Boron Levels on Yielp Characteristics of Sunflower.

Sunflower (Helianthus annus L.) is an important source of renewable energy in Brazil. However, it requires more boron (B) for its development than other species. The aim of this study was to evaluate and discuss morphological and production characteristics due to B doses of cultivating sunflower Dow AgroSciences M734. The experiment was carried in Palmas, Tocantins State, Brazil. Data were collected during July to August of 2015, in greenhouse conditions, using an Oxisol. The experimental design was complete randomized, with six B doses (0; 2; 4.5; 9; 18 and 36 mg dm^-3) and 4 replications and using borax as B source. Characteristics evaluated were: stem height (SH), stem curvature (SC), capitulum length (CL), number of achenes (NA), weight of 1000 achenes (WA) and grain yield (GY). Data were estimated and compared by F test at 5%, and when significant, regression was adjusted. B doses did not affect (P>0.05) stem curvature and weight of 1000 achenes. On the other hand, stem height, capitulum length, number of achenes and weight of 1000 achenes were affected (P<0.05) and were adjusted to a quadratic regression model. SH = 120.43+0.1797X-0.0225X², R²=0.52, CV=7.26%; CL=6.72+0.0387X-0.0025X², R²=0.80, CV=8.75%; NA=253.33+12.43X-0.4385X², R²=0.87, CV=14.45% and WA=494.43+23.73X-0.8957X², R²=0.86, CV=19.80%. The highest stem height (120.78 cm) was obtained with 3.99 mg B dm^-3 while capitulum length was highest (6.86 g) with 7.74 mg B dm^-3 and number of achenes was 341.41 with 14.17 mg B dm^-3. Grain yield increased with B doses, since capitulum length and number of achenes also increased, therefore, maximum grain yield (645.12 kg ha^-1) was achieved with 13.25 mg B dm^-3. The results indicated that 13.25 mg B dm^-3 is necessary to maximum sunflower production.