two sites). Surface vegetation was monitored from burning to harvest in the plots from which soil samples were taken to determine the fraction of the seedbank germinating (three sites). Seedbank size (1700–4000 seedlings m^?2) varied depending on a single species, Mimosa diplotricha. Burning reduced emergence of most species, but stimulated emergence in others. Densities in the seedbank were not correlated with above‐ground abundances in the field, except for some species. Most species emerging after 50 days from the soil samples (40% of seedlings) were absent from the field after 190 days. Whilst the data from this study are derived from only four fields, the weed problems after short‐term fallowing appeared to be due to a larger fraction of the seedbank emerging, possibly due to shallow burial, and to a floristic shift towards adaption to burning, rather than the size of the seedbank per se.     

Germinable soil seedbanks of central Queensland rangelands invaded by the exotic weed Parthenium hysterophorus L.

The germinable soil seedbank was determined at two sites in central Queensland on four separate occasions between February 1995 and October 1996. These sites were infested with parthenium weed ( Parthenium hysterophorus L.), a serious invasive exotic weed. During this period, the seedbank varied between 3282 and 5094 seeds m⁻² at the Clermont site, and between 20 599 and 44 639 seeds m⁻² at the Moolayember Creek site. Parthenium hysterophorus exhibited a very abundant and persistent seedbank, accounting for 47–73% of the seedbank at Clermont and 65–87% of the seedbank at Moolayember Creek. The species richness and species diversity of the seedbank, and the seed abundance of many species, was lower at Moolayember Creek during spring (the time of year when the most dense infestations of the weed originate). Parthenium hysterophorus seedlings also emerged more rapidly from the soil samples than did those of all other species. Hence, it seems that various aspects of the weed's seed ecology, including abundance and the persistence of its seedbank and the rapid emergence of its seedlings, are major factors contributing to its aggressiveness in semiarid rangeland communities in central Queensland. The domination by P . hysterophorus of the seedbanks of these sites suggests that the weed is having a substantial negative impact on the ecology of these plant communities. The diversity of these seedbanks was found to be lower in comparison with that observed in other grassland communities that were not dominated by an invasive weed species. Hence, the prolonged presence of P . hysterophorus may have substantially reduced the diversity of these seedbanks, thereby reducing the ability of some of the native species to regenerate in the future.     

Early autumn soil disturbance decreases persistence of volunteer summer‐annual oilseed rape (Brassica napus)

Volunteer summer‐annual oilseed rape (sOSR; Brassica napus) is an ongoing concern in Canadian crop production. Large harvest seed losses and secondary dormancy in this species generate a persistent volunteer seedbank. Yield loss in subsequent crops, potential sOSR oil profile contamination and herbicide‐resistance trait introgression create a need for effective sOSR seedbank management. This field study evaluated the effects of timing and type of implement of post‐harvest soil disturbance and seeding a winter cereal on volunteer sOSR population persistence and demographic life‐stage transition rates at five locations in Manitoba, Canada. Following sOSR harvest and supplemental seed rain, seedbank densities ranged from 6770 to 15360 and 50 to 2610 seeds m^?2 among sites in autumn and spring respectively. In contrast to European research on winter‐annual oilseed rape, early autumn soil disturbance, shortly after sOSR harvest, was the best strategy to decrease volunteer sOSR persistence (3% population persistence from autumn to spring, compared with 6% in zero tillage). Substantial autumn seedling recruitment (38% of the autumn seedbank) and subsequent winterkill contributed to lower population persistence. Soil disturbance in spring stimulated spring seedling recruitment compared with other disturbance timings (11% and 3% of the spring seedbank, respectively). The implement used for soil disturbance and seeding winter wheat (Triticum aestivum) had minimal effect on population persistence. This research showed that timing of post‐harvest soil disturbance should be utilised as an effective tactic to decrease population persistence of volunteer sOSR via stimulation of autumn seedling recruitment and concomitant winterkill.     

