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To thrive as a successful weed in natural pastures, a plant must have not only highly competitive ability, but also the resilience to endure environmental stress and rapidly reclaim space once those stressors diminish and the other non-stress-tolerant plants die. Acanthostyles buniifolius [(Hook. ex Hook. & Arn.) R.M.King & H.Rob.], known as chirca, is a widely spread weed in South American natural pastures. It is known for its remarkable ability to withstand environmental stress and flourish in environments with prevalent stressors. The study evaluated the memory effect of water stress (drought) in chirca plants. The experiment was conducted in a greenhouse in a randomized block design with three replications. Treatments included Control = control plants without water deficit kept at 100% of the soil water-holding capacity (WHC); Primed plants = plants that were primed with water stress at 141 days after emergence (DAE) and received recurrent stress at 164 DAE; Naïve plants: plants that only experienced water stress at 164 DAE. To reach water stress, plants were not watered until the soil reached 15% of the soil’s WHC, which occurred ten days after water suppression in the priming stress and nine days after water suppression in the second stress. During periods without restriction, the pots were watered daily at 100% of the WHC. Primed plants exposed to water deficit better-maintained water status compared to the naïve plants; glycine betaine is an important defense mechanism against water deficit in chirca; naïve plants have a higher concentration of proline than plants under recurrent stress, demonstrating the greater need for protection against oxidative damage and needs greater osmotic regulation. Recurrent water deficits can prepare chirca plants for future drought events. These results show that chirca is a very adaptative weed and may become a greater threat to pastures in South America due to climate change, especially if drought becomes more frequent and severe.

Minimum tillage in rice production is increasing in southern Brazil, reaching 60% of the total planted area. Compared to conventional tillage, in this system there is an increase in the occurrence of perennial weeds, such as Luziola peruviana and Leersia hexandra, which are amphibious plants, as they can occur in both flooded environments and aerobic conditions. These weeds are controlled in burn-down before rice planting by glyphosate applications, the efficacy of which depends on the soil moisture. This study aimed to evaluate the effect of different soil moisture regimes in L. hexandra and L. peruviana growth and photoassimilate partitioning. Both species were assessed under soil moisture regimes of flooded, saturated, 7 kPa, 15 kPa, 40 kPa, and 100 kPa (experiment 1) and flooded, saturated, and 7 kPa (experiment 2). Plants were sampled immediately after drainage (3 months after transplant) and 1 and 2 weeks after drainage. The results showed that as soil moisture levels decreased, growth and development parameters were negatively affected in both species. Photoassimilate partitioning was affected by water regime and differences were observed between species. The total soluble sugars and starch content decreased in the leaves, and sucrose concentration increased in the roots following drainage. Soil drainage affects the growth and alters carbohydrate partitioning of these weeds, increasing the sugar storage in roots. The agronomic impact of these findings is that this behavior may affect herbicide transport in phloem and may affect herbicide efficacy.

(1) Background: Eragrostis plana Ness is a invasive C4 perennial grass in South America and very adaptable to environmental stresses. Our hypothesis is that there is a transgenerational cross-talk between environmental stresses and weed response to herbicides. This study’s objectives were to: (1) evaluate if E. plana primed by drought stress (DRY), a sub-lethal dose of quizalofop-p-ethyl (QPE), or a combination of both drought and herbicide stresses (DRY × QPE), produce a progeny with decreased sensitivity to quizalofop and (2) investigate the potential mechanisms involved in this adaptation; (2) Methods: A population of E. plana was isolatedly submitted to treatments for drought, quizalofop or drought plus quizalofop for two generations. The progenies were analyzed for sensitivity to the herbicide quizalofop and performed biochemical, chromatographic and molecular analyses.; (3) Results: In the G2 generation, the quizalofop-treated CHK population had reduced stomatal conductance and increased hydrogen peroxide and lipid peroxidation. On the other hand, there was no change in stomatal conductance, hydrogen peroxide level, and lipid peroxidation in the quizalofop-treated DRY population. In addition, this population had increased antioxidant enzyme activity and upregulated CYP72A31 and CYP81A12 expression, which was accompanied by reduced quizalofop-p-ethyl concentrations; (4) Conclusions: E. plana demonstrated a capacity for transgenerational adaptation to abiotic stresses, with the population exposed to drought stress (DRY) becoming less sensitive to quizalofop-p-ethyl treatment.

Florpyrauxifen-benzyl (FPB) is a new class of auxinic herbicide developed for selective weed control in rice. This study aimed to evaluate the effect of environmental conditions, P450 inhibitors, rice cultivar response, and gene expression on FPB selectivity in rice. Field experiments established in a randomized block design showed that rice plant injury due to two FPB rates (30 and 60 g ai ha−1) was affected by planting time and rice stage at herbicide application. The injury was higher at the earliest planting season and more in younger plants (V2) than larger (V6 and R0). However, no yield reduction was detected. Under greenhouse conditions, two dose-response experiments in a randomized block design showed that spraying malathion (1 kg ha−1) before FPB application did not reduce herbicide selectivity. The addition of two P450 inhibitors (dietholate and piperonyl butoxide, 10 g a.i. seed-kg−1 and 4.2 kg ai ha−1, respectively) decreased the doses to cause 50% of plant injury (ED50) and growth reduction (GR50). However, it seems not to compromise crop selectivity. BRS Pampeira cultivar showed lower ED50 and GR50 than IRGA 424 RI. A growth chamber experiment was conducted in a completely randomized design to evaluate the gene expression of rice plants sprayed with FPB (30 and 60 g ai ha−1). Results showed downregulation of OsWAKL21.2, an esterase probably related to bio-activation of FPB-ester. However, no effect was detected on CYP71A21 monooxygenase and OsGSTL transferase, enzymes probably related to FPB degradation. Further research should focus on understanding FBP bio-activation as the selective mechanism.

