Most of Alberta’s acid soils occur in the grey wooded soil zone. This is a result of hundreds of years of acidic organic material from the leaves of deciduous trees, needles from coniferous trees and other acidic organic material being added to the surface of soil. Most of Alberta’s soils that have developed under forest vegetation are acidic.
In southern Alberta, soils on the Milk River Ridge and in the Cypress Hills tend to be acidic as these soils, are much older than the rest of Alberta.
“Acidic soils have a relatively low soil pH, a measure or indicator of how acidic or basic a soil is,” says Dr. Ross McKenzie, research scientist with Alberta Agriculture and Rural Development. “A soil pH of 7.0 is neutral, soil below a pH of 7 is acidic and above pH of 7 is alkaline or basic.
“For the past decade it has been noted that the surface soil pH has been declining in fields that are direct seeded. This is primarily the result of nitrogen fertilizer and presently it is not a problem, but it is a situation that must be monitored.”
The effect of acid soils on crops is generally poor growth of a sensitive crop such as alfalfa or pulse crops such as pea. This may indicate an acid soil condition. With N-fixing crops such as alfalfa or pea, the rhizobium bacteria which live in association with plant roots, do not survive very well in acidic soils or when soil pH declines below 6. When soils are strongly acidic, pH below 5.5, Aluminum (Al) and Manganese (Mn) are more soluble and may increase to toxic levels.
“The first step in the management of acid soils is to identify the extent and severity of the problem. This can be done by taking soil samples of various locations in a field to determine the size, extent and severity of the problem,” says McKenzie. “While poor yields of acid-sensitive crops may indicate an acid soil condition, soil tests are the only sure method of identifying an acidity problem.
“An application of lime is the only way to correct soil acidity. Once careful sampling of fields and identifying the areas with acid soils has been done, the lab can provide a Lime Requirement Test, to determine the rates of lime required.
The fact sheet Liming Acid Soils can be viewed or downloaded from Alberta Agriculture and Rural Development’s website.