Diversity and assembly of weed communities: contrasting responses across cropping systems

Diversity and weed community composition of mid-season plant stands and autumn seedbanks were examined in spring barley–red clover cropping systems that varied according to crop rotation, tillage and weed management. Weed plant and seed density data collected over 4 years were used in the calculation of species richness (number of species), evenness (Shannon's E) and diversity (Shannon's H′), and in multivariate analysis (canonical discriminant analysis) of weed communities. Weed diversity indices were low (H′ < 2.0) but sensitive to management practices. Evenness had intermediate values (E = 0.4–0.8), suggesting little evidence of truly dominant species, particularly in the seedbanks. The difference in the number of species between treatments was never large (approximately two to four species). Overall, diversity indices were highest in the low disturbance treatments, particularly those with minimum weed management. Factors affecting ordination were somewhat different from those affecting diversity. Tillage had little effect on weed diversity indices but had a more major role in determining weed community composition. Seedbanks in no-till and monoculture-chisel plough treatments appeared to have more distinctive species composition compared with other treatments. Weed species assembly in seedbanks showed little discrimination across treatments and over time, confirming the ability of seedbanks to buffer disturbances across a variety of cropping systems. The use of diversity indices revealed part of the complexity of weed communities associated with disturbance in cropping systems, whereas ordination singled out species–cropping systems associations, which may be more meaningful to weed management.     

A modelling approach using seedbank and soil properties to predict the relative weed density in organic fields of an Italian pre-alpine valley

In 1996, a study was conducted on the seedbanks of a pre‐alpine valley in northern Italy which had been organically farmed since 1986. The seedbanks were evaluated using soil cores taken from 16 organic fields located at various altitudes and seed numbers were determined using the ‘seedling emergence method’. Thirteen soil properties were also evaluated. In 2003, the germinable seedbank was assessed in five other fields chosen at random. Soil properties were evaluated by the same method as in 1996. Using the data of the first 16 fields as the analysis data set and those of the latter five as an independent validation data set, a quadratic weed seedbank‐soil properties model was built with partial least square regression analysis. The model estimates the relative abundance of the various species as the sum of the contribution of individual soil properties and has a high predictive capacity. With a novel graphic approach, it is possible to describe the nonlinear relationship between each soil property and weed species relative abundance, giving a rational, quantitative, explanation as to why some species are widespread (e.g. Chenopodium album, Galinsoga parviflora and Chenopodium polyspermum), whereas others tend to concentrate in specific fields (e.g. Spergula arvensis). The approach can, when some hypotheses hold, give a rational basis for the explanation of the relative abundance of species in a weed community and constitutes a useful methodology for study and research.     

The effect of different tillage systems on the composition of the seedbank

The soil seedbank of a wheat crop grown with four tillage systems (mouldboard plough, disk, chisel and no-tillage) for 3 years was analysed. Density and composition of seedbanks varied according to tillage system and depth. The mouidboard plough crop had seedbanks with the lowest seed density and there was no difference in density or composition at 0-5 cm and 5-10 cm depth whereas no—tillage had a more dense seed bank, especially in the upper part of the soil profile. Diversity of seedbanks also increased from mouidboard plough, to disk, to chisel, to no-titlage, which had the most diverse bank. Therefore, the data strongly support the hypothesis that the systems causing less disturbance allow the build-up of a larger and more diverse soil seed bank.     

Potential of weed seedbanks for managing weeds: a review of recent New Zealand research

Weed seedbanks are the primary source of weeds in cultivated soils. Some knowledge of the weed seedbank may therefore be appropriate for integrated weed management programs. It would also be very useful in planning herbicide programs and reducing the total herbicide use. However, a number of problems are inherent in the estimation of the seedbank size for arable weeds that usually have annual life cycles. In a long-term research project we have investigated the dynamics of weed seedbanks in corn fields for the past 8 years. Specific studies have included (i) developing cheap and efficient methods for estimating the weed seedbank; (ii) developing guidelines for efficient soil sampling (including the number and size of samples); (iii) influence of cultivation methods on weed seed distribution; (iv) mapping the spatial variability of the seedbank; (v) estimating the rate of seedbank decline for certain weed species; and (vi) assessing the potential of using the weed seed content in the soil to predict future weed problems. This paper reviews and summarizes the results of our research on the above aspects. The strong correlation between seedlings emerged in the greenhouse and seeds extracted in the laboratory for the most abundant weed species has demonstrated the potential for using the weed seed content of the soil to predict future weed infestations. The next step is to establish correlations with field emergence under commercial conditions using the sampling guidelines developed in our studies. Subsequently, we aim to offer the weed seedbank estimation as a commercial service to farmers for planning the most appropriate weed management options.     

