Seeds Weeds Needs

ILGM

Buy Cannabis Seeds Online

Important parameters that influence weed seeds’ germination and seedlings’ emergence can affect the efficacy of false seedbed as weed management practice. These parameters consist of environmental factors such as soil temperature, soil water potential, exposure to light, fluctuating temperatures, nitrates concentration, soil pH and the gaseous environment of the soil. Soil temperature and soil water potential can exert a great influence on composition of the weed flora of a cultivated area. Base soil temperatures and base water potential for germination vary among different weed species and their values can be possibly used to predict which weeds will emerge in a field and also the timing of emergence. Predicting the main flush of weeds in the field could maximize the efficacy of false seedbed technique as weed management practice. Timing, depth and type of tillage are important factors affecting weed emergence and subsequently the efficacy of false seedbed. The importance of shallow tillage as weed control method in the false seedbed technique has been highlighted. Further research is needed to understand and explain all the factors that can affect weed emergence so as to maximize the effectiveness of eco-friendly weed management practices such as false seedbed in different soils and under various climatic conditions. Weed and Seed Strategy This report presents an overview on the Weed and Seed Strategy developed under the U.S. Department of Justice, Executive Office for Weed and Seed, a multi-agency initiative Manage the Weed Seed Bank—Minimize “Deposits” and Maximize “Withdrawals” One of the most important—yet often neglected—weed management strategies is to reduce the number of weed seeds present in

Key Factors Affecting Weed Seeds’ Germination, Weed Emergence, and Their Possible Role for the Efficacy of False Seedbed Technique as Weed Management Practice

Important parameters that influence weed seeds’ germination and seedlings’ emergence can also affect the efficacy of false seedbed as weed management practice. These parameters consist of environmental factors such as soil temperature, soil water potential, exposure to light, fluctuating temperatures, nitrates concentration, soil pH, and the gaseous environment of the soil. Soil temperature and soil water potential can exert a great influence on composition of the weed flora of a cultivated area. Base soil temperatures and base water potential for germination vary among different weed species and their values can possibly be used to predict which weeds will emerge in a field as well as the timing of emergence. Predicting the main flush of weeds in the field could maximize the efficacy of false seedbed technique as weed management practice. Timing, depth, and type of tillage are important factors affecting weed emergence and, subsequently, the efficacy of false seedbed. The importance of shallow tillage as a weed control method in the false seedbed technique has been highlighted. Further research is needed to understand and explain all the factors that can affect weed emergence so as to maximize the effectiveness of eco-friendly weed management practices such as false seedbed in different soils and under various climatic conditions.

Introduction

Weeds that exist with crops early in the season are less detrimental than weeds that compete with the crop later in the growing season, and this principle has supported the timely use of weed management practices (Wyse, 1992). Either early- or late-emerging weeds produce great proportions of viable seeds that can remain in the soil profiles for a long time period, contributing to the perpetuation and the success of weeds (Cavers and Benoit, 1989). As a result, in most arable crop systems, weed management strategies focus mainly on reducing weed density in the early stages of crop growth (Zimdahl, 1988). However, confining weed management to a narrow temporal window increases the risk of unsatisfactory weed management due to unfavorable weather (Gunsolus and Buhler, 1999). Weed seed banks are the primary source of persistent weed infestations in agricultural fields (Cousens and Mortimer, 1995) and if their deposits are increased, greater herbicide doses are required to control weeds afterwards (Taylor and Hartzler R, 2000). Annual weed species increase their populations via seed production exclusively (Steinmann and Klingebiel, 2004), whereas seed production is also important for the spread of perennials (Blumenthal and Jordan, 2001).

Consequently, it is preferable to focus on depleting the seed stock in the soil through time rather than viewing weeds just as an annual threat to agricultural production (Jones and Medd, 2000). This approach is reinforced not only by ecological (Davis et al., 2003) but also by economic simulation models (Jones and Medd, 2000). False seedbed technique is a method providing weed seed bank depletion. The principle of flushing out germinable weed seeds before crop sowing forms the basis of the false seedbed technique in which soil cultivation may take place days or weeks before cropping (Johnson and Mullinix, 1995). Germination of weed seeds is stimulated through soil cultivation (Caldwell and Mohler, 2001). Irrigation is suggested to provide the adequate soil moisture required for sufficient weed emergence. In the case of false seedbed, emerged weeds are controlled by shallow tillage operations (Merfield, 2013). Control of weeds and crop establishment should be delayed until the main flush of emergence has passed in order to deplete the seedbank in the surface layer of soil and reduce subsequent weed emergence (Bond and Grundy, 2001).

False seedbed technique aims to reduce weed seed bank by exploiting seed germination biology. Thus, the efficacy of such management practices is directly associated with all the factors affecting germination of weed seeds and seedling emergence. Soil temperature, diurnal temperature variation, soil moisture, light, nitrates concentration in the soil, and the gaseous environment of the soil can regulate seed germination and weed emergence (Merfield, 2013). Except for the case of environmental factors, tillage is the most effective way to promote weed seed germination because the soil disturbance associated with tillage offers several cues to seedbank residents such as elevated and greater diurnal temperature, exposure to light, oxygen, and release of nitrates in the soil environment (Mohler, 2001). The aim of this review paper is to give prominence to the significance of environmental factors and tillage for weed seed germination and seedlings emergence and, therefore, for the efficacy of false seedbed technique as weed management practice.

The Impact of Soil Temperature and Water Potential on Weed Seed Germination and their Roles for Predicting Weed Emergence

The longevity of weed seeds into the soil profiles is attributed to the phenomenon of dormancy that prevents seed germination even when the environmental conditions are ideal (Benech-Arnold et al., 2000). Dormancy is distinguished into two types: primary and secondary dormancy (Karssen, 1982). The end of primary dormancy is sequenced by the establishment of secondary dormancy and this sequence has been defined as dormancy cycling (Baskin and Baskin, 1998). In adapted weed species, dormancy is alleviated during the season preceding the period with favorable conditions for seedling development and plant growth, while dormancy induction takes place in the period preceding the season with environmental conditions unsuitable for plant survival (Benech-Arnold et al., 2000). Furthermore, seeds from summer annual species are released from dormancy by low winter temperatures. High summer temperatures may induce entrance of the same seeds into dormancy again, which is referred to as secondary dormancy. On the contrary, seeds from winter annuals are released from dormancy by high summer temperatures whereas low winter temperatures induce their entrance into secondary dormancy (Forcella et al., 2000). Relatively dry seeds lose dormancy at a rate which is temperature-dependent. In hydrated seeds, high temperatures reinforce or induce dormancy whereas low temperatures between −1 and 15°C may stimulate germination (Roberts, 1988).

