Soil acidity is a major issue facing farmers worldwide. Over time, soils naturally become more acidic due to leaching of basic cations and acid rain. This increased acidity can have detrimental effects on crop yields and soil health. Fortunately, the application of lime can help reverse soil acidity. But what does lime do to soil?
An Introduction to Agricultural Lime
Lime is a soil amendment made from ground limestone rock. It primarily consists of calcium carbonate (CaCO3) and magnesium carbonate (MgCO3). Limestone is crushed and screened to create a powdery lime material that can be easily spread onto fields.
Agricultural lime has a few key functions:
- Neutralizes acidity in soil
- Provides calcium and magnesium to plants
- Improves soil structure and tilth
Farmers can better utilize this invaluable tool by understanding the chemistry behind liming.
What Does Lime Do to Soil
Most soils have a naturally acidic pH, generally between 5 and 7. Acidity occurs due to positively charged hydrogen ions (H+) in the soil that cling to the negatively charged cation exchange sites on soil particles. It prevents essential nutrients like calcium, magnesium, and potassium from accessing those sites.
When lime is applied to acidic soils, it dissociates into calcium and magnesium ions, carbonate and hydroxide ions. The carbonate neutralizes hydrogen ions, forming water and carbon dioxide gas that escapes the soil. Meanwhile, the calcium and magnesium ions displace the remaining hydrogen and aluminium ions on the cation exchange sites.
It raises the soil pH, increases base saturation, and provides essential plant nutrients. It also reduces the solubility of aluminium and manganese to non-toxic levels for crops.
Key Benefits of Liming Acidic Soils
Liming acidic soils provides a wide array of benefits for crops and soil health:
Raises Soil pH
Lime is highly effective at increasing soil pH in acidic soils. Even small applications can increase pH by 0.5 to 1 unit. The degree of change depends on the soil's buffering capacity. Soils with low cation exchange capacity (CEC) will see greater pH increases from liming.
Provides Calcium and Magnesium
Lime supplies essential macronutrients. Calcium is vital for plant structure, and magnesium aids in photosynthesis. Liming can prevent calcium and magnesium deficiencies.
Improves Nutrient Availability
By displacing hydrogen and aluminium ions, liming opens up cation exchange sites to hold positively charged nutrients like potassium, calcium, and magnesium. It improves their availability for plant uptake.
Stimulates Microbial Activity
Acidic soils restrict beneficial microbial activity. Liming raises pH to create a more favourable environment for microbes to thrive. They mineralize nutrients and contribute to soil organic matter.
Reduces Aluminum and Manganese Toxicity
Aluminium and manganese solubility increases in acidic soils. Liming precipitates these elements into inert compounds, preventing toxicity issues.
Improves Soil Structure
Lime can enhance soil aggregation, porosity, and friability. Calcium bridges clay particles while carbonates increase soil organic matter. It creates better-structured soil.
Determining Lime Application Rates
The amount of lime needed depends on the crop's soil pH, buffering capacity, and target pH. Soil tests help determine the lime requirement by measuring pH and exchangeable acidity.
Generally, it takes 1-2 tons of lime per acre to increase pH by 0.5 units. Finer lime reacts faster, while lime pellets react slower but are more accessible to apply. Dolomitic lime provides both calcium and magnesium.
Calcitic lime (pure calcium carbonate) is preferred for high-magnesium soils. Lime should be incorporated into the top 6 inches of soil for rapid response.
Timing of Lime Applications
Liming is most effective 1-6 months before planting to allow time for the lime to react. Fall liming for spring crops is ideal, as lime slowly dissolves over the winter. Avoid liming at planting, as the rapid pH shift can damage seeds and seedlings.
For perennial crops, lime every 2-3 years to maintain pH levels. Surface applications are practical in no-till systems but can take longer to react compared to incorporated lime.
The Impact of Liming on Crop Yields
Multiple studies have shown liming acidic soils boost crop yields, often quite dramatically. A 10-year study on corn showed liming increased yields by 16-28% compared to unlimed soils. Similar yield increases have been observed for soybeans, wheat, and other crops.
The bottom line is liming gives an excellent return on investment through higher yields, more significant profits, and healthier soils. Pay close attention to soil pH and maintain it in the ideal range for each crop.
Frequently Asked Questions:
How long does lime take to raise pH?
Lime reacts slowly over months to years. Finer lime reacts within 2-6 months while pellets can take over 12 months to increase pH.
Can too much lime be harmful?
Excess liming can cause nutrient imbalances and deficiencies. It's best to lime based on soil test recommendations.
When should lime be applied?
For annual crops, apply lime 1-6 months before planting. For perennials, lime every 2-3 years to maintain pH.
Conclusion
Liming is a foundational soil management practice that helps reverse soil acidity issues. By neutralizing acidity and providing essential nutrients, lime creates a fertile soil environment for crops to thrive. Follow soil test recommendations, use quality liming sources, and apply it well before planting to maximize the benefits. Healthy, properly limed soils will grow healthier, higher-yielding crops.