Changes in the environment, specifically rising temperature and increasing atmospheric carbon dioxide concentration [CO2], can alter the growth and physiology of weedy plants. These changes could alter herbicide efficacy, crop-weed interaction, and weed management. The objectives of this research were to quantify the effects of increased atmospheric [CO2] and temperature on absorption, translocation and efficacy of cyhalofop-butyl on multiple-resistant (MR) and susceptible (S) Echinochloa colona genotypes. E. colona, or junglerice, is a troublesome weed in rice and in agronomic and horticultural crops worldwide. Cyhalofop-butyl is a grass herbicide that selectively controls Echinochloa spp. in rice. Maximum 14C-cyhalofop-butyl absorption occurred at 120 h after herbicide treatment (HAT) with >97% of cyhalofop-butyl retained in the treated leaf regardless of [CO2], temperature, or genotype. Neither temperature nor [CO2] affected herbicide absorption into the leaf. The translocation of herbicide was slightly reduced in the MR plants vs. S plants either under elevated [CO2] or high temperature. Although plants grown under high [CO2] or high temperature were taller than those in ambient conditions, neither high [CO2] nor high temperature reduced the herbicide efficacy on susceptible plants. However, herbicide efficacy was reduced on MR plants grown under high [CO2] or high temperature about 50% compared to MR plants at ambient conditions. High [CO2] and high temperature increased the resistance level of MR E. colona to cyhalofop-butyl. To mitigate rapid resistance evolution under a changing climate, weed management practitioners must implement measures to reduce the herbicide selection pressure. These measures include reduction of weed population size through reduction of the soil seedbank, ensuring complete control of current infestations with multiple herbicide modes of action in mixture and in sequence, augmenting herbicides with mechanical control where possible, rotation with weed-competitive crops, use of weed-competitive cultivars, use of weed-suppressive cover crops, and other practices recommended for integrated weed management.

(1) Background: Elevated atmospheric CO2 concentration affects the growth and development of the rice crop. In Southern Brazil, rice is traditionally produced with continuous irrigation, implying a significant amount of water used. Besides, continuous flooding favors the uptake of toxic elements such as arsenic (As) and cadmium (Cd). In this work, one Brazilian rice cultivar (IRGA 424) was tested for the effects of elevated CO2 concentration and different water regimes on rice yield, and As and Cd accumulation in grain. (2) Methods: Rice was grown in two CO2 concentrations (400 and 700 µmol mol−1) and two irrigation regimes (continuous and intermittent). It was evaluated the number of tillers, plant height, aboveground dry weight (ADW), water use efficiency (WUE), rice yield components, and As and Cd concentration in rice grain. (3) Results: Rice plants were taller and had a higher WUE when cultivated at e[CO2]. The ADW and the rice yield component were not affected by CO2 levels nor water regimes. Intermittent flood regimes had a lower average As concentration. The Cd concentration in the samples in both growing seasons and all treatments was below the limit of quantitation (8.76 μg kg−1). (4) Conclusions: Enhanced CO2 concentration did not affect rice yield, increased the WUE, and reduced As concentration in grains. Regarding water management, the intermittent regime enhanced WUE and promoted a reduction in As concentration in grains.

ABSTRACT: Despite all advances obtained with the pesticide use worldwide and in Brazilian agriculture, there is still a lack of technologies for agricultural aircrafts. The objective of this study was to evaluate the drift produced by the use of conical nozzles and electrostatic system in aircraft application. The experimental design was completely randomized with a factorial arrangement and four replications. Treatments included two spraying equipment: electrostatic system with 5L ha-1 of spray volume and conical nozzle with 15 and 20L ha-1. In all treatments, azoxystrobin fungicide was used at a dose of 100g a.i. ha-1 and paraffinic mineral oil at a dose of 0.5% v.v. Volume median diameter (VMD) and droplet density were estimated using water sensitive paper. Evaluations of drift distance were performed with glass collectors distributed horizontally on the soil surface, 50m before the application band, at the application site and 12,5, 25, 50, 75, 100, 150, 200 and 300m after the application site, along the wind direction. Azoxystrobin concentration in glasses were quantified by UHPLC-MS/MS. Results indicated that the drift distance can reach more than 300 meters away from the application site, with variable concentrations according to the equipment used. Electrostatic system reduced drift when compared to hydraulic conical nozzles.

