Within each vegetation plot, five soil sub-plots will be established (60 sub-plots total among all study areas). Using a stratified random approach, the sub-plots will be located randomly within the vegetation plot ensuring that the sub-plots are dispersed along the length of the transect.
In June/July, soil samples of the A and B horizons will be collected from each sub-plot. These will be sieved through a 2 mm mesh, air dried and sent to Brookside Laboratory (New Knoxville, OH) for standard agronomic analysis that includes measurement of the following: pH, total N, P, K, S, Ca, Mn, Na, B, Fe, Mg, Cu, Zn, Al and organic matter content. Soil texture will also be assessed.
Annual nitrogen (N) mineralization rates will be measured using a field incubation technique. At each sub-plot, a 3.7 cm PVC tube will be pounded 10 cm into the soil. The tube will be capped with plastic film and loosely covered with an anchored plastic cup. This technique maintains an aerobic environment for soil microbes and prevents plant uptake of mineralized N. At the time the incubation tubes are placed, a similar soil core will be gathered and analyzed for ammonium- and nitrate-N. Following one month of incubation, samples will be retrieved and similarly analyzed. Mineralization rates for ammonium- and nitrate-N are calculated as the difference between initial and final amounts. To generate annual rates, the mineralizations will be initiated at six-week intervals beginning in May and lasting until October. Winter rates will be estimated from a November to April incubation. Ammonium- and nitrate-N concentrations will be analyzed by extracting 10 g of sieved soil in 50 ml of 2 M KCl. The extract will be filtered and analyzed using standard colorimetric procedures on an OI Segmented Flow Autoanalyzer. During the fall and winter of 2000, nitrogen mineralization potentials will be evaluated using laboratory incubation procedures and compared with field rates to evaluate the sources of variation in field mineralization rates.