Weedy rice is of the same species as cultivated rice, Oryza, and is a common rice weed exhibiting allopathic characteristics. Incorporation of allelopathic traits from weedy rice into cultivated rice may have a positive impact on rice yield. The overall objective of this study was to characterize weedy rice accessions based on the allelopathic potential to suppress barnyardgrass. These accessions, once discovered, may be used in identifying phenotypic traits and genes associated with their weed suppressive trait. Ten weedy rice accessions, and five rice cultivars (Rex, CL163,Rondo, PI312777, PI338046) were screened using a stair-step technique. The allelopathic potential was calculated based on the percent inhibition of barnyardgrass. The best performing accessions were phenotyped for root characteristics in a lab setting. Lastly, 30 SSR markers were used to evaluate the weedy rice to identify markers associated with the trait. Accessions identified in this study should be considered in the development of weed-suppressive rice cultivars.

I investigated how competitor species respond to chemical cues released from the red tide dinoflagellate Karenia brevis. K. brevis produces a mix of unstable, relatively polar, allelopathic organic molecules that are produced and released at low concentrations. The production of these compounds also varies greatly within and among strains of K. brevis. The majority of these compounds caused sublethal reductions in competitor growth. In laboratory experiments, these compounds inhibited the growth of competitors Asterionellopsis glacialis, Skeletonema grethae, Prorocentrum minimum, and Akashiwo sanguinea, although each species was susceptible to a different sub-set of K. brevis compounds. Cell physiological state and population densities were important in dictating the susceptibility of competitors to allelopathy: phytoplankton were most susceptible to K. brevis allelopathy when in earlier growth stages (rather than later stages) and in lower cell concentrations. However, these compounds have limited negative effects on natural, mixed populations of competitors from both near and offshore environments, and competitors from inshore and offshore environments appear to respond similarly to K. brevis allelopathy. In the sensitive competitor, Thalassiosira pseudonana, allelopathic compounds ultimately caused a reshuffling of cellular nitrogen pools, altered carbon storage and impaired osmotic regulation as determined using a nuclear magnetic resonance (NMR) based metabolomics approach. By characterizing the pool of primary metabolites present in the cell after exposure to K. brevis cues, we inferred which metabolic pathways may be affected by allelopathy. For instance, concentrations of betaine and the aromatic metabolite homarine were suppressed, indicating that K. brevis allelopathy may disrupt this competitor’s ability to osmoregulate. Exposure to K. brevis cues enhanced the concentrations of glutamate and the fatty acid caprylate/caprate in T. pseudonana, suggesting that protein degradation was enhanced and that energy metabolism was altered. This contrasts with the response to K. brevis allelopathy of the diatom Asterionellopsis glacialis, which was much more resistant to chemical cues produced by K. brevis, likely through as yet unidentified detoxification pathways. Overall, my dissertation research provides insight into how species-specific, antagonistic interactions among phytoplankton competitors can affect community structure through direct or indirect mechanisms, highlights the potential role of allelopathy in the maintenance of K. brevis blooms, and uses a novel tool set (i.e., metabolomics) to determine the molecular targets of K. brevis allelopathy. It further demonstrates that planktonic communities are complex and dynamic ecological systems and that interspecific interactions between phytoplankton can have unexpected, cascading impacts in marine systems.

