How Does the PH in Soil Effect the PH in Water?

The pH of soil can change the pH of water.

The pH of soil directly affects the chemical reactions that take place when water and fertilizer are applied. As water migrates through the soil, it reacts with with hydrogen ions and soil particles, becoming either more acidic or more basic.

pH

The term pH refers to the amount of "potential hydrogen" in a substance. When two substances react with each other, they exchange hydrogen ions, affecting the pH of both substances. Low pH (between pH 0.0 and 6.9) means the substance is acidic; high pH (between pH 7.1 and 14.0) means the substance is alkaline.

Soil

The pH of soil is affected by its natural composition, the type and amount of fertilizers or amendments applied, as well as by the porosity and water holding ability of the soil. These soils naturally contains pH buffers, typically in the form of calcium carbonate (limestone), that neutralize acidic substances on contact.

Water

Rainwater has a natural pH of 6.0 to 6.5, which is slightly acidic due to dissolved carbon dioxide reacting with the water to form a dilute acid (carbonic acid). However, the pH of the water applied to the soil may be different than the pH of the water that leaches from the soil. As water migrates through the soil, it exchanges and picks up hydrogen ions that are present. In acidic soils, free hydrogen ions in solution may be picked up by the water and discharged into runoff. In alkaline soils, the slight acidity of water is neutralized, producing runoff high in buffering alkaline earth elements (barium, calcium, magnesium and strontium).

References

• North Carolina State University: Plant Nutrients
• Washington State University: Soil pH
• UC Davis: Changing pH in Soils
• NASA: Soil pH