Nitrogen Fertilizer Levels and Plant Density Effect on Sunflower (Heliantus annuus L.) Growth and Productivity under Libyan Conditions

Abstract

A field experiment was carried out in private farm at El-Ghafara, Al-Maamorah district, Libya during 2025 summer season to study the effect of four nitrogen fertilizer levels, i.e. 70, 105, 140 and 175 kg/ ha and four plant densities (55500, 66600, 83300 and 111000 plant/ ha resulted from 30, 25, 20 and 15 cm spacing between plants on growth traits and productivity of sunflower variety Sakha 53. Randomized complete block design in split-plot arrangement in three blocks was used, where the four nitrogen levels were randomly distributed as whole plot and the four plant densities were randomly occupied as sub-plot. Increasing N levels was gradually increased the studied traits, where 175 kg N/ ha produced the tallest and thickest plants (189.77 and 2.22 cm), respectively, highest leaf area/ plant and leaf area index (1735.50 cm² and 1.37), latest flowering (49.24 days), largest disc diameter (19.73 cm), highest number and weight of seeds/ disc (992.45 and 65.48 g), however the heaviest 100-seed weight (6.83 and 6.89 g) and highest seed yield (4.328 and 4.365 t/ ha) resulted from 140 and 175 kg N/ ha, respectively, and the highest oil yield (1.692 t/ ha) resulted from 140 kg N/ ha application. Conversely, the highest seed oil percentages (42.72 and 41.28 %) resulted from 70 and 105 kg N/ ha, respectively.

On the other hand, the studied traits were significantly affected by plant densities, except number of days from sowing to 50 % flowering, the lowest density (55500 plant/ ha) produced thicker stems (2.05 cm), highest leaf area/ plant (1567.75 cm²), largest disc diameter (17.38 cm), highest number of seeds, seed weight/ disc and 100-seed weight (9.38.73, 60.70 g and 6.70 g), respectively. On the contrast, the highest plant density (111000 plant/ ha) produced the tallest plants (175.16 cm), highest LAI (1.65), seed and oil yield and seed oil percent (4.616 t/ ha, 1.905 t/ ha and 41.29 %), respectively. Interaction between (175 kg N/ ha) and any plant density produced the tallest and thickest plants, maximum leaf area/ plant and number of seeds/ disc.

However, interactions between both (140 or 175 kg N/ ha) and any plant density under study showed the latest flowering, largest disc diameter and heaviest 100-seed weight, The highest density (111000 plant/ ha) fertilized with any nitrogen level showed maximum LAI, highest seed and oil yields. The heaviest seed weight/ disc (70 g) resulted from (55500 plants/ ha) fertilized with 175 kg N/ ha.