What Makes Soil Acidic?


Acidic soil makes some plants grow better and some grow worse. There are several causes of acidic soil, including naturally occurring materials in the soil, acidic plants such as ferns and raspberries and pollution. Acidic soil refers to soils that contain acids, such as sulfuric acid or nitric acid. It's the opposite of basic soil on the pH scale, like hot is the opposite of cold. These soils have a pH below 7, neutral soils have a pH of 7 and basic soils have a pH above 7 on the pH scale of 0 to 14.

Acid Rain

Acid rain is one cause of acidic soil. The internal combustion engine in a car produces several compounds including nitrogen and sulfur compounds. These compounds are released into the air, and later fall with rain, introducing nitrogen and sulfur based acids into the soil. Acid rain affects soils far away from where the cars produced pollution, even across oceans.

Regional Effects

Plants prefer acidic or basic soils depending on their region. According to gardener Marion Owen, strawberries and watermelons and others grown in swamp regions in the Southeast grow best in acid soils, and many other plants prefer slightly acidic soils. Plants from desert or ocean environments, like cacti and seaweed, grow best in basic soils. The continued growth of similar plants over time affects the area further, as peat bogs can become so acidic that all growth is stopped.

Farmers' Tools

It's possible for a farmer to change the pH of the soil. According to the Georgia nursery worker S.D. Coleman, examine the leaves of the plants for burning effects to see if the soil has a harmful pH. Plants grown in acidic soil usually have an acidic pH. Grind them up, and mix them with the soil to make the soil more acidic. To make the soil more basic, mix in lime until the desired pH is reached. Lime is obtained by heating limestone or from a garden supply store.

Industrial Waste

Governments can use large scale waste products to change the acidity of soils. Fly ash produced by coal power plants releases many small particles of carbon and other materials. This fly ash can be captured and used to make acidic soil, although as with acid rain it may contain other materials that are harmful to plants. Sewage sludge can be processed at water treatment plants and used to make soil basic.

Humic Acid

Humic acid also may be added to soil to make it more acidic. Humic acid includes many different types of acids produced by acidic plants and their decomposition, including fulvic acid. Humic acid can break apart certain soils, causing them to release additional compounds including other acids. Applying humic acid can create similar effects to those produced by wetland plants, and permanently increase the acidity of the soil.

Keywords: acid rain, acid soil, humic acid, fulvic acid, swamp soil

About this Author

Eric Novinson has written articles on Daily Kos, Associated Content, and on his blog and has been a writer for five years. He has a business administration degree from Humboldt State University.