Articles
QUANTIFYING THE ACIDITY AND BASICITY OF FERTILIZERS IN CONTAINER SUBSTRATES
Article number
891_17
Pages
159 – 166
Language
English
Abstract
Fertilizer is a major factor affecting substrate-pH during crop production.
Industry provides an estimate, reported in calcium carbonate equivalents (CCE) per unit weight of fertilizer, of the potential acid or base effect of blended fertilizers.
This acid-base estimation can be an important tool for pH management if predicted accurately and using the appropriate assumptions.
The current acid-base estimate is based on an agronomic method (Pierres Method, PM) developed in the 1920s using a mineral field soil system.
Certain assumptions of this protocol may not be appropriate for the soilless substrates and water-soluble fertilizers in containerized plant production.
The objective was to evaluate the predicted CCE using PM against experimental data, and to identify components of an alternative approach to quantify the potential fertilizer effect on pH of soilless container substrates.
Various experimental protocols, which included nutrient uptake charge balance (electroneutrality) and residual alkalinity measurements, were developed and compared with the acidity values expected using PM. These experimental measurements found that PM overestimated the amount of fertilizer acidity applied.
Components of an alternative approach are suggested for acid-base estimation which assumes charge balance upon uptake of fertilizer salts, in which anionic salt uptake is assumed basic and cation uptake is acidic with associated plant root exudation of OH– or H+ respectively.
This new protocol would consider the relative proportions at which nutrients are taken up and required by plants in predicting the net potential acid or base effect of fertilizers on substrate-pH, in addition to purely chemical processes.
Acidification from ammonium-nitrogen uptake, and soil processes such as nitrification, which PM assumptions exclude, should be considered to represent the potential pH effect of fertilizers in containerized production.
Industry provides an estimate, reported in calcium carbonate equivalents (CCE) per unit weight of fertilizer, of the potential acid or base effect of blended fertilizers.
This acid-base estimation can be an important tool for pH management if predicted accurately and using the appropriate assumptions.
The current acid-base estimate is based on an agronomic method (Pierres Method, PM) developed in the 1920s using a mineral field soil system.
Certain assumptions of this protocol may not be appropriate for the soilless substrates and water-soluble fertilizers in containerized plant production.
The objective was to evaluate the predicted CCE using PM against experimental data, and to identify components of an alternative approach to quantify the potential fertilizer effect on pH of soilless container substrates.
Various experimental protocols, which included nutrient uptake charge balance (electroneutrality) and residual alkalinity measurements, were developed and compared with the acidity values expected using PM. These experimental measurements found that PM overestimated the amount of fertilizer acidity applied.
Components of an alternative approach are suggested for acid-base estimation which assumes charge balance upon uptake of fertilizer salts, in which anionic salt uptake is assumed basic and cation uptake is acidic with associated plant root exudation of OH– or H+ respectively.
This new protocol would consider the relative proportions at which nutrients are taken up and required by plants in predicting the net potential acid or base effect of fertilizers on substrate-pH, in addition to purely chemical processes.
Acidification from ammonium-nitrogen uptake, and soil processes such as nitrification, which PM assumptions exclude, should be considered to represent the potential pH effect of fertilizers in containerized production.
Authors
C.N. Johnson, P.R. Fisher, R.P. Vetanovetz, W.R. Argo
Keywords
ammonium, calcium carbonate, greenhouse, lime, limestone, peat, pH, Pierre
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