(1) Background: The Clearfield™ system (CL) is currently the primary tool for selective weedy-rice management in irrigated rice. However, herbicide persistence in the soil may cause damage to successive crops. Thus, it is necessary to understand agricultural practices that can favor the dissipation of these herbicides. The objective of this study was to analyze the factors that affect the persistence of imidazolinones and to use this information to provide management strategies to mitigate carryover in lowland rice. (2) Methods: A literature review was performed, and the publications were selected using the soil half-life parameter. The data were summarized according to the biotic conditions, soil parameters, and environmental variables. (3) Results: Imidazolinone dissipation in soil occurs primarily through biodegradation. The herbicide biodegradation rate depends on environmental conditions such as temperature and bioavailability of the herbicide in the soil. Herbicide bioavailability is affected by soil conditions, with higher bioavailability in soil with higher pH, less clayey texture, moderate organic matter content, and higher soil moisture levels. Therefore, environmental conditions that favor biological activity, especially high temperatures, reduce the herbicide half-life in the soil. Strategies to mitigate carryover should focus on improving herbicide availability and enhancing biological activity in the soil, especially in the rice off-season, when low temperatures limit herbicide biodegradation. Cover and rotational crops, such as ryegrass and soybean, are recommended, with the potential to mitigate soil residues. (4) Conclusions: The establishment of crops other than rice would automatically enhance degradation rates as soil amendment practices such as pH correction and drainage practices would favor soil availability and biological activity.

Weeds represent an increasing challenge for crop systems since they have evolved adaptability to adverse environmental conditions, such as salinity stress. Herbicide effectiveness can be altered by the quality of water in which the weed is growing. This research aimed to study the combined effect of salt stress and recurrent selection with a sublethal dose of imidazolinone herbicides in the shifting of the sensitivity of Echinochloa colona (L.) Link (junglerice) to imidazolinone herbicides. This study was divided into two experiments; in experiment I, three recurrent selection cycles were conducted in Pelotas/RS/Brazil with imazapic + imazapyr at 0.125× the field rate; and in experiment II, three recurrent selection cycles were conducted in Fayetteville/AR/USA with imazethapyr, at 0.125× the recommended dose. Salt stress was implemented by irrigation with 120 mM sodium chloride (NaCl) solution. The effective dose for 50% control of the population (ED50) values increased from the field population to the second generation (G2) after recurrent selection with a sublethal dose of imidazolinone combined with salt stress, supporting the hypothesis of reduced susceptibility by the combination of these abiotic factors. Recurrent exposure to a sublethal dose of imazapic + imazapyr or imazethapyr, combined with salt stress, reduced susceptibility of Echinochloa colona (L.) plants to imidazolinone herbicides.

Global climate change, specifically rising temperature, can alter the molecular physiology of weedy plants. These changes affect herbicide efficacy and weed management. This research aimed to investigate the combined effect of heat stress (HS) and sublethal doses of herbicides (four active ingredients) on adaptive gene expression and efficacy of herbicide on Echinochloa colona (L.) Link (junglerice). Three factors were evaluated; factor A was E. colona generation (G0-original population from susceptible standard; G1 and G2 were progenies of recurrent selection), factor B was herbicide treatment (florpyrauxifen-benzyl, glufosinate-ammonium, imazethapyr, quinclorac and nontreated check) and factor C was HS (30 and 45 °C). The herbicides were applied at 0.125× the recommended dose. Recurrent exposure to HS, combined with sublethal doses of herbicides, favors the selection of plants less susceptible to the herbicide. Upregulation of defense (antioxidant) genes (APX: Ascorbate peroxidase), herbicide detoxification genes (CYP450 family: Cytochrome P450), stress acclimation genes (HSP: Heat shock protein, TPP: Trehalose phosphate phosphatase and TPS: Trehalose phosphate synthase) and genes related to herbicide conjugation (UGT: UDP Glucosyltransferase) was significant. The positive regulation of these genes may promote increased tolerance of E. colona to these herbicides.

Echinochloa colona (junglerice) is a problematic global weed for many crops, primarily controlled with herbicides. Drought stress alters the overall plant physiology and reduces herbicide efficacy. This research aimed to study the joint effect of drought stress (DS) and recurrent selection with sublethal dose of herbicide on adaptive gene expression and herbicide efficacy on E. colona. Three factors were evaluated: (A) E. colona generation (G0, original population from susceptible standard; G1 and G2, progenies of recurrent selection); (B) herbicide treatment (florpyrauxifen-benzyl, 0.25×; glyphosate, 0.125×; quinclorac, 0.125× the recommended dose; and nontreated check); (C) DS (50% and 100% field capacity). Recurrent exposure to sublethal herbicide dose, combined with drought stress, favors the selection of plants less susceptible to the herbicide. Upregulation of defense (antioxidant) genes (APX: ascorbate peroxidase), herbicide detoxification genes (CYP450 family: cytochrome P450), stress acclimation genes (HSP: heat-shock protein, TPP: trehalose phosphate phosphatase, and TPS: trehalose phosphate synthase), and genes related to herbicide conjugation (UGT: UDP glucosyltransferase) in the G2 population was significant. Recurrent exposure to sublethal herbicide dose under drought stress reduces junglerice sensitivity to herbicide, seemingly due to “imprinted” upregulation of metabolic and protection genes in response to these stresses.

