Sources of nitrous oxide emissions from agriculturally managed peatlands

The draining and fertilization of peatlands for agriculture is globally an important source of the greenhouse gas nitrous oxide (N2O). Hitherto, the contribution of major sources to the N2O emission-that is, fertilization and nitrogen (N) release from peat decomposition-has not yet been deciphered. This hampers the development of smart mitigation strategies, considering that rewetting to halt peat decomposition and reducing N fertilization are promising N2O emission-reduction strategies. Here, we used machine learning techniques and global N2O observational data to generalize the distribution of N2O emissions from agriculturally managed peatlands, to distinguish the sources of N2O emissions, and to compare mitigation options. N2O emissions from agriculturally managed croplands were 401.0 (344.5-470.9) kt N year(-1), with 121.6 (88.6-163.3) kt N year(-1) contributed by fertilizer N. On grasslands, 64.0 (54.6-74.7) kt N2O-N year(-1) were emitted, with 4.6 (3.7-5.7) kt N2O-N year(-1) stemming from fertilizer N. The fertilizer-induced N2O emission factor ranged from 1.5% to 3.2%. Reducing the current fertilizer input by 20% could achieve a 10% N2O emission reduction for croplands but only 3% for grasslands. Rewetting 1.9 Mha cropland and 0.26 Mha grassland would achieve the same N2O emission reductions. Our results suggest that N2O mitigation strategies for managed peatlands should be considered separately across land-use types and climatic zones. For croplands, particularly in the tropics, relevant N2O mitigation potentials are achievable through both fertilizer N reduction and peatland rewetting. For grasslands, management schemes to halt peat degradation (e.g. rewetting) should be considered preferentially for mitigating N2O and contributing to meeting climate goals.