Assessment of direct nitrous oxide emissions and emission factors from sugarcane plantations using different rates of chemical fertilizer application in western Thailand

The default emission factor (EF) of 1.00% for direct nitrous oxide (N2O) emissions, as recommended by the Intergovernmental Panel on Climate Change (IPCC), is often applied in countries that lack region-specific N2O EFs, such as Thailand. However, this approach introduces significant uncertainty due to the spatial variability and complex dynamics governing N2O emissions, potentially leading to inaccurate estimates. This study quantified direct N2O emissions and derived EFs from chemical fertilizer applications at varying rates (0, 100, 150, 200, and 250 kg N ha-1) in sugarcane plantations located in Kanchanaburi (KB) and Ratchaburi (RB) provinces, western Thailand. The results showed that using nitrogen (N) fertilizer significantly stimulated N2O emissions at both study sites, with higher N input correlating to greater emissions. The cumulative N2O emissions for N application rates ranging from 0 to 250 kg N ha-1 varied from 1.16 to 3.85 kg N2O ha-1 in KB and from 1.33 to 3.90 kg N2O ha-1 in RB. The calculated N2O EFs averaged 0.68% (0.66-0.71%) in KB and 0.70% (0.64-0.83%) in RB, with an overall mean EF of 0.69%, representing a 0.31% reduction from the IPCC's default value. This reduction is relatively attributed to rainfall patterns, soil properties, N application rates, and N utilization by plant in the area. The findings suggest that Thailand's current national N2O inventory, based on the default EF, may be overestimated if country-specific EFs resemble the area-specific data observed in this study. While chemical fertilizer application increased N2O emissions, its role in enhancing soil nutrient availability is essential for boosting crop productivity. Notably, the highest fertilizer input (250 - 75 - 149 kg N - P - K ha-1) did not result in a proportional increase in yield, suggesting that applying fertilizer beyond crop demand may not maximize productivity. Thus, optimizing fertilizer application to match crop nutrient requirements presents a straightforward and practical strategy to reduce N2O emissions while maintaining food security.