A UWA study has challenged claims that biochar is more effective in minimising nitrogen leaching from soil than traditional clay amendments.
The article published by CSIRO Publishing titled “Clay and biochar amendments decreased inorganic but not dissolved organic nitrogen leaching in soil” gives a recent update on the new research.
Clay is commonly used in agriculture to ameliorate water repellence and improve water retention, however in dryer climates such as Australia, biochar has been claimed to be more useful because it has a greater water holding capacity.
Biochar, a type of charcoal, has been proposed as an alternative to clay because of its porous structure enabling it to better retain nutrients and moisture while at the same time storing carbon.
Biochar is generally alkaline and could be a useful additive in place of products such as lime to improve the quality of acidic soils (typically pH of 5-6) in regions such as the Wheatbelt of WA.
These properties are claimed to assist in improving soil fertility and increase agricultural productivity making use of biochar increasingly appealing to farmers.
However, the study found that biochar does not possess significantly better nutrient absorption qualities than clay, although both are acknowledged as beneficial in reducing nitrogen leaching.
UWA’s Soil Research Winthrop Professor Robert Gilkes says although there a number of clear benefits he still has concerns.
“The whole situation is complicated because putting biochar in soils is also claimed to be a way of stopping carbon getting into the atmosphere.
“I think the proponents of burying biochar need to be clear that it’s only slowing down the rate of carbon transfer back into the atmosphere, not preventing it.
“There are several ways in which you can catch carbon dioxide, this is just one.
“One of the downsides is that biochar production is a costly and wasteful process which doesn’t provide any benefits.
“It is no more nutrient absorbing than clay,” Professor Gilkes says.
Biochar is produced via pyrolysis, a process which actually produces energy through use of renewable sources, with the biochar (a carbon sink) retrieved as a by-product.
“The idea is that companies and countries can bury their carbon in the ground which reduces their carbon input into the atmosphere and in turn reduce their carbon liabilities,” Professor Gilkes says.
Clay is often readily available from the sub-soil and has been used for many years in some farming enterprises, so determining whether biochar offers a viable alternative needs serious consideration.
“In my view recent research has not been able to demonstrate an affective, valuable role for biochar in agriculture,” Professor Gilkes says.