Browsing by Author "Torbert, John L."
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- The fate of applied phosphorus on a piedmont soil and its effect on loblolly pine growth twenty years after applicationTorbert, John L. (Virginia Polytechnic Institute and State University, 1982)A loblolly pine phosphorus fertilization trial was evaluated 20 years after establishment on a Tatum silt loam in the Virginia Piedmont. Triple superphosphate (TSP) was applied at 160 kg P/ha and ground rock phosphate (GRP) was applied at both 160 kg P/ha and 670 kg P/ha. Lime (4.48 T/ha) was applied with and without the TSP treatment. Tree growth was not significantly affected by treatment and foliar phosphorus levels were above 0.10% indicating that a deficiency was not the immediate growth limiting factor. Double-acid-extractable soil phosphorus critical levels established for the Coastal Plain do not appear useful for diagnosing tree requirements for this Piedmont soil. A critical level of 1.0 ppm double-acid-extractable phosphorus would be more applicable to this soil. GRP was more effective than TSP after 20 years at increasing phosphorus uptake, probably due to a slower dissolution rate and the inclusion of F-ions which reacted with soil Al to reduce phosphorus fixation. Although an increase in the A horizon pH persisted for 20 years, there was no increase in phosphorus uptake as a direct response to this higher pH. Liming may have some long-term merit when applied in conjunction with a water soluble phosphorus fertilizer such as TSP by reducing the transformations of applied phosphorus to unavailable forms.
- Loblolly Pine (Pinus taeda L.) Plantation Response to Mechanical Site Preparation in the South Carolina and Georgia PiedmontCerchiaro, Michael Paul (Virginia Tech, 2003-10-21)Site preparation is fundamental for establishing loblolly pine (Pinus taeda L.) plantations, but long-term sustainability of plantations established using mechanical treatments is in question because of concerns regarding soil tillage and the removal of harvest residue and soil organic matter. A study was installed in 1981 on 12 locations in northeastern Georgia and west-central South Carolina to evaluate pine plantation response to mechanical site preparation. Site preparation treatments induced gradients of organic matter manipulation and soil tillage. The treatments included: Control, Chop/Burn, Shear/Disc, Shear/V-Blade, Shear/Rake, and Shear/Rake/Pile. Research was conducted to address the following objectives: (i) compare rotation-age forest response to several intensive site preparation treatments used to establish pine plantations in the Piedmont of the southeastern United States; (ii) correlate growth response with the gradients of soil organic matter removal, soil tillage, and hardwood control; (iii) determine the influence of intensive management on the amount of carbon contained in pine plantations. All site preparation treatments increased year-18 volume accumulation compared to the control treatment. Chop/Burn and Shear/Disc treatments, with pine volumes of 214 m3 ha-1 and 232 m3 ha-1, respectively, conserved harvest residue and out-performed the Shear/Rake treatment (191 m3 ha-1), which completely removed harvest residue. Treatments that included tillage provided growth benefits that lasted throughout the rotation even when tillage was accompanied by complete organic matter removal. Hardwood competition had the greatest influence on pine volume accumulation, explaining over 54% of the variation in pine growth at age 18. Treatments that included tillage most effectively controlled hardwood competition. At year 18, site preparation treatments significantly affected soil organic matter (SOM) content; however, soil nitrogen, foliar nitrogen, bulk density, and macroporosity were not affected by site preparation. All treatments were equally deficient in foliar nitrogen. The Shear/Disc and Shear/Rake/Disc treatments had a significantly positive relationship between foliar nitrogen and pine volume. These treatments had lower hardwood basal areas (below 15%), indicating that once hardwoods were controlled, nitrogen became limiting to pine growth. Using pre-harvest characterization data, carbon accumulation during old-field succession increased fourfold compared to agricultural sites on the nearby Calhoun Experimental Forest. Carbon accumulation on these old-field loblolly pine sites reached quasi-equilibrium after 40 years as shown by uncut reference stands. Site preparation significantly affected the amount of soil C in the upper 20 cm of the soil. Those site preparation treatments that removed harvest residue and accelerated SOM decomposition through tillage had the lowest soil carbon levels. The Shear/Rake/Disc treatment had 10% lower soil carbon content than the Control and Shear/V-Blade treatments.
