Physiological and Morphological Responses of Corn Related to Urea Application in Different Growth Stages.

Studies on optimum periods of nitrogen (N) application are extremely important for the best fertilizer management of corn. The objectives of this study were to evaluate the response of corn to nitrogen fertilization and the correlation between physiological and morphological characteristics in relation to shoot dry biomass production. The experiment was conducted under field conditions, from 2011 to 2012, in Piracicaba/SP, Brazil, and the treatments were: topdressing with N-urea at different growth stages (V4, V6, V8, V10 and V12), including a control. The following variables were analyzed: photosynthetic pigments (total chlorophyll (CT), chlorophyll a (CA), chlorophyll b (CB) and carotenoids (CRT); SPAD index (SI); Leaf Area (LA) evaluated in V14 phenological stage; Plant Height (PH) and shoot dry biomass (SDB) evaluated at flowering and during kernel dough stage, respectively. The experiment was carried out in randomized blocks with four replicates. The data were subjected to variance analysis using the F test (p<0.05), LSD test for mean comparison and Pearson correlation test was also performed to verify the possible correlation between variables. There were significant differences for the treatments concerning SI, SDB, PH and LA variables. For them, it could be seen that treatments differed only from the control; the fertilization period did not provide differences on the analyzed variables. A positive correlation between SI with SDB, CB, CRT, LA and PH was observed. This is important because the nutritional and physiological conditions of the plant can be measured in advance and indirectly by this index. The CT correlated significantly only with other photosynthetic pigments. The LA presented correlation with SI as well as with CA, CB, CRT, PH and SDB, the same ocurred for the correlation between PH and SDB. This shows the importance of using SI, LA and PH variables to estimate the accumulation of SDB.