INFLUENCE OF SAMPLING DATE AND SUBSTRATE ON NITROGEN MINERALIZATION - COMPARISON OF LABORATORY-INCUBATION AND BURIED-BAG METHODS FOR 2 MASSACHUSETTS FOREST SOILS

Nitrogen (N) mineralization potential and net N mineralization in situ were measured monthly over 7 months for the forest floor horizons (Oi, Oe, Oa) and mineral soil (0-15 cm) of a pine stand and the mineral soil (0-15 cm) of a maple stand in Massachusetts, United States. In all cases, N mineralization potential per unit organic matter (anaerobic laboratory incubation) varied significantly by sampling month but was unrelated to the seasonal pattern for net N mineralization (buried-bag method). The organic horizons in the pine stand exhibited the most variable N mineralization potential, with the Oe horizon having more than a fourfold seasonal range. For the pine stand the Oe horizon also had the highest N mineralization potential (per unit organic matter) and the highest net N mineralization in situ (per unit area). In general, temporal and depth-wise variability should be considered when sites are assessed with respect to the pool of mineralizable N.