Research show long-term value of lime

23 Feb, 2005 10:00 PM

THE application of lime to acidic soils has long term effects in terms of increasing the pH of the soil profile, according to research conducted by the Liebe Group.

Research officer Marcus Hemsted explained that the research had been carried out due to widespread farmer concern over subsoil acidity.

Mr Hemsted said that many farmers wanted to know if liming had long term effects, and whether or not it moved down the soil profile.

Using a long term trial carried out by Aglime Australia in 1986, at Ian Bowman's farm at Carnamah, the Liebe Group compared the pH of the soil in 1993 to 2004 levels.

"Comparing the 5t/ha lime treatment between 1993 and 2004 shows that the lime may have moved to a depth of 10 to 20cm, as it is at this depth that the greatest increase in pH was seen," Mr Hemsted said.

Mr Hemsted reminds farmers that lime application is not a once-off event.

"The removal of grain causes ongoing reductions in topsoil pH," he said.

"This was reflected in the drop in pH in the 0-10cm zone for all treatments.

"However, it must be noted that the first year of no-till was in 2003, therefore cultivation may have played a part in the distribution of lime through the soil profile."

Mr Hemsted explained the importance of particle size.

"Limes applied that have a significant proportion of their total under 0.5mm are the key in raising soil pH," he said.

"The lime used in this trial was more than 95 to 99 per cent under this particle size.

"Given this, growers should expect to see downward movement of lime, especially taking into account the laws of lime chemistry and solubility.

This data also supports works in NSW, where similar quality limes are applied at similar rates, ensuring topsoil pH is above 5.5, resulting in subsoil pH change of the order of 0.05 per annum.

This equates to one pH unit per 20 years.

"From the data it can be noted that the topsoil pH in the 1.25 and 2.5 tonnes per hectare treatments was not sufficient to get above the ideal pH 5.5 figure," Mr Hemsted said.

"This may be because there is still sufficient acid present on the top 10 cm to consume available lime."

Monitoring the trials will continue, and a reliming program will be initiated on the trial in collaboration with Steve Carr Aglime Australia.

As part of the Liebe Group's Soil Health Project, soil biological parameters are presently being analysed by Dr Dan Murphy from the University of WA.


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