Influence of weed management strategies on soil seedbank diversity

The role of three weed management strategies on weed populations and community dynamics was investigated from 1989 to 1994. These were chemical weed control (CH), integrated weed control (IN) and mechanical weed control (ME). Weed populations and communities were analysed by univariate (species richness, rank:frequency diagrams) and multivariate (correspondence analysis) methods. Species richness of the soil seedbank differed with weed management strategies and over time, with an observed annual number of species that ranged from 18 to 32. The seedbank was dominated by the same pool of species in all cases, but these species responded differently among years and management strategies; their rank (relative abundance) and densities changed between strategy and within a strategy among the years. In the last 2 years of the study, the soil seedbank was characterized mainly by #Capsella bursa-pastoris     

Long‐term effect of different tillage systems on the emergence and demography of Bromus diandrus in rainfed cereal fields

The adoption of no‐tillage systems in semi‐arid cereal fields in northern Europe has resulted in difficulties in controlling Bromus diandrus. However, in some fields, lower densities are observed in continuous long‐term no‐tillage management than in other reduced tillage systems. A cumulative effect on the seedbank could promote changes in the period of seedling emergence and in population demography. This study evaluated the effect of long‐term mouldboard plough (MbP), chisel plough (ChP), subsoiler (SS) and no‐tillage (NT) on the population dynamics of B. diandrus. The work was carried out in a barley (Hordeum vulgare)–wheat (Triticum aestivum)–barley rotation during three seasons where these soil management systems had been applied for the last 22 years. Cumulative emergence (CE) and densities of B. diandrus followed a gradient of ChP > SS > NT > MbP. This cumulative effect over time resulted in significant differences in population demography. A previous hydrothermal emergence model developed for this species estimated the percentage of emergence prior to the date of sowing to be: 71%, 92% and 53% for the seasons 2008–2009, 2009–2010 and 2010–2011 respectively. Furthermore, the reduction in CE observed was on average 53% in SS, 92% in NT and 98% in MbP in comparison with that recorded in ChP. The long‐term effect of different tillage systems tended to cause changes to soil characteristics (photo‐inhibition of germination, soil temperature, water availability) affecting B. diandrus demography, reaching equilibrium in weed densities over years, which were significantly lower in MbP and NT than in ChP or SS.     

Long-term management of Striga hermonthica: strategy evaluation with a spatio-temporal population model

The parasitic weed Striga hermonthica poses a serious threat to cereal production in sub-Saharan Africa. Striga hermonthica seedbanks are long-lived; therefore, long-term effects of control strategies on the seedbank only emerge after several years. We developed a spatially explicit, stochastic model to study the effectiveness of control strategies in preventing invasion of S. hermonthica into previously uninfested fields and in reducing established infestations. Spatial expansion of S. hermonthica and decrease in millet yield in a field was slower, on average, when stochasticity of attachment of seedlings to the host was included and compared to the deterministic model. The spatial patterns of emerged S. hermonthica plants 4–7 years after point inoculation (e.g. seeds in a dung patch) in the spatial-stochastic model resembled the distribution typically observed in farmers' fields. Sensitivity analysis showed that only three out of eight life cycle parameters were of minor importance for seedbank dynamics and millet yield. Weeding and intercropping millet with sesame or cowpea reduced the seedbank in the long term, but rotations of millet with trap crops did not. High seedbank replenishment during years of millet monoculture was not sufficiently offset by seedbank depletion in years of trap crop cultivation. Insight from simulations can be employed in a participatory learning context with farmers to have an impact on S. hermonthica control in practice.     

