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Soil Electrical Conductivity and Water Content Affect Nitrous Oxide and Carbon Dioxide Emissions in Intensively Managed Soils

Adviento-Borbe, M. A. A., Doran, J. W., Drijber, R. A., Dobermann, A.
Journal of environmental quality 2006 v.35 no.6 pp. 1999
agricultural soils, soil salts, solubility, saline soils, soil salinity, electrical conductivity, greenhouse gases, gas emissions, nitrous oxide, carbon dioxide, biological activity in soil, microbial activity, ammonium nitrogen, nitrate nitrogen, soil water content, soil pore system, soil respiration, silt loam soils
Accumulation of soluble salts resulting from fertilizer N may affect microbial production of NO and CO in soils. This study was conducted to determine the effects of electrical conductivity (EC) and water content on NO and CO 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 soil EC of 0.5, 1.0, 1.5 and 2.0 dS m The soil cores were incubated at 25°C for 10 d. Average CO production decreased with increasing EC at both soil water contents, indicating a general reduction in microbial respiration with increasing EC. Average cumulative NO production at 60% WFPS decreased from 2.0 mg NO-N m at an initial EC of 0.5 dS m to 0.86 mg NO-N m at 2.0 dS m At 90% WFPS, NO production was 2 to 40 times greater than that at 60% WFPS and maximum NO losses occurred at the highest EC level of 2.0 dS m 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 NO emissions need to be accounted for in ecosystems models for predicting soil greenhouse gas emissions.