Weed Seedbank Density Research Articles

Effects of cultural practices on weed community and seedbank dynamics in a potato rotation

ContextStagnant yields and declining soil health are common characteristics of high-intensity, low-residue cropping systems, such as potato, particularly in northeastern North America. Incorporating cultural practices including cover cropping and manure application is a way to combat declines in agroecosystem health and potato productivity. However, manure application and the use of cover crops may exacerbate weed issues through seedbank additions. ObjectiveThis study was aimed at investigating how the cultural practices of cover cropping and manure application and their associated management activities can alter weed community dynamics and weed seedbank composition in a northeastern North American potato rotation. MethodsThe study evaluated the use of eight cover crop mixtures—annual and perennial grasses and legumes—grown over two years with/without manure added in year one of the rotation. It also examined the effects of the cover crop mixtures and the presence/absence of manure on the weed community and on seedbank dynamics within a three-year potato rotation between 2019 and 2021. ResultsIn year one of the study and directly after application, manure plots had greater weed seedbank density and species richness; however, this did not result in greater in-season weed biomass. Manure application resulted in a gradual decline in weed seedbank density over time regardless of cover crop treatment. Further, manure application increased the in-season competitive ability of cover crops, resulting in greater weed suppression per unit of cover crop biomass. In contrast, in the absence of manure, weed seedbank density remained largely unchanged through time regardless of cover crop treatment. We found that management practices associated with annual and perennial cover crops had distinct ecological filtering effects throughout the rotation on the weed community and prevented the dominance of any particular species. ConclusionTogether, our results demonstrate that combining the cultural practices of annual or perennial cover cropping and manure application contributes to weed suppression and should be considered an important component of sustainable potato production.

Weed seedbank as influenced by tillage and herbicide in direct seeded rice‐mustard cropping sequence in lateritic soil of eastern India

AbstractThe above‐ground community dynamics of weeds represent the soil weed seedbank in an agro‐ecosystem. Hence, understanding the seedbank will offer an idea for future weed management tactics. We aimed to determine the density of weed seedbank and emergence of major weeds in direct seeded rice (DSR) (Oryza sativa L.)—mustard (Brassica campestris L. var. yellow sarson) cropping sequence under varied tillage and herbicide combinations. The present study on weed seedbank was conducted using seedling emergence method after collecting the soils at the harvest of mustard at the completion of 2 years field experimentation. The experiment was conducted in split‐plot design with two tillage practices [zero tillage (ZT) and conventional tillage (CT)] in main plot and eight weed management practices in DSR [oxadiargyl followed by (fb) bispyribac‐sodium, penoxsulam + cyhalofop‐butyl, oxadiargyl fb penoxsulam + cyhalofop‐butyl, fenoxaprop‐p‐ethyl + ethoxysulfuron, oxadiargyl fb fenoxaprop‐p‐ethyl + ethoxysulfuron, pendimethalin fb bispyribac‐sodium, unweeded control, and weed free check] as subplot. The carry‐over effect of tillage and weed management practices were recorded in mustard crop. Seed emergence study revealed that ZT reduced the emergence of grassy weeds (by 13.7%) and total weed emergence (19.5%) in comparison to the CT (p < 0.05). However, emergence of broadleaf weeds was 24.5% higher in ZT than in CT. The higher infestation was recorded for Ludwigia parviflora (Jacq.) Raven under penoxsulam + cyhalofop‐butyl, fenoxaprop‐p‐ethyl + ethoxysulfuron, Cyperus iria (L.) under fenoxaprop‐p‐ethyl + ethoxysulfuron, and Eleusine indica (L.) Gaertn. under pendimethalin fb bispyribac‐sodium, oxadiargyl fb bispyribac‐sodium. Sole application of post‐emergence (POE) herbicide decreased the total weed emergence by 22.2%–28.1% than unweeded control (p < 0.05). Whereas, sequential application of PRE + POE herbicides decreased the total weed emergence by 32.8%–36.9% than unweeded control (p < 0.05). Notably, sedge weeds such as Cyperus iria (L.) and Fimbristylis miliacea (L.) Vahl were lower in ZT than in CT under herbicide treated plots (by 66.6%–84.3%) than unweeded control. Thus, ZT with oxadiargyl 90 g a.i. ha−1 fb fenoxaprop‐p‐ethyl + ethoxysulfuron (90 + 15 g a.i. ha−1) as tank‐mix can be effectively used to lower the weed seedbank density vis‐à‐vis managing complex weed flora in DSR and rice‐mustard cropping sequence.

