Estimations of emission factors for fertilizer-induced direct N₂O emissions from agricultural soils in Japan: Summary of available data

Abstract

Agricultural fields are significant sources of anthropogenic atmospheric nitrous oxide (N₂O). We compiled and analyzed data on N₂O emissions from Japanese agricultural fields (246 measurements from 36 sites) reported in peer-reviewed journals and research reports. Agricultural fields were classified into three categories: upland fields, tea fields and rice paddy fields. In this analysis, data measured over a period of more than 90 days for upland fields and 209 days for tea fields were used to estimate annual fertilizer-induced emission factors (EF) because of limitations in the available data. The EF is defined as the emission from fertilized plots minus the background emission (emission from a zero-N control plot), and is expressed as a percentage of the N applied. The mean of N₂O emissions from upland fields with well-drained soils was significantly lower than that from poorly drained soils. Mean (± standard deviation) N₂O emissions measured over a period of more than 90 days from fertilized upland fields were 1.03 ± 1.14 kg N ha⁻¹ and 4.78 ± 5.36 kg N ha⁻¹ for well-drained and poorly drained soils, respectively. Because the ratio of the total areas of well-drained soils and poorly drained soils was different from the ratio of the number of available EF data for each soil category, we used a weighted mean to estimate EF for all upland fields. The EF was estimated to be 0.62 ± 0.48% for all fertilized upland fields. Mean N₂O emissions and the estimated EF for fertilized tea fields measured over a period of more than 209 days were 24.3 ± 16.3 kg N ha⁻¹ and 2.82 ± 1.80%, respectively. The mean N₂O emission and estimated EF from Japanese rice paddy fields were 0.36 kg N ha⁻¹ and 0.31 ± 0.31% for the cropping season, respectively. Significant uncertainties remain in these results because of limitations in the available data.

Key words:

• background emission
• fertilizer-induced emission factor
• rice paddy field
• tea field
• upland field
• soil drainage

ACKNOWLEDGMENT

This work was supported by the Global Environment Research Fund “S-2-3a”, Ministry of the Environment, Japan.