Thais Fernanda Stella de Freitas

Validação de escala de desenvolvimento para cultivares brasileiras de arroz irrigado

The number of days after emergency is commonly used to define the rice plant stage, despite the existence of a growth scale. The use of chronological time is not ideal, once it is dependent of the cultivar life cycle and environmental conditions, which are known to affect the plant development. The goal of this study was to validate a rice growth scale for three Brazilian flooded rice cultivars, with different life cycles and in three sowing dates. The experiment was conducted in tanks in Porto Alegre, RS, Brazil. The three sowing dates were October 14, November 13 and December 18, 2003, and the cultivars chosen were BR-IRGA 409, medium cycle, IRGA 417, early cycle, and IRGA 421, very early cycle. Each cultivar was sowed in three lines, spaced 0.15m from each other, to produce a population of 250 plants m-2. Ten plants composed each sample. The R1 stage (panicle differentiation) was reached when the plants had seven expanded leaves in all treatments, independently of the chronological plant age. A reduction in the number of expanded leaves at the R2 stage (flag leaf collar formation) was only observed for IRGA 421 in the last sowing date. However, the number of days required for each cultivar to reach R2 stage was different. As the sowing date was delayed, the chronological time between each growth stage was reduced. The rice growth scale was much more efficient than the chronological age to determine the plant stage. Therefore, using the rice growth scale is possible to interfere at the correct moment, allowing high yields and rational resource use.

Produtividade de arroz irrigado e eficiência da adubação nitrogenada influenciadas pela época da semeadura

The potential grain yield of late flooded rice is important for decision making of producers. Yields of rice crops sown after the recommended period are restricted due to unfavorable climatic conditions. The objective of this research was to evaluate grain yield and agronomic, technical and economic efficiency of broadcast nitrogen for flooded rice sown in December in the state of Rio Grande do Sul, Brazil. The field experiment was carried out in 2005/2006, in Cachoeirinha. Treatments consisted of two sowing dates, recommended (November) and late (December), four seeding rates (50, 100, 150, and 200 kg ha-1) and four nitrogen levels (0, 60, 120, and 180 kg ha-1). The experiment had a randomized block design using split plots with three replications. Rice grain yield and response to nitrogen topdressing were reduced by the late sowing date. The doses for maximum technical and economic efficiency were reduced with the sowing delay, and nitrogen agronomic efficiency was reduced with the sowing delay and N fertilizer dose. The number of panicles m-2 did not respond to nitrogen broadcast and was one of the most limiting yield components.

Práticas de manejo integradas para produção de arroz irrigado

The objective of this work was to perform a technical and financial evaluation of integrated management practices for lowland rice (Oryza sativa). The experiment was carried out in Cachoeirinha, in the state of Rio Grande do Sul, Brazil. A randomized block design with split-split plots with four replications was used.The three growing seasons (2003/2004, 2004/2005, and 2006/2007) were the main plots, the sowing dates (preferential and late) were the split plots, and the management practice systems (low, average, high and veryhigh) were thes plit-split plots. The management practice systems varied in terms of seeding rate, fertilizer rate, herbicide rate, nitrogen fertilizer topdress management, and irrigation management. The grain yield and financial return responses to the improvement of management practices were greater at the preferential sowing date, at the end of October, than on the first week of December. At the preferential sowing date, the financial return increased with the improvement of management practices, due to the increased income resulting from the higher grain yield.

Associação de glyphosate e imidazolinonas no controle de arroz-vermelho em arroz Clearfield®

The objective of this research was to evaluate the effects of the utilization of glyphosate and imidazolinones herbicides, in isolated or associated applications, on the effectiveness of red rice (Oryza sativa) control and grain yield of Clearfield-rice. The experiment was conducted under field conditions in 2007/08, in Cachoeirinha, RS, Brazil, using a randomized block design in a two-factorial design 2x6, with four replicates. The factor A was composed by two levels of glyphosate, applied during the subperiod between sowing and crop emergence at the early coleoptile stage of the rice plants; and the factor B consisted of six treatments with imazethapyr+imazapic, applied in association with glyphosate or when the rice crop plants had three expanded leaves. The crop and weed populations, red rice control and grain yield of crop were evaluated. The results show that the glyphosate application at the early coleoptile stage of the crop reduced 75% the red rice population and increased 40% the grain yield, in relation to the situation without weed control. The use of imidazolinones and their association with glyphosate provided effective control of red rice and increased the grain yield, independent of rates and application system.