Soil Nitrous Oxide Emissions from Sugarcane Field Affected by Nitrogen Fertilizer Rate and Inhibitors of Urea Hydrolysis and Nitrification Process

Abstract

Reducing nitrogen fertilizer use and applying urea hydrolysis (UIs) and nitrification inhibitors (NIs) can help mitigate soil N<inf>2</inf>O emissions, though data on their effectiveness in non-Annex I countries is limited. This study assessed the effects of different N rates, UIs, NIs, and their combinations (UINIs) on soil N<inf>2</inf>O emissions in sugarcane (Saccharum officinarum L.) and bare soil fields. Fertilizer rates followed farmer practices (F) and soil analysis (S). Synthetic inhibitors, including N-(n-butyl) thiophosphoric triamide and dimethylpyrazole phosphate, were tested, alongside plant-based inhibitors derived from garlic, neem seed, and praxelis. In the sugarcane fields, reducing N rates and adding NIs decreased soil N<inf>2</inf>O emissions up to 19.1%, compared to F treatment. UINIs and UIs reduced emissions by 17.0 and 15.9%, respectively, with praxelis contributing an 18.9% reduction. Although inhibitors showed potential in suppressing microbial activity during dressing application, the cumulative N<inf>2</inf>O mitigation effect varied and was not consistently significant across treatments. Inhibitor use led to reductions in soil N<inf>2</inf>O emission factors (EF) by 1.1 to 1.6% in sugarcane plots, compared to 1.8% for the S treatment. Surprisingly, the F treatment showed the lowest soil N₂O EF (0.6%), possibly due to the higher N inputs. Inhibitor treatments markedly improved agronomic efficiency to 1.17 t cane kg⁻¹ N compared to the F treatment, demonstrating enhanced nitrogen use efficiency. The study indicates that reducing N rates and using UIs, NIs, and UINIs can significantly reduce greenhouse gas (GHG) emissions in agriculture, providing valuable insights for Thailand’s national GHG inventory and mitigation strategies.