Land-use type affects NO production pathways in subtropical acidic soils.

The change in land-use from woodland to crop production leads to increased nitrous oxide (NO) emissions. An understanding of the main NO 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 NO 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 NHNO and NHNO to determine the dominant NO production pathway for the different land-uses. The average NO emission rates for VE, CO and SP were 5.30, 4.23 and 3.36 μg N kg dry soil d, greater than for SB and ET at 0.98 and 1.10 μg N kg dry soil d, respectively. NO production was dominated by heterotrophic nitrification for SB and ET, accounting for 51 and 50% of NO emissions, respectively. However, heterotrophic nitrification was negligible (<8%) in SP, CO and VE, where autotrophic nitrification was a primary driver of NO production, accounting for 44, 45 and 66% for SP, CO and VE, respectively. Denitrification was also an important pathway of NO production across all land-uses, accounting for 35, 35, 49, 52 and 32% for SB, ET, SP, CO and VE respectively. Average NO emission rates via autotrophic nitrification, denitrification and heterotrophic nitrification increased significantly with gross nitrification rates, NO contents and C:N ratios respectively, indicating that these were important factors in the NO production pathways for these soils. These results contribute to our understanding and ability to predict NO emissions from different land-uses in subtropical acidic soils and in developing potential mitigation strategies.