Effects of soil type and nitrate concentration on denitrification products (N2O and N2) under flooded conditions in laboratory microcosms

Abstract

Denitrification products nitrous oxide ((N2O) and nitrogen (N2)) were measured in three flooded soils (paddy soil from Vietnam, PV; mangrove soil from Vietnam, MV; paddy soil from Japan, PJ) with different nitrate (NO3–) concentrations. Closed incubation experiments were conducted in 100-mL bottles for 7 d at 25°C. Each bottle contained 2 g of air-dried soil and 25 mL solution with NO3– (concentration 0, 5 or 10 mg N L−1) with or without acetylene (C2H2). The N2O + N2 emissions were estimated by the C2H2 inhibition method. Results showed that N2O + N2 emissions for 7 d were positively correlated with those of NO3– removal from solution with C2H2 (R2 = 0.9872), indicating that most removed NO3– was transformed to N2O and N2 by denitrification. In PJ soil, N2O and N2 emissions were increased significantly (P < 0.05) by the addition of greater NO3– concentrations. However, N2O and N2 emissions from PV and MV soils were increased by the addition of 0 to 5 mg N L−1, but not by 5 to 10 mg N L−1. At 10 mg N L−1, N2 emissions for 7 d were greater in PJ soil (pH 7.0) than in PV (pH 5.8) or MV (pH 4.3) soils, while N2O emissions were higher in PV and MV soils than in PJ soil. In MV soil, N2O was the main product throughout the experiment. In conclusion, NO3– concentration and soil pH affected N2O and N2 emissions from three flooded soils.