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I am just about to start a set of acid diffusions on KCl soil extracts to determine 15N enrichment of NO3 and NH4 fractions within the extracts.  I know the typical method is to diffuse the samples first for NH4, then let me sit open for ~6 days to volatilize remaining NH4 and then resealing them to capture the NO3-N.  However, I have also talked to people who have recommended doing simultaneous diffusions (ie. divide the sample into two separate containers and diffuse one for NH4 and the other for total N.  The mass balance difference will be used to provide the estimate of NO3-N).  If anyone has experience with acid diffusions and could give me their two bits about which technique is best to use, it would be greatly appreciated.






Jennifer Bennett, PhD

Research Associate

Forest Nutrition Cooperative

North Carolina State University

3106 Jordan Hall   Box 8008

Raleigh, NC  27695-8008

(919) 513-4041

(919) 515-6193 (fax)