Influence of Seaweed Extract on the Amount of Phosphorus Fertilizer for Onion Production
Rebaka Sultana
*
Department of Horticulture, Sher-e-Bangla Agricultural University, Dhaka 1207, Bangladesh.
Jasim Uddain
Department of Horticulture, Sher-e-Bangla Agricultural University, Dhaka 1207, Bangladesh.
Abul Hasnat M. Solaiman
Department of Horticulture, Sher-e-Bangla Agricultural University, Dhaka 1207, Bangladesh.
Mohammad Humayun Kabir
Department of Horticulture, Sher-e-Bangla Agricultural University, Dhaka 1207, Bangladesh.
Khadija Akhter
Department of Plant Pathology, Sher-e-Bangla Agricultural University, Dhaka 1207, Bangladesh.
Ruhul Amin
Department of Entomology, Sher-e-Bangla Agricultural University, Dhaka 1207, Bangladesh.
*Author to whom correspondence should be addressed.
Abstract
Phosphorus (P) is an essential nutrient for onion (Allium cepa L.) growth and bulb formation; however, its low use efficiency due to soil fixation processes often leads to excessive fertilizer application, increasing production costs and environmental risks. This study investigated the potential of seaweed extract (SE) derived from Ascophyllum nodosum to reduce phosphorus fertilizer requirements in winter onion production while maintaining or improving growth, yield, and quality. A field experiment was conducted at the Horticultural Farm of Sher-e-Bangla Agricultural University, Dhaka, Bangladesh, during November 2024–March 2025 using a randomized complete block design with six treatments and six replications. Treatments comprised T₁ (100% recommended NPK dose, control), T₂ (90% P + 1 L ha⁻¹ SE), T₃ (80% P + 2 L ha⁻¹ SE), T₄ (70% P + 3 L ha⁻¹ SE), T₅ (60% P + 4 L ha⁻¹ SE), and T₆ (50% P + 5 L ha⁻¹ SE). Results demonstrated that treatment T₃ consistently outperformed all other treatments, recording the highest plant height (62.30 cm at 90 DAT), leaf number (6.60 at 90 DAT), pseudostem diameter (1.66 cm at 90 DAT), chlorophyll content (64.03 SPAD), individual bulb weight (69.5 g), and total yield (20.85 t ha⁻¹). Furthermore, T₃ produced superior bulb quality attributes, including vitamin C (5.49 mg 100 g⁻¹), total phenol content (6.26 mg g⁻¹), total chlorophyll (1.97 mg g⁻¹), and enhanced mineral composition (Na 1.59%, K 2.22%, S 1.24%). The lowest values for all parameters were observed in T₆. These findings indicate that integrating seaweed extract at 2 L ha⁻¹ with 80% of the recommended phosphorus dose (T₃) effectively compensates for reduced phosphorus input by improving nutrient use efficiency, photosynthetic capacity, and physiological performance. This sustainable approach reduces dependence on chemical fertilizers, lowers production costs, and minimizes environmental impacts while enhancing both productivity and nutritional quality of onion. Further research is recommended across different agro-ecological zones and onion varieties to validate these findings.
Keywords: Onion (Allium cepa L.), seaweed extract, phosphorus reduction, bulb quality, yield