The effects of vegetation control and fertilization on net nutrient release from decomposing loblolly pine needles

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.