Thesis (MSc)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: Annual medic pastures play an important role in conservation agriculture (CA) practices in the Western Cape, because of the beneficial role it plays in rotation systems and the fact that it can re-establish on its own. In the Overberg medic pastures are the main pasture short rotation crop, but farmers in recent years shifted away from including medics. This was due to unsuccessful re-establishment and a visible decrease in dry matter production. This trend started after CA practices were implemented for a few years. A field study conducted during 2013 investigated medic re-establishment and production following a wheat, barley, oat and medic pasture production year ( WM, BM, OM and MM) of which residues were left on the soil surface at different cover percentage levels (100%, 75%, 50%, 25% and 0%). The objective of this study was to determine what the effect of different amounts of residues was on annual medic re-establishment and production. Data from this study suggest that management of annual medic pastures should aim to re-sow the medic pasture if plant count drops below 78 pants per square meter. Weed management is of cardinal importance as it competes for resources, light and space and decrease medic pasture re-establishment and production. The data also indicates that the wheat/medic sequence is the best option when applying a short cash crop/annual pasture cropping system. Producers should manage their animals to ensure that a 50% to 75% cover is left on top of the soil following the grazing of residues during the summer months. The study in 2013 should have been replicated, but due to the low levels of re-establishment and production a decision was made to re-plant the trial sites. The field study conducted during 2014 investigated the medic/clover establishment and production following a re-plant. Medics were replanted following a W, B, O and M season, respectively. Residues again were manipulated to different cover percentages (100%, 75%, 50%, 25% and 0%). The objective was again to look at the amount and type of residues on medic/clover establishment and production following re-plant. Data from this study indicated that it might be advisable for annual medic/clovers to be re-sown after a cereal production year rather than a medic pasture year. With the production of medic/clover pastures not being affected by the residue cover percentage, a 100% residue cover following re-plant is best in rotations, if the optimal effect of CA wants to be observed. If animals are included in the production cycle, grazing of residues during summer months can occur until 50% cover is left. Soils will take longer to reach its potential, but by including animals the gross margin is more stable year on year. Two supplementary studies were conducted to investigate the germination of annual medics under controlled conditions. The objectives of the first supplementary study was to investigate the physical barrier effect of residues at different percentage cover (100%, 75%, 50%, 25% and 0%) and a possible allelopathic action from different types of residues (wheat, barley, oat and medic) on the annual medic cultivar Cavalier (one of the cultivars used during 2014 field re-plant). The different amounts of residue had no significant effect on percentage emergence of Cavalier. The 0% residue cover having the slightly higher germination could be because there are no physical obstructions preventing seedlings to establish. The different types of residue cover had no significant effect on the germination of annual medics, as the germination under wheat, barley, oats and medic residues did not differ from the control. The control had a slightly higher germination percentage (85%), while germination under residues was just below the recommended germination rate of 80-85%. This could be an indication of allelopathy from residues. The objective of the second supplementary study was to investigate the allelopathic effects of different residue leachates (wheat, barley, oat and medic) at different levels of concentrations (100% leachate, 75%, 50%, 25% and distilled water being the control) on Cavalier germination. The interaction between leachate type and concentration were significant. Low levels of leachate concentration did not have a significant impact on medic germination when compared between each other and the control. When the concentration percentage was increased differences were detected. Cavalier germination decreased drastically when medic