Karrikins promote germination of physiologically dormant seeds of Chrysanthemoides monilifera ssp. monilifera (boneseed)

Physiological dormancy in weed species has significant implications for weed management, as viable seeds may persist in soil seedbanks for many years. The major stimulatory compound in smoke, karrikinolide (KAR₁), promotes germination in a range of physiologically dormant weed species allowing targeted eradication methods to be employed. Control of Chrysanthemoides monilifera ssp. monilifera (boneseed), a Weed of National Significance in Australia, may benefit from adopting such an approach. In this study, we hypothesised that seeds of C. monilifera ssp. monilifera exhibit physiological dormancy, germinate more rapidly as dormancy is alleviated, show fluctuations in sensitivity to KAR₁ and form a persistent soil seedbank. Seeds responded to 1 μM KAR₁ (40–60% germination) even during months (i.e. March, April, July, August) when seeds were observed to be more deeply dormant (control germination: 7–20%). Seeds germinated readily over a range of cooler temperatures (i.e. 10, 15, 20, 20/10 and 25/15°C) and were responsive to KAR₂ (~50% germination) as well. Eradication efforts for C. monilifera ssp. monilifera may benefit from use of karrikins to achieve synchronised germination from soil seedbanks, even at times of the year when C. monilifera ssp. monilifera seeds would be less likely to germinate, allowing more rapid depletion of the soil seedbank and targeted control of young plants.     

Germination rates of weedy radish populations (Raphanus spp.) altered by crop‐wild hybridisation,not human‐mediated changes to soil moisture

Cultivated plants are known to readily hybridise with their wild relatives, sometimes forming populations with weedier life‐history strategies than their progenitors. Due to altered precipitation patterns from human‐induced global climate change, crop‐wild hybrid populations may have new and unpredictable environmental tolerances relative to parental populations, which would further challenge farming and land‐management weed control strategies. To recognise the role of seed dormancy variation in weed invasion, we compared seedbank dynamics of two cross‐type populations (wild radish, Raphanus raphanistrum, and crop‐wild hybrid radish, R. raphanistrum × R. sativus) across a soil moisture gradient. In a seed‐burial experiment, we assessed relative rates of seed germination, dormancy and seed mortality over two years across cross types (crop‐wild hybrid or wild) and watering treatments (where water was withheld, equal to annual rainfall, or double annual rainfall). Weekly population censuses in 2012 and 2013 assessed the frequency and timing of seedling emergence within a growing season. Generally, germination rates were two times higher and seed dormancy was 58% lower in hybrid versus wild populations. Surprisingly, experimental soil moisture conditions did not determine seedbank dynamics over time. Yet, seed bank dynamics changed between years, potentially related to different amounts of annual rainfall. Thus, variation in seedbank dynamics may be driven by crop‐wild hybridisation rates and, potentially, annual variation in soil moisture conditions.     

Size and composition of the weed seedbank after 7 years of different cover-crop-maize management systems

The objective of this study was to obtain detailed information on the long‐term weed suppression potential of four winter soil cover types included in an arable crop system managed at various input levels. We used weed seedbank size and composition to assess weed suppression potential. A field experiment was established in 1993 as a split‐split‐plot design with four replications, including two tillage systems [a conventional system (CS) including ploughing in the cover crops and a low‐input system (LIS) including no tillage with surface mulching of the cover crops] in the main plots, three mineral nitrogen fertilization rates for the main crop in the sub‐plots and four soil cover types (main crop residue, rye, crimson clover and subterranean clover) in the sub‐sub‐plots. Seedbank sampling took place in winter 2000/01. The weed seedbank was analysed with the seedling emergence method. Data were analysed using anova and multivariate techniques. Results indicated that the seedbank density in the LIS was about five times higher than in the conventional input system. In the CS, use of a rye cover crop resulted in a lower seedbank density with respect to the crop residue treatment (?25%), whereas in the LIS the subterranean clover cover crop decreased weed seedbank density as compared with the other cover crops and the crop residue treatment (?22% on average). Differences in species composition were mainly related to tillage system. Implications for cover crop management and the development of sustainable cropping systems are discussed.     

