Gross N transformation rates and related NO emissions in Chinese and UK agricultural soils.

The properties of agricultural soils in various regions of the world are variable and can have a significant but poorly understood impact on soil nitrogen (N) transformations and nitrous oxide (NO) emissions. For this reason, we undertook a study of gross N transformations and related NO emissions in contrasting agricultural soils from China and the UK. Seven Chinese and three UK agricultural soils were collected for study using a N tracing approach. The soil pH ranged from 5.4 to 8.7, with three acidic soils collected from Jinjing, Lishu and Boghall; one neutral soil collected from Changshu, and the other six alkaline soils collected from Quzhou, Zhangye, Changwu, Jinzhong, Boxworth and Stetchworth. Our results showed that the main N transformation processes were oxidation of ammonium (NH) to nitrate (NO) (O), and mineralization of organic N to NH. The gross autotrophic nitrification rates calculated in the three acidic soils were between 0.25 and 4.15 mg N kg d, which were significantly lower (p < 0.05) than those in the remaining neutral and alkaline soils ranging from 6.94 to 14.43 mg N kg d. Generally, soil pH was positively correlated (p < 0.001) with gross autotrophic nitrification rate and cumulative NO emissions, indicating that soil pH was an important factor regulating autotrophic nitrification and NO emissions. There was also a significant positive correlation between the gross autotrophic nitrification rate and cumulative NO emissions, highlighting the importance of this process for producing NO emissions in these agricultural soils under aerobic conditions. Gross NH immobilization rates were very low in most soils except for the Jinjing soil with the lowest pH. In conclusion, the gross autotrophic nitrification rates and related NO emissions were controlled by soil pH irrespectively of the soil's origin in these agricultural soils.