Factors Affecting pH Establishment and Maintenance in Peat Moss-Based Substrates
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Date
2005-05-02
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Abstract
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.
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buffer capacity, inherent pH, base saturation, CEC, Sphagnum species, reactivity, Limestone specific surface
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Degree
PhD
Discipline
Horticultural Science
