Factors in Acid Soils Detrimental to Plant Growth

Acid Soil Complex -- plant growth problems at low pH are often multi-faceted.

1. ALUMINUM toxicity.

Affects plant roots Sparsely branched large diameter roots at low pH.

Tissue levels of Al relate poorly to toxicity.

2. Manganese toxicity.

Affects plant tops. Occurs below pH 5.5. Cotton, soybean, and tobacco are sensitive.

3. Iron toxicity minor problem

4. Calcium deficiency. Peanut, tobacco, and tomato are sensitive.

5. Magnesium deficiency.

Conditions that are conducive to Mg deficiency are:

1. low CEC
2. use of low magnesium liming material
3. high rate of NH₄⁺ fertilizer
4. high rate of K fertilizer
5. excessive leaching of soil profile
6. crops with high requirement for Mg -- tobacco, cotton, and soybean.

6. Molybdenum deficiency (soybeans and cauliflower).

In most cases liming to pH 5.5 to 6.0 alleviates Mo deficiency. In some cases liming > 6.0 needed to eliminate Mo deficiency.

7. Nitrogen, phosphorous, and sulfur deficiency because of slow organic matter decomposition minor problem.

8. Reduced phosphorous availability due to precipitation with aluminum.

9. Poor nodulation of legumes.

Factors Affecting Lime Reaction

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Relative Neutralizing Value

Relative ability of a liming material to neutralize acidity compared with pure CaC03

Chemical measure which:

reflects chemical composition oxide, hydroxide, carbonates (handout)
level of impurities

Does not necessarily relate to rate and extent of reaction in soil.

Fineness

The smaller the particle the faster the reaction. (overhead)

Effective calcium carbonate or neutralizing index. An attempt to integrate calcium carbonate equivalence and fineness so that various liming materials can be compared. (p. 254, note 8-2).

Lime law (handout/overhead)

 

Chemical Composition

Dolomite particles are less reactive than calcitic.

"When lime is required and soil test for magnesium is medium plus or above, any source of lime may be used. When lime is required and soil test magnesium is medium or less, use dolomitic limestone. The use of dolomitic limestone every time the soil is limed will not result in magnesium toxicity or cause a ration imbalance situation in the soils in South Carolina." (Circular 476, p. 13)

Incorporation and Mixing

Expose as much lime surface area to as much soil surface area as possible.

 

Time and Frequency of Liming

At anytime in the cropping sequence that soil pH is below the acceptable range.

Frequency of liming is dependent on several factors.

1. Neutralization by acid forming nutrient sources; particularly those containing organic N, ammonium N, and ammonia N.

2. Organic matter decomposition and carbon dioxide release.

3. Leaching of basic cations.

4. Removal of basic cations by crop harvesting.

5. Erosion of topsoil, releaving acid subsoil behind.

6. Acid rain.

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