Browsing by Author "Allen, H. Lee"

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    Effects of a Control Release Nitrogen Fertilizer and Thinning on the Nitrogen Dynamics of a Mid-Rotation Loblolly Pine Stand in the Piedmont of Virginia
    Elliot, James Robertson (Virginia Tech, 2006-12-15)
    Nitrogen deficiency is characteristic of many mid-rotation loblolly pine (Pinus taeda L.) plantations in the Piedmont region of the southeastern USA. Fertilization with urea is the most common method used to correct this deficiency. Previous studies show that urea fertilization produces a rapid pulse of available nitrogen (N) with only a portion being utilized by plantation trees. Controlled release fertilizers release available N more slowly over a longer period of time and therefore may result in greater uptake efficiency. The objective of this study was to compare Nitroform®, a urea-formaldehyde controlled release N fertilizer versus urea and a control by measuring the effects of the two fertilizer treatments on N availability and loss as: total KCl extractable-N, total ion exchange membrane-N (IEM-N), N mineralization, and N volatilization, in a mid-rotation loblolly pine plantation in the Piedmont of Virginia. In addition, mid-summer and mid-winter fertilizations were compared to assess fertilizer uptake as a function of season. After the summer fertilization, Nitroform® significantly increased total KCl-extractable N, IEM-N, and N mineralization for two to three months over urea and the control. Three hundred times more N volatilized from urea than from controlled release Nitroform®. Interestingly, seven months after the summer application, the controlled release Nitroform® showed marked immobilization for three months while urea demonstrated greater N mineralization. After the winter application, fertilization with urea demonstrated greater soil inorganic N concentrations for two to three months over Nitroform®, very little N was immobilized, and volatilization was only 10 times that of Nitroform®. After summer and winter fertilizations, both fertilizer treatments significantly increased soil inorganic N concentrations and N volatilization over controls, however did not significantly increase N mineralization over controls when average response was tested over the entire sampling period. In addition to the fertilizer effects measured, a thinning only treatment was also incorporated into this study with soil N-availability indices compared to a control with no thinning or fertilization. The results from the thinning only treatment demonstrated no significant increases over the control in total KCl extractable-N, IEM-N, N-mineralization, or N volatilization when average responses were tested over the entire sampling period.
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    Juvenile Southern Pine Response to Fertilization Is Influenced by Soil Drainage and Texture
    Albaugh, Timothy J.; Fox, Thomas R.; Allen, H. Lee; Rubilar, Rafael A. (MDPI, 2015-08-14)
    We examined three hypotheses in a nutrient dose and application frequency study installed in juvenile (aged 2–6 years old) Pinus stands at 22 sites in the southeastern United States. At each site, eight or nine treatments were installed where nitrogen was applied at different rates (0, 67, 134, 268 kg ha−1) and frequencies (0, 1, 2, 4 and 6 years) in two or four replications. Phosphorus was applied at 0.1 times the nitrogen rate and other elements were added as needed based on foliar nutrient analysis to insure that nutrient imbalances were not induced with treatment. Eight years after treatment initiation, the site responses were grouped based on texture and drainage characteristics: soil group 1 consisted of poorly drained soils with a clayey subsoil, group 2 consisted of poorly to excessively drained spodic soils or soils without a clay subsoil, and group 3 consisted of well-drained soils with a clayey subsoil. We accepted the first hypothesis that site would be a significant factor explaining growth responses. Soil group was also a significant factor explaining growth response. We accepted our second hypothesis that the volume growth-cumulative dose response function was not linear. Volume growth reached an asymptote in soil groups 1 and 3 between cumulative nitrogen doses of 300–400 kg ha−1. Volume growth responses continued to increase up to 800 kg ha−1 of cumulatively applied nitrogen for soil group 2. We accepted our third hypothesis that application rate and frequency did not influence the growth response when the cumulative nitrogen dose was equivalent. There was no difference in the growth response for comparisons where a cumulative nitrogen dose of 568 kg ha−1 was applied as 134 kg ha−1 every two years or as 269 kg ha−1 every four years, or where 269 kg ha−1 of nitrogen was applied as four applications of 67 kg ha−1 every two years or as two applications of 134 kg ha−1 every four years. Clearly, the sites examined here were limited by nitrogen and phosphorus, and applications of these elements to young stands effectively ameliorated these limitations. However, there were differences in the response magnitude that were related to soil texture and drainage. Juvenile fertilizer applications resulted in high stocking levels early in the rotation; this condition should be considered when undertaking juvenile fertilization programs.