leachate concentration increased, indicating allelopathic effects. Cavalier germination followed the same trend, just not as drastic, when wheat leachate concentration increased. This indicates that wheat could also have a negative allelopathic effect. With oat leachate Cavalier germination did not decrease except when 100% concentrate was used, which could indicate a small allelopathic effect. Cavalier germination following barley leachate showed no effect as concentration increased, even showing the odd increase. Depending on repeatability or follow-up studies of these experiments, data suggest that re-plant of medic pastures is beneficial if plant count drops below sustainable levels. Management of weeds during the medic pasture year improves production. Annual medic pastures should be re-planted following a cereal production year rather than a previous pasture year. Thus single medic rotations are preferred, for example WMWM rotation. Greater amounts of residues are beneficial for CA effects, but allelopathic effects of wheat and oat residues should be taken in consideration during re-establishment and residue levels should be lowered. / AFRIKAANSE OPSOMMING: Eenjarige medic weidings speel ʼn belangrike rol in bewaring landbou (CA) praktyke in die Wes Kaap, vanweë sy vermoë om jaarliks op sy eie te hervestig en sy voordelige rol in rotasie stelsels. Eenjarige medic weidings is tans die hoof kort rotasie gewas in die Overberg, maar boere is tans besig om dit uit die rotasie uit te sluit. Dit is as gevolg van lae hervestiging sowel as die opvallende afname in produksie. Hierdie waarnemings het na ʼn paar jaar na die toepassing van CA praktyke begin. Gedurende 2013 is daar ʼn veldstudie voltooi rakende medic weiding hervestiging en produksie wat na ʼn koring, gars, hawer en medic weiding produksie jaar volg (WM, BM, OM en MM). Gedurende die studie is stoppels by verskillende persentasie vlakke van bedekking op die grond gelaat (100%, 75%, 50%, 25% en 0% bedekking). Die doel van die studie was om die invloed van verskillende tipes en hoeveelhede stoppels op die hervestiging en produksie van eenjarige medic weidings vas te stel. Data van hierdie studie dui aan dat jaarlikse medic weidings so bestuur moet word dat medics in die Overberg area se plant telling nie laer as 78 plante per vierkante meter daal nie. Onkruid bestuur is van kardinale belang, omdat dit kompeteer met medics en veroorsaak ʼn verlaging in hervestiging en opbrengs. Data dui ook aan dat ʼn koring/medic stelsel die beste opsie is wanneer ʼn kort kontant gewas/eenjarige weiding gewas stelsel toegepas word. Produsente moet hul vee so bestuur dat ʼn 50 tot 75% stoppel bedekking gedurende die somer maande oorgelaat word na beweiding. Die herhaling van die 2013 veld studie was van plan, maar ag gevolg van lae hervestiging en produksie was die proef kampe oor geplant. Die veldstudie in 2014 was medic/klawer vestiging en produksie na herplanting ondersoek. Die medic/klawer saad is geplant na ʼn koring, gars, hawer en medic weiding seisoen onderskeidelik. Stoppels is weereens na verskillende bedekking persentasies verander (100%, 75%, 50%, 25% en 0% bedekking). Die doel was om te kyk wat die effek van verskillende tipes en hoeveelhede stoppels op eenjarige medic/klawer weiding is na herplant. Data wys dat medic/klawer weidings verkieslik herplant moet word na ʼn graan produksie jaar as ʼn medic weiding produksie jaar. Die medic/klawer weiding is nie geaffekteer deur die hoeveelheid stoppels op die grond oppervlakte nie, dus is ʼn 100% stoppel bedekking verkieslik vir optimale CA effekte. As diere in die sisteem teenwoordig is, kan stoppels bewei word gedurende die somer maande tot ʼn 50% bedekking bereik word. Grond sal langer vat om sy potensiaal te bereik, maar die jaarlikse bruto marge sal meer stabiel wees. Twee aanvullende studies is onderneem en ontkieming van eenjarige medics is ondersoek onder beheerde toestande. Die doelwit van die eerste aanvullende studie was om te kyk na die fisiese versperring effek van stoppels by verskillende persentasie bedekking (100%, 75%, 50%, 25% en 0%) en ʼn moontlike allelopatiese effek van verskillende tipe stoppels (koring, gars, hawer en medic) op die eenjarige medic kultivar Cavalier. Verskillende hoeveelhede stoppels het geen beduidende uitwerking op die vestiging van Cavalier gehad nie. Die 0% stoppel bedekking het ʼn effens hoër vestiging gehad. Dit kon wees as gevolg van geen fisiese versperring wat die saailing verhoed om te vestig nie. Die verskillende tipes stoppels het geen beduidende uitwerking