Effects of nitrification and urease inhibitors on nitrous oxide emissions and concentrations driven by soil moisture...

Soil moisture and nitrogen (N) fertilizer control the balance between nitrous oxide (N₂O) production and consumption in soil. However, the impact of nitrification and urease inhibitors on soil N₂O production and consumption under varying soil moisture levels remains insufficiently understood. In this study, a soil column experiment was conducted to investigate N₂O concentrations and accumulation at different soil depths (0, 5, 15, 30, and 60 cm) in sandy soil over two months. The soil was collected from a drip-irrigated field subjected to long-term cotton cultivation in an arid region. Four fertilizer treatments were applied: urea, urea + nitrification inhibitor (Dicyandiamide, DCD), urea + nitrification and urease inhibitors [N-(n-butyl) thiophosphoric triamide, NBPT], and an unfertilized control. These treatments were tested under three soil moisture levels [23%, 46%, and 70% water-filled pore space (WFPS)]. The results showed that treatments with inhibitors significantly reduced cumulative surface N₂O emissions by 33.2%-58.2% compared to urea alone. Notably, the treatment with both DCD and NBPT achieved the greatest reductions in surface emissions and in N₂O concentrations at 5 cm and 15 cm soil depths at 70% WFPS. Additionally, across all N fertilizer sources, 70% WFPS led to increased N₂O concentrations in the soil profile compared to lower soil moisture levels. Column N₂O accumulation was positively correlated with surface cumulative N₂O emissions under all three moisture conditions. Our study highlights that under high soil moisture conditions, DCD and NBPT can significantly mitigate intense N₂O emissions in sandy soils. This emission reduction is likely attributed to enhanced nitrification within the 0-15 cm soil layer rather than reduced N₂O diffusivity and denitrification along the soil profile. Therefore, we recommend applying nitrification and urease inhibitors under high soil moisture conditions as an effective strategy to reduce N₂O emissions in sandy soils.