Nitrous oxide emissions from an intensively managed greenhouse vegetable cropping system in Northern China

Nitrous oxide (N2O) emissions from a typical greenhouse vegetable system in Northern China were measured from February 2004 to January 2006 using a close chamber method. Four nitrogen management levels (NN, MN, CN, and SN) were used. N2O emissions occurred intermittently in the growing season, strongly correlating with N fertilization and irrigation. No peak emissions were observed after fertilization in the late Autumn season due to low soil temperature. 57-94% of the seasonal N2O emissions came from the initial growth stage, corresponding to the rewetting process in the soil. The annual N2O emissions ranged from 2.6 to 8.8 kg N ha-1 yr-1, accounting for 0.27-0.30% of the annual nitrogen input. Compared with conventional N management, site-specific N management reduced N fertilization rate by 69% in 2004 and by 76% in 2005, and consequently reduced N2O emissions by 51% in 2004 and 27% in 2005, respectively. High N2O emissions coming from the initial growth stage can be attributed to the rewetting process in the greenhouse soil.