Contribution of nitrogenous sources to carbon mineralization and soil health

The non-judicious use of nitrogen (N) fertilizers in agricultural soils increases environmental pollution, greenhouse gases (GHGs) emission, and ammonia (NH3) volatilization. Nitrogen sources undergo numerous biological and chemical transformations that may positively or negatively impact soil organic carbon (SOC) dynamics and soil health. To determine the impact of various N sources on carbon mineralization, soil health, and NH3 volatilization in alkaline calcareous soil, an incubation experiment was executed using three N sources i) urea as NH4-N, ii) calcium nitrate as NO3-N, and iii) ammonium nitrate as both NH4- and NO3-N, and a control without N addition. The results showed that urea addition had the highest C-CO2 emission and N-NH3 volatilization compared with other treatments. The microbial biomass carbon (MBC) and metabolic quotient (qCO2) were increased by all N sources, with significantly higher values (327.76 mg C kg-1 soil and 0.32 qCO2, respectively) observed with urea. The SOC decreased, and β-glucosidase enzyme activity increased with NH4-N sources. At the same time, the activities of acid phosphatase and leucine aminopeptidase enzymes significantly enhanced with NH4NO3, except for chitinase. It was concluded that adding inorganic NH4-N in alkaline calcareous soils under controlled conditions resulted in higher emissions of CO2, and NH3 volatilization due to higher microbial activities. Therefore, the selection of N sources should be based on their potential contribution to GHGs emission, C mineralization, and soil health, which are crucial for sustainable crop production, particularly in alkaline calcareous soils with low SOC.