Measurements of N2O emissions from different vegetable fields on the North China Plain

Abstract

Few studies have measured the N2O emission fluxes from vegetable fields. In order to identify the characteristics and the influencing factors of N2O emissions from different vegetable fields, we measured N2O emissions for a full year from four typical fields, including an open-ground vegetable field that has produced vegetables for over 20 years (OV20), a recently developed open-ground vegetable field that was converted from a maize field three years earlier (OV3), a recently developed greenhouse vegetable field that was converted from a maize field 3 years earlier (GV3) and a typical local maize field (Maize). Four different fertilization treatments were set additionally in the recently developed open-ground vegetable field. These were: no fertilizer or manure (OV3_CK), manure only (OV3_M) and the combination of manure with different rates of chemical fertilizer application (OV3_MF1 and OV3_MF3). The results showed that N2O emission fluxes fluctuated between 0.3 ± 0.1 and 912.4 ± 80.0 mg N2O–N m−2 h−1 with the highest emission peak occurring after fertilization followed by irrigation. Nitrogen application explained 64.6–84.5% of the N2O emission in the vegetable fields. The magnitude of the emission peaks depended on the nitrogen application rate and the duration of the emission peaks was mainly associated with soil temperature when appropriate irrigation was given after fertilization. The N2O emission peaks occurred later and lasted for a longer period when the soil temperature was <24 °C in May. However, emission peaks occurred earlier and lasted for a shorter period when the soil temperature was around 25–33 °C from June to August. The annual N2O emissions from the fertilized vegetable fields were 1.68–2.38 times higher than that from the maize field, which had an emission value of 2.88 ± 0.10 kg N ha−1 a−1. The N2O emission factor (EF) of manure nitrogen was 0.07% over the whole year, but was 0.11% and 0.02% in the spring cucumber season and the autumn cabbage season, respectively. The EF of chemical nitrogen was 1.10–1.78% for the vegetable field over the whole year and it was higher in recently developed vegetable field than in the established field (1.54–1.78% vs. 1.10%). Vegetable fields may contribute greatly to the national greenhouse gas inventories due to the high fertilizer application rates, frequent irrigation and an increased number of tillage–planting cycles.