The ability of soils to neutralize acids is called the soil’s acid Neutralizing Capacity (ANC). To measure this property, you need to know the soil pH, potential carbon dioxide concentrations, and potential nitric oxide concentrations. ANC is expressed as mg of calcium carbonate per gram of soil. This article explains how to calculate acid neutralizing capacity and all three properties and uses them to evaluate the suitability of a site for greenhouse operation.
What is Soil pH?
Potential hydrogen (pH) measures the acidity or alkalinity of the soil. A pH of 7 is neutral, less than seven is acidic, and greater than 7 is alkaline. The pH of soil influences the availability of nutrients for plants and can affect the kinds of microorganisms that can live in the soil. Many greenhouse crops are susceptible to even small changes in soil pH.
What is Potential CO2?
The potential CO2 concentration of the soil is an expression of the soil’s ability to regulate the amount of CO2 entering the soil from the atmosphere. If the soil is more alkaline, more CO2 is adsorbed, whereas a more acidic soil will release CO2 into the atmosphere.
This potential CO2 concentration is an excellent measure of the soil’s buffering capacity. If the soil has a very high CO2 potential, any acids entering the soil will be rapidly adsorbed, and the soil will have a high ANC and be able to neutralize even large amounts of CO2.
What is the Measure of NO^-?
The potential nitric oxide concentration measures the amount of nitric oxide in the soil solution. NO^- is very unstable and is decomposed by soil microbes to nitrous and nitric acid.
When the soil is acidic, nitric acid is readily absorbed by soil particles and converted to nitrates and water. When the soil is alkaline, nitric acid is not adsorbed but can oxidize to nitrous acid, which is very soluble and readily available to plants.
How To Calculate Acid Neutralizing Capacity? How to Calculate the Sum of ANC and CaCO^2
To calculate the sum of ANC and CaCO^2, you need the soil pH, potential CO2, and potential NO^- concentration. There are formulas for each of these properties to calculate the value in mg/g. The sum of all three values is the ANC of the soil. This example shows how to calculate ANC in the greenhouse site previously described.
- Calculate pH: The soil pH is 6.6.
- Calculate potential CO2: The potential CO2 concentration of the soil is 92.
- Calculate potential NO^-: The potential NO^- concentration of the soil is 5.
- Calculate ANC: The ANC of the soil is 97.