Comparative effects of zinc oxide nanoparticles and conventional zinc on growth and yield attributes of cowpea

Zinc deficiency is a widespread micronutrient constraint that limits growth, reproductive development and yield formation in legume crops, particularly under alkaline soil conditions. Nano-enabled fertilisers have recently emerged as a promising approach to enhance nutrient use efficiency and crop productivity due to their higher surface area and improved reactivity compared with conventional fertilisers. The present study evaluated the comparative effectiveness of zinc oxide nanoparticles (ZnO-NPs) and conventional bulk zinc on growth, yield attributes and seed productivity of cowpea. A pot experiment was conducted at Chaudhary Charan Singh Haryana Agricultural University, Hisar, during the summer season of 2023–24 using the variety Kashi Kanchan under a Completely randomised design with 13 treatments and 3 replications. Zinc was applied as a foliar spray at concentrations of 400, 500 and 600 ppm in both nanoparticle and bulk forms with one or two applications at critical growth stages. Zinc fertilisation significantly improved vegetative growth, reproductive traits and yield compared with the untreated control. Among the treatments, foliar application of 600 ppm ZnO nanoparticles applied twice (25 and 50 days after sowing) results in maximum plant height (61.70 cm), number of branches (7.89), pods per plant (23.22), seeds per pod (13.04) and seed yield per plant (20.32 g), which remained statistically at par with 500 ppm ZnO nanoparticles applied twice, a yield increase of approximately 26 % over the control. Nano-zinc treatments consistently outperformed bulk zinc fertilisers, indicating enhanced nutrient availability and physiological efficiency. Correlation and path coefficient analyses revealed that pod length, pod weight, seeds per pod and pods per plant were the principal determinants of seed yield. Quadratic regression analysis further indicated an optimum ZnO-NP concentration of approximately 550 ppm for maximising seed productivity. The findings highlight the agronomic potential of nano zinc fertilisation as an effective strategy for improving nutrient use efficiency, yield and sustainable production of cowpea.