Background nitrous oxide emissions in agricultural and natural lands: a meta-analysis

This study aimed at better characterising background nitrous oxide (N2O) emissions (BNE) in agricultural and natural lands. We compiled and analysed field-measured data for annual background N2O emission in agricultural (BNEA) and natural (BNEN) lands from 600 and 307 independent experimental studies, respectively. There were no significant differences between BNEA (median: 0.70 & mean: 1.52 kg N2O -aEuro parts per thousand N ha(-1) yr(-1)) and BNEN (median:0.31 & mean:1.75 kg N2O -aEuro parts per thousand N ha(-1) yr(-1)) (P > 0.05). A simultaneous comparison across all BNEA and BNEN indicated that BNEs from riparian, vegetable crop fields and intentional fallow areas were significantly higher than from boreal forests (P < 0.05). Correlation and regression analyses supported the underlying associations of soil organic carbon (C), nitrogen (N), pH, bulk density (BD),and/or air temperature (AT) with BNEs to a varying degree as a function of land-use or ecosystem type (Ps < 0.05). Although overall BNEN tended to be lower than BNEA on median basis, results in general suggest that land-use shifts between natural and managed production systems would not result in consistent changes in BNE.