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DIVISION S-3—SOIL BIOLOGY & BIOCHEMISTRY

A Rapid Method to Estimate Potentially Mineralizable Nitrogen in Soil

^a Fac. de Ciencias Agrarias, Univ. Nac. de Mar del Plata (UNMP)- Est. Exp. Agropecuaria Balcarce, Inst. Nac. de Tecnología Agropecuaria (INTA), Unidad Integrada Balcarce, C.C. 276, (7620) Balcarce, Argentina
^b Dep. of Crop and Soil Sciences, Univ. of Georgia, Athens, GA 30602
^c USDA-ARS. J. Phil Campbell Sr. Natural Resource Conservation Center, 1420 Experiment Station Road, Watkinsville, GA 30677

* Corresponding author (mcabrera{at}uga.edu)

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.

Abbreviations: SMBC, soil microbial biomass C • TC, total C • TN, total N

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