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    Long-term Effects of Fertilization on Phosphorus Biogeochemical Pools in Forest Soils
    Miller, Bradley W. (Virginia Tech, 2009-02-02)
    Southern pines are typically limited by nitrogen (N) and phosphorus (P) availability in the soil environment. While the absolute quantities of P in forests soils may be large, the concentration of inorganic P in the soil solution is typically very small (< 0.01 mg L²-1). A onetime application of just 56 kg P ha²-1 can substantially increase growth of pine stands over a 20 year rotation (Pritchett and Comerford, 1982; Allen et al., 1990). Phosphorus fertilization of Pinus radiata in New Zealand has also shown long-term effects on labile P pools in the soil which improved stand growth during the subsequent rotations (Ballard, 1978; Gentle et al., 1986). Identifying and quantifying the biologically available P pools in the soil environment will help foresters in making site-specific P fertilizer prescriptions. I examined soil phosphorus pools using the Hedley sequential fractionation procedure and Mehlich-3 soil tests in a long-term loblolly pine (Pinus taeda L.) fertilization trial from four sites in the Atlantic and Gulf Coastal Plains. After 22 years, fertilization effects were limited to the surface depths. Mehlich-3 extractable P was largest in the soil surface (0-10 cm) of the fertilized treatments plots. Hedley labile and moderately labile P pools were also largest in the soil surface and decreased with depth. Results from the Hedley fractionation procedure suggested that the Virginia site has a large pool of organic P in the soil surface. Organic P pools can represent 20-90% of the total P present in most mineral soils increasing with the age of the soil (Condron et al., 2005). This increase in organic P pool suggests that biological cycling becomes more important as the stand develops (Wells and Jorgensen 1975). I used solution 31P nuclear magnetic resonance (NMR) spectroscopy to characterize organic P extracted with NaOH-EDTA in the surface of a Paleaquults from coastal Virginia. Total NaOH-EDTA extractable P was significantly larger in the fertilized treatment. Concentrations ranged from 0.1 mg P L²-1 in the control plots to 5.1 mg P L²-1 in fertilized plots. The surface soils in both treatments were dominated by inorganic orthophosphate. Monoester P compounds were the only organic P compounds detected and were present in very low quantities. The significant increase of NaOH/EDTA extractable P in the soil surface of the VA site suggested there has been a beneficial long-term effect of fertilization similar to the observations from the Mehlich-3 soil test. Results from oxalate loading experiments on ligand exchangeable versus dissolvable P pools in the bulk soil suggested that the long-term effect of P fertilization increased oxalate dissolvable P pools. Plants and microbes have evolved a variety of mechanisms to increase P uptake in low P soil environments. These mechanisms include changes in root morphology and architecture, preferential root growth into high P microsites, the secretion of low-molecular-mass organic acids (LMMOA), and uptake via symbiotic relationships (Fox and Comerford, 1992b; Raghothama, 1999; Hinsinger, 2001; Raghothama, 2005). Results from soil samples taken from the ectomycorrhizal rhizosphere found that loblolly pine mycorrhizal roots modified the soil environment, possibly making recalcitrant P more available. In addition, the long-term effect of fertilization was a 396% increase in biologically available P. Fertilization increased loblolly pine volume growth by 57 m¹3 ha and increased the P content in the litter layer by 118%. After the stand was harvested and replanted, mineralization of the litter layer may also increase soil P pools. Results from this long-term fertilization experiment in the Coastal Plain province of Virginia have demonstrated that there has been a significant increase in soil (33.6 kg P ha²-1) and biologically available P pools (3.0 kg P ha²-1).