A rapid method to estimate potentially mineralizable nitrogen in soil

Rapid estimates of mineralizable N in soil are important for management decisions and soil quality assessments. We adapted and evaluated a rapid method based on measuring the gas pressure generated when soil is treated with Ca(ClO)(2) in a closed vessel. An experiment was conducted to determine the effects of reaction time, soil/reagent, and soil/water ratios on the gas pressure generated by the method. Based on this experiment, 5 g of soil, 5 mL of deionized water, 0.3 g Ca(ClO)(2), and a reaction time of 25 min were selected as optimum conditions. The method was evaluated with 60 Cecil (fine, kaolinitic, thermic Typic Kanhapludults) sandy loam samples ranging in organic C from 4 to 16 g C kg(-1). Nitrogen mineralized in 24 d and soil microbial biomass C (SMBC) were measured and related to the Ca(ClO)(2) method and to two other rapid methods, the flush of CO2 during 3 d following rewetting of a dry soil, and the NH4-N extractable with hot 2 M KCl. The Ca(ClO)(2) method (mmol kg(-1)) was strongly correlated with net N mineralized in 24 d (r = 0.77) and with microbial biomass C (r = 0.90). The method was also correlated with the flush of CO2 during 3 d following rewetting of dried soil (r = 0.85) and with the NH4-N extractable with hot 2 M KCl (r = 0.86). These results indicate that the Ca(ClO)(2) method may be useful to make rapid estimates of mineralizable N and microbial biomass C in soil. Additional work is needed to investigate the nature of the compounds oxidized by the method.