op die ontkieming van eenjarige medics nie, die vestiging onder koring, gars, hawer en medic stoppels het nie statisties verskil van die kontrole nie. Die kontrole het wel ʼn effense hoër persentasie vestiging gehad (85%), terwyl die vestiging onder die stoppels onder die aanbevole koers van 80-85% was. Dit kan dalk ʼn allelopatiese effek van die stoppels aandui. Die doel van die tweede aanvullende studie was om die allelopatiese effek van die verskillende tipes stoppels (koring, gars, hawer en medic) by verskillende vlakke van konsentrasie (100%, 75%, 50%, 25% van die onverdunde loogsel en gedistilleerde water as kontrole) op Cavalier ontkieming. Daar was ʼn beduidende interaksie tussen tipe en konsentrasie loogsel. Met lae konsentrasie vlakke van loogsel was daar nie ʼn werklike impak op Cavalier ontkieming tussen die verkillende tipes en die kontrole nie. Slegs wanneer die konsentrasie persentasie verhoog is, is verskille waargeneem. Cavalier ontkieming het drasties af geneem soos die medic loogsel konsentrasie toegeneem het, wat ʼn negatiewe allelopatiese en verhoogde osmolaliteit effek wys. Cavalier ontkieming het dieselfde tendens gewys wanneer koring loogsel konsentrasie verhoog was, maar nie so drasties soos medic loogsel. Dit dui daarop dat koring ook ʼn negatiewe allelopatiese effek wys. Met hawer loogsel het Cavalier ontkieming slegs by die 100% konsentrasie pyl afgeneem, wat op ʼn lae allelopatiese effek dui. Cavalier ontkieming onder gars loogsel het geen verandering gewys as konsentrasies toegeneem het nie, en het selfs ʼn toename in ontkieming in party gevalle ondergaan. Afhangend van herhaling of op-volg studies van hierdie eksperimente, wys die data dat dit voordelig is om medic weidings te herplant as plant telling onder 78 plante per vierkante meter daal. Die bestuur van onkruid tydens die medic weidings jaar verbeter opbrengs. Eenjarige medic weidings moet herplant word na ʼn graan produksie jaar liewer as ʼn vorige weidings jaar. Medics moet dus in ʼn eenjarige rotasie stelsel wees, byvoorbeeld WMWM rotasie. Meer stoppels is voordelig vir CA promosie, maar allelopatiese stowwe van koring en hawer stoppels moet in ag geneem word en stoppels moet verlaag word vir hervestiging.

Thesis (Ph. D.)--Drexel University, 2004. / Includes abstract and vita. Includes bibliographical references (leaves 106-116).

Casuarina equisetifolia L. is a noxious plant species known to be invasive in the West Indies. Not much is known about its impact on its host environment. This study’s objective was to quantitatively compare physical and chemical soil differences between sites dominated by and devoid of Casuarinas. This study also conducted growth chamber experiments to determine potential for allelopathy. It was demonstrated that sites dominated by Casuarinas differed significantly in K, P, organic matter, and leaf litter depth. Application of Casuarinas leachate showed reduction in germination of radish and bean seeds by at least 32% and 70%, respectively. Once germinated no growth suppression of seedlings were observed with applications of Casuarinas leachate. Investigation with liquid chromatography mass spectrometry (LC-MS) revealed the potential presence of the allelochemical chalepin. This research demonstrates that Casuarinas have the potential to modify their host environment and therefore perpetuate their existence as a noxious invasive species.

Resumo: A soja [Glycine max (L.) Merrill] é uma importante oleaginosa cultivada no Brasil e vem avançando em novas áreas, incluindo as de pastagens. Problemas quanto à queda de produção são relatados por sojicultores quando utilizam pastagens de Urochloa dessecada com o herbicida glyphosate e imediatamente semeiam a soja. Objetivou-se, por meio de um conjunto de experimentos, avaliar os efeitos de épocas de dessecação de U. ruziziensis (Germain & Evrard) Morr. & Zulaoga, da quantidade da cobertura morta formada e da incorporação ou deposição desta na superfície do solo, sobre a nodulação, desenvolvimento e características produtivas da soja transgênica 'M-SOY 7908 RR' no sistema de plantio direto, assim como a extração, isolamento e identificação de substâncias químicas majoritárias de U. ruziziensis com efeito alelopático e a sua possível relação com a precipitação pluvial. Inicialmente, foram conduzidos dois experimentos a campo. Em Colina (SP) foram testadas quatro épocas de dessecação da cobertura vegetal: 30, 20, 10 e 0 dias antes da semeadura (DAS) da soja, enquanto em Jaboticabal (SP) os tratamentos corresponderam a seis épocas de dessecação: 25, 20, 16, 12, 7 e 0 DAS. Nos dois anos agrícolas utilizou-se 1,44 kg e.a. ha-1 do herbicida glyphosate para a dessecação. A dessecação de U. ruziziensis no mesmo dia da semeadura da soja reduziu a altura das plantas, o número de vagens por planta e a produtividade de grãos. A época recomendada para o manejo químico de U. ruziziensis com glyphosate está entre 10 e 20 dias antes da semeadura da soja. Na sequência, foram conduzidos três experimentos sob condições semi controladas, na FCAV-UNESP. No primeiro experimento os tratamentos constituíram da incorporação ou deposição na superfície do solo de três quantidades... