Effect of Foliar Spraying with Nano-Zinc and Addition of Organic Fertilizer and Humic Acid on the Growth and Yield of Broccoli

Broccoli (Brassica oleracea var. italica) is a nutrient-demanding vegetable crop whose growth and productivity are strongly influenced by soil fertility and nutrient availability. This field experiment was conducted in Babylon Governorate, Iraq, during the 2025-2026 growing season to evaluate the individual and combined effects of foliar-applied nano-zinc, organic manure, and humic acid on growth and yield traits of broccoli. The experiment was arranged as a factorial trial in a randomized complete block design with three replications. Treatments included three nano-zinc concentrations (0, 1.5, and 3 g L⁻¹), three organic-manure treatments (no manure, cattle manure at 20 t ha⁻¹, and sheep manure at 20 t ha⁻¹), and three humic-acid rates (0, 10, and 20 L ha⁻¹). The highest treatment levels significantly improved plant height, leaf number, main head diameter, and total head yield. The triple interaction Z2O2H2 recorded the highest plant height (79.67 cm), leaf number (28.87 leaves plant⁻¹), main head diameter (26.33 cm), and total yield (29.87 Mg ha⁻¹), compared with the untreated control Z0O0H0, which recorded 42.33 cm, 16.33 leaves plant⁻¹, 13.33 cm, and 12.60 Mg ha⁻¹, respectively. These results indicate that integrating foliar nano-zinc at 3 g L⁻¹ with sheep manure at 20 t ha⁻¹ and humic acid at 20 L ha⁻¹ is an effective fertilization strategy for improving broccoli growth and productivity under the conditions of the study.