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

Resumen

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.