Combining Urea with Chemical and Biological Amendments Differentially Influences Nitrogen Dynamics in Soil and Wheat...

Nitrogen (N) losses from fertilized fields pose a major concern in modern agriculture due to environmental implications. Urease inhibitors, such as N-(n-butyl) thiophosphoric triamide (NBPT), nitrification inhibitors (NI), like dicyandiamide (DCD), and sulfur-oxidizing bacteria (SOB) could have potential in reducing N losses. For evaluating their effectiveness, investigations were undertaken through incubation and greenhouse experiments by mixing a urea fertilizer with sole NBPT, DCD, and SOB, as well as combined, on ammonia volatilization losses from silt loam soil. An incubation experiment was conducted in 1 L airtight plastic jars with adequate aeration and constant temperature at 25 °C for 10 days. Three replications of each treatment were conducted using a completely randomized designed. The ammonia emission rate gradually increased until the highest (17.21 mg NH₃ m^-2 h^-1) value on the third day with sole urea and some other treatments except NBPT alone, which prolonged the hydrolysis peak until the fifth day with the lowest ammonia emission rate (12.1 mg NH₃ m^-2 h^-1). Although the DCD and SOB treatments reduced ammonia emission, their difference with urea was nonsignificant. Additionally, mixing NBPT with urea exhibited the highest population of nitrifying bacteria in soil, indicating its potential role in promoting the nitrification process. In a greenhouse experiment, 10 treatments, i.e., T₁ = control, T₂ = N₁₂₀ (urea fertilizer equivalent to 120 kg N ha^-1), T₃ = N₉₀ (90 kg N ha^-1), T₄ = N₉₀ + NBPT, T₅ = N₉₀ + DCD, T₆ = N₉₀ + SOB, T₇ = N₉₀ + NBPT + DCD, T₈ = N₉₀ + NBPT + SOB, T₉ = N₉₀ + DCD + SOB, and T₁₀ = N₉₀ + NBPT + DCD + SOB, were applied to investigate the wheat yield and N uptake efficiency. The highest N recovery efficiency (31.51%) was recorded in T₅ where DCD was combined with urea at 90 kg ha^-1.