Resposta de Populações de Plantas Daninhas ao Plantio e a Taxas Reduzidas de Herbicida e Nitrogênio na Produção de Trigo (Triticum aestivum)

Field experiments were carried out in 1999 and 2000 to investigate the effects of conventional (CT) and no-tillage (NT) systems, interacting with three herbicide dose levels and three nitrogen (N) levels on weed growth and wheat production of two varieties. There was a higher grain yield for NT system compared with CT in one year. CT weed biomass was lower than from NT weed biomass, in both varieties. No differences on wheat biomass and grain yield were observed between full and reduced herbicide rates. N fertilizer increased wheat biomass and grain yield significantly. Only N medium level had an effect upon weed biomass with respect to non-fertilized plots, while the highest fertilization rate lowered weed biomass. Conventional tillage, reduced herbicide rates and nitrogen fertilization were effective ways of limiting weed production in wheat.Experimentos foram conduzidos sob condições de campo em 1999 e 2000 a fim de investigar os efeitos dos plantios convencional (PC) e direto (PD), em combinação com três doses de herbicidas e três de nitrogênio (N), no crescimento de plantas daninhas e produção de duas variedades de trigo. Foi observada produção maior de grãos PD, comparado ao PC, durante um ano. A biomassa das plantas daninhas no PC foi menor do que no PD, para as duas variedades. Nenhuma diferença em biomassa e produção de grãos de trigo foi observada entre as doses de herbicida integral e reduzida. N aumentou a biomassa do trigo e produção de grãos significativamente. Apenas o nível médio de N teve efeito sobre a biomassa das plantas daninhas em relação à não-aplicação de N, enquanto uma taxa maior de N diminuiu a biomassa das plantas daninhas. No plantio convencional, doses reduzidas de herbicida e aplicação de N foram efetivos na limitação do crescimento das plantas daninhas no cultivo de trigo.Facultad de Ciencias Agrarias y Forestale

Senescence and yield responses to plant density in stay green and earlier-senescing maize hybrids from Argentina

Increases in maize (Zea mays L.) yield over the past few decades have been associated with breeding for tolerance to progressively higher plant densities. Since high plant density exacerbates interplant competition, it has been suggested that improved resource capture through delayed senescence might be advantageous in such situations. The main objectives of this work were to determine (1) the time-course of canopy senescence, (2) post-silking C and N accumulation and (3) yield responses of contemporary maize hybrids with different expression of the stay green (SG) character grown in a range of plant densities from moderate to intense crowding stress. Three experiments consisting of a combination of different plant densities (from 6 to 10 pl m−2) and commercial hybrids with different timing of senescence were carried out. High density accelerated leaf senescence at the lower canopy layer. The SG hybrids delayed senescence and retained green leaves at physiological maturity at all tested densities. One of these hybrids (NK880), with a strong SG character, retained green leaves at all canopy layers, even at the lower layer exposed to limiting irradiance. Lower canopy leaves maintained high respiratory rates in NK880, while leaves of the NSG hybrid (DK682) senesced and their respiration became not detectable. At the highest tested density, the NSG DK682 achieved greater grain yields than the SG NK880. Increased density reduced kernel weight (KW), and this decrease was more pronounced for the SG NK880 (6–18% comparing 10 vs. 8 pl m−2). In spite of delayed senescence in NK880, no hybrid differences were found for post-silking dry matter accumulation and plant dry matter at physiological maturity. Unexpectedly, plant nitrogen content (Nc) at harvest was similar (Exp. I) or even lower (P < 0.05, Exp. II) in the SG NK880. This was the result of lower net N accumulation during the post-silking period (Exp. I) or lower Nc achieved at silking (Exp. II) in the SG NK880. A strong positive relation was found between KW and N concentration in kernels, with %N in kernels being below the critical N concentration to achieve potential KW (around 1.4%) in the SG hybrid. This suggests that yield in NK880 was limited by N. In the SG genotype, N remobilization from vegetative organs did not seem to compensate for the N deficit for optimum grain growth. In summary, at high densities the NK880 hybrid displayed a strong, constitutive SG character, even if it accumulated less N, and senescence delay was not reflected in higher grain yield.Fil: Antonietta, Mariana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico La Plata. Instituto de Fisiología Vegetal; Argentina; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Agrarias y Forestales; ArgentinaFil: Fanello, Diego Darío. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico La Plata. Instituto de Fisiología Vegetal; Argentina; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Agrarias y Forestales; ArgentinaFil: Acciaresi, H. A.. Universidad Nacional de La Plata. Facultad de Ciencias Agrarias y Forestales; ArgentinaFil: Guiamet, Juan Jose. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico La Plata. Instituto de Fisiología Vegetal; Argentina; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Agrarias y Forestales; Argentin

Resposta de Populações de Plantas Daninhas ao Plantio e a Taxas Reduzidas de Herbicida e Nitrogênio na Produção de Trigo (Triticum aestivum)

