Inhibitory Effects of Dicyandiamide and Neem ( <i>Azadirachta indica</i> ) on N Dynamics and Greenhouse Gas Emissions in Paddy Saline‐Sodic Soils: A Laboratory Study

Application of nitrification inhibitors (NIs) with nitrogen (N) fertilizer is an efficient way to increase soil N availability with minimum greenhouse gas (GHG) emissions from different soil types; however, there is scarce information for salt‐affected soils. This study explored the effect of two NIs—dicyandiamide (DCD) and neem leaf powder—applied with urea on the soil N content and the emissions of nitrous (N 2 O) oxide, methane (CH 4 ), and carbon dioxide (CO 2 ) using aerobic and anaerobic conditions in a 56‐day incubation experiment with three different levels of salinity and sodicity in saline‐sodic soils. Urea combined with both NIs had a slight impact on delaying nitrification and significantly decreased the nitrate (NO 3 − ‐N) content compared to urea alone, while the release of all GHG was successfully suppressed except CO 2 . The levels of all GHG emissions were the greatest with anaerobic conditions and peaked when the soils were submerged for 14 days, while the inhibition of GHG emissions due to these NIs with anaerobic conditions was less effective than for aerobic conditions. Based on a paired comparison between NIs, both NIs equally reduced CH 4 emission; however, neem leaf powder reduced significantly more N 2 O than DCD. The findings from this study indicated that, to some extent, both NIs could be used to increase the efficiency of N fertilizer in these salt‐affected soils; however, there were no determinable impacts of these NIs on GHG emissions from soil with the highest levels of salinity and sodicity, reflecting that their inhibitory effects were wholly retarded at such levels.