5.2 Soil acidity and liming

Soil acidity can wreak havoc on plant growth and crop yields. It's caused by various factors, from leaching to acid rain, and affects nutrient availability. Understanding soil acidity is crucial for managing agricultural productivity and maintaining healthy ecosystems.

Liming is the go-to solution for correcting soil acidity. By adding calcium-rich materials, farmers can neutralize acidity, improve nutrient availability, and boost soil health. Calculating the right amount of lime is key to achieving optimal pH levels for different crops.

Soil Acidity and Its Impact

Causes and effects of soil acidity

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• Leaching of base cations depletes soil of Ca, Mg, K
• Acid rain introduces H+ ions, lowers pH
• Nitrogen fertilization releases H+ during nitrification
• Organic matter decomposition produces organic acids
• Reduced root growth restricts nutrient uptake
• Stunted plant development leads to lower biomass production
• Decreased crop yields impact agricultural productivity
• Reduced availability of macronutrients (N, P, K, Ca, Mg, S) limits plant growth
• Increased availability of micronutrients (Fe, Mn, Zn, Cu) may cause toxicity
• Phosphorus fixation by aluminum and iron decreases P availability

Process of soil acidification

• Hydrogen ion accumulation in soil solution lowers pH
• Displacement of base cations from soil particles by H+ ions
• Weathering of primary minerals releases Al3+ and Fe3+
• Release of Al³⁺ ions at pH below 5.5 increases toxicity
• Inhibition of root growth and function reduces nutrient absorption
• Interference with nutrient uptake disrupts plant metabolism
• Increased Al solubility as pH decreases exacerbates toxicity
• Buffer capacity of soils affecting rate of acidification varies with soil type

Liming and Soil Management

Liming for soil acidity correction

• Calcium carbonate neutralizes soil acidity (agricultural limestone)
• Dolomitic limestone provides both Ca and Mg
• Quick lime reacts rapidly with soil moisture (calcium oxide)
• Hydrated lime offers fast pH adjustment (calcium hydroxide)
• Neutralization of soil acidity improves nutrient availability
• Improved nutrient availability enhances plant growth
• Enhanced soil structure and microbial activity boost soil health
• Particle size of liming material affects dissolution rate
• Chemical purity and neutralizing value determine liming efficiency
• Soil texture and organic matter content influence liming needs

Calculation of lime requirements

• Target pH for specific crops varies (e.g., 6.5 for alfalfa, 5.5 for potatoes)
• Initial soil pH determines starting point for adjustment
• Soil buffer capacity resists pH change
• Soil buffer tests measure pH buffering (SMP buffer)
• Exchangeable acidity measurement quantifies H+ and Al3+

1. Determine lime requirement in tons per acre
2. Adjust for liming material's neutralizing value
3. Consider depth of incorporation for effective distribution

• Lime requirement formula: $LR = (Target pH - Initial pH) × Buffer capacity × 2000 lbs/acre$