Articles
RESIDUAL LIME AND PH BUFFERING IN CONTAINER SUBSTRATES
Article number
819_28
Pages
249 – 256
Language
English
Abstract
Unreacted residual limestone plays a key role in buffering of pH change over time in container substrates.
Different methods for quantifying residual alkalinity in substrates were evaluated.
A gasometric method based on a Chittick apparatus quantified residual carbonate and bicarbonate [in units of CaCO3 equivalent (CCE) per liter of substrate], whereby a strong mineral acid (HCl) was applied to a substrate sample and the evolved CO2 gas was measured by liquid volume displacement.
A pH titration method quantified the relationship between substrate-pH and milliequivalents of reacted base, a measure of total substrate alkalinity.
These protocols were used to quantify substrate-pH and residual CCE in response to different carbonate lime rates in a peat substrate, and the effect of mineral acid drenches or ammonium fertilizer applied to different research or commercial media components and lime sources.
Residual CCE increased as applied CaCO3 concentration increased, particularly at pH above 7 because of limited CaCO3 solubility.
Increasing residual CCE was correlated with greater pH buffering, in both a greenhouse plant experiment using a 100% ammonium-N, acid-reaction fertilizer, and when substrates were drenched with HCl.
Commercial substrates varied widely in residual CCE, ranging from 0.96 to 4.91 g CCEL-1 of substrate.
Addition of acid through plant uptake of ammonium fertilizer or direct application of mineral acid reduced residual CCE over time.
Residual limestone is an important substrate property which should be considered for pH management in greenhouse crop production.
Different methods for quantifying residual alkalinity in substrates were evaluated.
A gasometric method based on a Chittick apparatus quantified residual carbonate and bicarbonate [in units of CaCO3 equivalent (CCE) per liter of substrate], whereby a strong mineral acid (HCl) was applied to a substrate sample and the evolved CO2 gas was measured by liquid volume displacement.
A pH titration method quantified the relationship between substrate-pH and milliequivalents of reacted base, a measure of total substrate alkalinity.
These protocols were used to quantify substrate-pH and residual CCE in response to different carbonate lime rates in a peat substrate, and the effect of mineral acid drenches or ammonium fertilizer applied to different research or commercial media components and lime sources.
Residual CCE increased as applied CaCO3 concentration increased, particularly at pH above 7 because of limited CaCO3 solubility.
Increasing residual CCE was correlated with greater pH buffering, in both a greenhouse plant experiment using a 100% ammonium-N, acid-reaction fertilizer, and when substrates were drenched with HCl.
Commercial substrates varied widely in residual CCE, ranging from 0.96 to 4.91 g CCEL-1 of substrate.
Addition of acid through plant uptake of ammonium fertilizer or direct application of mineral acid reduced residual CCE over time.
Residual limestone is an important substrate property which should be considered for pH management in greenhouse crop production.
Publication
Authors
P.R. Fisher, Huang Jinsheng, W.E. Horner, C.N. Johnson, W.R. Argo
Keywords
calcium carbonate, Chittick, gasometric, greenhouse, growing media, peat, substrate-pH, titration
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