Weed Seed Bank Density in Seven-Year-Old Conservation in No-Till System

Weed management remains a challenge when introducing new cropping systems. In Lebanon, farmers are increasingly adopting conservation agriculture (No-till) because it saves energy and reduces water and nutrient erosion. However, introducing a new system will cause a significant shift in production and management practices and is expected to produce novel weed management challenges. Thus, knowledge of soil seed banks of weeds in such systems is vital in designing effective weed management strategies. The objective of this research was to assess the size of the weed seed bank in seven-year-old conservation no-till fields. Soil samples were collected from established till and no-till fields at a depth of 0-5 cm. Transient and persistent weed seeds banks were evaluated. Results provide tangible evidence that the weed seed bank at a depth between 0-5cm in no-till system is greater than in till system. The no-till fields contained almost seven times the density of monocot and dicot weed seeds than in the conventional tilled fields. Ongoing work that builds on present results will help gain knowledge pertaining to weed seed bank dynamics in no-till system compared with conventionally tilled system.

Impact of Rotational Sequence Selection on Weed Seedbank Composition in Australian Broadacre Crops

The use of competitive crops in successional rotations has been shown to reduce the growth and establishment of annual weeds by the depletion of the weed seedbank in broadacre cropping systems. However, the impact of specific crop rotational sequences contributing to weed seedbank density has not been quantified in the Riverina region of southern Australia. Trials were established in two locations in 2014–2018 to quantify the impact of selected annual rotations featuring grain, pulse, and pasture crops on weed infestation and seedbank dynamics with a focus on winter and summer annual weeds. The weed seedbank dynamics were evaluated by a twice-annual soil sampling regime (at planting and harvest), followed by soil sample screening for weed propagule germination and seedling establishment in a subsequent controlled-environment screening performed from 2014–2020. The weed seedling density decreased in the cereal rotations in years experiencing average to above-average rainfall, as crops established a dense canopy leading to reduced weed establishment and fecundity. Several rotational treatments were effective in suppressing the weed propagule numbers over time, including those using dual-purpose cereals only or a canola break-crop along with the cereals. Rotational selection can be an important and cost-effective tool in integrated weed management systems when applied over multiple growing seasons.

Long-Term Soil Nutrient Management Affects Taxonomic and Functional Weed Community Composition and Structure

Weed communities can be influenced by nutrient availability, nutrient form (e. g., ammonium vs. nitrate), amendment timing, amendment type (e.g., organic vs. inorganic), and by immigration of seeds during amendment applications. The objective of this research was to compare the long-term effect of different fertility treatments in a corn (Zea mays L.)-alfalfa (Medicago sativa L.) rotation on taxonomic and functional structure and composition of weed communities by analyzing the soil weed seedbank. After 14 years of a long-term experiment in Aurora, NY, United States, soils were sampled in five fertility treatments for corn years in the rotation: liquid dairy manure, semi-composted separated dairy solids; or inorganic nitrogen (N) as starter fertilizer with either no sidedress N, a low rate or a high rate of inorganic N as sidedress fertilizer. Soil was collected in early spring 2015 and a greenhouse weed seed germination bioassay was used to quantify the germinable soil weed seedbank. Total weed seedbank density, species richness, and evenness did not vary by treatment. However, fertility treatments modified the ecological niche represented by 20 environmental descriptors, which filtered the weed community creating distinct functional group assemblages. A trait-based analysis revealed that nitrophilic dicotyledons preferring alkaline soil were associated with high concentrations of inorganic N fertilizer, whereas highly specialist monocotyledons preferring high amounts of light were associated with low concentrations of inorganic N fertilizer. Because fertility treatments affected weed community composition but not seed bank density and richness, results encourage the development of holistic management strategies that adopt coherent weed management and crop fertilization.

