Abstract Background: The evaluation of selective herbicides for weed control in winter cereals is extremely important. Simple methods to evaluate alterations caused by herbicides in the growth and development of winter cereals can be performed with vegetation indices. Objective: Evaluate the potential of different vegetation indices by optical sensors to detect phytotoxicity caused by herbicides in winter cereals. Methods: The experiment was conducted under field conditions, in a randomized block design with four replications. Herbicides were sprayed when the plants were at Z24. The phytotoxicity was evaluated at 7, 14 and 21 days after treatment (DAT) and the normalized difference vegetation index (NDVI) and the normalized difference red edge index (NDRE) at 16, 22 and 37 DAT. Results: The herbicide 2,4-D was less phytotoxic to winter cereals, while metribuzin and saflufenacil caused higher percentages (up to 50%) of visible injuries. The NDRE discriminated more precisely than NDVI the variations in winter cereals, showing alteration in the chlorophyll content due to the phytotoxicity caused by the herbicides. The canonical correlation analysis found an inverse relationship between phytotoxicity and vegetation indices. Conclusions: The winter cereals studied were tolerant to herbicides, enabling the recovery of growth and development. The NDRE index was the most sensitive and showed greater potential in identifying injuries caused by herbicides. The canonical correlation analysis confirmed the inverse relationship between phytotoxicity and the reduction of vegetation indices.

ABSTRACT The objective of this study was to create a single mathematical equation able to estimate the leaf area of different cassava cultivars from one lineal dimension without destroying any plant tissue. Two hundred leaves per cultivar from ten cultivars were used to calibrate the model and more than one hundred leaves per cultivar were used to test its predictive capacity as independent data. All equations were the result of the nonlinear correlation between the leaf area and the length of its central lobe. To validate it as a “general” equation, another set of five cultivars were used. A “specific” equation for each cultivar was also calibrated to compare with the “general” equation’s performance. Cultivar Vassourinha has remarkably different leaf morphology from the other nine cultivars, making the “general” equation’s tendency line deviate and lowering its coefficient of determination. Therefore, one more equation was generated excluding that cultivar and, as a result, it was not possible to estimate the leaf area from all the cultivars using only the “general” equation. The “general without Vassourinha” equation has a high accuracy level when estimating leaf area of the other nine cultivars, plus the extra five cultivars that were included to validate the general equation; all of them present similar leaf morphology. Due to its importance, Vassourinha cultivar’s “specific” equation should be used when estimating leaf area for this cultivar or other cultivars with similar leaf morphology.

Resumo O objetivo desta pesquisa é destacar padrões climáticos que exerçam influência na variabilidade interanual da produtividade de arroz no Rio Grande do Sul (RS). Séries de produtividade de arroz de 47 municípios foram separadas em três grupos de acordo com sua produtividade (baixa, média e alta) baseado na análise de agrupamento. Correlações defasadas entre indicadores climáticos associados a padrões de teleconexão e a produtividade média de arroz de cada grupo evidenciaram a importância de cada índice para a variabilidade da produtividade da cultura no RS. Dentre os padrões de teleconexão, os que mais apresentaram correlações significativas e persistentes com a produtividade de arroz foram a Oscilação Quase Bianual (negativa), Oscilação Decadal do Pacífico (negativa), componente atmosférica (positiva) e oceânica (negativa) do fenômeno El Niño Oscilação Sul, além de anomalias de Temperatura da Superfície do Mar no Oceano Atlântico, entre 20° S-30° S e 20° O-40° O, (correlação negativa). A influência de alguns dos indicadores climáticos apresentados neste estudo ainda não havia sido discutida do ponto de vista agrícola e os resultados apresentados podem fornecer informações cruciais na tomada de decisões e na previsão de safra de arroz no Rio Grande do Sul.

Abstract The main of this work is to highlight climatic patterns that influence the interannual variability of rice yield in Rio Grande do Sul (RS). Series of rice yield data from 47 municipalities were separated into three groups according to their yield (low, medium and high) based on clustering analysis. Lag correlations between climatic indicators associated with teleconnections patterns and mean rice yield of each group evidenced the importance of each index for variability of the yield in RS. The most significant and persistent correlations with rice yield were the Quasi-Biennial Oscillation (negative), the Pacific Decadal Oscillation (negative) an atmospheric (positive) and oceanic (negative) components of the El Niño Southern Oscillation. In addition, Sea Surface Temperature anomalies in the Atlantic Ocean, between 20° S-30° S and 20° O-40° W (negative correlation) have a significant correlation with the rice yield. The influence of some of the climate indices had not yet been discussed from the agricultural point of view. These results can be a crucial information in decision-making and rice yield forecast in Rio Grande do Sul.

RESUMO A fenologia e o desenvolvimento da planta de arroz são eventos controlados por condições ambientais e fatores genéticos, sendo o potencial produtivo da cultura definido pela sua interação. Objetivou-se analisar o desempenho de genótipos de arroz irrigado em ecossistemas contrastantes e seus efeitos nas características morfofisiológicas. Dois ecossistemas foram analisados (tropical e subtropical), bem como cultivares recomendadas para regiões tropicais (BRS Catiana e BRS Jaçanã) e subtropicais (BRS Pampa, BRS 7 Taim e IRGA 424). O delineamento foi o de blocos casualizados, com quatros repetições, sendo fatores os genótipos, épocas de semeadura e sítios. Avaliou-se o desenvolvimento fenológico, dinâmica da biomassa, eficiência no uso da radiação e a produtividade de grãos. No ecossistema tropical, a demanda de graus-dia acumulados para o florescimento decresceu com maior magnitude que no subtropical, para as semeaduras tardias. No ecossistema subtropical, os valores de eficiência no uso da radiação foram similares e a produtividade elevada para todas as épocas de semeadura. Já no tropical, verificou-se variação nos valores de eficiência no uso da radiação e produtividade. Maiores acúmulos de graus-dia e de radiação solar na fase reprodutiva e de enchimento de grãos contribuíram para o aumento da produtividade em ambos os ecossistemas.

ABSTRACT Rice phenology and development are events controlled by environmental and genetic factors, and the yield potential of the crop is defined by their interaction. This study aimed at analyzing the performance of irrigated rice genotypes in contrasting ecosystems and their effects on morphophysiological characteristics. Two ecosystems (tropical and subtropical) were analyzed, as well as cultivars recommended for tropical (BRS Catiana and BRS Jaçanã) and subtropical (BRS Pampa, BRS 7 Taim and IRGA 424) regions. The experiments were arranged in a complete randomized block design, with four replicates, being the factors the genotypes, sowing times and sites. The phenological development, biomass dynamics, radiation use efficiency and grain yield were evaluated. The accumulated degree-days demand for flowering decreased faster in the tropical ecosystem than in the subtropical ecosystem for late sowing. The radiation use efficiency values were similar in the subtropical ecosystem and yield was high for all sowing dates. On the other hand, the tropical ecosystem showed a high variation for radiation use efficiency values and yield. The higher accumulation of degree-days and solar radiation during the reproductive and grain-filling phases contributed to increase yield in both ecosystems.