Land-use type affects N2O production pathways in subtropical acidic soils

Abstract

The change in land-use from woodland to crop production leads to increased nitrous oxide (N₂O) emissions. An understanding of the main N₂O sources in soils under a particular land can be a useful tool in developing mitigation strategies. To better understand the effect of land-use on N₂O emissions, soils were collected from 5 different land-uses in southeast China: shrub land (SB), eucalyptus plantation (ET), sweet potato farmland (SP), citrus orchard (CO) and vegetable growing farmland (VE). A stable isotope experiment was conducted incubating soils from the different land use types at 60% water holding capacity (WHC), using ¹⁵NH₄NO₃ and NH₄¹⁵NO₃ to determine the dominant N₂O production pathway for the different land-uses. The average N₂O emission rates for VE, CO and SP were 5.30, 4.23 and 3.36 μg N kg^-1 dry soil d^-1, greater than for SB and ET at 0.98 and 1.10 μg N kg^-1 dry soil d^-1, respectively. N₂O production was dominated by heterotrophic nitrification for SB and ET, accounting for 51 and 50% of N₂O emissions, respectively. However, heterotrophic nitrification was negligible (<8%) in SP, CO and VE, where autotrophic nitrification was a primary driver of N₂O production, accounting for 44, 45 and 66% for SP, CO and VE, respectively. Denitrification was also an important pathway of N₂O production across all land-uses, accounting for 35, 35, 49, 52 and 32% for SB, ET, SP, CO and VE respectively. Average N₂O emission rates via autotrophic nitrification, denitrification and heterotrophic nitrification increased significantly with gross nitrification rates, NO₃^- contents and C:N ratios respectively, indicating that these were important factors in the N₂O production pathways for these soils. These results contribute to our understanding and ability to predict N₂O emissions from different land-uses in subtropical acidic soils and in developing potential mitigation strategies.

Keywords: (15)N; Autotrophic nitrification; Denitrification; Heterotrophic nitrification; Nitrous oxide; Stable isotope.