Effect of nano-NPK fertilizer and BAP on growth and flowering of Viola tricolor

The interaction between nutrients and growth regulators may provide an effective means for enhancing the productivity of crops. The effects of nano NPK fertilizer (0, 0.5, 0.75, and 1 g pot^-1) in combination with 6-benzylaminopurine (BAP, 0, 50, and 75 ppm) on Viola tricolor L. growth and flowering were evaluated in a 4 × 3 factorial experiment in a completely randomized design with three replications, conducted in a shaded hot-house in Mosul, Iraq, during spring 2022. Results showed that applying NPK alone had a greater effect than that of applying BAP alone; however, the use of both NPK and BAP together resulted in a considerably stronger synergy when both products were added to the nutrient solution. The treatment with NPK1BAP75 had the most pronounced effects on plant height (68% increase), leaf number (94% increase), and branch number (16% increase) relative to control. Biomass accumulation was also maximum for this treatment with fresh and dry weight returns of 168 g and 56 g, respectively. Additionally, the photosynthesis rate and chlorophyll concentration increased by 72% and 107%, respectively, compared to the control. Combined application of nano NPK and BAP resulted in increased flowering response, as indicated by earlier bud opening and higher number of flowers compared to the control. Moreover to enhanced flowering capabilities, the accumulation of nutrients by plants increased dramatically, as evidenced by the increased potassium content in treated plants increasing over twelve times that of control group plants. Therefore, the combination of nano NPK 1 g pot^-1 combined with 75 ppm BAP was the most effective treatment, as it shows that an integrated approach to enhance plant growth and flowering is feasible for developing a sustainable and efficient agricultural production system.