Optimizing plant population and weed control methods for enhanced physiological growth and yield response of sunflower (Helianthus annuus L.) in the Nigerian Sudan savanna

Abstract

Sunflower (Helianthus annuus L.) production in the Sudan Savannah agroecological zone of Nigeria is significantly influenced by multiple agronomic factors, particularly plant population and weed control methods. This study was conducted at the Teaching and Research Farms of Bayero University Kano (BUK) and the National Horticultural Research Institute (NIHORT), Bagauda, during the 2018 and 2019 rainy seasons to assess the physiological growth, yield response, and weed control efficiency of sunflower under varying plant populations and weed control methods. The treatments consisted of three plant populations (22,500,000, 48,750,000, and 52,500,000 plants ha-1) and eight weed control methods, including mechanical, chemical, and allelopathic approaches. These were laid out in a split-plot design with three replications, with plant population and weed control methods the main plot and sub plots, respectively. Results revealed that the highest plant population (52,500,000 plants ha-1) significantly enhanced the physiological growth characters. The highest (0.07 g wk-1) relative growth rate (RGR) was recorded in 2019 at Bagauda, while the combined analysis showed 0.05 and 0.16 g wk-1 at Bagauda and BUK. Similarly, CGR peaked at 126.40 g cm-² wk-1 in 2019 at Bagauda and 106.40 g cm-² wk-1 in the combined analysis at BUK, while LAI reached its highest value at 4.59 in 2019 at Bagauda. However, kernel yield per hectare decreased at the highest plant population due to increased intraspecific competition. Among the weed control methods, (T3) application of pre-emergence Tithonia diversifolia extract fb post-emergence at 6 WAS recorded the highest weed control efficiency (WCE) of 76.3% at Bagauda and 82.88% at BUK, and significantly improved sunflower growth and yield components. The optimal plant population of 48,750,000 plants/ha combined with T3 was the most effective strategy for maximizing kernel yield while ensuring sustainable weed management. The weedy check consistently resulted in the lowest performance across all parameters. These findings suggest that an optimal plant population combined with allelopathic-based weed management can enhance sunflower productivity while minimizing weed interference in the Sudan Savannah region of Nigeria.