Synergistic impact of nitrogen fertilizer sources and soil applied humic acid on wheat morpho-physiological and biochemical mechanisms in a semi-arid region

Tahir Fazal ¹ Umar Arshad ² Sammia Ghazanfar ^3*

• ¹ Department of Agronomy, The Islamia University of Bahawalpur, Bahawalpur, Punjab, Pakistan
• ² College of Agronomy, Sichuan Agricultural University, Chengdu, Sichuan Province, China
• ³ Department of Soil Sciences, Faculty of Agriculture and Environment, Islamia University of Bahawalpur, Bahawalpur, Pakistan

Globally, increasing wheat production while reducing environmental impact is a critical challenge, particularly in regions where soil fertility is declining, and climate variability is increasing. Soil with low organic matter reduces buffering capacity, decreasing nitrogen fertilizer efficiency and causing losses through denitrification, volatilization, and leaching. To address these challenges, this study explores the synergistic impacts of various nitrogen (N) fertilizer sources and soil-applied humic acid (HA) on the morpho-physiological and biochemical responses of wheat (Triticum aestivum L.) in a semi-arid region. A field experiment was conducted using five N treatments N0: (Control-No N), N1:(Urea), N2: (Calcium ammonium nitrate), N3: (Ammonium sulphate), N4: (Urea + CAN + AS) and three soil applied HA levels, H0: (No HA), H1: (10L ha⁻¹ at tillering), H2: (split application of 5L ha -1 at tillering and 5L ha -1 at booting stage). Results revealed significant improvements when all three N sources (urea, CAN, AS) combined with two split applications of HA compared with the control, where no N or HA was applied. Physiological attributes showed significant improvements compared to the control, with increases of 56.08% in chlorophyll-a, 85.36% in chlorophyll-b, 54.92% in total chlorophyll content, 44.07% in membrane stability index, 43.01% in stomatal conductance, 46.91% in internal CO₂ concentration, 51.42% in transpiration rate, and 51.84% in photosynthetic rate. For morphological traits, plant height increased 37.5%, flag leaf area 67%, tillers m -2 90.1%, root length 86.65%, root fresh weight 81.60%, root dry weight 70.22%, shoot fresh weight 94.39%, shoot dry weight 91.08%, spike length 90%, nodes plant -1 61.52%, spikes plant -1 54.21%, grains spike -1 75%, 1000 grains weight 77.76%, grain yield kg ha -1 94.06%, and biomass yield kg ha -1 107.085 relative to the control. Biochemical activity demonstrated notable increases compared to the control, with superoxide dismutase, peroxidase, catalase, and ascorbate peroxidase activities increased by 44.59%, 50.22%, 57.63%, and 43.39%, respectively. These findings suggest that among N sources, the combined use of all three N sources yielded the best results, while split applications of HA performed best among HA applications, with their interaction producing the highest results.