Dynamics of gaseous production after addition of carbon and nitrogen in paddy and vegetable soils

【Objectives】The continuous monitoring of gaseous emission of carbon and nitrogen products including O2, NO, N2O, CH4 and N2 in soils after addition of carbon and nitrogen substrates will help to reveal the mechanism of greenhouse gases generation in typical red soils under different land uses.【Methods】Paddy and vegetable soils were collected under different land uses in the Jinjing watershed, middle and lower of Yangtze River. Two experiments were designed at 20℃ and 70% WFPS using automatic continuous online incubation and Robot testing system for 15 days. Experiment 1 was designed with six treatments including no nitrogen control, adding 40 mg/kg of ammonium N, 40 mg/kg of ammonium N+1% nitrification inhibitor, 40 mg/kg of nitrate N, 40 mg/kg of nitrate N+1% glucose under aerobic incubation, and 40 mg/kg of nitrate N+1% glucose under anaerobic conditions, using vegetable and paddy soils, respectively. Experiment 2 contained eight treatments: no nitrogen control, adding 40 mg/kg of ammonium N, 40 mg/kg of ammonium N+1% nitrification inhibitor, 40 mg/kg of ammonium N+1% straw, 40 mg/kg of ammonium N+1% glucose under anaerobic conditions, 40 mg/kg of nitrate N, 40 mg/kg of nitrate N+1% glucose, and 40 mg/kg of nitrate N+1% glucose under anaerobic conditions.【Results】Nitrification was main pathways of N2O emissions in the initial stage of aerobic incubation, denitrification was limited because of the low carbon and water content in vegetable soil. However, N2O and NO emissions were enhanced due to supply of adequate carbon and anaerobic conditions. Denitrification was the main pathway of N2O production in both aerobic incubation and waterlogged paddy soils. The generation of the gaseous products ranked of NO, N2O, and N2 when providing adequate carbon and anaerobic conditions in paddy soils, which was consistent with the order of three gases in the reaction chain of denitrification. N2 was the major product in waterlogged paddy soils with the application of ammonium nitrogen and carbon, N2O became the major product after adding nitrate. The main final product of denitrification was N2O under adequate soil carbon source condition. Large amounts of CH4 were detected under anaerobic conditions or adding carbon and NO-3 was almost depleted when CH4 was generating. 【Conclusions】N2O emission was mainly from nitrification in vegetable garden and produced from denitrification in aerobic and flooded paddy field in Jinjing watershed; denitrification of vegetable garden and paddy field was enhanced when enough carbon and anaerobic conditions provided; the composition and rates of denitrification products and the sequence of emission peaks were influenced by carbon and oxygen concentration.