Nitrogen Mineralization Following Vegetation Control and Fertilization in a 14‐Year‐Old Loblolly Pine Plantation

Vegetation control (VC) and fertilization (FR) can change N availability in southern pine plantations, but the magnitude, duration, and reasons for change are not fully understood. The effects of a factorial combination of vegetation control (none vs. complete) and fertilization (none vs. 224 kg N ha −1 and 56 kg P ha −1 ) on net N mineralization and soil temperature and moisture were investigated in a 14‐yr‐old loblolly pine ( Pinus taeda L.) plantation located on the Piedmont of North Carolina. Net N mineralization and soil temperature and moisture were measured monthly for 2 yr beginning in July 1998, four months after the treatments were applied. A companion aerobic laboratory incubation study of field‐moist soil was conducted at 28°C during the second year. Vegetation control increased soil temperature by 1.8°C during the growing season. Both vegetation control and fertilization increased field net N mineralization, and there was a strong positive interaction between the treatments. Net nitrification constituted 72% of net N mineralization for the combined treatment, and only 8% of net N mineralization for the other treatments. Seasonal patterns in net N mineralization were poorly correlated with soil temperature and moisture. The field and laboratory studies showed the same seasonal dynamics and magnitude of annual treatment effects on net N mineralization, suggesting other factors (e.g., labile C inputs) may be important in controlling net N mineralization.