Influence of Short-term Maize–Green Manure Cover Crop Rotations on Germinable Weed Seed Bank under Conservation Agriculture

The effects of one- and two-year maize-cover crop rotations on weed seed bank density and species composition were evaluated in fields at the University of Zimbabwe (UZ) and the International Maize and Wheat Improvement Center (CIMMYT, Harare) between 2014 and 2017. Nine cover crops were rotated, and maize and weed seed bank analyses were done using the seedling emergence method. Maize was used as the control. The results indicated that weed seed density was not significantly (p > 0.05) affected by cover crop mulch type across the seasons. There was a significant (p < 0.05) decline in weed density in the second maize phase of the rotation in UZ Field A. Bidens pilosa, Galinsoga parviflora, Amaranthus hybridus and Eleusine indica were the dominant weeds. B. pilosa density significantly decreased in the second season in UZ Field A but did not vary significantly among cover crops. Significant changes in weed species richness, evenness, and diversity were observed only in the second phase of the rotation in UZ Field A. The results suggest that maize-cover crop rotations could be effective in reducing seed bank size in the short term but have no short-term effect on weed species community composition.

IDENTIFICATION OF LOCAL SEEDS BANK WEED AND THE EFFECT OF WEEDING FREQUENCY ON GROWTH AND RESULTS OF CAYENNE (Capsicum frutescens)

Weed is a plant pest organism whose existence is very detrimental to the production of cultivated plants. Weeds and major plants compete to obtain nutrients, sunlight, and water so that their availability is limited to the main plants. Weed abundance in a cultivated land is inseparable from the presence of weed seed banks in the soil. This study aims to identify weed bank seeds in chili cultivation in Tandon Hamlet, Selogiri Subdistrict, Wonogiri Regency and find out the right weeding frequency to get the highest productivity of cayenne pepper. Identification of local weed bank seed by taking soil samples at four different depths, a) 0-5 cm depth; b) 5-10 cm depth; c) 10-15 cm depth; and d) a depth of 15-20 cm. The variables observed included weed frequency, weed density, and summed dominance ratio (SDR). The frequency of weeding of cayenne plants, using a randomized completely block design (RCBD) with one treatment factor, namely weeding frequency (without weeding; 1 weeding at 2 weeks after planting (MST); 2 times weeding at 2 MST and 4 MST; 3 times weeding at 2 MST, 4 MST, and 6 MST; 4 times weeding at 2 MST, 4 MST, 6 MST, and 8 MST). The results showed that the highest weed seed bank density was found in the depth of soil 0-5 cm and 5-10 cm. While the frequency of weeding shows the frequency of 3 times weeding gives the best results on the growth and production of cayenne

Effects of Long-Term Cover Cropping on Weed Seedbanks

Cool-season cover crops have been shown to reduce soil erosion and nutrient discharge from maize (Zea maysL.) and soybean [Glycine max(L.) Merr.] production systems. However, their effects on long-term weed dynamics are not well-understood. We utilized five long-term research trials in Iowa to quantify germinable weed seedbank densities and compositions after 10+ years of cover cropping treatments. All five trials consisted of zero-tillage maize-soybean rotations managed with and without the inclusion of a yearly winter rye (Secale cerealL.) cover crop. Seedbank sampling was conducted in the early spring before crop planting at all locations, with three of the five trials having grown a soybean crop the preceding year, and two a maize crop. Two of the trials (both previously soybean) showed significant and biologically relevant decreases (4,070 and 927 seeds m−2, respectively) in seedbank densities in cover crop treatments compared to controls. In another two trials, one previously maize and one previously soybean, no difference was detected in seedbank densities. In the fifth trial (previously maize), there was a significant, but biologically unimportant increase of 349 seeds m−2. All five trials' weed communities were dominated by common waterhemp [Amaranthus tuberculatus(Moq.)], and changes in seedbank composition from cover-cropping were driven by changes in this species. Although previous studies have shown that increases in cover crop biomass are strongly correlated with weed suppression, in our study we did not find a relationship between seedbank changes and the mean amount of cover crop biomass produced over a 10-years period (experiment means ranging from 0.5 to 2.0 Mg ha−1yr−1), the stability of the cover crop biomass production, nor the amount produced going into the previous crop's growing season. We conclude that long-term use of a winter rye cover crop in a maize-soybean system has the potential to meaningfully reduce the size of weed seedbanks compared to winter fallows. However, identifying the mechanisms by which this occurs requires further research into processes such as seed predation and seed decay in cover cropped systems.

