6.8 Considerations for Liming

When should lime be applied?

For Grazing

• if pH(CaCl2) <= 4.5, lime should be applied as soon as possible.

• if pH(CaCl2) between 4.5 -5.0, need to lime within the next few years. For sensitive plants such as lucerne, canola, barley or phalaris lime needs to be applied and incorporated before planting.

Lime requirement depends on

• Current soil pH 

• Presence of subsoil acidity 

• Target pH ie pH after liming the soil (see Table 5) 

• Type of crop/pasture

• Soil texture

• Lime quality

Figure 1:
Target pH for different land uses.

Subsoil acidity 

Where subsoil acidity occurs lime rates and target pH need to be high enough to ensure lime effect reaches the subsoil. As a rough guide lime moves down at 15 to 25 mm/year in most soils. 

• Lime only effects the subsoil if >2.5 t/ha applied T

• arget pH when liming needs to be pH(CaCl2) > 5.5 

• When surface pH (CaCl2) drops below 5.0 acidity starts to move into the subsoil

Highly sensitive plants

Plants highly sensitive to aluminium include: lucerne, canola, barley, tall wheat grass, balansa clover, strawberry clover. For these plants ensure target pH(CaCl2) > 5.5 and pH(Ca Cl2) does not drop below 5.0

Soil texture

Heavier textured soils require more lime to raise the soil pH.

Figure 2: 
Lime requirement to raise pH by about 1 unit (assuming lime is incorporated to 10 cm or surface applied, and a very high quality lime is used eg ENV at 90%)

Calculating lime requirement 

Current soil pH(CaCl2) = 4.6 

Extensive grazing property with perennial rye/clover pastures. Sandy loam texture

Lime to be incorporated to 10cm, average organic matter, good quality lime.

Factors influencing effectiveness

The effectiveness of lime application is influenced by: 

• Level of organic matter 

• Lime quality 

• Depth of incorporation 

For 15cm depth of incorporation (eg after potatoes, prior to vines) multiply rate by 1.5. 

Assume 10cm incorporation is equivalent to surface application even though surface application will take about 4 years to raise pH through the 0-10 cm layer.

Effect of lime on plant trace element levels 

Results from trials in the Mt Lofty Ranges indicate that the application of lime affects the level of trace elements in plants. 

• Lowers Manganese consistently in first couple of years and is worse just after liming. 

• Raises Molybdenum consistently in first couple of years. 

• Occasional lowering of Fe, Al and Zn at some sites.

• Rarely lowers Cu and B. 

These affects are only significant (ie. greater than 20% change in plant levels) where soils are already marginal eg. ironstone soils for manganese. High rates such as 6 t/ha are only slightly worse than 2.5 t/ha.

Lime quality measurements

• Purity           = percent calcium/magnesium carbonate &/or oxide 
                     = Neutralising Value (NV) 

• Fineness        = Particle Size Analysis 
                         ( < 300mm/ 300-850mm/ >850mm)

• Purity x Fineness = Effective Neutralising Value (ENV) 

• RH Value         = Ability to neutralise a weak acid solution 
                         (Similar to soil water) 

• Surface Area of Lime Particles - research tool however indicates large differences with some products having very high values.

Comments

RH value is the good but difficult to get done.

ENV is the next best and is good for comparing ground up rock sources but is inaccurate for some other sources that are dispersive. 

As a general guide good quality limes may have 

• 80% neutralising value 

• ENV Values of >75% 

• RH values of > 50

Where limes are of poorer quality rates need to be increased to have the same effect

6.8 Considerations for Liming

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