Acid soils Soil acidity causes reduced yields of acid-sensitive crops such as alfalfa and barley on many fields in central and northern Alberta. Some 5 to 6 million acres are sufficiently acid to cause reduced yields of alfalfa and one million acres are affected for growing barley. Acid soils are readily identified by a soil test showing a low pH. The soil reaction is alkaline when the pH value is above 7, neutral at 7, and acid below 7. Crops vary greatly in their tolerance to acidity. Yields of alfalfa are reduced at pH 6 and less, and barley at 5.5 and less.
Acid soils occur naturally and as a result of the long-term use of nitrogen fertilizers.
The acidifying properties of nitrogen fertilizer are shown in the following table. Note, however, that some acid soils are deficient in sulphur so the use of some ammonium sulphate or other sulphur-containing fertilizer may be required. Liming is a common practice that is used to neutralize acidity caused by natural leaching and the use of nitrogen fertilizers. Productivity of moderately acid soils can also be improved by growing more acid tolerant crops, but application of lime is the long-term solution to improving these soils. See Agdex 534-1, Liming Acid Soils .