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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.

This study examined the effects of vegetation control and nitrogen + phosphorus fertilization on decomposition and nutrient release dynamics of loblolly pine (Pinus taeda L.) needle litter. Needle litter was placed in litterbags and left to decompose on the forest floor, and changes in mass loss and nutrient (N, P, K, Ca, Mg, S, Mn, Zn, B, Cu) concentrations and contents were observed at 2-to 6-month intervals for 32 months. Fertilization had no effect on mass loss, while vegetation control resulted in a warmer and drier forest floor and led to reduced mass loss (k = 0.39 and 0.28 year -1 for fertilization and vegetation control, respectively). Concentrations of N, P, Ca, S, Zn, and Cu in the decomposing litter increased two-to three-fold over the 32 months, while concentrations of K, Mg, Mn, and B declined, increased, or did not change depending on time and treatment. Based on the release dynamics, the nutrient mobility series was as follows: Cu ≤ N ≤ S < P < Zn ≤ Ca < K ≤ Mn < Mg ≤ B. Fertilization had no effect on release dynamics; however, vegetation control reduced release of N, P, S, and Zn, and increased release of B. The mineral soil may be the main source of plant available N and P in midrotation southern pine stands based on the slow release of these elements from decomposing needle litter.Résumé : Cette étude examine les effets de la maîtrise de la végétation et d'un apport d'azote et de phosphore sur la dynamique de la décomposition et du relargage des nutriments dans la litière d'aiguilles de pin à encens (Pinus taeda L.). La litière d'aiguilles a été placée dans des sacs à litière sur la couverture morte de telle sorte qu'elle se dé-compose. Les changements dans la perte de masse, la concentration et le contenu en nutriments (N, P, K, Ca, Mg, S, Mn, Zn, B et Cu) ont été notés à intervalle de 2 à 6 mois pendant 32 mois. La fertilisation n'a eu aucun effet sur la perte de masse tandis que la maîtrise de la végétation a causé une augmentation de la température et une diminution de l'humidité dans la couverture morte entraînant une réduction de la perte de masse (k = 0,39 et 0,28 an -1 respectivement pour la fertilisation et la maîtrise de la végétation). La concentration de N, P, Ca, S, Zn et Cu dans la litière en décomposition a augmenté de deux à trois fois en 32 mois tandis que la concentration de K, Mg, Mn et B a diminué ou n'a pas changé dépendamment du moment et du traitement. Sur la base de la dynamique du relargage, la série de mobilité des nutriments serait Cu ≤ N ≤ S < P < Zn ≤ Ca < K ≤ Mn < Mg ≤ B. La fertilisation n'a pas eu d'effet sur la dynamique du relargage; cependant, la maîtrise de la végétation a réduit le relargage de N, P, S et Zn et augmenté celui du B. Le sol minéral serait la principale source de N et P disponibles pour les plantes dans les peuplements de pin à encens en milieu de révolution tel que suggéré par la lenteur du relargage de ces éléments dans la litière d'aiguilles en décomposition.[Traduit par la Rédaction] Gurlevik et al. 2502

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