Soil Acidity

Soil Buffering Capacity

Amount of acid or base that can be added to a solution before its pH significantly changes

Higher clay = higher buffering

CEC

Total number of cations a soil can hold, or its total negative charge. (Higher CEC= higher negative charge/more cations held!)

pH

A measure of how acidic or basic a substance or solution is.

(number/concentration of hydrogen ions)

Acid Deposition (acid rain)

Any form of precipitation with acidic components, such as sulfuric or nitric acid that fall to the ground from the atmosphere in wet or dry forms.

Importance of soil buffering

1. Ensures stability of soil pH.

2. Influences amount of amendments needed to change soil pH.

mechanisms of soil buffering

1. Al hydrolysis, dissolution, or precipitation of gibbsite in very acidic soils

2. Protonation or deprotonation of functional groups in organic matter (pH dependent charge)

3. Cation Exchange

4. Carbonate dissolution and precipitation (soil pH 7 and above)

Spatial Variation

Differences in soil properties, vegetation, and management practices can create spatial variability in pH.

Temporal Variation

Soil pH can fluctuate over time due to factors like rainfall, fertilization, and decomposition of organic matter.

Soil Depth

pH can vary with soil depth, often decreasing with increasing depth.

Biological Effect of Soil Acidity

1. Toxicity

2. Nutrient Availability

3. Microbial Effects

Nutrient Availability

Soil acidity affects the availability of essential nutrients to plants. Some nutrients become less available at low pH, while others become more available.

Microbial Effects

Soil microorganisms play a crucial roles in nutrient cycling and decompostition, and their activity is generally optimal at intermediate and high pH. Extreme acidity can inhibit microbial activity, affecting soil health.