O clorofilômetro e a cartela de cores têm sido utilizados para monitorar a adubação nitrogenada em diferentes culturas, com o pressuposto de que há uma relação entre suas leituras e o teor de nitrogênio (N) no tecido das plantas. O objetivo deste trabalho foi avaliar a utilização do clorofilômetro e da cartela de cores na estimativa do teor de N em folhas de arroz irrigado por alagamento. Foram utilizados dois experimentos instalados em um Planossolo Háplico, sendo o primeiro conduzido com cinco doses de N (0, 50, 80, 120 e 160kg ha-1 na forma de ureia) e a cultivar 'IRGA 417', e o segundo com seis cultivares de arroz irrigado de diferentes ciclos ('BR-IRGA 409', 'BR-IRGA 410', 'IRGA 417', 'IRGA 421', 'EPAGRI 108' e 'HÍBRIDO 2') com uma única dose de N. Foram realizadas avaliações com clorofilômetro e a cartela de cores nas folhas do arroz em diferentes épocas. Simultaneamente às leituras, foram coletadas amostras de folhas e nelas determinado o teor de N. Quando variaram as doses de N, houve correlação significativa entre as leituras do clorofilômetro e da cartela de cores com o teor de N nas folhas, independente da época de avaliação. Já quando variaram as cultivares, as leituras do clorofilômetro se correlacionaram com o teor de N (r=0,78; PThe chlorophyll meter and the color chart have been applied to monitor nitrogen fertilization in different crops, based on the assumption that there is a correlation between their readings and the nitrogen content (N) in the plant tissue. This research aims at assessing the use of the chlorophyll meter and the color chart to estimate the N content in leaves of flooded rice plants. Two experiments installed at a Albaqualf (Planossolo Háplico) were used, the first using five N doses (0, 50, 80, 120 and 160kg ha-1 as urea) and the cultivar 'IRGA 417', and the second with six flooded rice cultivars of different cycles ('BR-IRGA 409', 'BR-IRGA 410', 'IRGA 417', 'IRGA 421', 'EPAGRI 108' and 'HÍBRIDO 2') with one only N dose. Assessments with the chlorophyll meter and the color chart were carried out on leaves of rice at different growth stages. Along with the readings, leaves were sampled and the leaf N content was determined. When the N doses varied, there was a meaningful correlation between the readings from the chlorophyll meter and the color chart with the leaf N content, regardless the assessment period. When the cultivars varied, the chlorophyll meter readings correlated with the N content (r=0.78, P

A utilização de fertilizantes foliares, aplicados ao final do ciclo da cultura do arroz irrigado, pode proporcionar complementação nutricional para a planta e proteção contra patógenos com reflexos na produtividade. O objetivo do estudo foi avaliar a utilização de fertilizantes foliares, aplicados no estádio de emborrachamento, sobre a produtividade do arroz irrigado. O experimento foi conduzido no ano agrícola 2005/2006, em área experimental de várzea do Departamento de Fitotecnia da Universidade Federal de Santa Maria. O delineamento experimental utilizado foi o de blocos ao acaso com quatro repetições. Os tratamentos foram compostos por 10 fertilizantes foliares, dois produtos aplicados via sementes, um fungicida e a testemunha. Os fertilizantes não influenciaram qualquer parâmetro avaliado. As condições climáticas e o manejo da adubação anterior à aplicação dos tratamentos foliares propiciaram condições favoráveis para o arroz expressar o seu potencial produtivo, em torno de 10.000kg ha-1. Neste nível de produtividade, os produtos utilizados não aumentaram a produtividade do arroz irrigado.The use of foliar fertilizers applied to the reproductive phase of rice can improve the plant nutrition and protect the field against foliar diseases with gains in yield. The objective of this experiment was to evaluate the use of the foliar fertilizers applied to the booting stage in order to verify the irrigated rice yield. The experiment was carried out in 2005/06 in a lowland area in Santa Maria-RS, Brazil. The treatments, arranged in a randomized block design with four replications, were constituted by 10 foliar fertilizers available in the market, two products applied to seeds, a fungicide, and a check treatment. The treatments presented no effects on any of the variables studied. The suitable climatic conditions and the fertilizer management carried out before the application of the foliar treatments led to the achievement of about 10,000 kg ha-1 yield, showing that there was no limitation on the level of yield obtained. The products utilized in this study did not increase the irrigated rice yield.

