Managing Nitrogen to Optimise Sunflower Yield and Oil content

Abstract

Optimising grain yields and oil contents of sunflower within seasonal climatic constraints is critical to maximising profitability. While yields have on average continued to increase, growers often struggle to achieve oil contents above the industry standard of 40%. Since a bonus/discount system applies for oil contents above or below 40%, it would be beneficial for farmers to have tools available to target particular oil contents. The balance of nitrate and water in the soil profile at sowing has been utilised to target protein contents of cereal crops. Protein and oil contents of grains are inversely related. Thus, we hypothesised that a similar approach could be used to target oil contents of sunflower. Data on soil nitrate and water levels (1.5m depth) at sowing, grain yield and oil contents were collected from four nitrogen rate experiments in northern New South Wales and subjected to regression analysis. Fertiliser N rates were zero, 50, 75, 100, 125, 150 and 200 kg N/ha. Sowing soil water levels were in the range 137-207 mm. As nitrogen supply increased and the ratio of soil nitrate:water increased from 0.35 to 1.8, grain oil contents declined from 45 to 37%. Grain yields showed a slight decline through the nitrate:water range also. Matching nitrate:water at ratios 0.5-1.0 optimised oil contents above the required industry standard of 40% as well as grain yield. Oil contents were, on average, <40% when the nitrate:water ratio was >1.0. These results suggest that sunflower oil contents may be more specifically targeted and fertiliser N inputs more accurately determined for optimum profitability.