Effect of liquid nano urea and coated urea on gaseous N losses and agronomic efficiency under elevated CO2 and temperature interaction.

Ammonium fertilizers lose significant amounts of nitrogen, primarily through ammonia (NH₃) volatilization and nitrous oxide (N₂O) emissions, which results in low nitrogen use efficiency. Liquid Nano Urea (LNU) is considered more efficient than traditional soil-applied urea, potentially reducing synthetic N fertilizer use. A two years study growing wheat crop was conducted to evaluate the integrated application of neem coated urea (NCU) and LNU, NCU (100%) and Sulphur coated urea (SCU) under elevated CO2 and temperature interaction in T-FACE rings to assess gaseous nitrogen losses and agronomic use efficiency (AUE). LNU (4%N) was applied as two foliar spray in the first year (50% NCU + LNU), and a single foliar spray in second year (75% NCU + LNU). Exposure to elevated CO2 (seasonal average 580-585-ppm) and elevated temperature (+ 1.68-1.74 °C over ambient), significantly (p < 0.05) increased the emissions of nitrous oxide (N2O) and ammonia (NH3) compared to ambient conditions Integrated LNU + NCU exhibited lower N₂O losses, and NH₃ was non-detectable post-LNU foliar application. SCU significantly lowered NH₃ losses compared to NCU. Soil NH4+ was the highest with SCU under ambient, but reduced under elevated temperature (ET) and elevated CO2 and elevated temperature interaction (ECT). Wheat yield increased under elevated CO₂ (EC) and declined under ET in all N treatments. The decrease in grain N concentration under EC was the lowest with SCU. Microbial biomass carbon and nitrogen increased significantly under ECT. The agronomic use efficiency (AUE) reduced in all fertilized treatments under ECT as compared to the ambient. Wheat yields reduced with LNU + NCU application; however, this approach resulted in higher AUE due to the lower amount of N applied and reduced NH₃ and N₂O losses. The amount and timing of the foliar LNU application may need further optimisation for countering the lower wheat yields.