Tuesday, November 6, 2007
223-12
Direct Steam Distillation or ISNT Diffusion? Assessment of the Two Methods in Recovering Selected Organic N Compounds.
Trenton Roberts, Jeremy Ross, Richard Norman, Nathan Slaton, and C.E. Wilson. University of Arkansas, Dept. of Crop, Soil and Environmental Science, 115 Plant Science, Fayetteville, AR 72701
The recent success of Direct Steam Distillation (DSD) as an alternative to the Diffusion method (ISNT) for prediction of potentially mineralizable nitrogen has raised questions about whether or not the methods are measuring the same pool of soil organic nitrogen (SON). Direct Steam Distillation has been successfully correlated to ISNT with a slope of near 1.0 and high coefficients of determination (R2>0.80), but Y intercepts near -20.0 ppm of N. Benefits of DSD over ISNT include shorter analysis time and less cleanup, but DSD can be highly variable. Seventeen organic nitrogen compounds were selected for analysis and classified according to basic structure as Amino Acid, Amino Sugar, Nucleic Acid, or Other. Each compound was analyzed by adding 1 mg N as the pure compound and measuring the percent recovery of four replications. A significant difference in the percent N recovered was seen for 15 of the 17 compounds as well as a significant difference in the recovery of (NH4)2SO4 at p values >0.10. Recovery of N from Amino Acids was very low (<2.0%) except for Asparagine and Glutamine which saw recoveries as high as 58%. This suggested that a single amine group was being hydrolyzed rather than a combination of both amine groups. Results of N15 analysis suggest that a single amine group was responsible for a majority of the N that was recovered. Different amounts of each compound (from 0.2 mg N to 2.0 mg N) were analyzed to determine if the percent recovery was constant. A strong correlation between mg of N recovered and mg of N added was found for each compound (R2>0.99). High rates of recovery were found for Amino Sugars in both methods, but were significantly different in the range where most soils should fall (50 to 350 ppm N).