Carbon Dioxide and Nitrous Oxide Emissions from Naturally Occurring Sulfate-Based Saline Soils at Different Moisture Contents

Soil salinization may negatively affect microbial processes related to carbon dioxide (CO2) and nitrous oxide (N2O) emissions. A short-term laboratory incubation experiment was conducted to investigate the effects of soil electrical conductivity (EC) and moisture content on CO2 and N2O emissions from sulfate-based natural saline soils. Three separate 100-m long transects were established along the salinity gradient on a salt-affected agricultural field at Mooreton, North Dakota, USA. Surface soils were collected from four equally spaced sampling positions within each transect, at the depths of 0-15 and 15-30 cm. In the laboratory, artificial soil cores were formed combining soils from both the depths in each transect, and incubated at 60% and 90% water-filled pore space (WFPS) at 25 °C. The measured depth-weighted EC of the saturated paste extract (ECe) across the sampling positions ranged from 0.43 to 4.65 dS m−1. Potential nitrogen (N) mineralization rate and CO2 emissions decreased with increasing soil ECe, but the relative decline in soil CO2 emissions with increasing ECe was smaller at 60% WFPS than at 90% WFPS. At 60% WFPS, soil N2O emissions decreased from 133 μg N2O-N kg−1 soil at ECe < 0.50 dS m−1 to 72 μg N2O-N kg−1 soil at ECe = 4.65 dS m−1. In contrast, at 90% WFPS, soil N2O emissions increased from 262 μg N2O-N kg−1 soil at ECe = 0.81 dS m−1 to 849 μg N2O-N kg−1 soil at ECe = 4.65 dS m−1, suggesting that N2O emissions were linked to both soil ECe and moisture content. Therefore, spatial variability in soil ECe and pattern of rainfall over the season need to be considered when up-scaling N2O and CO2 emissions from field to landscape scales.