Field experiments were carried out in 1999 and 2000 to investigate the effects of conventional (CT) and no-tillage (NT) systems, interacting with three herbicide dose levels and three nitrogen (N) levels on weed growth and wheat production of two varieties. There was a higher grain yield for NT system compared with CT in one year. CT weed biomass was lower than from NT weed biomass, in both varieties. No differences on wheat biomass and grain yield were observed between full and reduced herbicide rates. N fertilizer increased wheat biomass and grain yield significantly. Only N medium level had an effect upon weed biomass with respect to non-fertilized plots, while the highest fertilization rate lowered weed biomass. Conventional tillage, reduced herbicide rates and nitrogen fertilization were effective ways of limiting weed production in wheat.Experimentos foram conduzidos sob condições de campo em 1999 e 2000 a fim de investigar os efeitos dos plantios convencional (PC) e direto (PD), em combinação com três doses de herbicidas e três de nitrogênio (N), no crescimento de plantas daninhas e produção de duas variedades de trigo. Foi observada produção maior de grãos PD, comparado ao PC, durante um ano. A biomassa das plantas daninhas no PC foi menor do que no PD, para as duas variedades. Nenhuma diferença em biomassa e produção de grãos de trigo foi observada entre as doses de herbicida integral e reduzida. N aumentou a biomassa do trigo e produção de grãos significativamente. Apenas o nível médio de N teve efeito sobre a biomassa das plantas daninhas em relação à não-aplicação de N, enquanto uma taxa maior de N diminuiu a biomassa das plantas daninhas. No plantio convencional, doses reduzidas de herbicida e aplicação de N foram efetivos na limitação do crescimento das plantas daninhas no cultivo de trigo.Facultad de Ciencias Agrarias y Forestale

Extensão bivariada do índice de confiabilidade univariado para avaliação da estabilidade fenotípica Bivariate extension of univariate reliability index for evaluating phenotypic stability

Com o presente trabalho, objetiva-se realizar a derivação teórica da extensão bivariada dos métodos de Annicchiarico (1992) e Annicchiarico et al. (1995) para estudar a estabilidade fenotípica. A partir dos ensaios com <img src="/img/revistas/cagro/v28n5/a11res01.gif" align=texttop>genótipos em <img src="/img/revistas/cagro/v28n5/a11res02.gif" align=texttop>ambientes e mensurações de duas variáveis, cada genótipo teve seu valor padronizado com relação a cada variável k = 1, 2. Essa padronização foi realizada em função da média do ambiente, da seguinte forma: Wijk = Yijk/<img src="/img/revistas/cagro/v28n5/a11res03.gif" align=top>&#215;100 ; em que Wijk representa o valor padronizado do genótipo i, no ambiente j para a variável k; <img src="/img/revistas/cagro/v28n5/a11res04.gif" align=top>representa a média observada do genótipo <img src="/img/revistas/cagro/v28n5/a11res05.gif" align=texttop>, no ambiente <img src="/img/revistas/cagro/v28n5/a11res06.gif" align=texttop>para a variável k e <img src="/img/revistas/cagro/v28n5/a11res07.gif" align=texttop>, a média de todos genótipos para o ambiente <img src="/img/revistas/cagro/v28n5/a11res06.gif" align=texttop>e variável k. Com os valores padronizados foram estimados o vetor média e a matriz de variância e covariância de cada genótipo. Foi obtida a derivação teórica da extensão bivariada do índice de risco (Ii) de Annicchiarico com sucesso e foi proposto um segundo índice de risco baseado nas probabilidades bivariada (Prb i); os dois índices apresentaram grande concordância nos resultados obtidos em um exemplo ilustrativo com genótipos de melões.<br>The objective of this work was to obtain the theoretical derivation of the bivariate extension to the methods proposed by Annicchiarico (1992) and Annicchiarico et al. (1995) for studing phenotypic stability. Considering assays with <img src="/img/revistas/cagro/v28n5/a11res01.gif" align=texttop>genotypes in <img src="/img/revistas/cagro/v28n5/a11res02.gif" align=texttop>environments and two variates, every genotype had the response of each variate (k = 1, 2) standardized. This standardization has been made using the environment means as follows: Wijk = Yijk/<img src="/img/revistas/cagro/v28n5/a11res03.gif" align=top>&#215;100 ; where Wijk represents the ith genotype standard value in the jth environment for the kth variate; <img src="/img/revistas/cagro/v28n5/a11res04.gif" align=top>represents the observed mean of the ith genotype, in jth environment for the kth variate e <img src="/img/revistas/cagro/v28n5/a11res07.gif" align=texttop>the overall genotypes means for jth environment to kth variate. Considering the standardized values, the genotypes mean vector and covariance matrix were estimated. The theoretical derivation of the bivariate reliability index (Ii) of Annicchiarico was wasked out and a second risk index was proposed based on the bivariate probabilities (Prb i); the two indexes proposed has shown good agreement to the results in an example with melon genotypes