Nitrogen Balance Approach to Sunflower Fertilization

Abstract

There is very limited information on sunflower (Helianthus annus L.) response to nitrogen (N) fertilizer in comparison to other crops. The N‐balance method has been proposed to estimate fertilizer rates for many crops but this system has not been developed for sunflower fertilization and thus there is a lack of specific parameters for the use of the N‐balance method in sunflower fertilization. The objectives of this experiment were to analyze the response of sunflower yield and yield components to N fertilizer, and to estimate parameters needed to develop a working N balance method. A 2‐year study was conducted in Balcarce, Argentina. Five N fertilizer rates were broadcasted (0, 25, 50, 100, and 200 kg N ha^− 1) when the crop reached three pairs of fully expanded leaves. Nitrogen fertilization increased sunflower grain and oil yields, but had no effect on grain oil concentration. A positive response of grain number and grain yield to crop N uptake at the end of flowering was found. In order to maximize yield, sunflower required 47 kg N Mg^− 1 grain and an uptake of 150 kg N ha^− 1. Crop N uptake was linearly related to N supply (soil NO₃ ⁻–N at fertilization + mineralized soil N between fertilization and end of flowering + fertilizer N). A 59% uptake efficiency of N supply was estimated. An N supply of 231 kg N ha^− 1 was required to maximize sunflower yield.

Keywords:

• Nitrogen fertilizer
• Sunflower
• N balance method
• Grain yield
• Oil yield