Sunflower: Response to Foliar Application of Boron in Southwest Coastal Uruguayan Soils

Although the cropping area of sunflower (Helianthus annus L.) in Uruguay decreased during the last decade, sunflower crop is being promoted for biodiesel production. Sunflower production is known to be particularly sensitive to boron (B) deficiency, therefore the nutrient may be beneficial to maximize yields. Crop response to foliar applied B has been reported in Argentina but there is no information available in Uruguay. A set of twelve field experiments was carried out on soils typical of the southwestern region with a B concentration that varied between 0.45 and 1.19 mu g(-1). Boron treatments consisted of foliar applied B at 300, 600 and 900 g B ha(-1) at flower bud stage plus a control. Boron application did not significantly increase grain yield or oil content. However, grain yield was reduced in three sites when B was applied at 900 g ha(-1) (P<0.10). Results indicate that the soils of this study would have an adequate supply of B for sunflower. It was concluded that it is unlikely to find responses to B in this type of soil and a preventive application should not exceed 340 g B ha(-1) to avoid the risk of toxicity.