Evaluation of a KCI-Hydrolyzing Method for Available Nitrogen in Soil by Pot Experiment

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Abstract
A KCl hydrolysis method for evaluating available N in soil was tested by pot experiments including 36 soils of varying type, content of organic matter and pH. The effect of 1 mo. storage of fresh soils on the analytical results was also investigated. Hydrolysis involved heating air-dry soil with 2 M KCl at a ratio of 1:10 for 20 h at 80.degree. C; the content of NO3-N and NH4-N in the soil extracts was determined. The content of inorganic N after hydrolysis was closely related to the plant uptake of N (r = 0.87). If only the NH4-N content after hydrolysis was used, the correlation coefficient was 0.84. The corresponding coefficients for N released by aerobic incubation and Kjeldahl N were 0.90 and 0.77, respectively. Storage of fresh soil samples for 1 mo. in cardboard boxes or in closed plastic bags at 4.degree. C had no significant effect on exchangeable NH4-N or NH4-N released by the hydrolysis of the air-dried soils. The release of NH4-N after storage in closed plastic bags at 20.degree. C decreased slightly. The NO3-N content increased during storage, especially when plastic bags were used.