Mara Grohs

Destino ambiental dos herbicidas do grupo das imidazolinonas: revisão

The herbicides of the imidazolinone group control a wide range of weed species. They are absorbed by weed roots and leaves and transported through the phloem and xylem, accumulating in the plant growing points. They inhibit the enzyme acetolactate synthase (ALS), which synthesizes the branched chain amino acids. When used in the field, a large portion of these herbicides reach the soil, where they can be absorbed by the roots of plants, sorbed into the soil colloids, or dissolved in soil solution, going through photolysis, hydrolysis, microbial degradation or leaching. The sorption of imidazolinone is faster and affects other processes. High contents of clay, organic matter and pH lower than 6.0 contribute to enhance the sorption and persistence of imidazolinones in soil. The most important way of dissipation is by microbial degradation, thus conditions favoring microbial development will also enhance imidazolinone degradation.

Persistence of the herbicides imazethapyr and imazapic in irrigated rice soil

The mixture of herbicides imazethapyr and imazapic is used to control red rice in irrigated rice crops. However, such herbicides might persist on the soil for a long period causing phytotoxicity on susceptible rice grown in succession. The objective of this work was to determine the effect of different soil tillage systems during the off-season on the residual phytotoxicity of imazethapyr and imazapic on non tolerant rice. Herbicide residues caused phytotoxicity on susceptible rice with the highest values being registered 25 days after emergence and decreasing after this period until almost disappearing 60 days after emergence. Herbicide residues affected plant stand, number of stems per m2, number of panicles per m2 and plant height, but did not affect grain yield. Soil movement decreased herbicide activity on the superficial soil layer (0-3 cm).

Carryover of Imazethapyr and Imazapic to Nontolerant Rice

Abstract The present work aimed to evaluate plant injury caused by residues in the soil of the formulated mixture of imazethapyr and imazapic to a nontolerant genotype of rice (IRGA 417) drilled at 371 and 705 d after herbicide application (DAA). Herbicide carryover reduced up to 55% of the grain yield of the IRGA 417 drilled at 371 DAA, and plant injury was still evident at 705 DAA but without grain yield reduction. Nomenclature: Imazethapyr; imazapic; rice, Oryza sativa L. ‘IRGA 417’

Lixiviação do imazethapyr em solo de várzea sob dois sistemas de manejo

Imazethapyr has been widely used in Rio Grande do Sul since the development of Clearfield TechnologyTM(CL) on rice, in a formulated mixture of imazethapyr + imazapic (75 + 25g L-1). However, the use of such technology raised the problem of herbicide carryover, which might affect non-tolerant crops in rotation with different intensities. The plant injury is related, among other factors, with the herbicide position in the soil profile. The present work had the objective of determining the depth positioning of imazethapyr on a lowland soil cultivated with rice in two soil tillage system: conventional system (CS) and no till system (NT), in an area where CL rice had been cultivated for two years followed by non tolerant rice in the third year. Herbicide concentration in soil samples was analyzed by HPLC-DAD. There is a higher concentration of imazethapyr in the topsoil (0-5cm) on the CS, when compared to the NT, while it leached until 20cm in both systems. In the CS, imazethapyr were uniformly distributed in the first 15 cm of soil, whereas in NT, imazethapyr were accumulated in 5-10 and 10-15cm layers.

Desempenho de cultivares de arroz com uso de reguladores de crescimento, em diferentes sistemas de cultivo

The objective of this work was to evaluate the effect of growth-regulating substances on initial establishment and agronomic performance of irrigated rice cultivars, in different cropping systems. The experiment was carried out in controlled environment and in field conditions, using the cultivars Irga 424 and Irga 425, and the products gibberellic acid, thiamethoxam and Haf Plus. At field, treatments were tested with conventional and pre-germinated sowing systems. In the controlled environment, the evaluated substances promoted the germination of Irga 425, with an increase of 50% in germination with the use of thiamethoxam and of 39% with Haf Plus and gibberellic acid. In the field, this performance was dependent on the system and the cultivar used. Gibberellic acid caused initial blanching, which reflected in plant height, tiller emission, and deposition of vegetal biomass. Thiamethoxam and Haf Plus stimulated tillering of rice cultivars in both cultivation systems. Although all the products stimulated the number of panicles per square meter, there is no influence on grain yield in the evaluated systems.

Arroz tolerante a imidazolinonas: banco de sementes de arroz-vermelho e fluxo gênico

The objective of this study was to evaluate the rotation of the irrigated rice Clear field® system with the conventional system in the evolution of the seed bank and the emergence of red rice biotypes resistant to the imidazolinone chemical group. The experiment was arranged in a randomized block design in a factorial scheme (2 x 4) with 4 replications. The first factor was constituted of the management systems used (Clearfield®x conventional) which consisted of the succession/rotation between the rice not tolerant to imidazoline, variety IRGA 417 (conventional), and the rice tolerant to imidazolinone, variety IRGA 422 CL (Clearfield®). The D factor was consti tuted by the variation between the conventional and the Clearfield®systems, over time. The use of the Clearfield®system provides a reduction of the seed bank after three years of use; however, it does not remove all the red rice seeds from the soil. The crossing between red rice and cultivated rice increases with the increase of infestation, reaching 2.9% after four crops.

