Impact of urease inhibitor (NBPT) on greenhouse gas emissions and rice yield in a rainfed transplanting rice system in Costa Rica

Weynner Giraldo Sanclemente ¹ Ana Gabriela Pérez-Castillo ^1* Mayela Monge-Muñoz ¹ Cristina Chinchilla-Soto ² Lourdes Chavarría-Pérez ³ Melvin Alpízar-Marín ⁴ Mohammad Zaman ⁵

• ¹ Laboratory of Greenhouse Gases and Carbon Capture, Environmental Pollution Research Center, Faculty of Sciences, University of Costa Rica, SanJosé, Costa Rica
• ² School of Agronomy, Universidad de Costa Rica, Montes de Oca, Costa Rica
• ³ Corporación Arrocera Nacional, San José, Costa Rica
• ⁴ University of Costa Rica, San José, San Jose, Costa Rica
• ⁵ Joint FAO/IAEA Programme of Nuclear Techniques in Food and Agriculture, Vienna, Austria

Rice crop production intensification has become one of the most important sources of greenhouse gases. In rainfed rice production, urea is the most common nitrogen (N) fertilizer used in Costa Rica. Urea has low efficiency in crops, which is associated with high risk of N gaseous losses. The use of urea coated with the urease inhibitor NBPT has been identified as a mitigation strategy for ammonia losses. However, this can increase N input to the system, potentially leading to higher N2O and CH4 emissions in rice fields. In 2022, a rainfed rice transplanting trial was conducted on a tropical Inceptisol in Costa Rican Central Pacific region to analyze yield and quantify N2O and CH4 emissions. The plots of 6m x 6m, with an experimental design of five complete randomized blocks, were treated with three N-fertilization treatments: urea (U; 144 kg N ha-1), urea plus NBPT (UI; 144 kg N ha-1) and control plots (without N). Total N was splitted in four applications. The yield did not exhibit a significant difference (p>0.05) between U and UI treatments (U: 5.72 ± 0.97 t ha-1, and UI: 5.86 ± 1.12 t ha-1). There were no significant differences in yield-scaled N2O emissions (U: 4.4 ± 1.9 ug N2O-N kg-1rice, UI: 4.2 ± 1.9 ug N2O-N kg-1rice) or yield-scaled CH4 emissions (U: 0.32 ± 0.20 mg CH4 kg-1rice, UI: 0.33 ± 0.18 mg CH4 kg-1rice). Under the experimental conditions, NBPT did not promote economic benefits, nor did it have an impact on greenhouse gas emissions.