Resumo

MORALES MORALES, E. Javier et al. Net assimilation rate and sunflower seed yield as a function of urea and slow release urea. Agrociencia [online]. 2015, vol.49, n.2, pp.163-176. ISSN 2521-9766.

Nitrogen is a nutrient which increases growth, leaf area duration and crop photosynthesis, characteristics that permit sunflower (Helianthus annuus L.) to increase seed yield per surface unit. The objective of the present study was to evaluate the net assimilation rate, yield and principal components in two sunflower cultivars (Periquero and Victoria) as a function of two types of urea (common urea and slow release urea), and three doses of N (40, 80 and 120 kg N ha^-1), in three localities of the Estado de México (Toluca, Balderas and Chalco). The experimental design was complete randomized blocks with factorial arrangement. The 36 treatments resulted from the combinations of the three localities, the two cultivars, the two types of urea and the three nitrogen levels. The data were analyzed with ANOVA and treatments means, were compared with the DSH test (p≤0.05). In order to know the relationship between seed yield and the net assimilation rate, simple linear regression was calculated. The analysis of the results indicated that in Chalco the sunflower yielded (732.0 g m^-2) more than Toluca (285.9 g m^-2) and Balderas (467.0 g m^-2) due to the higher net assimilation rate (0.89 g dm^-2 d^-1); Victoria, with average yield of 508.2 g m^-2 and harvest index of 0.33, was higher than Periquero by 5.1 % and 11.76 %, respectively. With common urea average grain production was 508 g m^-2 were compared, 5.2 % higher than that obtained with slow release urea. The best dose in this study was 120 kg N ha^-1, because its average yield was 541.5 g m^-2. It is concluded that net assimilation rate positively affected seed yield, since the regression equation y = 217.8 + 308.2 (x) (r² = 0.69**) means that for each unit of increment in net assimilation rate, yield increases 308.2 g m^-2.

Palavras-chave : Helianthus annuus L.; nitrogen fertilization; polymer urea; harvest index.

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