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 (N 2 O). Hitherto, the contribution of major sources to the N 2 O 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 N 2 O emission-reduction strategies. Here, we used machine learning techniques and global N 2 O observational data to generalize the distribution of N 2 O emissions from agriculturally managed peatlands, to distinguish the sources of N 2 O emissions, and to compare mitigation options. N 2 O 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 N 2 O-N year -1 were emitted, with 4.6 (3.7-5.7) kt N 2 O-N year -1 stemming from fertilizer N. The fertilizer-induced N 2 O emission factor ranged from 1.5% to 3.2%. Reducing the current fertilizer input by 20% could achieve a 10% N 2 O emission reduction for croplands but only 3% for grasslands. Rewetting 1.9 Mha cropland and 0.26 Mha grassland would achieve the same N 2 O emission reductions. Our results suggest that N 2 O mitigation strategies for managed peatlands should be considered separately across land-use types and climatic zones. For croplands, particularly in the tropics, relevant N 2 O 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 N 2 O and contributing to meeting climate goals.