Management and Soil Biology

Why is Soil Biology Important? | What Regulates Soil Biology? | Measuring Soil Biology | Soil Evaluation of Biological Productivity

The most important influences on soil biology in terms of management is energy supply (essentially the carbon in the soil), in the form of plant residues and animal manures. The energy or carbon drives the entire soil ecosystem which is important to help sustain biological functions for longer periods within the season in order to increase levels of microbial populations and associated benefits.

Habitat for soil biology is also important. It should be stable in terms of water and air supply and temperature, and should have an absence of toxicities such as salt and heavy metals. Finally, diversity of crops and plant species is important to capture the synergies between species and avoid build-up of pathogens

No till, stubble retention and direct drill

Soils are wetter and cooler under no-till systems than when cultivated, and more residues and manures are concentrated on the surface and in the top layer of the soil.

Occasional tillage may provide short-term benefits with weed control and decreasing pathogens. However, accelerated decomposition resulting from tillage may lead to loss of carbon due to more rapid breakdown of residues. No-till and stubble retention leads to a better synchronisation between nitrogen mineralisation and plant requirements. No-till tends to favour fungi proliferation over bacteria which is desirable in order to break down more complex organic compounds (lignin and cellulose) from retained stubble.

Rotations

Replacing monocultures (usually wheat) with rotations based on crop legumes, oilseeds and pastures can increase the size and diversity of the soil biological communities. Multiple ecological studies have shown that above-ground plant diversity strongly influences below-ground diversity.

Crop type and variety affect microbial composition and activity due to a number of factors: differences in the rhizosphere; differences near crop residue; direct effects due to chemical and biochemical properties of different plants (isothiocyanates in canola which act as a mild fumigant); and indirectly through different management practices. Rotations also facilitate management of soil-borne diseases by eliminating the occurrence of a continual pathogen host as well as improving soil nutrient supply due to the added benefit of nitrogen fixation in legumes.

Manage chemical inputs

Although we know little about the effects of pesticides on soil biology in Australia, minimal use of insecticides, fungicides and herbicides is a desirable management strategy. Repeated use of the same chemical can make the chemical less effective. Avoiding copper based products that are toxic to many microbial groups is also recommended.

Amendments

Use microbial inoculants and biological amendments with caution. Legume inoculants containing Rhizobia have a 50-year history of research and development and are well tested with proven beneficial products. However, there is an increasing stream of new “silverbullet” products that purport to fix nitrogen and enhance plant growth. Remember to check with your local agronomist if these products have been trialled in field tests - preferably in your region where there is similar climate and soil types.

Check that products are registered and if the product labels carry key information such as contents, storage, application rates and safety information. Check whether the product will be a long term solution and what exactly it claims to do. Determine if the product is part of a management package - if so, be aware that sound management may result in benefits to soil health, independent of associated amendments. If possible, consider conducting your own field trial before committing to large scale adoption of a product.

Checklist: What should you know about biological products?