First test for soil bacterial activity by Alex Nicol

CSIRO scientist Stephen Rogers

A TEAM of CSIRO scientists led by Matthew Colloff and Stephen Rogers has taken the first step in developing a commercial technique to measure the hiological health of the soil.

The test is based not on trying to identify and quantify the number of bacteria in the soil , but on the amount of genetic material present associated with the nitrogen cycle, "The fact is that science has identified only about 5 per cent of the bactcria living in soil ," says Dr Rogers.

"But fortunately the genetic material associated with nitrogen mineralisation, fixation and denitrification is common, We've developed a test that extracts this material from the soil and more importantly can determine whether or not it is active.

"Our present test is slow and expensive and we' ll need three to four years work to 'ground truth ' it and fine-tune it to the point where it will he commercially viable, Never the less it could already be useful in association with current trials on crop management techniques."'

The team associated with the development of the test worked with soil from three different areas in Australia: two, at Rutherglen in Victoria and Moora in WA, were on land associated with cereal trials. In each case, soil from a nearby un farmed area was sampled for comparison. Samples from all of the agricultural areas indicated that current agricultural practices were encouraging the development of bacteria associated with each phase of the nitrogen cycle. This included all common practices such as no-till , stubble retention, cultivation , stubble burning and pasture phase. Al l showed an increase in bacterial action a have un farmecl country.

Dr Rogers says that the eventual aim of the project will be to produce a commercially available test that will provide information, in conjunction with the typical deep soil N test, about the amount and level of activity of bacterial genetic material

"We want to be able to say that there's so much material available, capable of convening so much ammonia, fixing so much atmospheric nitrogen and responsible for so much denitrification. That would be of practical use in eliminating waste nitrogen fertiliser with implications both for the farmer's pocket and the environment."

The team is currently working to develop a test to determine the level of activity in the soil's carbon cycle and the use of sulphur in the soil.

Surprising reaction to stress factors

Focusing on what he describes as the soil's resilience. Dr Rogers and his team stressed the test soils either by increasing their level of salinity or by dosing them with antibiotics, While antibiotics quickly climinated bacteria associated with mineralisation, other types survived, and increasing salinity had no impact on bacterial activity,

"The indications are that the greater the diversification of genetypes present the more capablc the soil is of surviving stress ," said Dr Rogers, Diversity relates to the mutiplicity of types of bacleria in the soil - those associated with mineralisation, others with fixation of free nitrogen and another group associated with denitrification. Resilience comes from a good mix.

Contact: Dr Stephen Rogers 08 8303 8407

Region North, South, West