Stand and soil responses of a loblolly pine plantation to midrotation fertilization and vegetation control

Abstract

This study wasconducted in a 14-year-old midrotation loblolly pine (Pinus taeda L.) plantation to assess the effects of fertilizationand vegetation control (a) on soil net nitrogen mineralization, (b) litterdecomposition and (c) foliar nutrient concentrations and use, and vegetationgrowth. Fertilization (none, 224 kg haP) and vegetation control (none, complete) treatments were applied in a 2x2factorial design in March 1998. Soil net nitrogen mineralization was assessedby monthly field and laboratory incubations, litter decomposition and nutrient(N, P K, Ca, Mg, S, Mn, Zn, B, Cu) release dynamics were determined by thelitterbag method, foliar nutrient use of pines and hardwoods was estimated fromlitterfall and foliar nutrient concentrations, and growth was determined basedon annual measurements of diameter and height. Field net N mineralization rateswere 19, 18, 31, and 78 kg ha for control (C, notreatment), fertilization (F), vegetation control (VC), and vegetation controlplus fertilization (VC+F) treatments, respectively. Relative treatments responseswere similar in the laboratory incubations. Litter mass loss duringdecomposition was reduced by 9% after 32 months by vegetation control, andfertilization had no effect. The mobility of the nutrients was as follows: Cu≤N≤S<P<Zn≤Ca<K≤Mn<Mg≤B.Pine foliar N and P concentrations, and N and P use were significantlyincreased by fertilization, while effects of vegetation control on theseparameters were usually not significant. Fertilization significantly increasedannual volume growth of loblolly pine by up to 7 myr (32%) over the three years, while vegetation control had nosignificant effect.