Browsing by Author "Dean L. Hesterberg, Committee Co-Chair"

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Abiotic pathogen suppression: physiology and biology of aluminum toxicity to soilborne fungi
(2004-01-20) Fichtner, Elizabeth Jeanne; T. Jot Smyth, Committee Member; H. David Shew, Committee Chair; Dean L. Hesterberg, Committee Co-Chair; D. Mike Benson, Committee Member
An interdisciplinary approach was utilized to study the toxicity of aluminum (Al) to soilborne plant pathogens with the goal of developing a pathogen-suppressive potting medium containing non-phytotoxic, Al-organic matter complexes. Toxicological studies addressed the toxicity of monomeric Al species to Thielaviopsis basicola and Phytophthora parasitica and documented the sensitivity of these organisms to the metal. Until recently, research on Al-toxicity to fungi has only focused on the trivalent Al cation (Al³⁺) which is also considered the most phytotoxic Al ion. The toxicity of Al-hydrolysis species to fungi were tested by modeling in vitro test solution equilibria using GEOCHEM-PC and correlating the predicted values of Al-species activities with reduction in spore production of the two pathogens. Chlamydospore production of T. basicola was negatively correlated with Al³⁺ activity, whereas inhibition of sporangia production of P. parasitica was related to the activity of multiple monomeric Al species. Toxicity of Al to T. basicola was observed in solutions containing ≥ 20 micromolar Al. Sensitivity of P. parasitica to Al was observed at < 1.0 micromolar Al, suggesting that P. parasitica is more sensitive to Al than T. basicola. Using fluorescence microscopy, the localized accumulation of Al in pathogen tissues was detected using lumogallion, an Al-specific, fluorescent stain. Accumulation of Al was observed under various chemical conditions, ranging from salt solutions to more complex systems containing Al-peat complexes. An ecological approach was applied to study the dynamic interactions of soil chemical and physical properties with soil microflora for the suppression of P. parasitica in a medium amended with Al₂(SO₄)₃ and composted swine waste (CSW). Abiotic and biological mechanisms of pathogen suppression were incorporated into the CSW-amended medium. Al-mediated suppression resulted in reduction of sporangia production in medium exhibiting K-exchangeable Al levels > 2 micromolar Al. Biological suppression also resulted in reduction of sporangia production and this suppression was maintained after Al levels dropped below the threshold necessary for abiotic suppression. The incorporation of abiotic and biological control mechanisms into a potting media may facilitate suppression of a wide range of soilborne pathogens and enhance applicability of disease-suppressive media in a disease management strategy.
Factors Affecting pH Establishment and Maintenance in Peat Moss-Based Substrates
(2005-05-02) Rippy, Janet Fairbanks Miles; Dean L. Hesterberg, Committee Co-Chair; Theodore E. Bilderback, Committee Member; Eugene J. Kamprath, Committee Member; Paul V. Nelson, Committee Chair
Problems of inconsistent initial pH in peat moss substrates created using standard formulas for agricultural limestone additions, and substrate pH drift from the initial target may result from variations in the neutralization capacity of limestone and in the neutralization requirement of peat moss. This research was conducted to evaluate physical and chemical properties of limestone that may influence neutralization capacity, and properties of peat moss that may influence neutralization requirement. Limestones from twenty North American quarries were wet-sieved into eight particle diameter fractions (600 to < 38 μm). Specific surface of limestone particles was measured for each fraction. Reaction times were determined on three limestone particle size fractions. Particle size distribution, CaCO₃ and MgCO₃ contents, internal porosity, hardness, soundness, specific gravity, and specific surface were analyzed in multiple regressions with particle size included and also held constant at three size fractions to evaluate effects on limestone neutralization capacity. Peat moss samples were selected from Alberta, Canada bogs to represent the maximum range of species composition and the decomposition range (H1.5 to H4.0) used for commercial horticulture. Peat moss cation exchange capacity, base and iron saturation, inherent pH, buffer capacity and neutralization requirement were measured. These properties were analyzed in a multiple regression along with species composition, degree of decomposition, and detritus to determine effects on peat moss neutralization requirement. Limestones differed significantly in specific surface for each particle diameter fraction and in reaction times. There were significant variations in cation exchange capacity, base saturation, inherent pH, buffer capacity and neutralization requirement of peat mosses. Neutralization requirement was negatively correlated with base saturation, inherent pH, decomposition, [Fe²⁺], and sedge; and was positively correlated with S. angustifolium. Sphagnum species influenced cation exchange capacity, base saturation, and inherent pH. Inherent pH was most influenced by base saturation. Peat moss samples containing large amounts of S. fuscum had high cation exchange capacity and base saturation, and low degrees of decomposition. Adding specific surface measurements to those of particle size distribution and CaCO₃ content will further characterize limestone neutralization capacity; however, the problem of inconsistent initial pH can be better managed by understanding the inherent pH and base saturation of the peat mosses in the substrate. The problem of pH drift from the target can be controlled by ensuring an adequate amount of S. fuscum in the substrate.