Timing of weed emergence is dependent on the timing and rate of seed germination, which is dependent not only on soil temperature and but also on moisture potential (Gardarin et al., 2010). Of the many environmental factors that regulate seed behavior under field conditions, soil temperature has a primary influence on seed dormancy and germination, affecting both the capacity for germination by regulating dormancy and the rate or speed of germination in non-dormant seeds (Bouwmeester and Karssen, 1992). It has been recognized since at least 1860 that three cardinal temperatures (minimum, optimum, and maximum) describe the range of T over which seeds of a particular species can germinate (Bewley and Black, 1994). The minimum or base temperature (Tb) is the lowest T at which germination can occur, the optimum temperature (To) is the T at which germination is most rapid, and the maximum or ceiling temperature (Tc) is the highest T at which seeds can germinate. Seed germination rates also vary with increasing temperature as it increases in the suboptimal range and decreases above the optimum temperature (Alvarado and Bradford, 2002).

To account for the effect of temperature on the progress of germination, the concept of thermal time has been developed (Garcia-Huidobro et al., 1982). The application of thermal time theory to germination is based on the observation that for some species there is a temperature range over which the germination rate for a particular fraction of the seed population is linearly related to temperature. The base temperature Tb is estimated as the x-intercept of a linear regression of the germination rate with temperature (Gummerson, 1986). Once seeds have lost dormancy, their rate of germination shows a positive linear relationship between the base temperature and the optimum temperature and a negative linear relationship between the optimal temperature and the ceiling temperature (Roberts, 1988). For the case of the summer annual Polygonum aviculare (L.), Kruk and Benech–Arnold (1998) demonstrated that low winter temperatures alleviate dormancy, producing a widening of the thermal range permissive for germination as a consequence of a progressive decrease of the lower limit temperature for germination of the population (Tb). In contrast, high summer temperatures reinforce dormancy, which results in a narrowing of the thermal range permissive for germination through an increase of Tb.

Germination speed of Alopecurus myosuroides (Huds.) seeds decreased with temperature, whereas the final proportion of germinated seeds was not significantly influenced (Colbach et al., 2002b). Minimum temperature required for seed germination is different for various weed species. Minimum temperature required for seed germination has been estimated at 0°C both for the winter annual A. myosuroides (Colbach et al., 2002a) and the summer annual P. aviculare (Batlla and Benech-Arnold, 2005). However, Masin et al. (2005) estimated the base temperature for Digitaria sanguinalis (L.), Setaria viridis (L.), P. Beauv., Setaria pumila (Poir.), Roem. & Schultes and Eleusine indica (L.), at 8.4, 6.1, 8.3, and 12.6°C, respectively. Moreover, the mean Tb recorded for summer annuals Amaranthus albus (L), Amaranthus palmeri (S. Wats.), D. sanguinalis, Echinochloa crus-galli (L.) Beauv., Portulaca oleracea (L.), and Setaria glauca (L.) was ~40% higher as compared to the corresponding value recorded for winter annuals Hirschfeldia incana (L.) and Sonchus oleraceus (L.). Optimal temperature conditions required for terminating dormancy status vary among different species. For example, Panicum miliaceum (L.) seeds lost dormancy at 8°C while P. aviculare seeds were released from dormancy at 17°C (Batlla and Benech-Arnold, 2005). The two germination response characteristics, Tb and rate, influence a species’ germination behavior in the field (Steinmaus et al., 2000). Extended models should be developed to predict the effects of environment and agricultural practices on weed germination, weed emergence, and the dynamics of weed communities in the long term. This requires estimating the baseline temperature for germination for each weed species that are dominant in a cultivated area and recording seed germination in a wide range of temperatures (Gardarin et al., 2010).

The knowledge about seed germination for the dominant weed species of a cultivated area is vital for predicting weed seedlings emergence. The possibility of predicting seedling emergence is essential for improving weed management decisions. However, weed emergence is the result of two distinct processes, i.e., germination and pre-emergence growth of shoots and roots, which react differently to environmental factors and should therefore be studied and modeled separately (Colbach et al., 2002a). In temperate regions, soil temperature is probably the most distinct and recognizable factor governing emergence (Forcella et al., 2000). Soil temperature can be used as a predictor of seedling emergence in crop growth models (Angus et al., 1981). Soil temperature can also be used for predicting weed emergence, but only if emergence can be represented by a simple continuous cumulative sigmoidal curve and the upper few centimeters of soil remain continuously moist (Forcella et al., 2000).

Fluctuating temperatures belong to parameters that can remove the constraints for the seed germination of many weed species once the degree of dormancy is sufficiently low (Benech-Arnold et al., 2000). In particular, the extent and number of diurnal soil temperature fluctuations can be critical in lessening seed dormancy of several species. For example, alternating temperatures at 25 °C increased germination of Amaranthus retroflexus (L.), Amaranthus spinosus (L.), and Amaranthus tuberculatus (L.) from 23 to 65, 8 to 77, and 9 to 57%, respectively, as compared to non-alternating temperatures. Fluctuating temperatures from 2.4 to 15°C can terminate the dormancy situation in Chenopodium album (L.) seeds (Murdoch et al., 1989). Either four diurnal cycles of 12°C amplitude or 12 diurnal cycles of 6°C amplitude were necessary for the emergence of D. sanguinalis (King and Oliver, 1994). The number of cycles of alternating temperatures needed to end the dormancy situation has to be investigated. In Sorghum halepense (L.) Pers., a 50% increase in cycles of alternating temperatures can double the number of seeds that are released from dormancy (Benech-Arnold et al., 1990). Furthermore, if the demand for fluctuating temperatures to terminate dormancy in the seeds of this species is not satisfied, a loss of sensitivity to fluctuating temperatures occurs in a proportion of the population (Benech-Arnold et al., 1988). The variation among weed species regarding the demands for fluctuating temperatures for seed germination points out the need for further investigation regarding the effects of fluctuating temperatures in germination of noxious weed species in different regions around the world and under various soil and climatic conditions.

Soil moisture is a key parameter affecting the seed dormancy status of many species (Benech-Arnold et al., 2000; Batlla et al., 2004). First of all, the environmental conditions existing during seed development in parent plants and seed maturation affect the relative dormancy of the seeds. Less dormant seeds of Sinapis arvensis (L.) were produced from the mother plants under water stress conditions (Wright et al., 1999) while similar results have been reported regarding either winter annual grass species Avena fatua (L.) or summer perennial S. halepense (Peters, 1982; Benech-Arnold et al., 1992). Moreover, sufficient water potential has been noticed to increase the production of dormant A. myosuroides seeds (Swain et al., 2006).

The effects of water deficits on seed germination have been encapsulated in the “hydrotime” concept. This idea was first illustrated by Gummerson (1986) and further explained by (Bradford, 1995). The model of (Bradford, 1995) accounted for dormancy loss during after-ripening through changes in the base water potential of the seeds’ environment that permits 50% germination (Ψb(50)). Christensen et al. (1996) confirmed that Ψb(50) value of the population is decreased by the change in Ψb(50) due to after-ripening. The Ψb(50) value is saved as the Ψb(50) value of the population and serves as the initial value for the next time step. The process continues until the Ψb(50) value of fully after-ripened seeds is reached. The model described is only to consider dormancy changes, not only in relation to the thermal environment, but also as a function of the soil water status. The loss of primary dormancy does not secure some species germination if moisture demands are not met. For example, adequate water conditions are demanded to promote germination of Bromus tectorum (L.) (Bauer et al., 1998). Bauer et al. (1998) assumed that the temperature-dependent after-ripening process in this winter annual occurs at soil water potentials below ~-4 MPa. Martinez–Ghersa et al. (1997) reported that increased water content promoted seed germination of A. retroflexus, C. album, and E. cruss-galli.

