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 NO3-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 Nfertilization.The cumulative N2O-N emission reached a maximum at pH 8.55 and was stimulated by NO3-N fertilization(70.4 μg/kg).The minimum emissions appeared at pH 3.65 and were not stimulated by NO3-N or NH+4-N fertilization.Soil respiration increased significantly due to N-fertilization.Soil respiration increased positively with soil pH(R 2 = 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 NO3-N in soil significantly and positively affected the N2O emissions through denitrification.