Hostile soils under (long) microscope by Denys Slee

The answer lies in the subsoil... somewhere. Dr Garry O'Leary of CSIRO Land and Water tackles the massive task of identifying subsoil constraints on mallee farms.

Try finding a needle in a haystack... or locating subsoil constraints in a large paddock.

It's about the same order of difficulty according to CSIRO Land and Water scientist Garry O’Leary.

Dr O’Leary was recently appointed to work in the GRDC-supported Mallee Sustainable Farming Project and his first task is to pinpoint ways to efficiently and economically identify subsoil constraints to production at the farm level, and within paddocks.

The mallee country in western NSW, north-west Victoria and north-east SA can get pretty dry at times. The irony is that the subsoil in many paddocks can be wet, even after harvest.

Dr O’Leary says this apparent contradiction is due to the fact that annual plant roots are not able to grow to ‘normal’ depths because of the presence of toxicities such as high boron levels, salinity or very high pH levels.

“We think the problems are worse in SA and Victoria but the nature of them varies, as does their depth in the subsoil,” Dr O’Leary said.

“We do know that grain production in the Mallee has increased at only one-third the rate of that in higher-rainfall areas over the past 30 years. “There is little evidence of significant large-scale physical constraints to better crop production. But important chemical subsoil constraints over much of the agricultural land have been identified.

“Somehow we have to find practical ways to identify the subsoil problems and then develop farming systems to get better yields from these soils and to minimise adverse environmental impacts caused by water draining away from the root zone of plants.”

To get a handle on the task, Dr O’Leary is analysing numerous soil samples from 60 focus paddocks spread across the region. Where possible, these results will be matched against yield maps produced as part of the crop harvesting operation by farmers, and the two sets of results correlated.

As well, ground-based electromagnetic surveys will track subsoil salinity levels.

“We will also be looking at the feasibility of aerial electromagnetic surveys and ground-penetrating radar technologies to see if these techniques can be used by researchers, and ultimately farmers, to help identify problem subsoils,” Dr O’Leary said.

“I suspect the problem with toxicities will show up in waves in some paddocks and patches in others, but we have yet to find out.

“The breeding of crop and pasture varieties more tolerant to the toxicities will be important but there are likely to be other solutions, too.

“These are likely to include intensification of farming systems and a move away from long fallows.”

Program 3.5.2 Contact: Dr Garry O’Leary 03 5094 1203