Neutralizing Value of Liming Materials
This is the ability of the liming material to neutralize acidity. It is the amount of acid neutralized by the molecular weight of a liming material in relation to the amount neutralized by 100g of calcium carbonate, Ca CO3.
It is often expressed as a percentage of the neutralizing ability of an equal weight of pure Ca CO3.
Therefore the neutralizing value is usually called calcium carbonate (Ca CO3) equivalent. For example, let 100g of Ca CO3 neutralize an amount, X, of acidity.
Lime Requirement
The lime requirement is generally defined as the minimum amount of lime needed to raise the pH of an acid soil to pH 6.5 – 7.0 over a period of 2-3 years.
The practical reality of liming practices requires a smaller amount of lime mainly to raise the soil pH to a level tolerable to most agricultural crops or a level that gives maximum economic yield returns from any cropping venture. Factors contributing to the lime requirement of soils are as follows:
The Initial Soil pH
The initial soil pH would determine the magnitude of pH change required which is usually the difference between the original soil pH and the final pH wanted.
The final pH required will in turn depend on the cropping system since certain crops grow in a specific narrow range of pH while others adapt to a wide pH range. Furthermore, small amounts of lime may be required if acidity is restricted to the surface soil (plow layer).
Read Also: Measurement of Soil Acidity and Liming Practice
The Quality of Liming Material
The lime requirement is inversely proportional to the neutralizing value of the liming materials being used. The type and purity of the lime affect its neutralizing power.
Therefore, it is important to consider the purity and fines of the particle size of the lime being selected for use, especially in the tropics.
The contents of Ca and Mg in both the lime and the soil to be limed should also be taken into consideration.
Particle Size of the Liming Material
Certain liming materials such as CaCO3 are only slightly soluble and therefore their rate of reaction in soil depends on their particle size. The Lime requirement of a lime decreases with a decrease in the fineness of the particle.
Up to a limit, the finer the particle, the greater the neutralizing value. It should be noted that too fine particles may not be desirable owing to cuddling.
Crop needs can also dictate the lime requirement. Some crops such as groundnut and tobacco require more Ca for their nutrition.
Solubility of Lime Being Used
For example, Ca (OH)2 is more soluble, and will therefore react faster than Ca CO3 as liming materials.
Liming Materials
- Calcic limestone, Ca CO3
- Dolomitic lime (Ca Mg) CO3… most commonly used.
- Hydrated lime Ca (HO)2
- Air slaked lime (Ca (OH)2 + Ca CO3
- Refuse paper mill (Ca CO3 is the lime here)
- Sugar beet refuses lime
- Slage, Ca Si03 Ca(OH)2 + CaO + Mg
- Wood ashes, Ca CO3 Ca(OH)2 + K2 CO3.
In conclusion, soil reaction (pH) could be acid, neutral, or alkaline. Each of these reactions depends on the chemical condition of the soil.
However, a particular reaction has either a positive or negative influence on plant growth, nutrient availability and microbial activity.
Proper soil management for crop production requires the use of lime to bring soil pH to near neutral (pH 6-7.0) so as to benefit from the full potential of the soil.
Read Also: The Effect of pH of Soils on Micro-organisms