See also  Can You Eat Cannabis Seeds

The seed germination response to the soil water potential of wild plants could be correlated with the soil water status in their natural habitats (Evans and Etherington, 1990). The models which aim to predict weed germination and emergence need to record seed germination in a wide range of water potentials. Seeds of various weed species require different values of water potential in order to germinate. For instance, the base water potential Ψb for A. myosuroides was estimated at −1.53 (MPa) in the study of Colbach et al. (2002b) whereas the corresponding value recorded for Ambrosia artemisiifolia (L.) was −0.8 (MPa) as observed by other scientists (Shrestha et al., 1999). The value of minimum water potential for the germination of S. viridis seeds was −0.7 (MPa) (Masin et al., 2005) whereas the corresponding value recorded for Stellaria media (L.) Villars was −1.13 (MPa) (Grundy et al., 2000). Dorsainvil et al. (2005) revealed that the base water potential for germination for Sinapis alba (L.) was at −1 (MPa). Regarding weed emergence, although seeds of many species can germinate in a wide range of water potentials, once germination has occurred the emerged seedlings are sensitive to dehydration, and irreversible cellular damage may occur (Evans and Etherington, 1991). False seedbed is a technique that aims to deplete weed seed banks by eliminating the emerged weed seedlings. Thus, it is crucial to have knowledge about water demands for germination for the dominant weed species of the agricultural area where a false seedbed is planned to be formed. If these demands are not met, then they can be secured via adequate irrigation in the meantime between seedbed preparation and crop sowing.

The Possible Effects of Light, Gaseous Environment of the Soil, Soil Nitrates Content and Soil PH on Seed Germination of Various Weed Species

The reaction of seeds to light signals is dependent on phytochromes that consist of a group of proteins acting as sensors to changes in light conditions. Cancellation of dormancy by light is mediated by the phytochromes. All phytochromes have two mutually photoconvertible forms: Pfr (considered the active form) with maximum absorption at 730 nm and Pr with maximum absorption at 660 nm. The photoconversion of phytochrome in the red light (R)-absorbing form (Pr) to the far red light (FR)-absorbing form (Pfr), has been identified as part of the germination induction mechanism in many plant species (Gallagher and Cardina, 1998). Germination can be induced by Pfr/P as low as 10 −4 and is usually saturated by

There is evidence showing that other environmental factors, such as nitrates and gases, can also regulate seed bank dormancy (Bewley and Black, 1982; Benech-Arnold et al., 2000). For instance, germination of Sysimbrium offcinale (L.) Scop. is dependent on the simultaneous presence of light and nitrates (Hilhorst and Karssen, 1988), while in the case of Arabidopsis thaliana (L.) Heynh., nitrates modify light-induced germination to some degree (Derkx and Karssen, 1994). The seeds of summer annual species, S.officinale, showed increased sensitivity to nitrates and lost dormancy during the winter season (Hilhorst, 1990). Regarding the winter annual S. arvensis, Goudey et al. (1988) recorded maximal germination frequencies when NO 3 – content ranged from 0.3 to 4.4 nmol seed −1 for applied NO 3 – concentrations between 2.5 and 20 mol m −3 . In the same study germination was significantly lower in seeds containing more than 5 nmol NO 3 – . Although the mechanisms by which nitrates stimulate dormancy loss remain under investigation, they maybe act somewhere at the cell membrane environment (Karssen and Hilhorst, 1992). The evaluation of the effects of nitrates in regulating weed seeds’ germination and weed emergence is an area of interest for weed scientists and research needs to be carried out to get a better knowledge regarding this issue. There is also evidence that the range of pH values can promote germination of important weed species. For instance, Pierce et al. (1999) noticed that seed germination of D. sanguinalis decreased with increasing pH when soil was amended with MgCO3, whereas maximum root dry weights occurred at ranges from pH 5.3–5.8. A pH range of 5–10 did not influence seed germination of E. indica (Chauhan and Johnson, 2008). Cyperus esculentus (L.) germination rate at pH 3 was 14% as compared to 47% at pH 7, while germination of Sida spinosa (L.) was highest at pH 9 (Singh and Singh, 2009). In the experiment by (Lu et al., 2006) Eupatorium adenophorum (Spreng.) germinated in a narrow range of pH (5–7) whereas other researchers recorded a 19–36% germination rate for Conyza canadensis (L.) Cronquist. over a pH range from 4 to 10 (Nandula et al., 2006). As a consequence, another area available for research is the role of soil pH on seed germination and weed emergence especially in fields where false seedbed technique has been planned to be applied.

Oxygen and carbon dioxide are two of the most major biologically active gases in soil. Oxygen concentration in soil air does not usually fall below the limit of 19% (Benech-Arnold et al., 2000). During storage of seeds in soil, oxygen can have both detrimental and beneficial effects on the dormancy status of weed seeds. Results of an early study carried out by Symons et al. (1986) revealed that introduction to the cycle of secondary dormancy in the seeds of A. fatua was attributed to hypoxia. Hypoxic conditions did also cause a decrease in the germination capacity and rate of Datura stramonium (L.) (Benvenuti and Macchia, 1995). Moreover, B. tripartita seeds showed increased germination rates under 5 and 10% oxygen concentration as compared to the germination rate recorded under 21% oxygen concentration (Benvenuti and Macchia, 1997). Germination of E. crus-galli was increased with oxygen concentrations in the range among 2.5 and 5% and declined when the oxygen concentration level was above 5% citepbib20. However, low oxygen concentration or the inability to remove anaerobic fermentation products from the gaseous environment directly surrounding the seed may inhibit seed germination. The results of Corbineau and Côme (1988) indicated that low oxygen concentrations, or even hypoxia, can terminate dormancy situation in the seeds of Oldenlandia corymbosa (L.). The results of Experiment 1 carried out by Boyd and Van Acker (2004) revealed that oxygen concentration of 21% highest led to 31, 29, and 61% increased germination of Elymus repens (L.) Gould. as compared to oxygen concentrations of 5, 10, and 2.5%. In the same experiment, the greatest germination rate for Thlaspi arvense (L.) was also recorded with 21% oxygen concentration.