Sublethal adverse effects may result from exposure of aquatic organisms to insecticides at environmentally relevant concentrations. Fingerlings of the common carp (Cyprinus carpio, Linnaeus, 1758), grass carp (Ctenopharyngodon idella, Valenciennes, 1844), and bighead carp (Aristichthys nobilis, Richardson, 1845) were exposed to diafuran, an insecticide widely used during rice cultivation in Southern Brazil. The aim of this study was to verify the relationship between the lethal concentration (LC50) of diafuran and the acetylcholinesterase (AChE) activity in brain and muscle tissues of these species as a possible early biomarker of exposure to this insecticide. LC50 was determined for fish exposed to diafuran concentrations during 96 h (short term): common carp: control, 0.5, 1.0, 1.5, 2.0, 2.5 and 3.0 mg L-1; grass carp: control, 1.0, 2.0, 3.0 and 3.5 mg L-1 and, bighead carp: control, 0.5, 1.0, 1.5, 2.0, 3.0 and 4.0 mg L-1, as well as the determination of AChE at concentrations near LC50 for these species. LC50 values (nominal concentrations) were 1.81 mg L-1 for the common carp, 2.71 mg L-1 for the grass carp and, 2.37 mg L-1 for the bighead carp. All carps exposed to diafuran were lethargic (lower concentrations) or immobile. Diafuran inhibited the acetylcholinesterase activity in brain (~38%) and muscle (~50%) of all species. Muscle of bighead carp under control treatment showed higher specific AChE activity than brain (14.44 against 5.94 µmol min-1 g protein-1, respectively). Concentrations of diafuran used for rice cropping may affect Cyprinus carpio, Ctenopharyngodon idella and Aristichthys nobilis behaviors and the AChE activities in brain and muscle of these species may be an early biomarker of toxicity of this insecticide.Exposição a inseticidas em concentrações elevadas no ambiente podem ocasionar efeitos adversos subletais em organismos aquáticos. Alevinos de carpa húngara (Cyprinus carpio, Linnaeus, 1758), carpa capim (Ctenopharyngodon idella, Valenciennes, 1844) e carpa cabeça grande (Aristichthys nobilis, Richardson, 1845) foram expostos ao diafuran, um inseticida utilizado na cultura do arroz no sul do Brasil. O objetivo deste estudo foi verificar a relação entre concentração letal mediana (CL50) do diafuran e a atividade da enzima acetilcolinesterase (AChE) em cérebro e músculo dessas espécies, como um possível biomarcador inicial da exposição a este inseticida. A CL50 foi determinada com peixes expostos a concentrações de diafuran em 96 h: carpa húngara: controle; 0,5; 1,0; 1,5; 2,0; 2,5 e 3,0 mg L-1; carpa capim: controle; 1,0; 2,0; 3,0 e 3,5 mg L-1 e carpa cabeça grande: controle; 0,5; 1,0; 1,5; 2,0; 3,0 e 4,0 mg L-1, bem como a determinação da AChE em concentrações próximas da CL50 para essas espécies. Valores de CL50 (concentrações nominais) foram de 1,81 mg L-1 para carpa húngara, 2,71 mg L-1 para carpa capim e 2,37 mg L-1 para carpa cabeça grande. Todas as carpas expostas ao diafuran estavam letárgicas (menores concentrações) ou imóveis. Diafuran inibiu significativamente a atividade da AChE em cérebro (~38 %) e músculo (~50 %) de todas as espécies estudadas. Atividade da AChE em músculo para carpa cabeça grande foi mais alta que cérebro (14,44 contra 5,94 µmol min-1 g proteína-1, respectivamente). Este estudo demonstrou que concentrações de diafuran utilizadas na cultura do arroz podem afetar o comportamento de Cyprinus carpio, Ctenopharyngodon idella e Aristichthys nobilis, e a atividade da acetilcolinesterase cerebral e muscular pode ser um biomarcador inicial de toxicidade deste inseticida.

O objetivo deste trabalho foi avaliar a influência da população de plantas, das doses de nitrogênio e da aplicação de fungicida na parte aérea nas características agronômicas que determinam a produtividade do arroz irrigado. O experimento foi realizado no ano agrícola 2003/2004, no Departamento de Fitotecnia da Universidade Federal de Santa Maria, em Santa Maria, RS. O delineamento experimental foi de blocos ao acaso, com parcelas subdividas e quatro repetições. Os tratamentos constituíram-se de três populações de plantas (150, 265, 380plantas m-2), cinco doses de nitrogênio (0, 40, 80, 120, 160kg ha-1) e da aplicação ou não de fungicida na parte aérea da cultura. A adubação nitrogenada de cobertura foi igualmente parcelada, no início do perfilhamento e na diferenciação da panícula. A produtividade do arroz irrigado aumentou de forma quadrática com as doses de nitrogênio, respondendo até 97kg ha-1. A utilização de fungicidas para controle de doenças da parte aérea resultou em maior produtividade, independentemente da população de plantas e das doses de nitrogênio utilizadas. Desta forma, o arroz irrigado compensa seus componentes da produtividade com populações na faixa de 150 a 380 plantas m-2, sendo a maior produtividade obtida com a dose de nitrogênio de 97kg ha-1 e aplicação de fungicida, mesmo com baixa incidência de doenças.A field experiment was aimed at evaluating the effects of plant densities, nitrogen rates and chemical disease control on agronomic characteristics that affect grain yield of irrigated rice. The study was conducted during 2003/2004, in the Departamento de Fitotecnia of Universidade Federal de Santa Maria. The experiment was arranged in randomized blocks with sub-plots and four replicates, in Santa Maria-RS, Brazil and the treatments were: three plant densities (150, 260 and 380plants m-2), five nitrogen rates (0, 40, 80, 120 and 160kg ha-1) with and without chemical foliar disease control. The nitrogen was dressing was twice split at initial tillering and panicle differentiation. Grain yield increased in a quadratic fashion in response to nitrogen rates to up to 97kg ha-1. The use of fungicides to control foliar diseases resulted in higher grain yelds regardless of plant population or nitrogen fertilizer rates. Irrigated rice can compensate yield components between 150 and 380plants m-2. The most efficient rate of nitrogen was 97kg ha-1. Chemical foliar diseases control increases irrigated rice productivity even at low disease incidence.

