Soil properties and ammonia emissions in nitrification inhibitors treatment

It can be preliminary summarized that NI treatment increased NH3 emission in the soil which has relatively higher range of pH (5.4 to 7.9) and lower range of CEC (5.7 to 16.8 meq 100 g–1 soil) compared to the soil of studies reporting no increase in NH3 emission (pH 4.7 to 6.2 and CEC 10.0 to 24.0 meq 100 g–1 soil).

It has been well known that soil pH and CEC are important soil factors determining the magnitude of NH3 emissions from N fertilizer applied to agricultural soils (e.g., Nelson, 1982; Francis et al., 2008). Ammonia losses increase with higher soil pH because high H+ concentration in soil increases dissociation of NH4 to NH3, thus increasing the potential for volatilization (Sharpe and Harper, 1995; Francis et al., 2008).

However, significant amount of NH3 can be lost at soil pH values as low as 5.5 if large amount of urea or NH4+ are applied in soil surface (Nelson 1982). This can explain the observed significant increase in NH3 emission in NI treatment with low pH soils. High soil CEC reduce NH3 emission because CEC provides a mechanism by which NH4+ are removed from soil solution, thereby reducing NH4+ in the soil solution that is subject to volatilization (e.g., Hargrove, 1988; Al-Kanani et al., 1991; Whitehead and Raistrick, 1993; Sommer et al., 2003). These results indicate that soil which has properties for high potential of NH3 emission from N fertilizer also has high potential of increase in NH3 emission in NI treatments.

It has been known that high organic matter (OM) and clay content and fine-textured soils reduce NH3 emission (Nelson, 1982; Al-Kanani et al., 1991; Francis et al., 2008) because of the relative contribution of the OM and clay components to the CEC of the soil (Al-Kanani et al., 1991). Therefore, it is suggested that NI treatment in low soil pH and high CEC, OM and clay content and fine-textured soils may decrease the potential of increase in NH3 emission.