Saline-Sodic Soils: Potential Sources of Nitrous Oxide and Carbon Dioxide Emissions?

Increasing salt-affected agricultural land due to low precipitation, high surface evaporation, irrigation with saline water, and poor cultural practices has triggered the interest to understand the influence of salt on nitrous oxide (N2O) and carbon dioxide (CO2) emissions from soil. Three soils with varying electrical conductivity of saturated paste extract (ECe) (0.44-7.20 dS m−1) and sodium adsorption ratio of saturated paste extract (SARe) (1.0-27.7), two saline-sodic soils (S2 and S3) and a non-saline, non-sodic soil (S1), were incubated at moisture levels of 40%, 60%, and 80% water-filled pore space (WFPS) for 30 d, with or without nitrogen (N) fertilizer addition (urea at 525 µg g−1 soil). Evolving CO2 and N2O were estimated by analyzing the collected gas samples during the incubation period. Across all moisture and N levels, the cumulative N2O emissions increased significantly by 39.8% and 42.4% in S2 and S3, respectively, compared to S1. The cumulative CO2 emission from the three soils did not differ significantly as a result of the complex interactions of salinity and sodicity. Moisture had no significant effect on N2O emissions, but cumulative CO2 emissions increased significantly with an increase in moisture. Addition of N significantly increased cumulative N2O and CO2 emissions. These showed that saline-sodic soils can be a significant contributor of N2O to the environment compared to non-saline, non-sodic soils. The application of N fertilizer, irrigation, and precipitation may potentially increase greenhouse gas (N2O and CO2) releases from saline-sodic soils.