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Effective integrated weed management in agricultural landscapes depends on the ability to identify and manage processes that drive weed dynamics. The current study reports the effects of grazing management and crop rotation strategies on the seedbank and emerged weed flora in an integrated crop-livestock system (ICLS) experiment during a 12-year period under no-tillage in sub-tropical southern Brazil. During winter, Italian ryegrass cover crops were grazed by sheep: grazing management treatments included two stocking methods (continuous and rotational) and two forage allowances (10 and 20 kg of herbage dry matter available per 100 kg animal live weight). During summer, the crop rotation treatments involved either soybean-maize or soybean-soybean in succession with winter-grazed cover crops. The treatments were part of a factorial randomized complete block design. Treatment effects were evaluated on the weed seedbank and emerged weed flora populations during winter-grazed cover crop and summer crop growth as well as during the harvest phase. The current results demonstrate that crop rotation and grazing management exhibited interactive effects on the determination of weed outcomes in an ICLS. However, overall, compared with moderate forage allowance, high forage allowance during the winter-grazed cover crop caused lower emerged weed flora in subsequent crops (20% reduction during crop growth and 90% reduction at crop harvest) and 48% reduction in seedbank size. High forage allowance promoted more residue from winter-grazed cover crop biomass, which remained during the summer crop phases and probably resulted in a physical barrier to weed emergence.

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: Trees can modify the weed seed bank composition and distribution in the cropped area of an agroforestry system. This study aimed at analyzing the eucalyptus (Eucalyptus dunnii) effect on spatial distribution, functional traits abundance and weed seed bank botanic composition in an agroforestry system under no-tillage in Subtropical Brazil. The experiment was conducted in a randomized block design with five replications, and five positions between 4.5-year-old eucalyptus double rows [(4x3) x 20 m] as treatments. Soil sampling was performed at 0-20 cm and the method to quantify and identify seeds was the seedling emergence in trays, inside a greenhouse. Weed phytosociological indices (relative density, frequency and importance), functional traits abundance (life cycle, shade tolerance, reproduction, spread and seed form) and seed densities (m-2) of families and species were evaluated; 17 weed families and 49 species were found. The indices that contributed to the relative importance of families and species differed among the positions between rows. Eucalyptus grown as an intercrop changed the composition and size of the weed seed bank, in a different way for functional traits, families and species depeding on the distance from trees.

Weeds are a major constraint on food and feed production, and the excessive use of herbicides to control them is a global concern for food security, human health, and environmental sustainability. Under no-tillage systems, cover crop residues provide a physical barrier to weed emergence that reduce weed infestations and reliance on herbicides. In integrated crop-livestock systems, cover crops provide fodder to grazing animals, adding an additional source of revenue for farmers; however, grazing can cause a trade-off because it reduces biomass during the cover crop season and residues left on the soil surface in the next cash crop, which may increase weed infestation. In the current study, it was hypothesized that there is an optimal cover crop forage allowance during the grazing period that maximizes beef production while retaining enough cover crop biomass and residue to minimize weed infestations and maintain grain yield of the subsequent cash crop. Therefore, the effects of cover crop (mixed black oat + Italian ryegrass) forage allowances (based on sward height) during the winter grazing period on weed infestations, beef production, and soybean grain yield during the next summer season were evaluated. The experiment was conducted in several commercial fields involving two experimental protocols (one short-term and one long-term experiment) in Southern Brazil, and the results demonstrated that a moderate forage allowance in winter cover crops (i.e., maintaining 17.8 cm of winter grazed cover crop sward height) reduced weed infestations and increased soybean and beef production when compared with a lower forage allowance (i.e., < 10.7 cm of winter grazed cover crop sward height) or a higher forage allowance (i.e., > 17.8 cm of winter grazed cover crop sward height). Therefore, the current study provides evidence that it is possible to optimize forage allowance to sustainably intensify arable cropping systems using winter cover crops for direct grazing.

-White clover is tolerant to many herbicides, making difficult a chemical control of this species during soybean crop establishments. The objective of this research was to select herbicides applied postemergence to control white clover in soybean and know the effects of this control on soybean yield. Seven herbicides were assessed, applied postemergence, with or without sequential application of glyphosate, and two control treatments (no control and total control of white clover). Glyphosate (with two sequential applications), fomesafen (with a sequential application of glyphosate), chlorimuron-ethyl and lactofen have shown a satisfactory control of white clover (above 80%). The lower control efficiency has resulted in lower production of soybeans.Keywords: herbicide, Integrated Crop-Livestock System, interference, Trifolium repens, Glycine max. RESUMO -O trevo-branco apresenta tolerância a diversos herbicidas, o que torna difícil o controle químico dessa espécie durante o estabelecimento da cultura da soja. Os objetivos desta pesquisa foram selecionar herbicidas utilizados em pós-emergência que controlam o trevo-branco na cultura da soja e conhecer os efeitos desse controle na produtividade da soja. Foram avaliados sete herbicidas aplicados em pós-emergência, com ou sem aplicação sequencial de glyphosate, e dois tratamentos testemunhas (sem controle e controle total do trevo-branco

241. It is widely agreed that competition regulates plant populations and shapes 25 communities. Many studies have suggested that crop and grassland competition 26 can be used for cost-effective sustainable weed control. However, effective weed 27 management requires a precise knowledge of the effects of agronomic practices 28 and there is a lack of quantitative indicators to compare and predict the success of 29 weed biocontrol by competition. 30 2. We studied weed abundance dynamics over a 12-year period in crop-grassland 31 rotations (rotation treatments consisted of maize, wheat and barley crops, 32 alternating with temporary grassland maintained for three or six years in the 33 rotation and fertilised with two different levels of nitrogen). In addition to 34 classical statistical analysis of the different aforementioned rotation treatments, 35 we also modelled weed abundance as a function of the crop and grassland 36 competition, expressed here by biomasses harvested in the preceding years. 37 3. We show that weed abundance decreases over the years in grassland and 38 subsequent crops only if the grassland receives sufficient nitrogen fertiliser. Our 39 model had a much greater explanatory power than the rotation treatments. This 40 model estimates a critical biomass level above which weeds are suppressed in 41 subsequent years, and below which they tend to thrive. This critical biomass level 42 was 24.3 and 4.7 tonnes ha -1 of dry matter for crops and grassland, respectively, 43 highlighting the greater competitiveness of grasslands than of crops. Several clear 44 differences between weed functional groups emerged. 45 4. Synthesis and applications -This new modelling approach directly links the 46 interannual dynamics of weed populations to current and previous biomass 47 production levels. This approach facilitates the development of environment-48 friendly weed management strategies and paves the way for comparisons of the 49 competitiveness against weeds of crops and grassland under various pedoclimatic 50 conditions and agronomic practices.51 52 Keywords: weed management, weed ecology, weed biocontrol, weed modelling, weed 53 population dynamics 54 55 Introduction 56Most food and feed production systems worldwide make use of synthetic 57 herbicides for weed management. In this context, herbicide use has resulted in serious 58 environmental and ecological problems (Boutin et al., 2014). Highly effective 59 environment-friendly alternatives to chemical weed control, such as the use of crop and 60 grassland competition with weeds, could potentially reconcile agricultural production and 61 environment quality and play a key role in ensure global food security in the future (Petit 62 et al., 2018; Gaba et al., 2018). 63Many previous studies have shown how the manipulation of agronomic practices 64 (e.g. seed rate, crop cultivar and row spacing and direction) to improve the 65 competitiveness of the crop can help to control weeds (Sardana et al., 2017). Other studies 66 have suggeste...