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Comparison of Aglime, crushed limestone & G Lime

 

It is accepted by both industry and scientists throughout the world that the quality of agricultural lime is best measured by:


Neutralising value, Particle size & Solubility

 

In recent times some WA suppliers of various liming materials have made controversial claims about their products without proper emphasis on these properties.

 

To address these issues, Andrew Speechly, a University of WA student, undertook a project ‘Effect of Lime Source and Particle Size on Amending an Acid Sandplain Soil’.

 

Andrew collected bulk samples of liming materials


1. Limesand from Aglime of Australia's Dongara mine
2. Crushed Limestone from a commercial supplier at Capel
3. G Lime, a byproduct from quicklime manufacture

 

He measured particle size, neutralising value, and solubility as well as the effectiveness of each lime in increasing soil pH.

 

Neutralising Value

The neutralising value is a measure of the alkalinity of the lime relative to a pure calcium carbonate (100% NV). The results were as follows:


1. Limesand 93%

2. Crushed Limestone 74%

3. G Lime 104%

Particle Size

Fine particles dissolve faster and are better distributed throughout the soil. Andrew’s results show:

 

1. Limesand was the finest (most particles below 0.24mm)

2. Limestone was intermediate

3. G Lime contained mainly coarse material

 

Solubility

Solubility was measured by mixing particles below 0.5mm with soil from Carrabin (pH 4.3), wetting to 75% field capacity, sealing and storing at 20 degrees centigrade. Rates of each lime added to the soil were adjusted to be equivalent to 2t/ha of pure calcium carbonate. This experiment allows a true comparison of the solubility of each lime without interference from different NV’s or particle sizes.

 

After 8 weeks, it was evident that the solubility of G lime and limesand were similar in the size fraction between 0.50 to 0.25 but crushed limestone was less soluble.

Effect of bulk lime on soil pH

To test the effect of each lime product as purchased by farmers, bulk samples were mixed with soil and pH change measured as described previously. Again rates were adjusted to allow for differences in neutralising value.  Rates and costs per hectare are shown below:

 

  NV Rate (t/ha) Cost ($/Ha)
Limesand 93 2.1 $67
Crushed Limestone 74 2.7 $104
G Lime 104 1.9 $83

The approximate cost for each liming material based on a 200km lead was calculated by Aglime of Australia and shows limesand to be the lowest cost liming material.

 

At the end of 8 weeks, the limesand treated soil had a pH of 7.2, nearly half a unit higher than the other treatments.

 

This high pH change shown by limesand was due to a relatively high neutralising value, small particle size and high solubility.

 

The results clearly show that it is usually more profitable to purchase a lime with fine particle size (providing it also has high NV and solubility). Coarse particles take many years to dissolve (if they ever do) and do not have any economic value.

 

Each time a soil is limed, it is advisable to purchase a high quality fine lime to get immediate return on expenditure. Coarse particles in liming materials are unlikely to be profitable as they dissolve too slowly and are poorly distributed in the soil.

Independent research has proven Aglime is a superior liming material for WA’s acid soils as it is:

 

Low Cost

High NV

Low Particle size

Highly Soluble

 

Acknowledgements

Mr Andrew Speechly

Dr Andrew Rate (Dept of Soil Science and Plant Nutrition, University of WA)