Nitrification is a key process of the nitrogen cycle in soil, it oxidizes ammonia to nitrite and then to nitrate in the soil, it is a major source of N2O and NO in the atmosphere and is responsible for the reduced efficiency of ammonium fertilizers through leaching and denitrification of nitrate (Zerullaet al., 2001; Macadam et al., 2003). The results found in this study showed that the addition of NI with urea fertilizer increased the concentration of NH4 and decreased its conversion to nitrate. These results are supported by numerous studies that have also shown that Nis suppresses nitrification and therefore improves nitrogen efficiency (Di and Cameron 2005, 2006; Di et al. 2007; Moir et al. 2007; Sahrawat 2004; Singh and Verma 2007). As can be seen from the results (Table 1), all treatments applied (except Urea alone) reduced the NO3 concentration at all levels. Therefore, adding nitrification inhibitors (NIs) to fertilizers has been found to be beneficial for reducing nitrate leaching and nitrous oxide emissions, which, consequently, increases plant growth (Zaman et al., 2009) . This study demonstrated that the results were site- and experiment-specific, and nitrification inhibitors had different effects on different soil structures, depending largely on the concentration of inhibitors applied. Furthermore, several studies indicate that the potential effects of soil nitrification differ between ecosystems and that these differences do not appear to be directly associated with physical factors. or soil chemical characteristics (Clark et al., 1960, Hattenschwiler and Vitousek, 2000; Lata et al., 2004; Laverman et al. 2000; Lovett et al. 2004; Montagnini et al. 1989; Northup et al. 1995; Robertson, 1982a, Robertson, 1982b and Schimel et al., 1998). In many other studies, the... middle of the paper... outward variation has been shown. However, further studies are needed to evaluate the effects of nitrification inhibitors on ammonia volatilization, another important N loss pathway, as few studies have reported that nitrification inhibitors can increase ammonia volatilization from soils with pH high (Kim et al., 2012). Another interesting result found on DCD treatments is that DCD has a very short duration as its effect decreases significantly by the 30th day in almost all parameters in both media, compared to the other inhibitors applied; these findings are supported by Di et al. (2009). This conclusion is further supported by the absence of a significant impact on bacteria and archaea in the two media at day 30 of incubation. Similarly, O'Callaghan et al. (2010) also found that DCD was relatively benign and did not affect soil microbial communities, which is supported by our results.