Nitrous oxide emissions from black soils with different pH

N2O fluxes as a function of incubation time from soil with different available N contents and pH were determined. Cumulative carbon dioxide (CO2) emissions were measured to indicate soil respiration. A 144-hr incubation experiment was conducted in a slightly acidic agricultural soil (pHH2O 5.33) after the pH was adjusted to four different values (3.65, 5.00, 6.90 and 8.55). The experiments consisted of a control without added N, and with NH+4-N and NO−3-N fertilization. The results showed that soil pH contributed significantly to N2O flux from the soils. There were higher N2O emissions in the period 0–12 hr in the four pH treatments, especially those enhanced with N-fertilization. The cumulative N2O-N emission reached a maximum at pH 8.55 and was stimulated by NO−3-N fertilization (70.4 μg/kg). The minimum emissions appeared at pH 3.65 and were not stimulated by NO−3-N or NH+4-N fertilization. Soil respiration increased significantly due to N-fertilization. Soil respiration increased positively with soil pH (R2 = 0.98, P < 0.01). The lowest CO2-C emission (30.2 mg/kg) was presented in pH 3.65 soils without N-fertilization. The highest CO2-C emissions appeared in the pH 8.55 soils for NH+4-N fertilization (199 mg/kg). These findings suggested that N2O emissions and soil respiration were significantly influenced by low pH, which strongly inhibits soil microbial nitrification and denitrification activities. The content of NO−3-N in soil significantly and positively affected the N2O emissions through denitrification.