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Soybean (Glycine max) is an important oleaginous planted in Brazil that has been cropped in new areas, including pastures. Problems of reducing production have been reported by soybean growers when the crop is immediately sown after dissection of pastures of Urochloa spp. using glyphosate. Developing a set of experiments, the objectives were to evaluate the effects of the burndown timing of U. ruziziensis, the amont of mulch formed, and the incorporation and deposition of mulch onto soil surface on nodulation, development, and yield characteristics of transgenic soybean 'M-SOY 7908 RR cropped in no-tillage system, as well as to extract, isolate, and identify majority chemical substances from U. ruziziensis with allelopatic effect and to evaluate the possible relation between the allelopatic effect and the rainfall. Initially, two field trials were carried out. In Colina (SP), four burndown timing were tested, being 30, 20, 10, and 0 days before soybean sowing (DBS) and, in Jaboticabal (SP), burndown timing of 25, 20, 16, 12, 7, and 0 DBS was tested. In both seasons, glyphosate was applied at 1.44 kg a.e. ha-1 for U. ruziziensis dissection. Dissection of U. ruziziensis with glyphosate at the same day of soybean sowing reduced plant height, number of pods per plant, and grain yield. Recommended time for U. ruziziensis dissection is between 10 and 20 DBS. In the sequence, three experiments in semicontrolled conditions were carried out at FCAV/UNESP. In the first one, treatments constituted of the incorporation into soil or deposition onto soil surface of three mulch amounts of U. ruziziensis dissected using glyphosate. Treatments, hereafter expressed by T1, T2, and T3, corresponded to 2.5, 5.0, and 10.0 t ha-1 of mulch deposited onto soil surface, respectively, while T4, T5, and T6 corresponded to the same amounts of mulch... (Complete abstract click electronic access below) / Doutor

Lepidimoide is a naturally occurring disaccharide reported to be an oligosaccharin, i.e. to exhibit ‘hormone-like’ biological activity. It was found in cress (Lepidium sativum) root exudates and exerts apparently allelopathic effects on neighbouring Amaranthus seedlings. In the present study the effect of cress root exudates on hypocotyl and root length of Amaranthus caudatus and Lactuca sativa was studied. The seedlings of both species grown with Lepidium sativum seedlings had longer hypocotyls and shorter roots as compared to the control. In this study I found an active principle with biological effects similar to those of lepidimoide to be more abundant in cress seed-coat mucilage than in root exudates. The active principle peaked 24 hours after seed soaking, and thereafter plateaued. I also for the first time confidently proved that the bioactive compound(s) were exuded by cress and were not microbial digestion products or seed treatment chemicals. Quantitative tests of cress root exudates and cress seed-coat mucilage showed the presence of hexoses, pentoses, uronic acids and unsaturated uronic acid. The presence of unsaturated uronic acid might be of interest because the known structure of lepidimoide includes an unsaturated uronic acid. Active principle from mucilage was partitioned into the aqueous phase when shaken with ethyl acetate at pH 2, 6.5 and 12, showing it to be hydrophilic, unlike auxins and gibberellins. The mucilage was also heated at 130°C for 48 h and severe heating did not affect its biological activity, suggesting that if the compound is lepidimoide then it is heat-resistant. In an attempt to test whether the compound is of high or low Mr, the mucilage was partitioned into 75% ethanol-precipitated and non-precipitated fractions. The biological activity in the non-precipitated fraction was very high, and was further separated by gel-permeation chromatography (GPC). GPC on Bio-Gel P-10 and P-2 suggested that the active principle