This research was supported by the Office of Science (BER), U.S. Department of Energy (DE-FG02-04ER63913 and DE-FG02-08ER64515), the National Basic Research Program of China (2009CB118603), Nanjing Science and Technology Bureau (200901063), and Nanjing Agricultural University (NC2008003).
Journal of Geophysical Research--Biogeosciences
Nitrogen cycle -- Analysis, Nitrogen oxides -- Mathematical models, Agricultural chemicals -- Transport properties, Greenhouse gases -- China
The stable isotopic composition of nitrous oxide (N₂O) in agricultural soils can improve our understanding of the relative contributions of the main microbial processes (nitrification and denitrification) responsible for N₂O formation in soils, and can provide constraints for the atmospheric N2O budget. Here, we present soil profiles featuring N₂O concentrations and δ¹⁵N and δ¹⁸O values in N₂O over time, which permit the in situ identification of processes and sites of N₂O production in a rice-based ecosystem seeded with winter wheat. Our δ¹⁵N and δ¹⁸O soil profile values support the conclusion that denitrification is the dominant process behind N₂O production during the winter wheat season. The soil N₂O gas concentrations are higher below 10 cm than above 10 cm, and more depleted in ¹⁵N - N₂O at 10–15 cm depth compared to other soil depths, which indicates that the N₂O production zone is located at a depth of 10–15 cm within 0–20 cm. The δ¹⁵Nair and δ¹⁸OSMOW (δ¹⁸O of standard mean ocean water) values for soil gas N₂O averaged over the entire wheat growing season are +0.90 ± 2.9 (n = 64) and +39.3 ± 3.1 (n = 64), respectively. Given that paddy source N₂O is much heavier in both measured ¹⁵N and ¹⁸O compared to other fertilized soils, agricultural soils have been underestimated as a source of N₂O since isotopic constraints from rice agriculture have not been taken into account.
Xiong, Z. Q., M. A. K. Khalil, G. Xing, M. J. Shearer, and C. Butenhoff (2009), Isotopic signatures and concentration profiles of nitrous oxide in a rice-based ecosystem during the drained crop-growing season, J. Geophys. Res., 114, G02012, doi:10.1029/2008JG000827.