The levels of carbon dioxide in soil air ranges between 0.5 and 1% (Karssen, 1980a,b). When soils are flooded, the ratio of carbon dioxide to oxygen typically increases and can have detrimental effects on seed germination and seedling emergence. In very early studies, concentrations of carbon dioxide in the range of 0.5 and 1% have been reported to have a dormancy breaking effect in seeds of Trifolium subterraneum (L.) and Trigonella ornithopoides (L.) Lam. & DC. (Ballard, 1958, 1967). Elevated carbon dioxide concentrations combined with low oxygen concentrations may further strengthen the signal to germinate and promote germination below the surface during periods of high soil moisture content (Yoshioka et al., 1998), and this hypothesis was supported by the results of (Boyd and Van Acker, 2004). Ethylene, a gas with a well-known role as a growth regulator, is also present in the soil environment, with its usual value of the pressure ranging between 0.05 and 1.2 MPa (Corbineau and Côme, 1995). At these concentrations, it has break-dormancy effects on seeds of T. subterraneum (Esashi and Leopold, 1969), P. oleracea, C. album, and A. retroflexus (Taylorson, 1979). According to Katoh and Esashi (1975), at low concentrations in the soil ethylene promotes germination in Xanthium pennsylvanicum (L.) and similar observations have been made regarding A.retroflexus (Schönbeck and Egley, 1981a,b). However, these are results of old studies and it should be noted that a newer study stated that the role of ethylene in governing seed germination and seedling emergence cannot be clearly explained (Baskin and Baskin, 1998). The findings of another study where strains of a bacterium were evaluated as stimulators of emergence for parasite weeds belonging to Striga spp. were interesting. The bacterium Pseudomonas syringae (Van Hall) pathovar glycinea synthesizes relatively large amounts of ethylene. In the study of Berner et al. (1999) strains of P. syringae pv. glycinea had a stimulatory effect on the germination of seeds of the parasite weeds Striga aspera (Willd.) Benth. and Striga gesnerioides (Willd.) Vatke. Consequently, whether oxygen, carbon dioxide, and ethylene influences weed seeds’ germination and seedlings emergence is not yet clarified since variation has been reported among gases’ concentrations and various weed species. Thus, the role of the gaseous environment of the soil in seed germination and weed emergence needs to be further explained.

The Importance of Tillage as Stimulator of Weed Emergence and as Weed Control Method in False Seedbed Technique

The movement of the weed seeds within the soil profiles as a consequence of tillage creates variations in the dormancy of seeds (Ghersa et al., 1992). There is evidence that weed species’ timing and duration of emergence varies (Stoller and Wax, 1973; Egley and Williams, 1991), suggesting that timing of tillage interferes with the timing of species germination and acts as an assembly filter of weed communities (Smith, 2006). The results of Crawley (2004) revealed that the frequency of Papaver dubium (L.), A. thaliana, and Viola arvensis (Murray) was increased by 62.5, 66.5, and 72%, respectively, due to fall cultivation. In the same study, spring cultivation increased the frequency of C. album, Bromus hordeaceus (L.), and Galinsoga parviflora (Cav.) by 48, 88, and 92.5 %. Spring tillage acts as a filter on initial community assembly by hindering the establishment of later-emerging forbs, winter annuals, C3 grasses, and species with biennial and perennial life cycles, whereas fall tillage prevents the establishment of early-emerging spring annual forbs and C4 grasses. Species adapted to emerge earlier are therefore able to exploit the high availability of soil resources and be more competitive as compared to species that usually emerge later in the growing season when soil resource availability is restricted at a significant point (Davis et al., 2000).

Tillage events confined to the top 10 cm can provoke greater weed emergence than the corresponding events usually observed in untilled soil (Egley, 1989). Although no direct evidence exists of the effect of tillage on dormancy through modification of temperature fluctuations or nitrate concentration, it is well-known that tillage exposes seeds to a light flash before reburial, allows for greater diffusion of oxygen into and carbon dioxide out of the soil, buries residue, and promotes drying of the soil, thereby increasing the amplitude of temperature fluctuations and promoting nitrogen mineralization (Mohler, 1993). Tillage promotes seed germination, and this is a fundamental principle in which innovative management practices such as stale seedbed techniques that target the weed seed bank are based (Riemens et al., 2007). Weed emergence is an inevitable result of shallow soil disturbances in crop production, as it is indicated by Longchamps et al. (2012). Disturbances as small as wheel tracking can enhance seedling emergence. Results from past studies point out that promotion of seedling emergence is more dependent on the density of a given recruitment cohort rather than flush frequency (Myers et al., 2005; Schutte et al., 2013), and that the stimulatory effect of a particular shallow soil disturbance event dissipates over time and flushes occurring afterward feature seedling densities are similar to flushes recorded in untilled soils (Mulugeta and Stoltenberg, 1997; Chauhan et al., 2006). Plants react to the low fidelity between germination cues and recruitment potential and have become able to produce seed populations with different germination demands not only in qualitative but also in quantitative points to secure the longevity of the population. Thus, only a fraction of a population can germinate after performing shallow tillage operations (Childs et al., 2010). Soil type can also affect seedbank dynamics as it was shown by the results of a study conducted in Ohio. When the soil was sampled at 15 cm depth, the concentration of seeds was reduced with depth but the effect of tillage on seed depth was not the same for all three soil types that received the same tillage operation (Cardina et al., 1991).

False seedbed technique is based on the principle of using soil disturbance to provoke weed emergence and use shallow tillage instead of herbicide as a weed control method before crop establishment. False seedbed by inter cultivation decreased weed density and dry weight in finger millet (Patil et al., 2013). It is well-established that 5 cm is the maximum depth of emergence for most cropping weeds. If tillage overpasses this boundary, non-dormant seeds from deeper soil profiles are placed in germinable superficial soil positions. Re-tillage must be as shallow as 2 cm. Spring tine can be used in false seedbeds and multiple passes are suggested for more efficient weed control in cereal crops, while milling bed formers are more suited to vegetable crops (Merfield, 2013). Johnson and Mullinix (1995) found that shallow tillage was efficient against weeds like C. esculentus, Desmodium tortuosum (L.), and Panicum texanum (L.) in peanuts in a false seedbed. Similar results have also been observed in soybeans (Jain and Tiwari, 1995). An issue remaining under investigation is if the timing of weed elimination can affect the efficacy of such techniques. The results of Sindhu et al. (2010) were not clear regarding which treatment was superior among the stale seedbed prepared for seven days and the one prepared for 14 days before controlling weeds with tillage operations.

Conclusions

Important parameters that influence weed seeds’ germination and seedlings’ emergence can affect the efficacy of false seedbed as weed management practice. These parameters consist of environmental factors such as soil temperature, soil water potential, exposure to light, fluctuating temperatures, nitrates concentration, soil pH, and the gaseous environment of the soil. Soil temperature and soil water potential can exert a great influence on weed diversity of a cultivated area. Estimating minimum soil temperatures and values of water potential for germination for the dominant weed species of a cultivated area can give researchers the ability to predict weed infestation in a field and also the timing of weed emergence. Predicting weed emergence can answer the question of how much time weed control and crop sowing should be delayed in a specific agricultural area where false seedbed technique is about to be applied. As a result, if it was possible in the future to use environmental factors to make such predictions, this could maximize the efficacy of false seedbed technique as weed management practice. Timing, depth, and type of tillage are important factors affecting weed emergence and, subsequently, the efficacy of false seedbed. The importance of shallow tillage as a weed control method in the false seedbed technique has also been highlighted. In general, estimating the effects of environmental factors and tillage operations on weed emergence can lead to the development of successful weed management practices. Further research is needed to understand the parameters that influence weed emergence in order to optimize eco-friendly management practices such as false seedbeds in different soil and climatic conditions.

See also  How Many Weed Seeds Per Pot

Author Contributions

All authors listed have made a substantial, direct and intellectual contribution to the work, and approved it for publication.

