Mauro Antonio Rizzardi

ARROZ VERMELHO: ECOFISIOLOGIA E ESTRATÉGIAS DE CONTROLE

Interference caused by red rice (Oryza sativa L.) on cultivated rice (O. sativa L.) is the main factor that limits increasing grain yield potential of the cereal in the state of Rio Grande do Sul, Brazil. This literature review has the objective of describing ecophysiological characteristics of red rice, as well as to discuss strategies that favour cultivated rice in the competition process for environmental resources or that limit its establishment. Due to morphophysiological similarities between both, red rice control cannot be accomplished through the use of selective herbicides alone, requiring the combination of several integrated actions, involving preventive, cultural, physical and chemical methods. The presence of a high red rice population makes rice production impracticable, especially when the field extension turns hand weeding impossible. In such a condition, the most effective methods of control have been: the usage of pre-germinated seeds, early soil preparation combined with no-till seeding, and adaptation of crop rotation.

Perdas de rendimento de grãos de soja causadas por interferência de picão-preto e guanxuma

The level of reciprocal interference between weeds and crops is affected by the competing species and plant populations involved. This research was conducted in order to evaluate the possibility of using the retangular hyperbolic model for predicting soybean grain yield losses caused by beggarticks (Bidens spp.) and arrowleaf sida (Sida rhombifolia L.) infestations. To accomplish this, there were carried out two field experiments in Eldorado do Sul, RS, Brazil, during the 1999/00 and 2000/01 growing seasons. Treatments consisted of beggarticks and arrowleaf densities, which were located according to naturally ocurring population levels in the research area. Was detected that grain yield losses due to increasing densities of these weeds increased non-linearly. The retangular hyperbolic model suits better adjustments when is used grain yield losses than using soybean dry matter at flowering stage or biological yield losses. Through comparison of the parameters estimated for the adjusted model, it is concluded that beggarticks exerts greater interference in soybean than arrowleaf sida.

Métodos de quantificação da cobertura foliar da infestação de plantas daninhas e da cultura da soja

The utilization of mathematical models in order to predict grain yield losses due to weed infestations, which use leaf area measures, depends on the rapid and precise evaluation of this variable. This way, leaf cover, defined as the proportion of soil area accupied by the vertical projection of the foliage of a species, can be a viable alternative. The purpose of this research was to compare the efficiency of methods to evaluate leaf cover in quantifying soybean grain yield losses due to Bidens spp. (beggarticks) and Sida rhombifolia L. (arrowleaf sida). Weeds and crop leaf covers were evaluated 20 days after soybean emergency. It was proved that photographic methods of evaluating leaf cover, integrated to computing aids, are promising alternatives in quantifying this variable although visual evaluation was more practical and rapid to be performed.

Nível de dano econômico como critério para tomada de decisão no controle de guanxuma em soja

O nivel de dano economico (NDE) e um conceito simples que integra fatores biologicos e economicos que se destina a tornar os resultados de uma tomada de decisao lucrativos para o controle das plantas daninhas. O objetivo deste trabalho foi determinar o NDE para infestacoes de guanxuma (Sida rhombifolia), calculado na base de um unico ano, que justifiquem aplicacao economica de medidas para seu controle na cultura da soja. Foram conduzidos experimentos em campo em Passo Fundo e Eldorado do Sul-RS. Os tratamentos constaram de densidades de guanxuma e de epocas de semeadura da soja em relacao a dessecacao da cobertura vegetal (3, 7 e 11; e 20, 24 e 28 dias apos). Os valores de NDE variaram de 2 a 50 plantas m-2, e os de NDE otimo, de 1 a 6 plantas m-2. Verificaram-se respostas diferentes nas relacoes de interferencia cultura-plantas daninhas entre os ambientes estudados. O atraso na semeadura da soja em relacao a dessecacao da cobertura vegetal incrementa o grau de interferencia de guanxuma na cultura. Constatou-se que as sementes produzidas pelas plantas daninhas nao-controladas, ocorrendo em densidades abaixo do NDE, comprometem a adocao da tomada de decisao de controle com base neste criterio.

Interferência de plantas concorrentes em arroz irrigado modificada por métodos culturais

The optimization of a weed control program depends on early and reliable prediction of the impact of weeds on crop yield. This research aimed to evaluate the effects of rice cultivars and plant arrangements on flooded rice grain yield loss and to identify the explicative variable that provides the best adjustment to the model tested. Two field experiments were carried out during the 2000/2001 growing season. Treatments consisted of three rice cultivars (BRS-38 Ligeirinho, IRGA 417, and BR-IRGA 409), two row widths (15 and 25 cm), and plant populations (ten and six levels for the first and second experiments, respectively) of the rice cultivar EEA 406, mimicking red rice infestation.. Data were analyzed using the non - linear regression model of rectangular hyperbole, adjusted independently for the three studied factors. Results of the first experiment were used to evaluate data adjustment to the model and results of the second to validate the model generated in the first. IRGA 417 cultivar presented greater competitive ability than the other two. Reduction of row width increased the ability of rice cultivars to compete with the concurrent genotype. The rectangular hyperbolic model was suitable to estimate flooded rice grain yield loss due to interference of concurrent plants. The explicative variable leaf area of EEA 406 cultivar, in general, was equivalent to plant population as an independent variable in the mathematical model tested.

