Effect of slow release nitrogenous fertilizers and biochar on growth, physiology, yield, and nitrogen use efficiency of sunflower under arid climate.

Sunflower plants need nitrogen consistently and in higher amount for optimum growth and development. However, nitrogen use efficiency (NUE) of sunflower crop is low due to various nitrogen (N) losses. Therefore, it is necessary to evaluate the advanced strategies to minimize N losses and also improve sunflower productivity under arid climatic conditions. A field trial was conducted with four slow release nitrogenous fertilizers [SRNF (bacterial, neem, and sulfur-coated urea and N loaded biochar)] and three N levels (100% = 148 kg N ha⁻¹, 80% = 118 kg N ha⁻¹, and 60% = 89 kg N ha⁻¹) of recommended application (100%) for sunflower crop under arid climatic conditions. Results showed that neem-coated urea at 148 kg N ha⁻¹ significantly enhanced crop growth rate (CGR) (19.16 g m⁻² d⁻¹) at 60–75 days after sowing (DAS); leaf area index (2.12, 3.62, 5.97, and 3.00) at 45, 60, 75, and 90 DAS; and total dry matter (14.27, 26.29, 122.67, 410, and 604.33 g m⁻²) at 30, 45, 60, 75, and 90 DAS. Furthermore, higher values of net leaf photosynthetic rate (25.2 µmol m⁻² s⁻¹), transpiration rate (3.66 mmol s⁻¹), and leaf stomatal conductance (0.39 mol m⁻² s⁻¹) were recorded for the same treatment. Similarly, neem-coated urea produced maximum achene yield (2322 kg ha⁻¹), biological yield (9000 kg ha⁻¹), and harvest index (25.8%) of the sunflower crop. Among various N fertilizers, neem-coated urea showed maximum NUE (20.20 kg achene yield kg⁻¹ N applied) in comparison to other slow release N fertilizers. Similarly, nitrogen increment N₆₀ showed maximum NUE (22.40 kg grain yield kg⁻¹ N applied) in comparison to N₈₀ and N₁₀₀. In conclusion, neem-coated urea with 100% and 80% of recommended N would be recommended for farmers to get better sunflower productivity with sustainable production and to reduce the environmental nitrogen losses. [ABSTRACT FROM AUTHOR]