Germani Concenço

Phytosociological surveys: tools for weed science?

In simple terms, a phytosociological survey is a group of ecological evaluation methods whose aim is to provide a comprehensive overview of both the composition and distribution of plant species in a given plant community. To understand the applicability of phytosociological surveys for weed science, as well as their validity, their ecological basis should be understood and the most suitable ones need to be chosen, because cultivated fields present a relatively distinct group of selecting factors when compared to natural plant communities. For weed science, the following sequence of steps is proposed as the most suitable: (1) overall infestation; (2) phytosociological tables/graphs; (3) intra-characterization by diversity; (4) inter-characterization and grouping by cluster analysis. A summary of methods is established in order to assist Weed Science researchers through their steps into the realm of phytosociology.

Competitive ability of barley cultivars against ryegrass

Characterization of the competitive ability of barley varieties against weed species is relevant for the adoption of the cultural method of weed control; thus, it is possible to reduce both the production costs and environmental impacts caused by other management methods, including the use of chemicals. This work assessed the competitive ability of barley varieties against ryegrass. Trials were installed under greenhouse conditions at the 2008/2009 cropping season, in a completely randomized block design, with four replications. Treatments were arranged in a substitution series design constituted by five proportions of plants of both species: 100:0; 75:25; 50:50; 25:75; and 0:100. Barley varieties BRS Greta, BRS Elis and BRS 225 were tested against ryegrass as the competitor. The competitive analysis was carried out through diagrams applied to the substitutive design, plus determination of relative competitiveness indexes. Plant height, tillering, leaf area and shoot dry mass were evaluated. The presence of ryegrass reduced tillering, leaf area and dry mass accumulation for all varieties of barley tested, showing to be an aggressive competitor. Among the barley varieties tested, BRS Elis showed the highest competitive ability against ryegrass. Ryegrass requires the adoption of control techniques even when present at low proportions in the field.Characterization of the competitive ability of barley varieties against weed species is relevant for the adoption of the cultural method of weed control; thus, it is possible to reduce both the production costs and environmental impacts caused by other management methods, including the use of chemicals. This work assessed the competitive ability of barley varieties against ryegrass. Trials were installed under greenhouse conditions at the 2008/2009 cropping season, in a completely randomized block design, with four replications. Treatments were arranged in a substitution series design constituted by five proportions of plants of both species: 100:0; 75:25; 50:50; 25:75; and 0:100. Barley varieties BRS Greta, BRS Elis and BRS 225 were tested against ryegrass as the competitor. The competitive analysis was carried out through diagrams applied to the substitutive design, plus determination of relative competitiveness indexes. Plant height, tillering, leaf area and shoot dry mass were evaluated. The presence of ryegrass reduced tillering, leaf area and dry mass accumulation for all varieties of barley tested, showing to be an aggressive competitor. Among the barley varieties tested, BRS Elis showed the highest competitive ability against ryegrass. Ryegrass requires the adoption of control techniques even when present at low proportions in the field.

MANAGEMENT OF RED RICE (ORYZA SATIVA )A ND BARNYARDGRASS (ECHINOCHLOA CRUS-GALLI )G ROWN WITH SORGHUM WITH REDUCED RATE OF ATRAZINE AND MECHANICAL METHODS

SUMMARY The weedy variety of Oryza sativa occurs in several rice cultivation areas reducing both grain yield and quality. Prevention and crop rotation are considered the basic means to reduce its presence. Weed control in sorghum is generally attained with atrazine. In this study, the efficacy of both chemical and mechanical methods for control, under different soil tillage conditions, of weedy rice and barnyardgrass during sorghum cultivation was evaluated with the aim to reduce the application rate of atrazine. In the case of chemical control, the atrazine rate (1000, 1500, 2000, 2500 and 3000 ga.i. ha –1 ) and application timing (pre- and post-emergence) were assessed. With the mechanical control method, the number of interventions (interrow hoeing with sorghum at 3, 4–5 and 6–8 leaves) to avoid weed competition was determined. The effect of the tillage system on weed population was investigated comparing conventional (ploughing), minimumtillage (disc harrowing) and sod seeding (no-tillage) in combination with pre- and post-emergence herbicide treatments. The results showed that efficient control of weedy rice and barnyardgrass was achieved in lowlands with sorghum in rotation with rice. Both chemical and mechanical methods of weed control in sorghum gave a level of efficiency higher than 60%. The application of atrazine was more efficient in pre-emergence application, rather than in post-emergence treatments, in all soil tillage systems tested. On both weed species, the most suitable application rate was the pre-emergence treatment with 1500 ga.i. ha –1 , and the adoption of higher rates did not significantly increase the herbicidal efficacy. The adoption of two or three mechanical interventions resulted in sorghum yield higher than the chemical post-emergence application, and similar to the application of atrazine in pre-emergence. Higher yield results were in accordance to greater weed control, being obtained in the conventional tillage system.