Tillage practices affect weeds differently in monoculture vs. crop rotation

Reduced tillage practices are widely considered to be more sustainable than conventional tillage practices, but many producers remain reluctant to reduce tillage due to difficulties controlling weeds. Crop rotation is often put forward as the best means to manage weeds in reduced tillage systems, but uncertainties remain around how different tillage practices and crop rotations interact. Here, we assess the effects of four different tillage practices on weed seedbank density and composition in wheat (Triticum aestivum) monoculture (WWWW), and two different rotations, wheat-medic-wheat-medic (annual medic, Medicago spp.; WMWM), and wheat-canola-wheat-lupin (Brassica napus, Lupinus spp.; WCWL). We use data across a whole four-year rotation period from a long-term experiment replicated at two sites in South Africa’s winter rainfall region. The four tillage practices assessed follow a gradient of soil disturbance: conventional tillage (CT, soil inversion through ploughing), minimum tillage (MT, shallow soil loosening), no tillage (NT, direct drilling with tine openers) and zero tillage (ZT, direct drilling with disc openers). Our results indicate that tillage type had no effect on weeds within the wheat monoculture. Both crop rotations generally had lower weed densities and reduced dominance of grass weeds than the monoculture, but under ZT weed seed bank density in both rotations was similar to that found in monoculture. Thus the use of ZT with crop rotation is antagonistic in this system, possibly due to more limited chemical weed control options than in CT, MT and NT, or due to crop residue cover promoting weed establishment. Subsequently, we recommend that producers in the region seeking to reduce tillage opt for NT rather than ZT, and avoid a wheat monoculture. Weed researchers and agronomists should be wary of other such antagonistic interactions between weed management practices in different systems.

Weed density and diversity in a long-term cover crop experiment background

Cover crops (CC) are biological tools with a great potential for weed control, but the suppression level depends on the CC species and management. A 2-year study was performed in the eighth year of a long-term experiment located in Central Spain to study the effect of replacing winter fallow by barley (Hordeum vulgare L.) or vetch (Vicia sativa L.), on the weed control. Moreover, two CC termination dates were evaluated. Weed biomass, density, diversity, population composition and the seed bank were assessed. Ground cover and CC biomass, soil inorganic N and topsoil water content were determined throughout the season. Barley achieved a greater weed control compared to vetch in winter and early spring. Later in May, both CC residues decreased weed density compared to fallow (63% in 2015, 55% in 2016), and reduced the density of some broadleaf species (i.e. Xanthium spinosum L. reduced >50%). The weed seedbank density was not affected by CC but the effect on specific species confirmed the control over Xanthium spp. (78% reduction), and also warned of the incomplete weed control by CC. The year in which the biomass and ground cover increased between termination dates, delaying the CC termination reduced weed density >75%. Therefore, delaying the termination date was a mean to increase weed control but should be performed with caution to avoid pre-emptive competition with the cash crop. Results underline the relevance of CC species and the termination date as management tools for weed control, and must be considered to plan specific management strategies in different scenarios.

Recurrent Changes of Weed Seed Bank Density and Diversity in Crop—Livestock Systems

Core Ideas Crop phase can be used to modify weed diversity.Grazing in sod‐based rotations decreased Palmer amaranth seed bank.Weed seed banks respond rapidly to crop phase within diverse rotations. Weeds are important biodiversity components in agroecosystems, but weed competition with cash crops requires farmers to manage weeds, limiting biodiversity within agricultural fields. Crop rotation increases weed diversity, but weeds are still managed in all cash crop phases so yields are not negatively affected. In our research, a bahiagrass (Paspalum notatum Flüggé)–bahiagrass–peanut (Arachis hypogaea L)–cotton (Gossypium hirsutum L.) rotation exhibited recurrent changes in weed seed banks. The bahiagrass crop phases increased, whereas peanut and cotton phases decreased weed density and diversity. Increasing weed seed banks in bahiagrass did not negatively impact the cash crops peanut and cotton. Furthermore, including grazing in the rotation did not affect overall weed seed banks, but caused a 75% reduction in Palmer amaranth (Amaranthus palmeri S. Watson) populations, the most problematic weed species in peanut and cotton. Our results indicate that grazing bahiagrass will promote weed diversity and suppress Palmer amaranth, resulting in better weed management in the peanut and cotton rotation crops.