Dano econômico como critério na decisão sobre manejo de genótipos de arroz concorrentes em arroz irrigado

The economic thresholds (ET) for weedy rice infestations in rice fields allow to decide the management of the rice crop, rationalizing herbicide use. The aim of this research was to estimate ET for red rice and for EEA 406 rice cultivar, mimicking red rice, when competing with flooded rice. Three field experiments were carried out, during the 1999/2000 and 2000/2001 growing seasons. The investigated factors were populations of the concurrents genotypes on the three experiments and red rice relative emergence times (first study), EEA 406 rice cultivar (second study) and rice cultivars and row widths (third experiment). ET values for red rice were lower than those for EEA 406 genotype. The ET values estimated for EEA 406 varied widely, according to environment (seasons), emergence time, rice cultivar and row width variables. Earlier emergence of concurrent genotypes in relation to the crop, increase in row width, and use of very early maturity cultivars decreased the ET values. Increases in grain yield, selling rice price and in control efficiency, and control cost reduction, decreased ET levels, making cost effective the adoption of management practices under lower concurrent genotype populations.

Velocidade de estabelecimento em cultivares de arroz irrigado como característica para aumentar a habilidade competitiva com plantas concorrentes

Plants that present fast establishment possess priority in utilizing environmental resources; therefore, they present advantage in competitive ability with their neighbours. The objective of this research was to detect variations in speed of establishment in flooded rice cultivars. This way, there were conducted three experiments, two of them in the greenhouse and the other in the field. In both conditions, it was investigated the behavior of nine cultivars. In order to characterize speed of establishment, there were evaluated: emergency velocity, plant height, leaf area, and aerial weight of the seedlings 15 days after sowing. The genotypes Ligeirinho and XL 6 showed characteristics that attribute them fast establishment; whereas, Bluebelle and Formosa presented characteristics indicative of slow seedling establishment.

Comparação de modelos matemáticos na estimativa das perdas de produtividade de grãos em arroz irrigado

The objectives of this work were to compare mathematical models and identify, among morphologic variables, the one better adjusted to rice grain yield losses by interference of EEA 406 cultivar, simulating red rice. Four experiments were carried out, one in the field and the others in a greenhouse. Rice cultivars BRS-38 Ligeirinho, IRGA 417, and BR-IRGA 409, were studied in the field in row widths of 15 and 25 cm, and populations (ten levels) of concurrent cultivar. In greenhouse, tests in monocultures were carried out in a replacement series model. Data analysis were accomplished with application of linear and non linear regression models. The best adjustment of rice grain yield losses data was attained using the model with two parameters. Leaf area and soil coverage estimated better grain yield loss than dry weight of the simulating cultivar. The models show that reduction of crop row width increases the competitive ability of rice cultivars in relation to the concurrent genotypes.

Potencial de emissão de metano em lavouras de arroz irrigado

In the last years, great attention has been directed to potential problems caused by the greenhouse effect. Man, through industrial activities, fossil fuel consumption, forest destruction, and adoption of some agronomic practices, has been the main responsible for such phenomenon. The main gases that cause the greenhouse effect are carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and chlorofluorocarbons (CFCs). Methane stands out amongst them by the amount produced and by its activity in the absorbing atmospheric heat. The main methane producing sources are soils naturally flooded or cultivated under flooding conditions, which represent approximately 40% of the total methane emitted; from this amount, 37% is emitted by rice cultivated under flooding conditions. In this context, the present review has as main purposes to describe processes responsible for methane production and emission, as well as to discuss management practices and rice plant characteristics which affect emission of this gas. From the total methane originated in rice fields during its growth cycle, between 60 to 90% comes from rice plants. Although methane is not the main gas responsible for the greenhouse effect and rice crop does not represent the main methane source, the reduction in the emission could be accomplished through changes in rice cultural practices. Amongst alternatives that can be worked out are management of irrigation water and fertilizer applied, and cropping of rice cultivars that present lower number of aerenchyma and lower biomass production, whereas maintaining rice grain yields potential.

Ação dos herbicidas atrazine e glufosinate de amônio no aproveitamento de nitrogênio pelas plantas de milho

Plant absorption of nitrogen (N) present in soil or supplied through fertilization is regulated by a complex of enzymes that act in a jointly and ordered way in the plant. The purpose of this research was to investigate the effects of the herbicides atrazine and ammonium glufosinate in N absorption by plants and their effects on corn plant traits. In one of the experiments (experiment 1), three atrazine rates were tested (0, 200, and 2000 g a.i. ha-1), three ammonium glufosinate rates (0, 40, and 80 g a.i. ha-1), and two N rates (0 and 90 kg ha-1). In another experiment (experiment 2), three herbicide treatments were tested (atrazine, 200 g a.i. ha-1; ammonium glufosinate, 40 g a.i. ha-1; atrazine + glufosinate, 200 + 40 g a.i. ha-1; and a check), two N sources (urea and ammonium nitrate), and two N rates (0 and 100 kg ha-1). Effects of the treatments were evaluated at 10 and 20 days after herbicide application (DAA) in experiment 1, and when corn plants presented 10 developed leaves (15 DAA) and at tasseling (40 DAA) in experiment 2. Statistical analyses revealed that N side dressing application in corn promotes an increase in most of the grain yield components and increases grain yield by 35%, and that such effects occur regardless of the N source used, urea or ammonium nitrate. There was no interaction effect among factors related to herbicides that are inhibitors of photosystem II (atrazine) and to herbicides inhibitors of the glutamine synthesis (ammonium glufosinate) and N side-dressing application in corn. The use of these herbicides in reduced rates, applied alone or in combination, did not affect grain yield nor yield components. Atrazine shows little consistency in affecting chlorophyll and N contents in corn; nevertheless, in some cases, its action is favorable, especially when used at the recommended rate or even when sprayed alone. Ammonium glufosinate, applied at reduced rates, in general does not affect N content in corn; however, in some situations, chlorophyll content is affected and, when used at 80 g a.i. ha-1, promotes N content increase in the corn tissue.