Effects of growth reducer and nitrogen fertilization on morphological variables, SPAD index, interception of radiation and productivity of wheat

ABSTRACT The objective of this study was to evaluate the effect of growth reducer and nitrogen fertilization on morphological variables, SPAD index, radiation interception, and grain yield of three cultivars of wheat. The experimental design was a randomized block in factorial scheme 3x5x2, with three cultivars (Mestre, Iguaçú and Itaipú), five nitrogen doses (0, 40, 80, 120, 160 Kg ha-1), and application or no application of a growth reducer, with three replications. The following characteristics were evaluated: plant height, SPAD index, leaf area index (LAI), Global Radiation Interception (GRI) and grain yield. The Tukey test (p < 0.05) was used for the comparison between the means of cultivar and growth reducer factors, and for a regression analysis to evaluate N levels. Increasing the dose of nitrogen promotes an increase in LAI of plants of wheat crops differently among cultivars, which leads to a greater degree of global radiation interception. At doses higher or equal to 120 Kg ha-1 of nitrogen, there are significant differences in grain yield between treatments with and without the application of the growth reducer. The significant interaction between growth reducer and nitrogen dose, showed that applications of growth reducer increase the GRI at doses above and below 80 Kg ha-1 of nitrogen. Nitrogen rates of 138 and 109 Kg ha-1 are responsible for maximum grain yields of wheat, which is 4235 and 3787 Kg ha-1 with and without the use of growth reducer, respectively. RESUMO O objetivo deste trabalho foi avaliar o efeito de redutor de crescimento e de adubação nitrogenada sobre variáveis morfológicas, índice SPAD, interceptação de radiação global e produtividade, de três cultivares de trigo. O delineamento experimental utilizado foi o de blocos casualizados, em esquema fatorial 3x5x2, com três cultivares (Mestre, Iguaçú e Itaipú), cinco doses de nitrogênio (0, 40, 80, 120, 160 Kg ha-1) e aplicação, ou não, de redutor de crescimento, com três repetições. Avaliaram-se altura de planta, índice SPAD, índice de área foliar (IAF), interceptação de radiação global (IRG) e produtividade de grãos. Utilizou-se o teste de Tukey (p < 0,05), para a comparação entre as médias dos fatores cultivar e redutor de crescimento, e análise de regressão, para avaliação das doses de N. O aumento da dose de nitrogênio promove aumento no IAF de plantas na cultura o trigo, de forma diferenciada entre os cultivares, acarretando maior interceptação de radiação global. Em doses d