- Managing symbiotically-fixed nitrogen on mined land for tree cropsBrown, Sarah K. (Virginia Tech, 1994-08-19)Young mine soils constructed following surface-mining for coal contain low levels of organic matter and nitrogen. It was hypothesized that nitrogen-fixing plants could be incorporated into a reforestation system in a manner that would meet the short term and long-term nitrogen needs of crop trees while rebuilding the soil and litter nitrogen pools and restoring a stable nitrogen cycle. The nitrogen status of two interplanting studies containing legume ground covers was examined. The first study site was mined prior to 1940 and subsequently abandoned. In 1988, the land was reclaimed, and an interplanting study was established in 1990. Pitch x loblolly pines (Pinus x rigitaeda) and eastern white pines (Pinus strobus L.) were interplanted with four nitrogen-fixing species: black alder (Alnus glutinosa L. IGaertn.l), black locust (Robinia pseudoacacia L.}, bicolor lespedeza (Lespedeza bicolor) and autumn olive (Elaeagnus umbel/ata Thwnb.). Pitch x loblolly pine survival was good; however, eastern white pine survival was only fair, averaging 54%. All of the nurse tree species with the exception of black alder had fair survival rates. Black alder survival was extremely low at 19%. After the third growing season, a ground cover dominated by legumes averaged 79% cover. The black mine spoil on the site was extremely rich in nitrogen, averaging 5,115 mg·kg-1. When the black mine spoil was mixed with the native topsoil, a mine soil that was created had an extremely variable total nitrogen content. However, low mineralizeable nitrogen levels suggested that the nitrogen in the mine spoil was not generally available. Pine responses to the four nitrogen-fixing species were compared. Nurse trees had no effect on pine growth after three years. Pine foliar nitrogen levels were adequate across the study site even in the control treatments and in the microsites where few legumes were present. Microsites surrounding 50 pines of each species were studied. The pitch x loblolly pines grew larger at lower pH levels and higher coarse fragment content reflecting the pines' preference for moderately acid soils, coarse-textured soils. Some competition was present between the crop trees and herbaceous cover, but it was not a controlling factor in pine tree growth.
- Reclamation of surface-mined forest land in the southern AppalachiansTorbert, John L. (Virginia Tech, 1995)Most of the surface-mined land in the southern Appalachian coal fields of Virginia, southern West Virginia, and eastern Kentucky is forested before mining. For a variety of reasons, most surface-mined land will ultimately return to forest, either by design or through natural succession. The usefulness of forests on reclaimed surface-mined land for providing timber management opportunities depends on whether or not the land is reclaimed in a manner which creates a productive forest soil. Surveys of tree plantings on land that was mined prior to enactment of the 1977 Surface Mining Control and Reclamation Act (SMCRA) have shown that trees will grow well where 1) minesoils are non-toxic, 2) minesoils are deep, loose, and uncompacted, and 3) tree seedling establishment is not hindered by competition from an herbaceous ground cover. Several experiments were conducted to develop practical recommendations for post-SMCRA reclamation of surface-mined forest land to create these desirable minesoil conditions. An experiment designed to evaluate the effect of two contrasting spoil types revealed that the type of overburden material used as a topsoil substitute can have long-term effects on tree growth. After five years, average tree volume in a sandstone spoil was five times greater than tree volume in a siltstone spoil. In the southern Appalachians, oxidized (brown) sandstone is a good overburden to use as a topsoil substitute for forest land reclamation. A second experiment was conducted to evaluate the effect of surface grading practices on erosion, herbaceous ground cover, and tree survival and growth. After five years, study results revealed that traditional grading practices caused excessive soil compaction that resulted in higher erosion and poorer tree growth than treatments that left the soil in a loose condition. A third experiment was conducted to compare the effect of two herbaceous ground cover prescriptions (a tree-compatible ground cover versus the coal operator’s standard revegetation mix) on the establishment of white pine (Pinus strobus) and black locust (Robinia psuedoacacia) by direct seeding versus hand planting seedlings. After five years, on a minesoil derived from brown sandstone and rough-graded to reduce compaction, the tree-compatible ground cover produced more cover than the traditional ground cover, and the site index of the reclaimed land was estimated to exceed 30 m (100 ft). Based on results of this long term research program, recommendations for establishing a productive forest, capable of providing timber within a 30 year rotation are: 1) select an oxidized (brown) sandstone spoil for placement at the surface, 2) roughly grade the final surface to avoid compaction, 3) establish a tree compatible ground cover to protect the soil without overtopping trees, and 4) select an appropriate mixture of tree species and carefully plant trees by selecting good micro-sites for each seedling.