The scientists who breed Australia's crop varieties could have another challenge ­ matching them to different farming systems ­ if a prediction by CSIRO Plant Industry's John Kirkegaard is correct.

Dr Kirkegaard, a principal research scientist based in Canberra, said his research on the acid clay loams of southern New south Wales showed different varieties of wheat interacted differently with micro-organisms in soil.

Janz and H45 wheats interacted differently with soil organisms under different tillage systems and in rotations with canola, offering opportunities to exploit the interaction between different varieties and their management.

They responded differently to the biology existing in soil when they were planted, but they also left behind new biology that could affect other varieties of the same crop.

Dr Kirkegaard was speaking at the recent Soil Biology in Agriculture workshop in Tamworth, supported by the NSW Department of Primary Industries (NSWDPI) and the Grains Research and Development Corporation (GRDC).

He told his workshop audience another important message from his team's research was that management created as big a difference in soil biology as climate.

On the acidic loams of southern NSW, there was clear evidence that changes in agronomic practices ­ including variety selection ­ had improved the productivity and sustainability of farming systems.

However the vague term "soil health" did not relate well to either the broader environmental performance or the productivity of farming systems.

That was illustrated in a study of reduced early vigour in direct drilled wheat on a 15 year old trial site near Harden, where the widely promoted soil health benefits of direct drill were evident.

Soil organic matter, microbial biomass, earthworm populations, nematode and faunal diversity and disease suppression were all higher under the direct drilled, stubble-retained treatment than in the locally popular, district practice of late burn and single tine cultivation. .

The dilemma for researchers and advisers was that, in spite of the apparent improvements in "soil health", throughout the 15 years period the growth and productivity of crops were lower on the direct drilled stubble retained treatment.

This was associated with more water and mineral nitrogen being left in the subsoil., representing an increased risk of deep drainage and nitrogen leaching.

This scenario might not be true for all farming systems but it highlighted the need to be pragmatic about the benefits of management to preserve various components of the soil biology for their own sake.

The capacity of systems to achieve and sustain well-established, physiologically-based productivity remained the most useful benchmark.