Conflict of Interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Weed and Seed Strategy

This report presents an overview on the Weed and Seed Strategy developed under the U.S. Department of Justice, Executive Office for Weed and Seed, a multi-agency initiative in crime control and prevention.

Operation Weed and Seed was developed in 1991 by the U.S. Department of Justice as a strategy based on four fundamental principles: collaboration, coordination, community participation, and leveraging resources with a multi-agency approach to law enforcement, crime prevention, and neighborhood restoration. The approach is two-fold. First, law enforcement agencies and prosecutors must work together to “weed out” criminals from a specific target area. Then, the “seeding” process begins and brings prevention, intervention, treatment, and neighborhood revitalization services to the area. The Weed and Seed Strategy requires some key elements: (1) a steering committee to offer a governing structure for the initiative and (2) a strategic plan developed by assessing community problems and needs, sound resolutions and responses, and obtaining the necessary resources and participation. Today, Weed and Seed has grown to more than 300 high-crime neighborhoods across the country.

Manage the Weed Seed Bank—Minimize “Deposits” and Maximize “Withdrawals”

One of the most important—yet often neglected—weed management strategies is to reduce the number of weed seeds present in the field, and thereby limit potential weed populations during crop production. This is accomplished by managing the weed seed bank.

What is the Weed Seed Bank, and Why is it Important to Organic Farmers?

The weed seed bank is the reserve of viable weed seeds present on the soil surface and scattered throughout the soil profile. It consists of both new weed seeds recently shed, and older seeds that have persisted in the soil from previous years. In practice, the soil’s weed seed bank also includes the tubers, bulbs, rhizomes, and other vegetative structures through which some of our most serious perennial weeds propagate themselves. In the following discussion, the term weed seed bank is defined as the sum of viable weed seeds and vegetative propagules that are present in the soil and thus contribute to weed pressure in future crops. Agricultural soils can contain thousands of weed seeds and a dozen or more vegetative weed propagules per square foot.

The weed seed bank serves as a physical history of the past successes and failures of cropping systems, and knowledge of its content (size and species composition) can help producers both anticipate and ameliorate potential impacts of crop–weed competition on crop yield and quality. Eliminating “deposits” to the weed seed bank—also called seed rain—is the best approach to ease future weed management. Over a five-year period in Nebraska, broadleaf and grass weed seed banks were reduced to 5 percent of their original density when weeds were not allowed to produce seeds. However, in the sixth year, weeds were not controlled and the seed bank density increased to 90 percent of the original level (Burnside et al., 1986).

Weed seed banks are particularly critical in organic farming systems, which rely on cultivation as a primary means of weed control. Because a cultivation pass generally kills a fixed proportion of weed seedlings present, a high initial population will result in a high density of weeds surviving cultivation—escapes—and competing with the crop. Initial weed population is directly related to the density of seeds in the seed bank (Brainard et al., 2008; Teasdale et al., 2004); thus, effective cultivation-based weed control requires either a low seed bank density (Forcella et al., 1993) or multiple cultivation passes to achieve adequate weed control. In addition, dense weed stands (for example, a “sod” of smooth crabgrass or other grass weed seedlings) can interfere with the efficacy of cultivation implements in severing or uprooting weeds (Mohler, 2001b).

Cultivation efficacy—weed kill—can vary considerably based on equipment, soil conditions, weed growth stage, and operator experience. Eighty percent mortality would be considered quite respectable, a level of weed control far less than that achieved with most herbicides. Therefore, without the “big hammer” of selective herbicides to remove heavy weed populations from standing crops, effective measures to reduce weed seed banks become vital for the organic farmer.

Inputs (“Deposits”) and Losses (“Withdrawals)

Organic growers aim to manage their weed seed banks in the opposite fashion from a long term savings account: minimize “deposits,” and maximize “withdrawals” (Forcella, 2003). Weed seed bank deposits include:

  • The annual weed seed return (or seed “rain”) from reproductively mature weeds in the field or in field margins
  • Production of new rhizomes, tubers, and other vegetative reproductive structures by perennial weeds
  • Weed seeds brought into the field through inputs and farm operations, such as manure, mulch hay, irrigation water, farm machinery, and custom operators
  • Weed seeds introduced by natural forces beyond the farmer’s control, such as wind, floodwaters, and migrating birds

Whereas the first two kinds of deposits have the greatest influence on future population levels of existing weed species, the latter two can introduce new weed species to the farm—somewhat analogous to opening a new kind of bank account with a small initial deposit and a sky-high interest rate. Even two or three viable seeds or propagules of a highly aggressive new weed species can spell trouble in years to come. Thus organic farmers strive both to prevent heavy deposits through propagation of existing weeds, and to prevent establishment of new weed species by excluding their seed and promptly eradicating new invaders. This topic is discussed further in Keeping New Weedy Invaders Out of the Field.

Weed seed bank withdrawals include:

  • Seed germination
  • Fatal germination, in which the seed or propagule sprouts but fails to reach the soil surface due to excessive depth or death from allelochemicals (natural phytotoxic substances released by plants), microbial pathogens, insects, or other organisms in the soil
  • Consumption of weed seeds by ground beetles, crickets, earthworms, slugs, field mice, birds, and other organisms (=weed seed predation)
  • Loss of viability or decay of seeds over time

The first type of withdrawal—germination leading to emergence—is, of course, how weeds begin to compete with and harm crops each season. It is also the foremost mechanism for debiting the seed bank, an effective strategy if emerged seedlings are easily killed by subsequent cultivation or flaming (the stale seedbed technique, for example). Even in species with relatively long-lived seeds such as pigweeds, velvetleaf, and morning glory, the vast majority of weed emergence from a given season’s seed rain takes place within two years after the seeds are shed (Egley and Williams, 1990). Thus, timely germination (when emerging weeds can be readily killed) can go far toward minimizing net deposits into the seed bank from recent weed seed shed. Knowing when to promote or deter weed seed germination, and how to do so for the major weeds present, are important skills in seed bank management.

Weed Seed Bank Dynamics

Weed seeds can reach the soil surface and become part of the soil seed bank through several avenues. The main source of weed seeds in the seed bank is from local matured weeds that set seed. Agricultural weeds can also enter a field on animals, wind, and water, as well as on machinery during activities like cultivation and harvesting (explored further in Keeping New Weedy Invaders Out of the Field).

Weed seeds can have numerous fates after they are dispersed into a field (Fig. 1). Some seeds germinate, emerge, grow, and produce more seeds; others germinate and die, decay in the soil, or fall to predation. The seeds and other propagules of most weeds have evolved mechanisms that render a portion (a large majority in some species) of propagules dormant (alive but not able to germinate) or conditionally dormant (will not germinate unless they receive specific stimuli such as light) for varying periods of time after they are shed. This helps the weed survive in a periodically disturbed, inhospitable, and unpredictable environment. Weed seeds can change from a state of dormancy to nondormancy, in which they can then germinate over a wide range of environmental conditions. Because dormant weed seeds can create future weed problems, weed scientists think of dormancy as a dispersal mechanism through time.