Determination of paraquat and diquat: LC-MS method optimization and validation.

This study describes the optimization and single-laboratory validation of a single residue method for determination of two bipyridylium herbicides, paraquat and diquat, in cowpeas by UPLC-MS/MS in a total run time of 9.3min. The method is based on extraction with an acidified methanol-water mixture. Different extraction parameters (extraction solvent composition, temperature, sample extract filtration, and pre-treatment of the laboratory sample) were evaluated in order to optimize the extraction method efficiency. Isotopically labeled internal standards, Paraquat-D6 and Diquat-D4, were used and added to the test portions prior to extraction. The method validation was performed by analyzing spiked samples at three concentrations (10, 20 and 50μgkg(-1)), with seven replicates (n=7) for each concentration. Linearity (r(2)) of analytical curves, accuracy (trueness as recovery % and precision as RSD%), instrument and method limits of detection and quantification (LOD and LOQ) and matrix effects were determined. Average recoveries obtained for diquat were between 77 and 85% with RSD values ⩽20%, for all spike levels studied. On the other hand, paraquat showed average recoveries between 68 and 103% with RSDs in the range 14.4-25.4%. The method LOQ was 10 and 20μgkg(-1) for diquat and paraquat, respectively. The matrix effect was significant for both pesticides. Consequently, matrix-matched calibration standards and using isotopically labeled (IL) analogues as internal standards for the target analytes are required for application in routine analysis. The validated method was successfully applied for cowpea samples obtained from various field studies.

Effect of long-term agricultural management systems on occurrence and composition of weed species

Objetivou-se com este estudo avaliar a composicao de comunidades infestantes em funcao de distintos fatores de selecao, em areas vizinhas submetidas a distintos manejos de solo e usos por 16 anos. Quatro areas submetidas a manejos distintos (sistema de cultivo convencional, sistema plantio direto, integracao lavoura/pecuaria e pecuaria continua) foram amostradas em relacao a ocorrencia e severidade de especies de plantas daninhas no inicio da estacao de cultivo, sendo estimadas a abundância relativa, frequencia relativa e dominância relativa de cada especie daninha em cada area, bem como o Indice de Valor de Importância para cada especie. As areas tambem foram comparadas pelo coeficiente de similaridade de Sorensen. Areas onde forragens e pastejo nao estao inseridas na rotacao apresentaram numero de plântulas de especies daninhas 250% superior em relacao a areas periodicamente ou continuamente sob pastejo, enquanto a area de solo coberta pela comunidade de plantas infestantes foi 87% superior no tratamento com preparo convencional do solo, em relacao a media dos demais tratamentos. Plantas daninhas de folhas estreitas foram predominantes na area de preparo convencional do solo enquanto folhas largas predominaram na area de plantio direto, provavelmente devido tambem a fatores de selecao relativos ao herbicida. Na area de integracao lavoura/pecuaria pode haver a necessidade de controle de plântulas da especie semeada como forrageira durante o cultivo em sucessao a pastagem.

Phytosociology in agricultural areas submitted to distinct wintercropping management

Studies related to weed dynamics are essential for agricultural sustainability in tropical soils, as their interference can cause significant yield losses, especially in crops with lower competitive ability. This study aimed to assess the composition of weed communities in the third cropping season in areas submitted to distinct wintercroppings for two consecutive years. Evaluations were made in terms of species composition, level of infestation, and severity of occurrence of each weed species in relation to the others within the same area. The wintercropping management systems were: (1) Brachiaria ruziziensis; (2) corn intercropped with B. ruziziensis; (3) corn and (4) cowpea. Plant communities under these wintercrop systems were evaluated in the third year in terms of relative frequency, relative dominance, relative abundance and importance index for each species. Areas were also compared in terms of species composition by the Sorensens similarity coefficient. Two years of distinct wintercrop managements were not enough to cause a significant shift in terms of weed composition and severity in a given area. There is also evidence that some weed species are more favored by specific crops, although the causes of this selective behavior are not fully explored in this article. The presence of B. ruziziensis, either alone or intercropped with corn, resulted in lower similarity coefficients when compared to areas where this species was not present. It is suggested that several mechanisms briefly discussed may be involved in the impact of the presence of B. ruziziensis on the weed community.