Seed dormancy and soil seedbank of the invasive weed Chenopodium hybridum in north‐western China

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.     

Weed flora and soil seedbanks in fields dominated by Imperata cylindrica in the moist savannah of West Africa

Imperata cylindrica (L.) Raeuschel is a dominant and infamous grass weed in the savannah of West Africa. Research to reduce the weed to non-damaging levels is a priority activity at many agricultural institutions. The successful development and implementation of long-term I. cylindrica management strategies depend on the ability to predict changes in weed composition after I. cylindrica has been controlled effectively. The weed flora and soil seedbank were assessed from 329 fields dominated by this species in the fringes of the humid forest (HFF), coastal/derived savannah (CDS) and in the southern Guinea savannah (SGS) in 1996 and 1997. The objectives of the study were to correlate species composition of the weed flora with that of the soil seedbank and to determine the effect of management factors and soil properties on the composition of the weed flora. Species richness in the weed flora and in the weed seedbank was higher in the SGS than in the CDS and HFF. Mean weed density per field was generally higher in the HFF (156 ± 25.0 weeds m^–2) than in the CDS (108 ± 8.1 weeds m^–2) and in the SGS (92 ± 6.3 weeds m^–2). Weed composition varied with agroecological zone as well as with management factors and soil properties. Sørenson's index of similarity was low (mean=0.20) in all zones, indicating poor similarity between the weed flora above-ground and the soil seedbank.     

Etude de la dynamique d'une communaute adventice

Studies of the dynamics of a weed community: III. Long-term influence of cultivation techniques on the species composition of the seedbank The species composition of the seedbank was followed for eight years on four experimental plots differing in cultivation treatment (deep or shallow) and either treated or untreated with herbicides. The results show that the species composition was not affected by herbicides but there were quantitative changes: some species, such as Euphorbia exigua and Anagallis arvensis became more dominant without increasing in number. Conversely, in unweeded plots there were qualitative and quantitative changes in the species composition with the arrival of ‘opportunistic’ species such as Thlaspi arvense and Sinapis arvensis, which considerably increased in number although they were practically absent at the start. The type of cultivation modified these changes a little by mixing, in the cultivated layer, the annual additions of new seeds with the existing seedbank.     

Vertical distribution, size and composition of the weed seedbank under various tillage and herbicide treatments in a sequence of industrial crops

Investigations were conducted during the 2003, 2004 and 2005 growing seasons in northern Greece to evaluate effects of tillage regime (mouldboard plough, chisel plough and rotary tiller), cropping sequence (continuous cotton, cotton–sugar beet rotation and continuous tobacco) and herbicide treatment on weed seedbank dynamics. Amaranthus spp. and Portulaca oleracea were the most abundant species, ranging from 76% to 89% of total weed seeds found in 0–15 and 15–30 cm soil depths during the 3 years. With the mouldboard plough, 48% and 52% of the weed seedbank was found in the 0–15 and 15–30 cm soil horizons, while approximately 60% was concentrated in the upper 15 cm soil horizon for chisel plough and rotary tillage. Mouldboard ploughing significantly buried more Echinochloa crus‐galli seeds in the 15–30 cm soil horizon compared with the other tillage regimes. Total seedbank (0–30 cm) of P. oleracea was significantly reduced in cotton–sugar beet rotation compared with cotton and tobacco monocultures, while the opposite occurred for E. crus‐galli. Total seed densities of most annual broad‐leaved weed species (Amaranthus spp., P. oleracea, Solanum nigrum) and E. crus‐galli were lower in herbicide treated than in untreated plots. The results suggest that in light textured soils, conventional tillage with herbicide use gradually reduces seed density of small seeded weed species in the top 15 cm over several years. In contrast, crop rotation with the early established sugar beet favours spring‐germinating grass weed species, but also prevents establishment of summer‐germinating weed species by the early developing crop canopy.