Figure 1. Fate of weed seeds. Inputs to the seed bank are shown with black arrows and losses with white arrows. Figure Credit: Fabian Menalled, MSU Extension, Montana State University.

Maintaining excellent weed control for several consecutive seasons can eliminate a large majority of the weed seed bank, but a small percentage of viable, highly dormant seeds persist, which can be difficult to eliminate (Egley, 1986). Researchers are seeking more effective means to flush out these dormant seeds through multiple stimuli (Egley, 1986).

Weed species also differ in the seasonal timing of their germination and emergence. Germination of many species is governed by growing degree–days (GDD)—the summation of the number of degrees that each day’s average temperature exceeds a base temperature. This concept is founded on the assumption that, below the base temperature, the organisms (in this case seeds) are quiescent, and that as “thermal time” accumulates above this temperature, their development proceeds. In addition, some newly shed weed seeds must first undergo a period of unfavorably cold or hot conditions before they can germinate in response to favorable temperatures. This initial, or primary, dormancy delays emergence until near the beginning of the next growing season—late spring for warm-season weeds (dormancy broken by cold period over winter), and fall for winter annual weeds (dormancy broken by hot period in summer)—when emerging weeds have the greatest likelihood of completing their life cycles and setting the next generation of seed.

The Iowa State University Cooperative Extension Service has evaluated seed germination response of common weeds of field corn in relation to GDD calculated on a base temperature of 48°F beginning in early spring, and categorized the weeds into germination groups (cited in Davis, 2004). For example, winter annuals like field horsetail and shepherd’s purse germinate before any GDD accumulate in the spring; giant ragweed and common lambsquarters require fewer than 150 GDD and therefore emerge several weeks before corn planting; redroot pigweed, giant foxtail, and velvetleaf germinate at 150–300 GDD, close to corn planting time; whereas large crabgrass and fall panicum require over 350 GDD and usually emerge after the corn is up. A few species, such as giant ragweed, emerge only during a short (8 weeks). Knowing when the most abundant species in a particular field are likely to emerge can allow the farmer to adjust planting dates and cultivation schedules to the crop’s advantage.

Several factors other than mean daily soil temperature have a major impact on the timing of weed germination and emergence in the field. Adequate soil moisture is critical for germination, and good seed–soil contact is also important in facilitating the moisture uptake that is required to initiate the process. Thus more weeds may emerge from a firmed soil surface, such as occurs under planter press wheels, than from a loose, crumbly, or fluffy soil surface (Gallandt et al., 1999). For example, densities of common chickweed and common purslane in seeder tracks—in the crop rows—were roughly double those over the rest of the field, whereas annual grass weeds and yellow nutsedge did not show this pattern. (Caldwell and Mohler, 2001).

In addition, many weed seeds are also stimulated to germinate by light (even the very brief flash occasioned by daytime soil disturbance), fluctuations in temperature and moisture, or increases in oxygen or nitrate nitrogen (N) levels in the soil. Tillage, which exposes seeds to these stimuli, is therefore a critical determinant of seed germination. The timing of N fertilizer applications can also influence the number of weeds germinating. For example, many weed species can be stimulated by large increases in soluble N after incorporation of a legume cover crop, or inhibited by delayed applications of N fertilizer.

Shallow soil disturbance during periods of peak potential germination can be an effective tactic for debiting (drawing down) the weed seed bank (Egley, 1986). This phenomenon is exploited when timely cultivated fallow is used to reduce the weed seed bank, and in the establishment of a stale seedbed prior to planting. These tactics encourage the conditionally dormant portion of the seed bank to germinate so that the crop can be sown into a reduced initial weed population.

Weed seeds disperse both horizontally and vertically in the soil profile. While the horizontal distribution of weed seeds in the seed bank generally follow the direction of crop rows, type of tillage is the main factor determining the vertical distribution of weed seeds within the soil profile. In plowed fields, the majority of weed seeds are buried four to six inches below the surface (Cousens and Moss, 1990). Under reduced tillage systems such as chisel plowing, approximately 80 to 90 percent of the weed seeds are distributed in the top four inches. In no-till fields, the majority of weed seeds remain at or near the soil surface. Clements et al. (1996) have shown that soil texture may influence weed seed distribution in the soil profile under these different tillage systems (Fig. 2).

Figure 2. Vertical distribution of weed seeds in a loamy sand soil (top) and a silty loam soil (bottom). Figure credit: adapted from Clements et al. (1996) by Fabian Menalled, MSU Extension, Montana State University.

Understanding the impact of management practices on the vertical distribution of seeds is important because it can help us predict weed emergence patterns. For example, in most soils small-seeded weeds such as kochia, Canada thistle, and common lambsquarters germinate at very shallow depths (less than ½ inch). Large seeded weeds such as common sunflower have more seed reserves and may germinate from greater depths.

Thus, one strategy for managing the weed seed bank, especially for smaller-seeded weeds, is to maintain seeds at or near the soil surface. It is here that seeds experience the greatest exposure to environmental cues that will encourage germination—the most effective means of debiting the seed bank—as well as greater exposure to seed predators (see Encouraging Weed Seed Predation and Decay). Studies have confirmed that some weed seeds, including velvetleaf, morning glory, and pigweed, germinate in larger numbers in untilled than in tilled soil during the first year after seed shed (Egley and Williams, 1990). It may be tempting to use inversion tillage to place seeds below the depth from which they can emerge. This may be an effective strategy for species with short-lived seeds (see below), but it may simply protect longer-lived seeds from mortality factors like seed feeding animals and decomposer fungi, only to be returned to the soil surface by the next deep plowing event.

Factors Affecting Weed Seed Longevity

The number of viable seeds remaining from a given year’s weed seed return declines over time as a result of germination (successful or fatal), predation, and decay. The percentage remaining declines in an approximately exponential manner, similar to the decay curve for a radioactive chemical element—the time for the number to decline by 50% is roughly the same, regardless of the initial num. The half-life of weed seeds varies widely among weed species; for example, hairy galinsoga and some annual grass weeds, such as foxtail species, last only one to a few years, whereas some curly dock and common lambsquarters seed can last over 50 years.

The actual seed longevity in the soil depends on an interaction of many factors, including intrinsic dormancy of the seed population, depth of seed burial, frequency of disturbance, environmental conditions (light, moisture, temperature), and biological processes such as predation, allelopathy, and microbial attack (Davis et al., 2005; Liebman et al., 2001). Understanding how management practices or soil conditions can modify the residence time of viable seeds can help producers minimize future weed problems. For example, seeds of 20 weed species that were mixed into the top 6 inches of soil persisted longer in untilled soil than in soil tilled four times annually (Mohler, 2001a), which likely reflects greater germination losses in the disturbed treatment. On the other hand, a single tillage can enhance the longevity of recently-shed weed seeds, because buried seeds are usually more persistent compared to those left at the surface where they are exposed to predators, certain pathogens, and wide fluctuations of temperature and moisture. However, soilborne pathogens may also contribute to attrition of buried seeds, even in large-seeded species like velvetleaf (Davis and Renner, 2008).