Weed Dynamics in No-Till Rainfed Crops in Chaouia, Semi-Arid Morocco

Three on-farm research-managed trials were conducted in Settat province, Chaouia, semi-arid Morocco, from 2012-13 to 2014-15, to investigate the dynamics of germinable soil seedbank, weed density, and community composition of weeds in 3 crop rotations: continuous durum wheat, barley + pea/durum wheat/durum wheat, and canola/durum wheat/durum wheat. Initial germinable weed seedbank density estimated in September 2012, before no-till planting in November 2012 was 1890 seeds m-2. After two growing seasons, seedbank reductions were 23% in continuous durum wheat, 68% in canola/durum wheat/durum wheat, and 72% in barley + pea/durum wheat/durum wheat. In continuous durum wheat, weed densities before no-till planting were 273, 46, and 59 plants m-2 in November 2012, December 2013, and November 2014, respectively. In herbicide-free barley + pea/durum wheat/durum wheat, weed densities before no-till planting durum wheat were 128 and 42 plants m-2 in December 2013 and November 2014, respectively. In canola/durum wheat/durum wheat, weed densities before no-till planting wheat were only 20 and 25 plants m-2 in December 2013 and November 2014, respectively. This study demonstrated the combined merits of pre-plant glyphosate, herbicide use in wheat, herbicide-free barley + pea haying, and durum wheat rotation with either canola or barley + pea to manage weeds in no-till systems in semi-arid Morocco.

Weed Abundance and Community Composition following a Long-Term Organic Vegetable Cropping Systems Experiment

Weed management is a major constraint in organic cropping systems. In 2004, the Cornell Organic Vegetable Cropping Systems Experiment was established in central New York state using a split-plot randomized complete block design with two crop rotation entry points (split-plot factor). Four organic vegetable cropping systems that varied in cropping intensity and tillage (main plot factor) were compared: (1) intensive, (2) intermediate, (3) bio-extensive, and (4) ridge tillage. The basic crop rotation was cabbage, lettuce, potato, and winter squash, with additional short-season crops in the intensive system and with cover crops and fallow substituted for cabbage and potato in the bio-extensive system. In 2014, two uniformity trials were conducted in which oat and then a mixture of sorghum-sudangrass plus Japanese millet were grown uniformly over the entire experiment. Prior to sowing oat, soil samples were collected from each plot and an emergence bioassay was conducted to assess the soil weed seedbank. Crop biomass, weed density, and weed biomass were sampled in the uniformity crops. Soil weed seedbank density was three to four times greater in the intensive, intermediate, and ridge-tillage systems than in the bio-extensive system. The bio-extensive system also had lower weed density and weed biomass in the oat uniformity trial compared with the other three systems. Oat biomass did not differ between the cropping systems. Weed density and biomass in oat were also affected by the crop rotation entry point. Cropping system legacy effects on weed abundance and community composition were greater in the oat than in the sorghum-sudangrass plus Japanese millet uniformity trial. Our results illustrate the effects of different organic vegetable production practices on weed community structure and highlight the value of tilled fallow periods, cover crops, and prevention of weed seed rain for reducing weed populations.

Grazing intensities affect weed seedling emergence and the seed bank in an integrated crop–livestock system

Integrated crop-livestock systems (ICLS) are widespread worldwide. Although weeds can result in several types of losses, essential information regarding weed seedling emergence and seed banks is lacking in these systems for integrated weed management planning. This study investigated the effects of different grazing intensities (no grazing and grazed swards maintained at 10-, 20-, 30- and 40-cm sward heights) on weed seedling emergence and seed banks in a winter cover crop during the 15th year of an ICLS experiment under no-tillage management in subtropical Southern Brazil. We hypothesized that low grazing intensities would reduce weed interference and weed seed banks size in an ICLS. We determined treatment effects on weed species richness, seed bank population density, and seedling emergence during winter and summer. Higher sward heights in the winter-grazed cover crop reduced the number of weed species, the density of emerged weed seedlings, and the weed seed bank size compared with the non-grazed control. With a sward grazing height of 10cm, the seed bank contained an average of 3151 seeds m−2, and the weed population densities during the summer and winter were 11.8 and 21.7 plants m−2 greater, respectively, compared with the sward grazing height of 40cm. Fifteen years after adopting low grazing intensities (30- and 40-cm sward heights) in the ICLS, the size of the weed seed bank was reduced by 42.1% compared with the non-grazed treatment. Decreasing the grazing intensity reduced the number of weed species, the density of emerged weed seedlings, and the weed seed bank density; therefore, integrated weed management strategies should consider minimizing grazing intensities in an ICLS.