Phosphorus Leaching in the Coastal Plain Soils of North Carolina.
(2007-11-01) Kang, Ji-Hoon; Robert O. Evans, Committee Member; Aziz Amoozegar, Committee Member; Deanna L. Osmond, Committee Chair; Dean L. Hesterberg, Committee Co-Chair
Some soils in areas of intensive livestock farming have shown significant phosphorus (P) leaching. The objectives of this research were: i) to examine the relationships between soil properties and P sorption capacity, ii) to investigate leaching of P as affected by fertilizer sources, iii) to examine the effects of manure-derived dissolved organic carbon (DOC) on P sorption, and iv) to evaluate deep leaching of P. The P sorption maximum (Smax) of seventy two soil samples from various horizons of Coastal Plain soils of North Carolina (NC) was determined according to the Langmuir equation. Soil samples were analyzed for pH, clay content, organic matter (OM) content, oxalate extractable Al (Alox), Fe (Feox), and P (Pox), Mehlich-3 extractable Al (AlM3), Fe (FeM3), and P (PM3). The Smax was positively correlated with extractable Al (r = 0.76 for Alox and r = 0.86 for AlM3) and OM content (r = 0.61). The positive linear relationship between OM and Smax showed a change point where there was a two-fold decrease in the regression slope for OM > 42 ± 4 g kg-1. Results indicated that Al and Fe in organic-rich soils were likely to be less accessible for P sorption compared to those in mineral soils. Leaching of P as affected by fertilizer sources was investigated with repacked soil columns (10-cm long). The fertilizer sources were dairy lagoon liquid (DL), poultry compost (PC), poultry litter (PL), swine lagoon sludge (SS), swine lagoon liquid (SL), triplesuperphosphate (TSP), and dissolved KH2PO4 (KP). When these fertilizer sources were applied on a total P basis (75 and 150 kg ha-1) as a pulse, inorganic P sources (TSP and KP) showed about two-fold greater P loss than organic P sources (PC, PL, SL and SS). The loss of source-derived P was well correlated with water extractable P in source materials (r2 = 0.87). Enhanced P transport was observed in the soil columns treated with liquid wastes as compared to the KP. Concurrent sorption of P and DOC was investigated with batch sorption experiments using the aqueous extracts of PL and SS in Autryville sandy loam. The presence of manure-derived DOC did not inhibit P sorption, while the sorption of DOC decreased in the presence of manure-derived P. Results suggested that the formation of new surface sites through metal bridges between manure-derived OM and mineral oxides outweighed the competitive efficacy of DOC against P on the soil sorption sites. Deep leaching of P was evaluated with intact soil columns (90-cm long) collected from the Coastal Plain regions of NC. The selected sites were dominated by Autryville loamy sand, Cape Fear loam, and Goldsboro fine sandy loam, and Wasda muck. A limited pore volume of leached water (2.1 ± 0.1) resulted in low concentration of dissolved reactive P in most column leachates (< 0.02 mg L-1) except Wasda muck (0.034 mg L-1). The increased P concentration in Wasda muck was attributable to the higher Mehlich-3 P concentration in deep subsoils (22 to 69 mg kg-1 at 75-90 cm depth) than the other soils (0 to 7 mg kg-1 at 75-90 cm depth).