had Mr ~500–750, compatible with oligosaccharide(s), suggesting that a particular oligosaccharide may be the active principle. TLC separation of bioactive fractions from P-2 showed that the bioactive compound migrated between GalA and Gal but co-migrated with sucrose; however, paper chromatography separation proved that the compound is not sucrose and might be a different disaccharide (lepidimoide). From the structure of lepidimoide, Fry et al. (1993) proposed that lepidimoide is formed by the lyase-catalysed cleavage of a pectic polysaccharide, rhamnogalacturonan-I (RG-I). So I tried to prepare lepidimoide or lepidimoide-like compounds by the action of RG-I lyase from Pichia pastoris on purified potato RG-I. The lyase showed its activity but the digest did not demonstrate biological activity, which might be due to presence of tris-HCl buffer in the solution. An attempt was also made to prepare lepidimoide by methyl esterification and -elimination of purified potato RG-I but again the product did not show any biological activity, which might be due to presence of borate buffer in the solution. This part of research might be useful for future work on preparation of lepidimoide and lepidimoide-like compounds.

The purposes of this study were to determine if Rhododendron macrophyllum has the potential to inhibit the growth of other species through the production of water-soluble toxins which are leached out of its litter by rainfall, and to determine if this potential is realized in the field. The study was therefore composed of two part: 1) a series of bioassays to determine the presence an activity of water-soluble phytotoxins in R. macrophyllum leaf litter, and 2) a field study to describe vegetational patterns associated with R. macrophyllum in a western Cascades clearcut.

Harmful algal blooms' global amplification has driven research on growth characteristics and instigating mechanisms. These blooms prosper under diverse environmental conditions, creating challenges identifying bloom initiation. The haptophyte, Prymnesium parvum, plagues the southwestern United States with massive system disruptions and huge fish kills caused by its toxin. Despite many abiotic factors' association with P. parvum blooms, low nutrient levels stress the alga increasing toxin production, eliminating nutrient competition, and alleviating grazing pressures. This model examines the relationship between nutrient availability and P. parvum toxin production against another phytoplankton and a single grazing zooplankton, using a Monod function relating population growth rate with limiting nutrient concentrations. Sensitivity analyses emphasize plankton biological parameters most influential in accumulating biomass. The impact of toxin production on zooplankton grazing rates underscores P. parvum's need for top-down control suppression. The toxin production equation increases production when P. parvum experiences low specific growth rates from nutrient availability and low biomass. This equation is analyzed against previously published allelopathic relationships, comparing plankton reactions and bloom endurance. The model's toxin production equation proves more ecologically feasible, incorporating competing phytoplankton species' mortality and variables easily verified through laboratory experiments. Though not intended for management strategy development, the model explores and supports the proposed strategy of incorporating hydraulic flushing, pulsed and continuous inflows, to eliminate biomass accumulation. Inflows relieve stressful nutrient-limiting conditions, introducing resources affecting bloom stability and plankton community dynamics. The faster-growing competing phytoplankton gains survival advantages when inflow rates fall lower than its maximum specific growth rate, but greater than P. Parvum's, emphasizing the accurate measuring of competitors' maximum specific growth rates and identifying a dilution rate range where P. parvum loses at nutrient intake. Inflows with various nutrient levels representing different source waters from freshwater lakes were tested for impacts on plankton dynamics. Adding any hydrological effect reduced P. parvum biomass. Disruptions create disturbance, removing P. parvum's system-dominating position, allowing the phytoplankton to exceed P. parvum's density. The model highlights the importance of P. parvum's toxin's presence to maintain dominance and emphasizes flushing agitation as potential and feasible management schemes to deter bloom continuation and increase species diversity.