Conservation Management and Crop Rotation Effects on Weed Populations in a 12-Year Irrigated Study

Potato, dry bean, and sugar beet production have increased markedly in recent years on irrigated cropland in Alberta, Canada. Concerns exist about declining soil quality and increased soil erosion when these low-residue crops are grown in sequence in short-duration rotations. A 12-yr rotation study was conducted to determine the merits of adopting various conservation practices (reduced tillage, cover crops, composted manure) and longer-duration rotations to develop a more sustainable production system for these row crops. This article reports on weed density and weed seedbank data collected in the study. Weed densities recorded prior to applying postemergence herbicides indicated that conservation compared with conventional management treatments had greater weed densities in 30 to 45% of the cases in 3-, 4-, and 5-yr rotations. In contrast, a 6-yr conservation rotation that included 2 yr of timothy forage resulted in similar or lower weed densities than rotations with conventional management practices. Residual weed densities recorded 4 wk after applying postemergence herbicides were only greater in conservation than conventional rotations in 2 of 12 yr, regardless of rotation length. Weed seedbank densities at the conclusion of the 12-yr study were similar for 3- to 6-yr rotations under either conservation or conventional management. These findings indicate that implementing a suite of conservation practices poses little risk of increased weed populations in the long term. This knowledge will facilitate grower adoption of more sustainable agronomic practices for irrigated row crops in this region.

Evidence for indirect effects of pesticide seed treatments on weed seed banks in maize and soybean

Use of pesticide seed treatments (coating seeds with insecticides and/or fungicides) is a common practice in conventional maize and soybean production. Despite their widespread use, however, little is known about how this practice affects soil food webs and their associated ecosystem services. We conducted a two-year field experiment in central Pennsylvania, USA in which identical genotypes of maize (2013) and soybean (2014) were planted with and without pesticide seed treatments in a completely randomized design with five replications. We sampled the weed seed bank during both the corn (fall 2013) and soybean (summer 2014) phases of the rotation. After each sampling event, soil samples were transported to a temperature-controlled greenhouse facility and weed seed bank composition and density was assessed over a period of four months via the direct germination method. Seed bank data were analyzed with ANOVA and several multivariate techniques to determine the effect of pesticide seed treatments on seed bank density, diversity, and species composition. We hypothesized that pesticide seed treatments reduce the abundance of natural enemies (e.g., soil-dwelling seed predators and pathogens) that damage or destroy weed seeds in the soil, and therefore seed banks in treated plots would be larger and less diverse than those in untreated plots. In accordance with our hypothesis, weed seed banks were significantly less diverse in treated compared to untreated control plots (Shannon and Simpson’s indices of diversity, p<0.05). While not statistically significant, differences in mean germinable weed seed bank density, richness, and evenness were also in the direction that we hypothesized. These data provide the first evidence that we are aware of that weed seed banks, and hence weed populations, may be indirectly affected by pesticide seed treatments. Additional research will be necessary to determine the generality of these responses and their underlying mechanisms.

Weed seedbank size and composition in a long‐term tillage and crop sequence experiment

SummaryKnowledge of the effects of agricultural practices on weed seedbank dynamics is essential for predicting future problems in weed management. This article reports data relative to weed seedbank structure after 18 years of continuous application of conventional tillage (CT, based on mouldboard ploughing) or no tillage (NT) within three crop sequences (continuous wheat, WW; wheat–faba bean, WF; and wheat–berseem clover, WB). Tillage system did not affect the size of the total weed seedbank, but altered both its composition and the distribution of seeds within the soil profile. In particular, the adoption of CT favoured some species (mainly Polygonum aviculare), whereas the continuous use of NT favoured other species (Papaver rhoeas, Phalaris spp. and Lactuca serriola). The effects of tillage system on weed seedbank size and composition were less pronounced in the WB cropping system than in either the WW or WF. Compared with WF and WB, WW resulted in an increase in total weed seedbank density (about 16 000 seedlings m−2 in WW, compared with 10 000 and 6000 seedlings m−2 in WF and WB, respectively) and a reduction in weed diversity, with a strong increase in some species (e.g. Polygonum aviculare). Our results for the effect of NT application on weed seedbank size and composition suggest that farmers should only apply such a conservative technique within an appropriate crop sequence.