Resposta do arroz irrigado ao uso de inibidor de urease em plantio direto e convencional

O objetivo do presente trabalho foi avaliar a volatilizacao de N-NH3 e a resposta do arroz irrigado ao uso de ureia com inibidor de urease em dois sistemas de cultivo, direto e convencional. Para tanto, desenvolveu-se um experimento em campo, no ano agricola 2008/09, na UFSM em Santa Maria/RS. O delineamento utilizado foi de blocos ao acaso em esquema bifatorial (2x5), sendo o fator A constituido por ureia e ureia revestida com B e Cu (inibidor de urease) e o fator B composto por diferentes intervalos de entrada de agua (0, 3, 6, 9, 12 dias) apos a aplicacao das fontes de nitrogenio (N). Os resultados demonstram que o inibidor de urease retarda e diminui a conversao de N para NH3, reduzindo as perdas por volatilizacao, comparativamente a ureia sem inibidor. Entre os sistemas, as perdas sao potencializadas no sistema plantio direto. O inibidor de urease nao traz beneficios a produtividade em qualquer um dos sistemas de cultivo utilizados e o estresse causado na planta de arroz pelo atraso no inicio da irrigacao e mais prejudicial do que as perdas causadas pela volatilizacao de N-NH3.

Agronomic performance of rice to the use of urease inhibitor in two cropping systems

A utilizacao de ureia recoberta com inibidor de urease pode tornar-se uma ferramenta util para aumentar a eficiencia da adubacao nitrogenada em cobertura na cultura do arroz irrigado, diminuindo assim perdas do nutriente por volatilizacao de NH3 (amonia). Com isso, o objetivo desse trabalho foi avaliar a volatilizacao de NH3 e a resposta do arroz irrigado ao uso de ureia recoberta com inibidor de urease em dois sistemas de cultivo, direto e convencional. Para tanto, conduziram-se experimentos em campo, nos anos agricolas 2007/2008 e 2008/2009, na UFSM em Santa Maria-RS. O delineamento utilizado foi o delineamento experimental blocos completos casualizados em esquema bifatorial (2x5), com duas fontes, ureia e ureia+NBPT e cinco intervalos de inicio da irrigacao (0; 3; 6; 9; 12 dias) apos a aplicacao das fontes de N. Os resultados das duas safras demonstram que o inibidor de urease presente na ureia retarda e diminui a conversao de N para NH3, reduzindo as perdas por volatilizacao, comparativamente a ureia sem inibidor. Entre os sistemas, as perdas sao potencializadas no sistema plantio direto. O comportamento da variavel resposta em relacao a produtividade e variavel nos dois sistemas de cultivo utilizados e o estresse causado na planta de arroz pelo atraso no inicio da irrigacao e mais prejudicial do que as perdas causadas pela volatilizacao de NH3.

Fontes alternativas à ureia no fornecimento de nitrogênio para o arroz irrigado

Urea is the main source of N used in agriculture, but has large losses in irrigated rice. The objective of this study was to evaluate the efficiency of N sources alternative to urea for use by rice applied at different stages of plant development through the quantification of N-NH3 and agronomic parameters. The experiment was conducted in the field in the agricultural years 2007/08 and 2008/09. The experimental design was randomized blocks with four replications. The treatments consisted of different N sources applied at seeding, tillering and at the stage of floral differentiation: control without N, urea, urea + urease inhibitor, two sources of liquid N (N-28 and N-30) ammonium sulfate and urea + sulfur. In both seasons, the volatilization of N-NH3 at seeding was almost negligible, whereas in the V4 stage, the source that was less volatilized was the ammonium sulfate. Yield response varied among years, probably due to the availability of N in the soil and climatic aspects. When economically advantageous, the use of urease inhibitor and ammonium sulfate provide yields similar to urea supply.

Produtividade, fitotoxicidade e controle de arroz-vermelho na sucessão de cultivo de arroz irrigado no Sistema CLEARFIELD®

The objective of this study was to evaluate the CLEARFIELD ® system regarding the control of red rice, influences on productivity, as well as the possible phytotoxicity caused by carryover soil formulated mixture of imazethapyr and imazapic in tolerant rice genotype (IRGA 422CL) and non-tolerant (IRGA 417), which served as indicator plants. The experimental design was randomized blocks in a factorial scheme (4x3) with subplots, the main plots represented by rotating tolerant rice (IRGA 422CL) and rice not tolerant to imidazolinone (IRGA 417). In sub-plot treatments were applied to control red rice in different stages of the post-emergence (V4), pre + post emergence (day of seeding V4). Phytotoxicity was characterized based on the color of the leaves, width, growth and development of the leaf. It was observed that phytotoxicity was greater when the herbicide was applied post-emergence, effects remaining until 383 days after application. The control of red rice is not efficient with the use of only one agricultural year of CLEARFIELD® system and the best level of control and yield was obtained after two or three consecutive years of this system.