Hierarchy of factors driving N ₂ O emissions in non‐tilled soils under different crops

Summary Nitrous oxide ( N 2 O ) is emitted to the atmosphere as a by‐product of nitrification and denitrification by soil microbial processes. Differences in climate, soil and management regulate these processes, causing N 2 O emissions to vary in space and time. This study aimed to identify and rank the soil properties that control N 2 O emissions in non‐tilled soils under different crops. Over a period of 2 years, gas samples were taken from closed chambers and soil properties were determined once per season. N 2 O emission rates were highly variable (from −15 to 314 µg N 2 O‐N m −2 hour −1 ). A regression tree analysis allowed us to classify soil N 2 O emissions into three groups, separated by topsoil temperature (primary factor) and water‐filled pore space ( WFPS , secondary factor). N 2 O emissions were small (mean 4.22 µg N 2 O‐N m −2 hour −1 ) with topsoil temperature less than 14°C (Group 1), large (mean 61.87 µg N 2 O‐N m −2 hour −1 ) with topsoil temperature between 14 and 23°C and WFPS more than 58.5% (Group 2) and moderate (mean 21.4 µg N 2 O‐N m −2 hour −1 ) with topsoil temperature more than 23°C and WFPS less than 58.5% (Group 3). These emission groups allow for more efficient sampling of N 2 O emissions in the field: in winter, when topsoil temperatures are less than 14°C and N 2 O emissions are expected to be small or even negligible, sampling frequency can be reduced; in autumn and spring, when topsoil temperatures are more than 14°C and WFPS is more than 60–70%, sampling frequency should be increased.