Soil electrical conductivity and water content affect nitrous oxide and carbon dioxide emissions in intensively managed soils

Accumulation of soluble salts resulting from fertilizer N may affect microbial production of N2O and CO2 in soils. This study was conducted to determine the effects of electrical conductivity (EC) and water content on N2O and CO2 production in five soils under intensive cropping. Surface soils from maize fields were washed, repacked and brought to 60% or 90% water-filled pore space (WFPS). Salt mixtures were added to achieve an initial in situ soil EC of 0.5,1.0,1.5 and 2.0 dS m(-1). The soil cores were incubated at 25 degrees C for 10 d. Average CO2 production decreased with increasing EC at both soil water contents, indicating a general reduction in microbial respiration with increasing EC. Average cumulative N2O production at 60% WFPS decreased from 2.0 mg N2O-N m(-2) at an initial EC of 0.5 dS m(-1) to 0.86 mg N2O-N m(-2) at 2.0 dS m(-1). At 90% WFPS, N2O production was 2 to 40 times greater than that at 60% WFPS and maximum N2O losses occurred at the highest EC level of 2.0 dS m(-1) Differences in the magnitude of gas emissions at varying WFPS were due to available substrate N and the predominance of nitrification under aerobic conditions (60% WFPS) and denitrification when oxygen was limited (90% WFPS). Differences in gas emissions at varying soil EC may be due to changes in mechanisms of adjustment to salt stress and ion toxicities by microbial communities. Direct effects of EC on microbial respiration and N2O emissions need to be accounted for in ecosystems models for predicting soil greenhouse gas emissions.