Abstract

Molybdenum (Mo) foliar spray may improve the nitrogen acquisition by the plants and increase the crop yield. The effects of Mo foliar spray on nitrogen nutrition, achene yield and yield components of sunflower were investigate in this study. The experiment was carried out on a Rhodic Hapludox in Chavantes, São Paulo, Brazil under conventional tillage system. Treatments consisted of five Mo concentrations [0 (control), 26, 52, 78 and 104 g ha^–1 of Mo] applied as foliar spray at the growing stage of eight developed leaves – V8 (18 days after plants emergence). Foliar application of Mo rates reduced the nitrate (NO₃^–) concentration, and increased the concentrations of ammonium (NH₄⁺), total nitrogen (N) and Mo in the leaf tissue of sunflower. Molybdenum foliar spray did not affect the plant height, stem diameter, capitulum diameter and number of achenes per capitulum of sunflower. Application of 58 and 68 g ha^–1 of Mo resulted in increased of the thousand achenes mass (40%) and achene yield (27%) of sunflower, respectively, compared to the control. Molybdenum foliar spray improves the nitrogen nutrition and the achenes mass resulting in the increased achene yield of sunflower. Results suggest that Mo deficiency can compromise the nitrogen metabolism of plants, and result in lower achene yield of sunflower.

Key words: Helianthus annuus L., molybdoenzymes, nitrate assimilation, plant nutrition.