Improving the management of mineral fertilizers for nitrous oxide mitigation: The effect of nitrogen fertilizer type, urease and nitrification inhibitors in two different textured soils

The production of nitrous oxide (N2O) in soil is mainly related to nitrification and denitrification processes, taking place under aerobic and anaerobic conditions, respectively. Oxygen, ammonium (NH4(+)) and nitrate (NO3-) concentrations in soil are the main factors controlling the N2O production processes. Many studies confirm that N2O emissions in agroecosystems are stimulated by increasing the N fertilizer rate. Beside the N rate, the fertilizer formulation may affect soil N2O emissions, though the effects are still unclear and may be different according to soil type, soil water content and oxygen availability expressed as soil water filled pores space (WFPS). Enhanced efficiency fertilizers, such as fertilizers with nitrification and urease inhibitors (NIs, UIs) may slow down N2O production processes, although different results were reported regarding their effectiveness. This study contributed to the evaluation of the effect of mineral N fertilizer formulation on N2O and CO2 emissions, through two laboratory experiments carried out on soil cores distributing to two different textured soils: i) nitrate or ammonium-based fertilizer under increasing WFPS levels (Exp.1), and; ii) NIs and UI with various N fertilizers, including a new NI (DMPSA) (Exp.2). The highest N2O and CO2 emissions were recorded after the application of an ammonium-based fertilizer in both soils, suggesting the preponderance of nitrifying organisms. The results confirmed that WFPS is a key driver for N2O emissions, with highest N2O emissions occurring at WFPS > 75%, while CO2 emissions decreased linearly with increasing WFPS across all fertilizer treatments and in both soils. NIs were effective only in the soil with the highest nitrification activity and the lowest clay content, decreasing N2O emissions by an average of 50%, while the UI did not reduce N2O emissions in either soil. These results proved that soil characteristics significantly affect NIs capacity to mitigate N2O emissions from soil.