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      Estimation of leaf area index in the sunflower as a function of thermal time1 Translated title: Estimativa do índice de área foliar do girassol em função da soma térmica

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          Abstract

          The aim of this study was to obtain a mathematical model for estimating the leaf area index (LAI) of a sunflower crop as a function of accumulated thermal time. Generating the models and testing their coefficients was carried out using data obtained from experiments carried out for different sowing dates in the crop years of 2007/08, 2008/09, 2009/10 and 2010/11 with two sunflower hybrids, Aguará 03 and Hélio 358. Linear leaf dimensions were used for the non-destructive measurement of the leaf area, and thermal time was used to quantify the biological time. With the data for accumulated thermal time (TTa) and LAI known for any one day after emergence, mathematical models were generated for estimating the LAI. The following models were obtained, as they presented the best fit (lowest rootmean- square error, RMSE): gaussian peak, cubic polynomial, sigmoidal and an adjusted compound model, the modified sigmoidal. The modified sigmoidal model had the best fit to the generation data and the highest value for the coefficient of determination (R2). In testing the models, the lowest values for root-mean-square error, and the highest R2 between the observed and estimated values were obtained with the modified sigmoidal model.

          Translated abstract

          O objetivo deste trabalho foi obter um modelo matemático que estime o índice de área foliar (IAF) para a cultura do girassol em função da soma térmica acumulada. A geração dos modelos e o teste de seus coeficientes foram realizadas com dados obtidos de experimentos conduzidos em diferentes datas de semeadura nos anos agrícolas de 2007/08, 2008/09, 2009/10 e 2010/11, com os híbridos de girassol Aguará 03 e Hélio 358. Utilizou-se as dimensões lineares das folhas para determinação não destrutiva da área foliar e a soma térmica para quantificar o tempo biológico. Conhecidos os dados de soma térmica acumulada (STa) e IAF para um mesmo dia após a emergência, gerou-se modelos matemáticos que estimam o IAF. Foram obtidos, por apresentarem os melhores ajustes (menor raiz quadrada do quadrado médio do erro, RQME), os modelos de pico gaussiano, polinomial cúbico, sigmoidal e um modelo ajustado composto, denominado sigmoidal modificado. O modelo sigmoidal modificado obteve melhor ajuste aos dados de geração e o maior valor do coeficiente de determinação (R2). No teste dos modelos obteve-se os menores valores da raiz do quadrado médio do erro e maior R2entre valores observados e estimados para o modelo sigmoidal modificado.

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          Maximum-minimum temperatures as a basis for computing heat units

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            Molecular regulation of leaf senescence.

            Leaf senescence is a process of programmed cell death, which is induced in an age-dependent manner and by various environmental cues. The mechanisms that regulate the induction and progression of leaf senescence remain unclear because of their complexity. However, recent genetic and reverse-genetic approaches have identified key components of the regulation of leaf senescence and have revealed glimpses of the underlying molecular mechanisms.
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              Relationships among phenological growing season, time-integrated normalized difference vegetation index and climate forcing in the temperate region of eastern China

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                Author and article information

                Contributors
                Role: ND
                Role: ND
                Role: ND
                Role: ND
                Role: ND
                Journal
                rca
                Revista Ciência Agronômica
                Rev. Ciênc. Agron.
                Universidade Federal do Ceará (Fortaleza )
                1806-6690
                June 2015
                : 46
                : 2
                : 404-411
                Affiliations
                [1 ] Departamento de Defesa Agropecuária, Secretaria da Agricultura, Pecuária e Agronegócio Brasil
                [2 ] Universidade Federal de Santa Maria Brazil
                [3 ] Programa de Pós-Graduação em Engenharia de Sistemas Agrícolas
                [4 ] Instituto Federal de Educação, Ciencia e Tecnologia Farroupilha Brazil
                Article
                S1806-66902015000200404
                10.5935/1806-6690.20150020
                13bf4024-de15-4767-b3d2-4cb3988d4391

                http://creativecommons.org/licenses/by/4.0/

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                SciELO Brazil

                Self URI (journal page): http://www.scielo.br/scielo.php?script=sci_serial&pid=1806-6690&lng=en
                Categories
                AGRONOMY

                Horticulture
                Helianthus annuus,Leaf analysis,Modelling,Análise foliar,Modelagem
                Horticulture
                Helianthus annuus, Leaf analysis, Modelling, Análise foliar, Modelagem

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