See also  Germinating Cannabis Seeds For Hydroponics

Although seed longevity of agricultural weeds is a cause for notoriety, and a proportion of the population may remain viable for several years or decades, most of the seeds of many weed species will either germinate or die shortly after being dispersed from the parent plant. The seeds of many grasses are particularly short lived. For example, in a field study conducted near Bozeman, MT, wild oat seeds were incorporated into the top four inches of a wheat–fallow field, and approximately 80 percent of them died during the first winter (Harbuck, 2007). It is important to note, however, that postdispersal survival varies widely among weed species.

Evaluating the Weed Seed Bank

One way to estimate a field’s weed seed bank is to wait and see what weeds emerge during the first season. However, knowing something about seed bank content before the season starts can help the farmer prevent severe weed problems before they develop. Davis (2004) recommended the following simple procedure for scouting the weed seed bank:

A little effort in understanding your weed seedbank [sic] can give you valuable information about what weeds to expect in a given growing season, weed density, and when most weed germination will take place. To get a weed preview, you can germinate weeds indoors as you’re waiting to plant. For summer annual weeds, such as velvetleaf, foxtail, lambsquarters, and pigweed, March–April is a good time to sample weed seedbanks [sic] in the North Central region. Using a soil probe or a garden trowel, take 20 samples to a 2” depth in a ‘W’ pattern from the field you’re interested in. Place the soil in a pie dish, put in a warm place (> 65 º F) and keep moist. Within one to two weeks, you should have an idea of what weeds will be emerging in your field as the soil warms.

~ Davis, 2004

For a more representative sampling, collect sufficient soil samples to fill several pie dishes, or a seedling flat. The larger the sample, the more closely the observed weed emergence will reflect field populations.

Keep in mind that this method is not likely to reveal all the species present in a field. However, in combination with field observations on seasonal patterns of weed emergence, greenhouse weed emergence tests can help anticipate when control tactics are likely to be needed in the coming season, and to begin developing a seed bank management strategy.

Some Weed Seed Bank Management Practices

Use these strategies to minimize annual inputs (deposits) to the weed seed bank:

  • Kill weeds before they set seed—before flowering to be safe, because some weeds (such as hairy galinsoga) can mature seeds from flowers that are pollinated before the weeds are pulled or severed . If in doubt, attempt to thresh the seeds from the fruits or flowers of flowering weeds; dough-consistency and firm seeds can be considered mature and should be removed from the field if possible.
  • Control creeping perennial weeds before they can form new rhizomes, tubers, or other propagules.
  • Keep crops ahead of the weeds—small weeds overshadowed by a good crop canopy may have less than 1% of the seed forming capacity of vigorous individuals growing in full sun.
  • Walk fields to remove large weed escapes before they flower. Getting the largest 10% of individuals can reduce seed production by 90% or better.
  • Mow field margins to minimize seed set by weed species that have the potential to invade fields. (Balance this with the potential role of field margins as beneficial insect habitat).
  • Mow or graze fields promptly after harvest to interrupt weed seed production.
  • Utilize good sanitation practices to prevent introduction of new weed species into the field, and remove new invaders before they propagate.

Another measure that can help contain seed bank populations is to increase the diversity of crop rotations. Although data on the effects of crop rotations on weed seed banks in organic systems have not been consistent, there is some evidence suggesting that more diverse rotations, especially those that include one or more years in red clover, alfalfa, or other perennial sod crops, can help reduce seed inputs from velvetleaf and other annual weeds, and promote seed bank declines through seed predation and decay (Davis et al., 2005; Teasdale et al., 2004; Westerman et al., 2005).

Use these strategies to maximize losses (withdrawals) from the weed seed bank:

  • Till or cultivate to stimulate weed seed germination at a time when the seedlings can be easily knocked out by additional cultivation or flaming (stale seedbed), or will be freeze-killed before they can reproduce. Rolling after tillage can further enhance germination by improving seed–soil contact.
  • If practical, time this tillage or cultivation to take place when seeds of the major weeds present are least dormant, and/or during the season of the weeds’ peak emergence, in order to maximize the seed bank withdrawal.
  • Time crop planting to facilitate destruction of flushes of weed seedling emergence. For example, if the major weeds in a given field are known to reach their peak emergence in mid May, delay corn planting until end of May to allow time to remove this flush prior to planting.
  • Maintain habitat for weed seed predators—vegetation or mulch cover—in at least part of the field for as much of the year as practical.
  • Reduce or avoid tillage during critical times for weed seed predator activity. If a significant weed seed rain has occurred, leave weed seeds at the surface for a period of time before tilling to maximize weed seed predation.

Because soil microorganisms can play a role in weed seed decay, maintaining a high level of soil biological activity through good organic soil management might be expected to shorten the half-life of weed seed banks. In addition, incorporation of a succulent legume or other cover crop may either stimulate weed seed germination by enhancing soil nitrate N levels, or promote weed seed or seedling decay as a result of the “feeding frenzy” of soil microorganisms on the green manure residues. However, the potential of these practices as weed seed bank management tools requires verification through further research.

While it is sometimes advantageous to cause weed seeds to germinate, it is important at other times to keep them quiescent long enough for the crop to get well established. Several practices can help reduce the number of weeds emerging in the crop.

  • Cultivate at night or with light shields over the cultivation implement to minimize the light stimulus to weed seeds.
  • Leave a loose soil surface after planting or cultivation to reduce seed–soil contact for near-surface weed seeds, thereby deterring germination. If practical, cover newly seeded rows with loose soil to reduce within-row weed emergence.
  • Minimize soil disturbance at or near the time of planting. Do major tillage in fall or very early spring several weeks before planting. Use flame or very shallow cultivation to prepare the seedbed.
  • Avoid practices that result in early pulses of nitrogen that may stimulate weed emergence. Use split N fertilizer applications and slow releasing forms of N, such as compost and legume–grass cover crop mixtures) to make N availability patterns over the season match N needs of the crop rather than the weeds.
  • Avoid planting crops in fields with heavy populations of weeds with similar life cycles. For example, fields dominated by late emerging summer annual weeds might best be planted in early crops like peas.
  • Time crop planting to take place well before the most abundant weed species in the field are expected to emerge.
  • Time crop planting to take place after the expected major weed seedling flushes, and remove the latter by shallow cultivation or flame weeding.
  • Invert the soil to a depth from which weed seeds cannot emerge (most effective for weeds with small, short-lived seeds).

Incorporated green manures or surface residues of cover crops can reduce the establishment of small-seeded weeds through allelopathy and/or physical hindrance. Thus, these practices can provide a measure of selective weed control for transplanted or large-seeded crops, which are tolerant to the stresses imposed by cover crop residues. This selectivity does not apply to small-seeded, direct sown vegetables like carrots and salad greens, which are at least as sensitive to these cover crop effects as small-seeded weeds.

Challenge of Weed Seed Bank Diversity

Remember that none of these strategies can be expected to eliminate the weed seed bank, and also that you may need to change seed bank management strategy as the seed bank itself changes. The reason the weed seed bank is so difficult to manage is because it contains not only many seeds, but many different kinds of seeds, with typically 20 to 50 different weed species in a single field. In other words, the grower may have to deal with 20 to 50 different plant survival strategies! Thus, there will almost always be some weeds that tolerate, or even thrive on, whatever combination of seed bank management strategies the farmer adopts.

