Annual nitric and nitrous oxide fluxes from Chinese subtropical plastic greenhouse and conventional vegetable cultivations.

As intensive vegetable cultivation is rapidly expanding in China and elsewhere worldwide, its environmental consequences on nitrous oxide (N(2)O) and nitric oxide (NO) emissions deserve attention. We measured N(2)O and NO fluxes simultaneously for a full year from Chinese subtropical vegetable fields. Clearly, both N(2)O and NO emissions varied greatly in different vegetable crop seasons within a year, highlighting the importance of whole-year measurement for achieving temporally accurate annual direct emission factors. A revised "hole-in-the-pipe" model well described quantitative relationships between N(2)O plus NO fluxes and soil-specific conditions. Annual background N(2)O and NO emissions were 0.73-5.0 and 0.26-0.56 kg N ha(-1) yr(-1), respectively, for the vegetable cultivations. The farmers' fertilization practice increased N(2)O and NO emissions. Annual direct emission factors for greenhouse and conventional vegetable fields, respectively, were 1.1% and 1.9% for N(2)O, and 0.36% and 0.32% for NO, indicating there is a need to consider a differentiation of emission factors for managed vegetable cultivations.