Gross, Background, and Net Anthropogenic Soil Nitrous Oxide Emissions from Soybean, Corn, and Wheat Croplands

Agricultural soils are the largest single source of N 2 O emissions globally. However, soils left uncultivated would still release N 2 O. Distinguishing anthropogenic from natural emissions (i.e., background emissions) in crops is important if we want to assess the net effect of human activity. This study aimed to characterize N 2 O emissions from croplands and unmanaged grasslands to estimate the net anthropogenic emissions and to gain a better insight into their main drivers. We established a replicated manipulative field experiment in the Pampas Region of Argentina to quantify soil N 2 O emissions from corn ( Zea mays L.), wheat ( Triticum aestivum L.), and soybean [ Glycine max (L.) Merr.] crops, and from adjacent unmanaged grassland plots for 1 yr. We also analyzed the main controls of N 2 O emissions and the correlation between the normalized difference vegetation index (NDVI) and N 2 O fluxes. Background emissions represented between 21 and 32% of total emissions from croplands, depending on crop type. No differences were detected in N 2 O emissions between total and background during winter and peak crop growing season. NDVI showed a significant correlation with N 2 O fluxes which was positive in grasslands and negative in growing season of soybean crops. Our results showed that N 2 O emissions from croplands were higher than background emissions, but also that background represented an important fraction of cropland emissions. Higher emissions in croplands occurred during pre‐seeding, after harvest, and after N fertilization in fertilized crops. In addition, our study informs about N 2 O emissions from crops and unmanaged systems in South America where field data are very scarce. Core Ideas We measured soil N 2 O emissions in South America where field data are very scarce. Nonanthropogenic fluxes represented 21 to 32% of crop N 2 O emissions. NDVI, a plant productivity index, improved seasonal estimation of N 2 O flux.