For example, some but not all weed species have light-responsive seeds, and dark cultivation reduces emergence only in the light responders. Similarly, careful nitrogen (N) management can reduce problems with nitrate responders but have no effect on nonresponders and could even favor a weed that is well adapted to low levels of soluble N. The best approach to weed seed bank management is to design your strategy around the four or five most serious weeds present, then monitor changes in the weed flora over time, noting what new weed species emerge as the original target weed species decline. Then change your seed bank management strategy accordingly. Plan on making such adjustments every few years, and if possible, keep a sense of curiosity and humor about the weeds!

This article is part of a series on Twelve Steps Toward Ecological Weed Management in Organic Vegetables. For more on managing the weed seed bank, see:

References and Citations

  • Brainard, D. C., R. R. Bellinder, R. R. Hahn, and D. A. Shah. 2008. Crop rotation, cover crop and weed management effects on weed seedbanks and yields in snap bean, sweet corn and cabbage. Weed Science 56: 434–441. (Available online at: http://dx.doi.org/10.1614/WS-07-107.1) (verified 23 March 2010).
  • Burnside, O. C., R. G. Wilson, G. A. Wicks, F. W. Roeth, and R. S. Moomaw. 1986. Weed seed decline and buildup under various corn management systems in Nebraska. Agronomy Journal 78: 451–454. (Available online at: https://www.agronomy.org/publications/aj/abstracts/78/3/AJ0780030451) (verified 4 April 2011).
  • Caldwell, B., and C. L. Mohler. 2001. Stale seedbed practices for vegetable production. HortScience 36: 703–705.
  • Clements, D. R., D. L. Benoit, and C. J. Swanton. 1996. Tillage effects on weed seed return and seedbank composition. Weed Science 44: 314–322. (Available online at: http://www.jstor.org/stable/4045684) (verified 23 March 2010).
  • Cousens, R., and S. R. Moss. 1990. A model of the effects of cultivations on the vertical distribution of weed seeds within the soil. Weed Research 30: 61–70. (Available online at: http://dx.doi.org/ 10.1111/j.1365-3180.1990.tb01688.x ) (verified 23 March 2010).
  • Davis, A. S. 2004. Managing weed seedbanks throughout the growing season [Online]. New Agriculture Network Vol. 1 No. 2.
  • Davis, A. S., J. Cardina, F. Forcella, G. A. Johnson, G. Khttp://eorganic.info/node/2806/editegode, J. L. Lindquist, E. C. Lusheri, K. A. Renner, C. L. Sprague, and M. M. Williams. 2005. Environmental factors affecting seed persistence of annual weeds across the US corn belt. Weed Science 53: 860–868. (Available online at: http://dx.doi.org/10.1614/WS-05-064R1.1) (verified 23 March 2010).
  • Davis, A. S., and K. A. Renner. 2006. Influence of seed depth and pathogens on fatal germination of velvetleaf (Abutilon theophrasti) and giant foxtail (Setaria faberi). Weed Science 55: 30–35. (Available online at: http://dx.doi.org/10.1614/W-06-099.1) (verified 23 March 2010).
  • Davis, A. S., K. A. Renner, and K. L. Gross. 2005. Weed seedbank and community shifts in a long-term cropping systems experiment. Weed Science 53: 296–306. (Available online at: http://dx.doi.org/10.1614/WS-04-182) (verified 23 March 2010).
  • Egley, G. H. 1996. Stimulation of weed seed germination in soil. Reviews of Weed Science 2: 67–89.
  • Egley, G. H., and R. D. Williams. 1990. Decline of weed seeds and seedling emergence over five years as affected by soil disturbance. Weed Science 38: 504–510. (Available online at: http://www.jstor.org/stable/4045064) (verified 23 March 2010).
  • Forcella, F. 2003. Debiting the seedbank: Priorities and predictions. p. 151–162. In R. M. Bekker et al. (ed.) Seedbanks: Determination, dynamics and management. Aspects of Applied Biology 69. Association of Applied Biologists, Wellesbourne, UK.
  • Forcella, F., K. Eradat-Oskoui, and S. W. Wagner. 1993. Application of weed seedbank ecology to low-input crop management. Ecological Applications 3: 74–83. (Available online at: http://www.jstor.org/stable/1941793) (verified 23 March 2010).
  • Gallandt, E. R., M. Liebman, and D. R. Huggins. 1999. Improving soil quality: Implications for weed management. p. 95–121. In D. D. Buhler (ed.) Expanding the context of weed management. Food Products Press, New York.
  • Harbuck, K. Z. 2007. Weed seedbank dynamics and composition of Northern Great Plains cropping systems. MS Thesis. Montana State University, Bozeman, MT.
  • Liebman, M., C. L. Mohler, and C. P. Staver. 2001. Ecological management of agricultural weeds. Cambridge University Press, New York.
  • Menalled, F. 2008. Weed seedbank dynamics and integrated management of agricultural weeds. Montana State University Extension MontGuide MT200808AG. (Available online at: http://www.msuextension.org/publications/AgandNaturalResources/MT200808AG.pdf) (verified 11 March 2010).
  • Mohler, C. L. 2001a. Weed life history: identifying vulnerabilities. p. 40–98. In M. Liebman et al. Ecological management of agricultural weeds. Cambridge University Press, New York.
  • Mohler, C. L. 2001b. Mechanical management of weeds. p. 139–209. In M. Liebman et al. Ecological management of agricultural weeds. Cambridge University Press, New York.
  • Teasdale, J. R., R. W. Magnum, J. Radhakrishnan, and M. A. Cavigelli. 2004. Weed seedbank dynamics in three organic farming crop rotations. Agronomy Journal 96: 1429–1435. (Available online at https://www.agronomy.org/publications/aj/articles/96/5/1429?highlight=JmFydGljbGVfdm9sdW1lPTk2JnE9KGF1dGhvcjolMjJUZWFzZGFsZSUyMikmcT0oam91cm5hbDphaikmbGVuPTEwJnN0YXJ0PTEmc3RlbT1mYWxzZSZzb3J0PQ%3D%3D ) (verified 4 April 2011).
  • Westerman, P. R., M. Liebman, F. D. Menalled, A. H. Heggenstaller, R. G. Hartzler, and P. M. Dixon. 2005. Are many little hammers effective? Velvetleaf (Abutilon theophrasti) poplution dynamics in two- and four-year crop rotation systems. Weed Science 53: 382–392. (Available online at: http://dx.doi.org/10.1614/WS-04-130R) (verified 23 March 2010).

Published August 20, 2013

This is an eOrganic article and was reviewed for compliance with National Organic Program regulations by members of the eOrganic community. Always check with your organic certification agency before adopting new practices or using new materials. For more information, refer to eOrganic’s articles on organic certification.

Welcome to the public website of eOrganic, the Organic Agriculture Community of the Extension Foundation.

How useful was this post?

Click on a star to rate it!

Average rating 4 / 5. Vote count: 1

No votes so far! Be the first to rate this post.