No sistema pré-germinado de cultivo de arroz, a área é inundada antes da semeadura e, cerca de três dias após, promove-se a drenagem inicial para favorecer o estabelecimento das plântulas, ocasionando a perda de água e de nutrientes. Assim, testaram três manejos de irrigação: [M1], retirada da água três dias após a semeadura; [M2], retirada de água aos 30 dias após a semeadura e [M3], sem retirada de água, associados a cultivares de arroz, com o objetivo de avaliar a produtividade do arroz e a perda de nutrientes via água de drenagem. Os manejos testados não influenciaram os parâmetros avaliados na cultura do arroz. Para a produtividade, os valores oscilaram conforme as características de cada ano, obtendo-se médias de 5.100, 9.565 e 7.078kg ha-1 para as safras 2002/03, 2003/04 e 2004/05, respectivamente. Apenas em 2003/04, as cultivares diferiram em produtividade. Nas safras 2002/03 e 2003/04, as perdas de fósforo foram semelhantes entre os tratamentos, mas, em 2004/05, ocorreram maiores perdas quando a água foi retirada aos três dias após a semeadura. Para potássio, as maiores concentrações também foram observadas nas amostras de água coletadas aos três dias após a semeadura. Os resultados indicam que deve-se manter lâmina contínua, pois este manejo proporciona a preservação dos nutrientes dentro da lavoura, não afeta a produtividade e reduz o impacto ambiental nos mananciais hídricos.In the pre-germinate system, the rice field is flooded before sowing and about three days later, the initial drainage takeplace in order to promote the plants initial growth but there occurs loss of nutrients and water. Then, three irrigation managements have been evaluated: water removal three days after sowing, water removal 30 days after sowing and without water removal, associating three rice cultivars with the objective to measuring rice grains yield, and loos nutrients with water removal. The water managements evaluated have not influenced the rice plant parameters. The grains yield varied according to the year, with an average 5,100, 9,565 and 7,078kg ha-1 ha in the years 2002/03, 2003/04 and 2004/05, respectively. Only in 2003/04, the grains yield was different among the rice cultivars. In 2002/03 and 2003/04, the phosphorous nutrient was similar among treatments, but in 2004/05 a great loss occurred when water removed three days after sowing. Concerning potassium, the highest concentrations were observed in water when it was removed three days after sowing. Results demonstrate that a continuous water sheet should be kept to preserve the nutrients within the field since it does not affect the crop yield and reduce the environmental impact of the water bodies.

Irrigated rice production can involve environmental contamination with pesticides due to the proximity of the fields to rivers and to management problems. During three years (2000 to 2003) the rice herbicides clomazone, propanil and quinclorac were quantified in water during the rice growing season, in the Vacacaí and Vacacaí-Mirim Rivers, located in Rio Grande do Sul (RS) State, Brazil. Water samples were taken at several locations in each river, selected by their importance in terms of rice drainage area. The samples were analyzed by HPLC-UV. At least one herbicide was detected in 41% of the samples from the Vacacaí River and 33% from the Vacacaí-Mirim River. The most frequent herbicide in both rivers and in each year was clomazone. The amount of herbicides in the river water was dependent on the rainfall regime. River water contamination by rice herbicides is probably caused by the rice water management used in the fields. The maintenance of flooded areas makes herbicides prone to contaminate the environment. To reduce the environmental contamination risk it is necessary to adopt measures to avoid overflow of flooded rice fields, keeping paddy water in the field for time enough to reduce the herbicide concentration before its release and enhancing the quality of the levees to reduce the probability of paddy rice overflow.No cultivo de arroz irrigado a possibilidade de contaminação dos mananciais hídricos é ampliada pelas características peculiares das áreas e do sistema de produção. Um estudo de monitoramento foi conduzido durante três anos (2000 a 2003), nos rios Vacacaí e Vacacaí-Mirim, localizados no Estado do Rio Grande do Sul, Brasil, buscando quantificar os herbicidas clomazone, propanil e quinclorac durante o período de cultivo do arroz. As amostras de água foram coletadas em vários locais em cada rio. Os locais de coleta foram selecionados pela importância em termos da captação da água de drenagem. As amostras foram analisadas por HPLC-UV. Herbicidas foram detectados nas águas dos rios durante no período de cultivo do arroz. Foi detectada a presença de pelo menos um herbicida em 41% das amostras no rio Vacacaí e 33% das amostras no rio Vacacaí-Mirim. O herbicida clomazone, foi detectado com maior freqüência nos dois rios. A quantidade de herbicida nas águas dos rios foi dependente do regime de chuva. A contaminação das águas dos rios pelos herbicidas utilizados no arroz provavelemente é decorrente do manejo de água adotado na região. A manutenção de áreas inundadas propicia a contaminação do ambiente por herbicidas. Para reduzir o risco de contaminação ambiental faz-se necessário à adoção de medidas que evitem a saída e liberação da água com resíduo das áreas de cultivo, mantendo-a na lavoura durante o tempo suficente para a redução da concentração do herbicida. A probabilidade de extravasamento pode ser reduzida com a melhor construção das taipas-ronda.

