Effect of Residual and Added Phosphorous on Sunflower (Helianthus annuus L.) in Wet Soil of Southwestern Coastal Bangladesh

Abstract

Management of fertilizer at the optimum rate is one of the most important components in producing maximum yield and profit from any crop. This experiment was carried out in a farmer's field at Pankhali Village, Dacope, Khulna, Bangladesh, during December 2018 to April 2019 to determine the effect of residual and added phosphorus on sunflower (Helianthus annuus L.) grown in wet and saline soil of southwestern Bangladesh. The experiment was conducted in a Randomized Complete Block Design (RCBD) with three replications. Six levels of phosphorus (0, 5, 7.5, 10, 12.5, and 15 kg P ha⁻¹) in the form of triple superphosphate were applied to the previous transplanted aman rice field and considered as residual phosphorus. A current phosphorus application at the rate of 50 kg P ha⁻¹ was applied to the sunflower field and considered as current phosphorus. The results showed that residual phosphorus levels had no significant effect on growth, crop phenology, yield attributes, or seed yield. Residual phosphorus from the lowest application rate (5 kg ha⁻¹) performed similarly to the highest rate (15 kg ha⁻¹). Significant yield differences were observed only between the treatment with no added phosphorus in the previous transplanted aman crop and the treatments receiving residual phosphorus. In contrast, current phosphorus application (50 kg P ha⁻¹) significantly influenced all growth parameters, yield-contributing characters, and seed yield. The interaction between residual phosphorus and current phosphorus application was non-significant for all measured parameters. The results revealed that current phosphorus application increased seed yield; however, the yield gap was only about 0.2 t ha⁻¹ compared with the yield obtained from the highest residual phosphorus treatment (15 kg P ha⁻¹). Residual phosphorus from the previous crop, together with inherent soil phosphorus, was sufficient to produce a remunerative seed yield of sunflower in the wet soils of southwestern coastal Bangladesh. Residual phosphorus fertilizers have economic significance for farmers because they reduce the need for fertilizer application in subsequent years. The findings of this study may help in recommending phosphorus rates for sunflower cultivation in this region and contribute to reducing production costs.