The challenge

Well-functioning soil biology is central to soil health, crop performance and resilience. A wide range of soil tests can measure the diversity, abundance and function of soil microbes, but growers and advisers lack clear guidance on which microbial tests (indicators) are most useful for practical on-farm monitoring and decision-making.

Some soil microbial indicators only reflect general biological activity and are too high-level to guide specific management actions to improve soil function or crop productivity. Others are too specific to be widely applied, and many shift with the season and recent rainfall, so a single sample taken at the wrong time can give a misleading picture.

Clear guidance on selecting appropriate indicators and sampling strategies would help growers, advisers and researchers diagnose soil constraints, track how the soil responds to management, and have greater confidence in soil biological testing. This would support more targeted decisions around soil amendments, rotations, regenerative practices and chemical inputs, and create a pathway to practical soil biology tools that are scientifically robust and relevant to Australian farming systems.

Our research

This project evaluated how different land management practices affect soil biology, how those changes link to soil function and crop health, and which soil tests are practical and cost-effective for farmers and advisers to use in monitoring soil biology.

The project drew on five existing Soil CRC field experiments that covered a range of soil management issues including regenerative versus conventional systems, calcareous soils, herbicide use, plant-based solutions to improve soil performance and crop history effects (Figure 1).

Over 400 soil samples were collected from the five sites, over a range of seasons and management treatments. Researchers analysed 89 soil properties, from standard chemical and physical tests to a range of soil biology indicators. The project assessed each indicator’s sensitivity to management, its relationship with soil function, and its suitability for routine use.

Key points

  • Soil protein (ACE) is a low-cost test that correlated with total carbon, microbial biomass and several enzyme activities, making it the most promising practical indicator of soil biological condition.
  • DNA-based indicators were better than most other soil microbial indicators at detecting the effects of farming practices and worked across different Australian cropping systems.
  • Tests that count specific organisms, such as crop diseases, beneficial mycorrhizal fungi and nematodes, were more useful for management decisions than tests that only measure the total amount or broad variety of soil life.
  • Site and season influenced most microbial indicators more than management. Results need to be judged against what is normal for that soil and district, not against a single national benchmark.
  • Soil microbial indicators are most useful when interpretated alongside soil chemistry, soil physics and crop performance.

Find out more

Read our research findings fact sheet to learn more.

Other project resources can be accessed on this page.