Made available in DSpace on 2014-06-11T19:33:40Z (GMT). No. of bitstreams: 0 Previous issue date: 2011-03-25Bitstream added on 2014-06-13T19:44:37Z : No. of bitstreams: 1 nepomuceno_mp_dr_jabo.pdf: 1277830 bytes, checksum: e1f6fbc84f1437cd0f07462d57343d7e (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / A soja [Glycine max (L.) Merrill] é uma importante oleaginosa cultivada no Brasil e vem avançando em novas áreas, incluindo as de pastagens. Problemas quanto à queda de produção são relatados por sojicultores quando utilizam pastagens de Urochloa dessecada com o herbicida glyphosate e imediatamente semeiam a soja. Objetivou-se, por meio de um conjunto de experimentos, avaliar os efeitos de épocas de dessecação de U. ruziziensis (Germain & Evrard) Morr. & Zulaoga, da quantidade da cobertura morta formada e da incorporação ou deposição desta na superfície do solo, sobre a nodulação, desenvolvimento e características produtivas da soja transgênica ‘M-SOY 7908 RR’ no sistema de plantio direto, assim como a extração, isolamento e identificação de substâncias químicas majoritárias de U. ruziziensis com efeito alelopático e a sua possível relação com a precipitação pluvial. Inicialmente, foram conduzidos dois experimentos a campo. Em Colina (SP) foram testadas quatro épocas de dessecação da cobertura vegetal: 30, 20, 10 e 0 dias antes da semeadura (DAS) da soja, enquanto em Jaboticabal (SP) os tratamentos corresponderam a seis épocas de dessecação: 25, 20, 16, 12, 7 e 0 DAS. Nos dois anos agrícolas utilizou-se 1,44 kg e.a. ha-1 do herbicida glyphosate para a dessecação. A dessecação de U. ruziziensis no mesmo dia da semeadura da soja reduziu a altura das plantas, o número de vagens por planta e a produtividade de grãos. A época recomendada para o manejo químico de U. ruziziensis com glyphosate está entre 10 e 20 dias antes da semeadura da soja. Na sequência, foram conduzidos três experimentos sob condições semi controladas, na FCAV-UNESP. No primeiro experimento os tratamentos constituíram da incorporação ou deposição na superfície do solo de três quantidades... / Soybean (Glycine max) is an important oleaginous planted in Brazil that has been cropped in new areas, including pastures. Problems of reducing production have been reported by soybean growers when the crop is immediately sown after dissection of pastures of Urochloa spp. using glyphosate. Developing a set of experiments, the objectives were to evaluate the effects of the burndown timing of U. ruziziensis, the amont of mulch formed, and the incorporation and deposition of mulch onto soil surface on nodulation, development, and yield characteristics of transgenic soybean ‘M-SOY 7908 RR cropped in no-tillage system, as well as to extract, isolate, and identify majority chemical substances from U. ruziziensis with allelopatic effect and to evaluate the possible relation between the allelopatic effect and the rainfall. Initially, two field trials were carried out. In Colina (SP), four burndown timing were tested, being 30, 20, 10, and 0 days before soybean sowing (DBS) and, in Jaboticabal (SP), burndown timing of 25, 20, 16, 12, 7, and 0 DBS was tested. In both seasons, glyphosate was applied at 1.44 kg a.e. ha-1 for U. ruziziensis dissection. Dissection of U. ruziziensis with glyphosate at the same day of soybean sowing reduced plant height, number of pods per plant, and grain yield. Recommended time for U. ruziziensis dissection is between 10 and 20 DBS. In the sequence, three experiments in semicontrolled conditions were carried out at FCAV/UNESP. In the first one, treatments constituted of the incorporation into soil or deposition onto soil surface of three mulch amounts of U. ruziziensis dissected using glyphosate. Treatments, hereafter expressed by T1, T2, and T3, corresponded to 2.5, 5.0, and 10.0 t ha-1 of mulch deposited onto soil surface, respectively, while T4, T5, and T6 corresponded to the same amounts of mulch... (Complete abstract click electronic access below)