Effect of Nano-NPK fertilizer and humic acid on vegetative growth and chemical properties of the vegetative parts of broccoli (Brassica oleracea var. Italica) in gypsiferous soil

• Kamil Fadhil jebur 1 Mohammed Jarullah Farhan 2

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This study investigated the growth response of broccoli (Brassica oleracea var. Italica) to soil-applied nano NPK fertilizer and humic acid in gypsiferous soil, with particular emphasis on vegetative growth parameters. Field experiments were conducted at the Research Station of the Department of Soil Science and Water Resources, College of Agriculture, Tikrit University, Iraq, during the 2024–2025 growing season. A Randomized Complete Block Design (RCBD) was adopted in a factorial arrangement, incorporating three rates of nano NPK fertilizer (20-20-20) at 0, 8, and 16 kg ha⁻¹, and three levels of humic acid at 0, 5, and 10 kg ha⁻¹, yielding nine treatment combinations with three replicates (n = 27 experimental units).

Results demonstrated that the application of nano NPK fertilizer at 16 kg ha⁻¹ significantly enhanced key vegetative growth indices, including plant height, leaf area, leaf chlorophyll content, shoot nitrogen concentration, and shoot potassium concentration, with percentage increases over the control of 9.93%, 31.83%, 12.74%, 25.12%, and 33.52%, respectively. The 8 kg ha⁻¹ nano NPK treatment yielded the highest improvements in leaf number and shoot phosphorus concentration, recording increases of 13.47%, 21.94%, and 24.14% above the control, respectively.

Humic acid application at 10 kg ha⁻¹ produced significant improvements across all assessed vegetative growth traits, namely plant height, leaf number, leaf area, leaf chlorophyll content, and shoot N, P, and K concentrations, with percentage increases over the control of 4.29%, 7.58%, 14.52%, 5.47%, 12.72%, 16.83%, and 23.14%, respectively. Furthermore, a significant interaction effect between nano NPK fertilizer and humic acid was observed. The H₂N₂ interaction treatment most effectively promoted plant height, leaf area, shoot nitrogen concentration, and shoot potassium concentration, while the H₂N₁ combination was superior in enhancing leaf number, leaf chlorophyll content, and shoot phosphorus concentration relative to the untreated control.

These findings suggest that the combined application of nano NPK fertilizer and humic acid represents a promising strategy for optimizing broccoli production in gypsiferous soils, offering potential benefits for sustainable crop management under challenging edaphic conditions.

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