Synthesis of Double-Coated Urea with Nano-Sulfur and Organic Materials and Their Effect on N2O Emission

Fertilizer coating is an emerging strategy in fertilizer management in the quest to decrease their loss and environmental impact. Nitrous oxide (N2O) is a significant greenhouse gas, and agricultural soils happen to be an important anthropogenic source of N2O gases, mainly because of the use of nitrogen (N) fertilizers such as urea. This study examined the effects of double urea coating with nano-sulfur (NS) and organic materials; lignite, biochar and compost on N2O fluxes from silt loam and sandy loam soils. N2O fluxes were measured using an N2O analyzer in a controlled environment for a period of 26 days. Cumulative N2O fluxes were calculated for different treatments (nano-sulfur; NS, NS + lignite, NS + biochar, and NS + compost) as coatings on urea fertilizer with propagated uncertainties. Sandy loam soil had higher maximum N2O emission (155.64 µg N m−2 h−1) compared to silt loam soil (24.47 µg N m−2 h−1). Uncoated urea and urea + NS coating resulted in higher N2O emissions in both soils. Meanwhile, NS + organic second layer coatings decreased the N2O fluxes, especially in sandy loam soil. The second organic layer coatings lowered the N2O emissions with relatively lower effects in silt loam soil (3.8–7.0%) and a higher reduction in sandy loam soil (35.2–41.5%). Among the second organic coating materials, NS + lignite performed best, followed by NS + biochar and NS + compost. The results indicate that the urea coating as fertilizer management strategy as well as soil texture have considerable effects on fertilizer-induced N2O emissions. The present study does not address the individual effects of organic coatings on N2O emissions; furthermore, the characterization of the size distribution and morphology of the synthesized nano-sulfur, as well as the physicochemical properties (e.g., particle size, pH, C/N ratio, elemental composition) of the lignite, biochar, and compost coating materials, are omitted. The results of these analyses, together with the physical and chemical characterization of the produced organo-mineral fertilizers, will be presented in a forthcoming paper.