Appropriate Nitrogen and Phosphorus Fertilizer Regime for Sunflower (Helianthus Annuus L.) In the Humid Tropics

Two field trials were conducted on the Research Farm of the Institute of Food Security, Environmental Resources and Agricultural Research, Nigeria during the late cropping seasons (Jun.–Nov.) of 2014 and 2015 to evaluate the agronomic performance of four recently released sunflower varieties (SAMSUN-1, SMASUN-2, SAMSUN-3 and SAMSUN-4) to three fertilizer regimes: Control, Split application of 30 kg N + 28 kg P₂O₅ at 21 days after sowing (DAS) and at anthesis and Single application of 60 kg N and 56 kg P₂O₅ at 21DAS. The experiment was laid out in a randomized complete block design using a 3 × 4 factorial arrangement and replicated three times. Data were collected on phenology, plant height, seed yield and yield attributes, and quality. The varietal effect was only significant in 2015 for head weight, a number of achene per head and 100 achene weight. Application of N and P fertilizer either as split or single significantly (P ≤ 0.05; F-test) enhanced plant height at R5 and R9, 100 achene weight, achene weight per head and grain yield in both years. Single application resulted in significantly (P ≤ 0.05) higher grain yield in 2014 than the split and control and was on par with a split. Significant variety × fertilizer regime was recorded for protein content in 2014 and 2015, and oil content in 2015. Therefore, a single application of N and P fertilizers at 21 WAS is recommended for adoption in the humid tropics to enhance seed and oil production of SAMSUN-3 and SAMSUN-4.