Abstract
Land use changes from cropland to orchards in Eastern China have raised serious concerns about the regional nitrogen (N) cycle and greenhouse gas balance. We measured soil nitrous oxide (N2O) emissions and methane (CH4) uptake using manual static chambers in an apple orchard. The primary aims were to assess the effect of N fertilizer application on gas fluxes and quantify the site-specific N2O emission factor (EFd). Field experiments were arranged in a randomized block design with three N input rates (0, 800 and 2600/2000 kg N ha−1 year−1). We found that orchard soils were a negligible CH4 sink (−1.1 to −0.4 kg C ha−1 year−1). Annual N2O emissions responded positively to N input rates, ranging from 34.1 to 60.3 kg N ha−1 year−1. EFd ranged from 1.00% to 1.65% with a mean of 1.34%. The extremely large background emissions of N2O (34.1–34.3 kg N ha−1 year−1) most likely originated from nitrate accumulation in the soil profile because of historical overuse of N fertilizer. We conclude that (1) site-specific EFd is suitable for assessing regional direct N2O emissions from upland orchards; and (2) conventional fertilization regimes must be avoided, and reduced N input rates are recommended in the study region.
Highlights
Nitrous oxide (N2 O) and methane (CH4 ) are potent greenhouse gases
Atmospheric concentrations of N2 O and CH4 have increased by 20% and 150%, respectively, since 1750, most likely due to human activities related to agriculture [1]
The net annual CH4 fluxes indicated that all treatments were slight sinks (Table 3), which was similar to previous results obtained for various upland agricultural sinks (Table 3), which was similar to previous results obtained for various upland agricultural ecosystems [23]
Summary
Nitrous oxide (N2 O) and methane (CH4 ) are potent greenhouse gases. Together, they are responsible for 30% of global radiative forcing [1]. Atmospheric concentrations of N2 O and CH4 have increased by 20% and 150%, respectively, since 1750, most likely due to human activities related to agriculture [1]. Reducing N2 O emissions from and enhancing CH4 uptake by upland agricultural ecosystems could help mitigate anthropogenic contributions to global warming [2]. Agricultural soils are responsible for 60–80% of anthropogenic N2 O sources [3,4]. Denitrification becomes the major source of Atmosphere 2017, 8, 181; doi:10.3390/atmos8100181 www.mdpi.com/journal/atmosphere
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