O objetivo do presente estudo foi avaliar a utilização de inóculos decianobactérias fixadoras de nitrogênio como alternativa à adubação química de nitrogênio na cultura do arroz irrigado. Para tanto, foram conduzidos quatro experimentos, nos anos agrícolas de 1999/00 a 2002/03, avaliando os tratamentos: testemunha sem aplicação de N em cobertura; 20 kg ha-1 de N aplicado em cobertura; 40 kg ha-1 de N aplicado em cobertura; 90 kg ha-1 de N aplicado em cobertura; 50 g ha-1 de Rizogram®; 100 g ha-1 de Rizogram®. Verificou-se interação dos tratamentos com os anos avaliados, o que pode ter ocultado o desempenho destes. Além disso, verificou-se que, para a variável “número de grãos por panícula”, a utilização de cianobactérias nas duas dosagens estudadas (50 e 100 g ha-1) produziu resultados semelhantes à adubação nitrogenada (90 kg ha-1), com potencialredução do número porcentual de espiguetas estéreis. Os tratamentos não afetaram o rendimento de grãos do arroz irrigado, devido às variações ambientais dos anos avaliados.A four-year experiment irrigated rice was carried out in order to evaluate the performance of Nostoc sp. and Tolypothrix sp. nitrogen-fixing cyanobacteria strains (Rizogram™), as an alternative to chemical nitrogen fertilization in irrigated rice. The treatments evaluated in the experiments included: control without top dressing Napplication; top dressing application of 20, 40 and 90 kg ha-1; 50 g ha-1 of Rizogram™, and 100 g ha-1 of Rizogram™. It was verified interaction between the years of the study and the treatments, which may have affected the performance of these treatments. Moreover, it was observed that, for the number of grains per panicle, the use of cyanobacteria in two studied rates (50 e 100 g ha-1) produced the same results as the nitrogen fertilization (90 kg ha-1), showing potential reduction of sterile spikelets. However, the treatments did not affected rice grain yield.

O experimento foi realizado em várzea sistematizada com o objetivo de comparar os efeitos do uso de doses de N em cobertura, associadas a níveis de suplementação energética, sobre o desempenho animal e a qualidade e produção de forragem. Os tratamentos foram: 300N+0,8S = adubação com 300 kg de N/ha + suplementação com grão de milho moído (0,8% do PV/dia); 200N+0,4S = adubação com 200 kg de N/ha + suplementação com grão de milho moído (0,4% do PV/dia); e 100N = adubação com 100 kg de N/ha, sem suplementação. Foram utilizados novilhos de corte da raça Charolês e suas cruzas com Nelore com idade inicial de 8 a 10 meses. A pastagem foi manejada sob lotação contínua e carga variável, no período de 15/07 a 03/11/2000, totalizando 110 dias de utilização. O teor de PB, a digestibilidade in vitro da MO (DIVMO) e a oferta de forragem (OF) foram maiores no início do período de pastejo e apenas a OF diferiu entre os tratamentos. As doses de N em cobertura, associadas a níveis de suplementação energética em pastagem de azevém, não alteraram o ganho médio diário dos animais, mas resultaram em maior carga animal e maior ganho de peso vivo por hectare.The experiment was carried out in a leveled lowland area cultivated with Italian ryegrass (Lolium multiflorum Lam.). The objective was to compare the effect of nitrogen (N) and different energy supplementation levels on the following parameters: herbage quality, herbage yield, and animal production. The treatments were: 300N + 0.8S - Italian ryegrass pasture plus 300 kg.ha-1 of N and supplementation with ground corn (0.8% LW/day), 200N + 0.4S - Italian ryegrass pasture plus 200 kg.ha-1 of N and supplementation with ground corn (0.4% LW/day) and 100N - Italian ryegrass pasture plus 100 kg.ha-1 of N without supplementation. Beef steers averaging eight to ten months old were used in the beginning of the experiment and allotted to continuous stocking with fixed stocking rate. Crude protein concentration, in vitro organic matter digestibility and forage on offer were greater in the beginning of the grazing period. Difference among treatments was observed only for forage on offer. Nitrogen levels, associated to different energy supplementation levels, did not affect average daily live weight gain, but resulted in greater stocking rate and, consequently, higher live weight gain/ha.

Com o objetivo de avaliar a influência dos componentes de produção de arroz no rendimento de grãos através da análise de trilha, avaliaram-se 88 genótipos de arroz em quatro anos agrícolas. Em cada ano, os experimentos foram conduzidos no delineamento em blocos completos casualizados, com quatro repetições. As variáveis analisadas foram: estatura de plantas, rendimento de grãos, esterilidade de espiguetas, número de grãos por panícula, massa de mil grãos e rendimento de engenho. As análises de variância, correlação e de trilha (Path Analysis) foram realizadas para cada variável, utilizando-se o programa computacional GENES. Os genótipos avaliados apresentaram diferenças significativas para todas as variáveis analisadas, nos quatro anos de experimento. A seleção de variáveis deve ser realizada em grupos de cultivares semelhantes entre si e a utilização de um maior número de variáveis possibilita melhores inferências sobre os componentes da produção do arroz. A massa de grãos é o componente de produção que mais afeta o rendimento da cultura do arroz.Eighty eight rice genotypes were evaluated during four years aiming to study the relationship among yield components. In each year, the experimental design was a completely randomized block design with four replications and the variables studied were: plant height, seed yield, spikelet sterility, number of seeds per panicle, 1000 seeds weight and head grains. The estimation of correlations and the path coefficient analysis were conducted with the GENES software. The genotypes showed significant variability for all the variables analyzed within each one of years. It was concluded that variable selection must be carried out among the cultivars that are more similar and using a greater number of variables allows better inferences about rice yield components. Grain weight was the yield of component that most affected seed yield rice plants.

