Evaluation of the Ammonia Diffusion Method for Determining Soil Gross N Mineralization Rates by 15N Dilution.
(S07-jin308297-oral)
Authors:
V.L. Jin* - Univ. of Georgia C.S. Romanek - Univ. of Georgia R.R. Sharitz - Univ. of Georgia
Abstract:
We evaluated the ammonia diffusion method for determining soil gross N mineralization rate (m) from
15N dilution in laboratory-incubated 15N-labeled soils extracted with 2M KCl. Hardwood (H) soils and sandhills (S) soils were labeled with (15NH4)2SO4 (d15N=760 per mil) at 1.3 mg N kg-1 soil.
Pre-incubation (T1) soils were extracted and diffused immediately after label addition. Post-incubation (T2) soils were incubated for 48 hours at 23C before extracting and diffusing. Triplicate samples of extracts and diffused N were taken daily over the five-day diffusion period to characterize changes in N concentrations and isotope values. We found negative linear relationships between diffusion-recovered
15N and extract NH4+-N for both H and S soils. We assumed 100% recovery of extractable-15N label
when extract NH4+-N concentrations were zero, and used these values to calculate m. We also used the conventional approach of calculating m with 15N values observed on the last day of diffusion. The observed m using Day 5 values was 0.15 mg N kg-1d-1 for both soil types, but m calculated from extrapolated 15N values were 0.19 and 0.05 mg N kg-1d-1 for H and S soils, respectively. Our findings suggest that m is sensitive to diffusion results, and that the conventional approach of using 15N values observed on the final day of diffusion may not adequately estimate m of some soils.
Speaker Information: Virginia L. Jin, Univ. of Georgia, Savannah River Ecology Laboratory Drawer E, Aiken, SC 29802; Phone: 803-725-7358; E-mail: [email protected]
Session Information: Thursday, November 6, 2003, 8:10 AM-10:45 AM Presentation Start: 9:45 AM