Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/22/2002
Publication Date: 11/1/2002
Citation: Picone, L.I., Cabrera, M.L., Franzluebbers, A.J. 2002. A rapid method to estimate potentially mineralizable nitrogen in soil. Soil Science Society of America Journal.
Interpretive Summary: Estimates of potential soil biological activity and nutrient mineralization are needed by agricultural producers to optimize fertilizer applications to meet economic and environmental goals. Rapid, reliable, and simple tools need to be developed. This study describes the potential of a simple chemical reaction vessel that can be used in the field to predict nitrogen mineralization. Conditions to obtain greatest sensitivity were optimized. The release of gas into an enclosed chamber following addition of a mild oxidant was strongly related to microbial biomass and potential activity. It is suggested that this simple analytical tool could be useful in rapid assessments of potential nitrogen availability, such that decisions on whether fertilization were necessary could be made on short notice throughout the growing season of a crop.
Technical Abstract: 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 hypochlorite 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 hypochlorite, and a reaction time of 25 min were selected as optimum conditions. The method was evaluated with 60 Cecil sandy loam samples ranging in organic C from 4 to 16 g/kg. Nitrogen mineralized in 24 d and soil microbial biomass C were measured and related to the Ca hypochlorite method and to two other rapid methods, the flush of CO2 during 3 d following rewetting of a dry soil and extractable Nh4-N with hot 2M KCl. The Ca hypochlorite method was strongly correlated with net N mineralization (r=0.77), microbial biomass (r=0.90), the flush of CO2 during 3 d (r=0.85), and extractable NH4-N with hot 2M KCl (r=0.86). These results indicate that the N meter may be useful to make rapid estimates of mineralizable N and microbial biomass C in soil.