Biochar and slow-releasing nitrogen fertilizers improved growth, nitrogen use, yield, and fiber quality of cotton under arid climatic conditions

The efficiency of nitrogenous fertilizers in South Asia is on a declining trajectory due to increased losses. Biochar (BC) and slow-releasing nitrogen fertilizers (SRNF) have been found to improve nitrogen use efficiency (NUE) in certain cases. However, field-scale studies to explore the potential of BC and SRNF in south Asian arid climate are lacking. Here we conducted a field experiment in the arid environment to demonstrate the response of BC and SRNF on cotton growth and yield quality. The treatments were comprised of two factors, (A) nitrogen sources, (i) simple urea, (ii)neem-coated urea, (iii)sulfur-coated urea, (iv) bacterial coated urea, and cotton stalks biochar impregnated with simple urea, and (B) nitrogen application rates, N₁=160 kg ha⁻¹, N₂ = 120 kg ha⁻¹, and N₃ = 80 kg ha⁻¹. Different SRNF differentially affected cotton growth, morphological and physiological attributes, and seed cotton yield (SCY). The bacterial coated urea at the highest rate of N application (160 kg ha⁻¹) resulted in a higher net leaf photosynthetic rate (32.8 μmol m⁻² s⁻¹), leaf transpiration rate (8.10 mmol s⁻¹), and stomatal conductance (0.502 mol m⁻² s⁻¹), while leaf area index (LAI), crop growth rate (CGR), and seed cotton yield (4513 kg ha⁻¹) were increased by bacterial coated urea at 120 kg ha⁻¹ than simple urea. However, low rate N application (80 kg ha⁻¹) of bacterial coated urea showed higher nitrogen use efficiency (39.6 kg SCY kg⁻¹ N). The fiber quality (fiber length, fiber strength, ginning outturn, fiber index, and seed index) was also increased with the high N application rates than N2 and N3 application. To summarize, the bacterial coated urea with recommended N (160 kg ha⁻¹) and 75% of recommended N application (120 kg ha⁻¹) may be recommended for farmers in the arid climatic conditions of Punjab to enhance the seed cotton yield, thereby reducing nitrogen losses.