Weed seed-bank responses to long-term fertilization in a rice-wheat rotation system

We studied the heterogeneity of soil weed seed-bank in a rice-wheat rotation system after long-term application of different organic or non-organic fertilizers, and the effects of major nutrients on the characteristics of the weed seed-bank. The soil was sampled in the Taihu area after a 31-year long-term fertilization experiment. Weed seeds were identified and counted in the surface soil of 12 differentially treated areas using microscopic examination, and analyzed by the Simpson, Shannon, Margalef, and Pielou indexes. The long-term application of organic fertilizers could significantly reduce the density of soil weed seed-bank; non-organic fertilizers and a combination of non-organic and organic fertilizers had a significant influence on the number of species and diversity of weeds. The application of organic fertilizers improved the Simpson, Shannon and Pielou indexes of soil weed seed-bank community and stabilized the community structure. In terms of the soil nutrient system itself, the soil organic materials and total nitrogen content are the main environmental factors affecting the distribution of soil weed seed-bank.

Organic Farmer Knowledge and Perceptions are Associated with On-Farm Weed Seedbank Densities in Northern New England

Weed management remains a high priority for organic farmers, whose fields generally have higher weed density and species diversity than those of their conventional counterparts. We explored whether variability in farmer knowledge and perceptions of weeds and weed management practices were predictive of variability in on-farm weed seedbanks on 23 organic farms in northern New England. We interviewed farmers and transcribed and coded interviews to quantify their emphasis on concepts regarding knowledge of ecological weed management, the perceived risks and benefits of weeds, and the perceived risks and benefits of weed management practices. To characterize on-farm weed seedbanks, we collected soil samples from five fields at each farm (115 fields total) and measured germinable weed seed density. Mean weed seed density per farm ranged from 2,775 seeds m−2to 24,678 seeds m−2to a soil depth of 10 cm. Farmers most often reported hairy galinsoga and crabgrass species (Digitariaspp.) as their most problematic weeds. The proportion of the sum of these two most problematic weeds in each farm's seedbank ranged from 1 to 73% of total weed seed density. Farmer knowledge and perceptions were predictive of total seed density, species richness, and proportion of hairy galinsoga and crabgrass species. Low seed densities were associated with farmers who most often discussed risks of weeds, benefits of critical weed-free management practices, and learning from their own experience. These farmers also exhibited greater knowledge of managing the weed seedbank and greater understanding of the importance of a long-term strategy. Targeted education focusing on this set of knowledge and beliefs could potentially lead to improved application and success of ecological weed management in the future, thus decreasing labor costs and time necessary for farmers to manage weeds.

Overcoming Weed Management Challenges in Cover Crop–Based Organic Rotational No-Till Soybean Production in the Eastern United States

Cover crop–based organic rotational no-till soybean production has attracted attention from farmers, researchers, and other agricultural professionals because of the ability of this new system to enhance soil conservation, reduce labor requirements, and decrease diesel fuel use compared to traditional organic production. This system is based on the use of cereal rye cover crops that are mechanically terminated with a roller-crimper to create in situ mulch that suppresses weeds and promotes soybean growth. In this paper, we report experiments that were conducted over the past decade in the eastern region of the United States on cover crop–based organic rotational no-till soybean production, and we outline current management strategies and future research needs. Our research has focused on maximizing cereal rye spring ground cover and biomass because of the crucial role this cover crop plays in weed suppression. Soil fertility and cereal rye sowing and termination timing affect biomass production, and these factors can be manipulated to achieve levels greater than 8,000 kg ha−1, a threshold identified for consistent suppression of annual weeds. Manipulating cereal rye seeding rate and seeding method also influences ground cover and weed suppression. In general, weed suppression is species-specific, with early emerging summer annual weeds (e.g., common ragweed), high weed seed bank densities (e.g. &gt; 10,000 seeds m−2), and perennial weeds (e.g., yellow nutsedge) posing the greatest challenges. Due to the challenges with maximizing cereal rye weed suppression potential, we have also found high-residue cultivation to significantly improve weed control. In addition to cover crop and weed management, we have made progress with planting equipment and planting density for establishing soybean into a thick cover crop residue. Our current and future research will focus on integrated multitactic weed management, cultivar selection, insect pest suppression, and nitrogen management as part of a systems approach to advancing this new production system.