Effects of nitrogen application rate, nitrogen synergist and biochar on nitrous oxide emissions from vegetable field in south China

Globally, vegetable fields are the primary source of greenhouse gas emissions. A closed-chamber method together with gas chromatography was used to measure the fluxes of nitrous oxide (N 2 O) emissions in typical vegetable fields planted with four vegetables sequentially over time in the same field: endive, lettuce, cabbage and sweet corn. Results showed that N 2 O fluxes occurred in pulses with the N 2 O emission peak varying greatly among the crops. In addition, N 2 O emissions were linearly associated with the nitrogen (N) application rate ( r = 0.8878, n = 16). Excessive fertilizer N application resulted in N loss through nitrous oxide gas emitted from the vegetable fields. Compared with a conventional fertilization (N2) treatment, the cumulative N 2 O emissions decreased significantly in the growing seasons of four plant species from an nitrogen synergist (a nitrification inhibitor, dicyandiamide and biochar treatments by 34.6% and 40.8%, respectively. However, the effects of biochar on reducing N 2 O emissions became more obvious than that of dicyandiamide over time. The yield-scaled N 2 O emissions in consecutive growing seasons for four species increased with an increase in the N fertilizer application rate, and with continuous application of N fertilizer. This was especially true for the high N fertilizer treatment that resulted in a risk of yield-scaled N 2 O emissions. Generally, the additions of dicyandiamide and biochar significantly decreased yield-scaled N 2 O-N emissions by an average of 45.9% and 45.7%, respectively, compared with N2 treatment from the consecutive four vegetable seasons. The results demonstrated that the addition of dicyandiamide or biochar in combination with application of a rational amount of N could provide the best strategy for the reduction of greenhouse gas emissions in vegetable field in south China.