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More field trials of Aglime and other liming products

 

The quality of a lime is measured by its neutralising value (NV) and particle size. These measurements, widely used throughout the world, are the best indicator of lime quality in WA.

 

Independent Field Trial

An independent field trial is being carried out by DAFWA to compare 5 different types of lime. The trial was located on Avondale Research Station at Beverley. It commenced in 1998.

 

Types of Lime

The limes used in the trial were:

 

Limesand: Aglime of Australia at Lancelin
Crushed Limestone: Bioworld lime from Lime Industries
Cement Kiln Dust: Fresh Agriburnt Lime
Dolomite: From Watheroo and Kojonup

 

 

 

 

 

 

Trial Design

The trial was designed to compare the effectiveness of each lime to increase soil pH and crop yield.

The neutralising value of each lime was measured and used to adjust its application rate. Those limes with low NVs were applied at higher rates than those with high NVs. This was done to ensure that the amount of neutralising material applied was the same for each type of lime.

 

Aglime’s limesand set the base rate. It was applied at 1 tonne/hectare and all other lime rates were adjusted. For example, crushed limestone had an NV of 68% compared with Aglime’s NV of 93%, some 36% higher. Therefore, crushed limestone was applied at 1.36 t/ha to compensate for its lower NV. No adjustment was made to account for differences in particle size between the limes in this trial.

 

Trial Management

The limes were spread by a multispreader at various rates (adjusted for NV) over three replicates. The trial was sown to Brookton wheat on 22/06/98.

 

Soil pH levels were measured before the limes were spread and again at the end of October 1998.

 

Results: Change in pH when Varying Rates of Application

The increase in topsoil pH above the control (nil lime) was greatest with limesand and cement kiln dust (burnt lime). Limesand increased the subsoil pH more than burnt lime. The Kojonup dolomite changed pH by a similar amount to limesand but it was applied at 1.8 times the rate. The crushed limestone had a relatively small effect on soil pH, despite being applied at 1.4 times the rate of Aglime’s limesand.

 

Source
Rate (t/ha)
Topsoil pH increase
Subsoil pH increase
Limesand
1.0
0.6
0.4
CK Dust
1.0
0.6
0.0
Watheroo D1
1.1
0.3
0.2
Kojunup D2
1.8
0.6
0.5
Limestone
1.4
0.1
0.2

Results: Change in pH when applied Tonne for Tonne

The limes were compared on an equal tonne for tonne basis by dividing each pH increase by the amount of lime applied. This gave the pH change per tonne for each lime.

 

The results show that at 1 tonne/ha, both limesand and burnt lime would change the topsoil pH by 0.6 units. However, limesand was far more effective than "burnt lime" in the subsoil. It should be noted that fresh "burnt lime" was used in this trial. It has a significantly higher neutralising value (103%) than that usually delivered to farmers (typically 80%). This reduction in neutralising value occurs as burnt lime absorbs water and carbon dioxide to form relatively insoluble calcium carbonate (whitewash).

 

At 1 tonne/ha, dolomite was around half as effective as limesand. It is less soluble than limesand due to its tightly bound crystalline structure. In addition, it generally has lower neutralising value and often contains up to 60% more coarse material than limesand.

 

Crushed limestone was least effective in changing soil pH due to its lower neutralising value and larger percentage of coarse particles.

Results: Yield

In the first year of the trial, there was no significant yield increases for any of the limes. In Aglime of Australia’s field trial program, wheat yield increases are typically measured in 30% of trial sites in the first year. Yield increases commence in 70% of sites in the 2nd or 3rd year after liming depending when the usually unresponsive lupin is grown in the rotation.

 

Conclusion

Aglime of Australia’s limesand was the most effective lime producing the largest pH increase in topsoil and subsoil.

 

Acknowledgements

Trial Results provided by Amanda Miller, Acid Soils Extension Officer, DAFWA Northam.