Physiology of Crops and Weeds Under Biotic and Abiotic Stresses

The application of knowledge with strong physiological basis of crop yield, allied to genetic and environmental factors, is essential in developing proper practices for crop management aiming high yields (Floss, 2008). Several aspects determine the performance of a particular crop plant in a given environment, such as temperature, water availability, incidence of pests, plant genetics and management applied. Although it is virtually impossible to control all these factors, plant behavior can be assessed when submitted to different levels of these factors to understand how the responses of the plant to that given stress are formed (Radosevich et al., 2007; Gurevitch et al., 2009). Population growth leads to an increasing demand for food, fibers and energy, and requires both expansion of the area for crops as well as higher crop yields. In both cases, one of the limiting factors is the occurrence of weed species. The high cost of human labor led farmers to choose weed control practices which allow reduction of the production costs (Silva et al., 2007). In the past, chemical management was used as the only method of weed control, but several problems led to the development of cultural methods as effective tools for lasting and low cost weed management. More recently the physiology and ecology of crops and weed species gained increasing importance in the development of methods of weed control (Radosevich et al., 2007; Gurevitch et al., 2009). Several studies of competition between crops and weed species were conducted and the results of these studies are being applied at planning of integrated management practices such as crop rotation, succession, crop-livestock integration and winter crops as tools for suppressing weed occurrence (Severino, 2005; Ceccon, 2007). Most of these studies allow modeling the dynamics of weeds infestation in certain crops and optimizing the system as a whole, based in dry mass accumulation, plants height, number of tillers or branches, number of inflorescences and other directly measured variables (Galon et al., 2007; Fleck et al., 2008; Bianchi et al., 2010).

Soil seed bank of plant species as a function of long-term soil management and sampled depth

This study aimed at assessing the level of weed infestation indifferent areas that were submitted to different soil management for 16 years. Four management systems were studied: (1) agriculture only under conventional tillage system; (2) agriculture only under no-till system; (3) crop-livestock integrationcrop-livestock integration; (4) livestock only. These areas were sampled at three soil depths (0-5, 5-10 and 10-15 cm), and soil was stored in plastic pots and taken to a greenhouse, where soil moisture and weight were standardized. Soil was kept near 70% moisture field capacity, being revolved every 20 days when all seedling emerged from soil were counted, identified and collected for dry mass assessment. The soil coverage by weeds, number of weed seedlings and dry mass of the weedy community were assessed. A phytoecological analysis was conducted. Weed composition is differentdifferent among management systems after 16 years. Areas with livestock showed much smaller number of weed species in comparison to systems where only grain crops are grown. The presence of livestock affects the potential of germination of soil seed bank. Agriculture systems are similar in terms of weed composition along soil profile, while systems involving livestock show little relation in what regards such sampled depths. Conservationist models of land exploration contribute to reduce severity of weed species occurrence in the long term.

Potential of plant species for bioremediation of soils applied with imidazolinone herbicides

Imidazolinone herbicides present physicochemical characteristics that allow them to persist longer in environment, with increased chances of soil and water contamination, as well as carryover effects on subsequent crops. Phytoremediation is shown as a promising technique to decontaminate soils polluted by herbicides. The aim of this study was to assess the potential of some winter grown species in removing residuals from soils contaminated with imazethapyr + imazapic and imazapic + imazapyr, using pre-emergence to control weeds in summer grown rice fields. The experiment was conducted in a completely randomized design, with four replications. All species were subjected to herbicide application at different doses. Imazethapyr + imazapic and imazapyr + imazapic were applied at doses of 0.0, 1.0 and 2.0 L ha-1, and 0.0, 140 and 280 g ha-1, respectively, in pre-emergence of the species. Brassica napus and Festuca arundinaceae are not tolerant to herbicides, with 100% of phytotoxicity (plant death) for all doses assessed. The herbicide imazapyr + imazapic proved to be less selective, causing the highest phytotoxicity in the species tested. The most tolerant species to the herbicides was Vicia sativa, which may be the most suitable one for phytoremediation programs in areas contaminated with imazethapyr + imazapic and imazapyr + imazapic.

Influence of Biotic and Abiotic Stress Factors on Physiological Traits of Sugarcane Varieties

The application of knowledge with strong physiological basis of crop yield, allied to genetic and environmental factors, is essential in developing proper practices for crop management aiming high yields. Several aspects determine the performance of a particular crop plant in a given environment, such as temperature, water availability, incidence of pests, plant genetics and management applied. Although it is virtually impossible to control all these factors, plant behavior can be assessed when submitted to different levels of these factors to understand how the responses of the plant to that given stress are formed [1; 2].