Tea-planted soils as global hotspots for N₂O emissions from croplands

Tea-planted soils generally receiving high nitrogen (N) fertilizer doses are more vulnerable to acidification, and turn into significant sources of the potent greenhouse gas nitrous oxide (N₂O). However, little is known about the magnitude of soil N₂O emissions from global tea plantations. Based on a global meta-analysis of field experimental data collected from major tea growing countries, we quantify annual N₂O emissions, calculate direct emission factors (EF_d) and identify key environmental controls of emissions from tea plantations. However, most data are from China and Japan, which is to be expected given that tea plantations in these countries represent >60% of the global area and the vital environmental research community in both countries. Results suggest that annual N₂O emissions from soils of global tea plantations are on average 17.1 kg N ha⁻¹ (or 8008 kg CO₂-eq ha⁻¹), being substantially greater than those reported for cereal croplands (662–3757 kg CO₂-eq ha⁻¹). The global mean EF_d for N applications to tea plantations equals 2.31% (with a 95% confidence interval of 1.91%–2.71%), being two times higher than the Intergovernmental Panel on Climate Change default value of 1%. Across tea plantations worldwide, total N₂O emissions are estimated to be 57–84 Gg N yr⁻¹, or 1.5%–12.7% of total direct cropland N₂O emissions. Given that tea plantations account for only 0.3% of total cropland area, our finding highlights that tea-planted soils are global hotspots for N₂O emissions and that these systems might be prime targets for climate change mitigation in the agricultural sector. Considering that tea is a high price commodity for which consumers may be willing to apply pressure for more climate-smart production, possible mitigation efforts include use of controlled-release fertilizers or nitrification inhibitors, and application of biochar and/or lime for increasing soil pH; i.e. measures that increase N use efficiency while reducing the climate footprint of tea production. (letter)