No sistema pré-germinado de cultivo do arroz irrigado, adota-se o manejo de retirada da água da lavoura, aproximadamente aos três dias após a semeadura, objetivando melhor estabelecimento das plântulas. No entanto, esta prática acarreta perda de água e nutrientes, além da reinfestação com plantas daninhas. A permanência da lâmina de água na lavoura, durante todo o ciclo da cultura, seria uma proposta de manejo capaz de minimizar estes problemas. Sendo assim, objetivou-se avaliar o desempenho de genótipos de arroz irrigado, quando submetidos ao cultivo em lâmina contínua, especialmente quanto ao acamamento de plantas, aspecto considerado limitante neste manejo de irrigação. Para tal, nos anos agrícolas de 2000/01 a 2002/03, foram conduzidos experimentos em área de várzea sistematizada, em solo classificado como Planossolo Hidromórfico eutrófico arênico. Os tratamentos foram compostos por 8, 12 e 15 genótipos no primeiro, segundo e terceiro ano, respectivamente. No ano 1, a produtividade média foi de 7279kg ha-1, sendo o genótipo IRGA 1572-11-1F-1-4-4 (8297kg ha-1) o mais produtivo em valores absolutos. A porcentagem de acamamento variou entre 0 e 60% e a maioria dos tratamentos situou-se entre 0-20%. Todos os genótipos exibiram acamamento de plantas, exceto El Paso L 144. No ano 2, a produtividade média foi de 8492kg ha-1 e o genótipo BRS-Pelota o mais produtivo (9282kg ha-1), não tendo sido verificado acamamento em nenhum dos genótipos. No ano 3, a produtividade média foi de 6202kg ha-1 e esteve relacionada à elevada porcentagem de plantas acamadas decorrente de intempéries climáticas, ocorridas na fase de maturação. Constatou-se que a produtividade dos genótipos pode ser elevada neste manejo de irrigação, mas o acamamento de plantas limita o potencial produtivo, dependendo das condições ambientais e do genótipo utilizado.

O objetivo do presente estudo foi avaliar a utilização de inóculos de cianobactérias fixadoras de nitrogênio como alternativa à adubação química de nitrogênio na cultura do arroz irrigado. Para tanto, foram conduzidos quatro experimentos, nos anos agrícolas de 1999/00 a 2002/03, avaliando os tratamentos: testemunha sem aplicação de N em cobertura; 20 kg ha-1 de N aplicado em cobertura; 40 kg ha-1 de N aplicado em cobertura; 90 kg ha-1 de N aplicado em cobertura; 50 g ha-1 de Rizogram®; 100 g ha-1 de Rizogram®. Verificou-se interação dos tratamentos com os anos avaliados, o que pode ter ocultado o desempenho destes. Além disso, verificou-se que, para a variável “número de grãos por panícula”, a utilização de cianobactérias nas duas dosagens estudadas (50 e 100 g ha-1) produziu resultados semelhantes à adubação nitrogenada (90 kg ha-1), com potencial redução do número porcentual de espiguetas estéreis. Os tratamentos não afetaram o rendimento de grãos do arroz irrigado, devido às variações ambientais dos anos avaliados.

ABSTRACT: The use of imidazolinone-tolerant rice cultivars allows selective control of weedy rice and barnyardgrass. However, in many situations, there is a need to add herbicides from other chemical groups to increase the spectrum of weed control. In this sense, saflufenacil has the potential to be used in mixture with imidazolinone herbicides. This study aimed to evaluate the interaction effects of the imazapyr+imazapic and saflufenacil herbicides in weedy rice and barnyardgrass and to investigate their impacts on the yield of the irrigated rice cultivar Puitá INTA CL. To reach these aims, greenhouse and field experiments were carried out during two growing seasons, with herbicide treatments sprayed separately and in mixtures of saflufenacil with imazapyr+imazapic. Results showed that saflufenacil did not interfere with control of weedy rice and barnyardgrass obtained with imazapyr+imazapic. The D50 values of imazapyr+imazapic for weedy rice control were 14.5+5, 9.1+3 and 12.5+4.2 g ha-1of imazapyr+imazapic for combinations with 0, 3.06 and 6.12 g ha-1of saflufenacil, respectively. In the field experiments, all doses of imazapyr+imazapic applied isolated or in mixture with saflufenacil provided control levels barnyardgrass above 90% at 28 days after herbicides application. Furthermore, saflufenacil did not cause damage or loss in the yield of the rice crop when mixed with imazapyr+imazapic. The Puitá INTA CL rice cultivar was tolerant of the tested herbicides, whether applied alone or in mixture, reaching grain yield of 9.987 kg ha-1 when applied 42 g ha-1 of saflufenacil plus 147+49 g ha-1 of imazapyr+imazapic.