Soil biodiversity is the variety of life that exists within the soil, including bacteria, fungi, earthworms and termites. A teaspoon of topsoil typically contains a vast range of different species and up to 6 billion microorganisms.
The maintenance of soil biodiversity is essential to both the environment and to agricultural industries.
- Soil is by far the most biologically diverse material on Earth.
- Soil contains a large variety of organisms which interact and contribute to many global cycles, including the carbon and nitrogen cycles.
- Soil provides vital habitats for micro-organisms such as bacteria, fungi, as well as insects and other organisms.
The diversity of organisms living within soils is critical to all earth ecosystems because soil organisms:
- are essential for the cycling of ecosystem nutrients
- are necessary for plant growth and plant nutrition
- improve the entry of water into soil and its storage in the soil
- provide resistance to erosion
- suppress pests, parasites and disease
- aid the capture of carbon
- are vital to the world's gas exchange cycles
- break down organic matter.
Soil biodiversity is recognised as a critical influence on agriculture as it can enhance sustainability through improved:
- soil structure
- soil water movement
- nutrient availability
- suppression of pests and diseases.
The Food and Agriculture Organization of the United States (FAO) estimates the socio-economic value of soil biodiversity exceeds US$1542 billion.
Soils and ecosystem biodiversity
Soils are a vital component of ecosystems because:
- the majority of plants grow in soil
- soils determine the nutrients such as nitrogen, phosphorus, sulfur, potassium, calcium, magnesium and micronutrients that are available for plants
- soils, with climate and topography, can determine the available water for plants
- soils can prevent some plant species from growing because of waterlogging, poor aeration, acidity, aluminium, heavy metals and high soil strength
- soils influence the distribution of animals as the occurrence of plant species provides food and shelter for them.
Examples of ecosystems and plant communities formed by a unique combination of soil and climate include:
- Bimble Box woodland on red earths on the Cobar Peneplain in north western NSW
- Coolabah woodland on grey cracking clay on the Darling Riverine Plain in north western NSW
- Iron bark forest on shallow clayey soils in the Sydney Basin
- Apple Bark (Angophora) forest on sandy soils in the Sydney Basin
- Myall (Acacia) woodland on grey cracking clay on the Darling Riverine Plain in western NSW
- Black Box woodland on poorly drained grey cracking clays on the Darling Riverine Plain in western NSW.
Maintaining soil biodiversity
Soils that support natural, non-agricultural ecosystems usually have the greatest soil biodiversity.
In agriculture, soils that receive less manufactured inputs (e.g. chemical fertilisers and pesticides) generally have higher soil biodiversity.
Grazing systems which encourage plant diversity usually have higher soil biodiversity, due to the greater availability of food resources from roots and litter, which support a greater variety of organisms in the soil.
Cropping systems generally have low soil biodiversity, unless they increase inputs of carbon and nitrogen to the soil, which will increase soil microbial populations. Crop management techniques that increase soil organic matter will also increase soil stability and soil biodiversity.
The application of organic matter to the soil, such as crop stubble, supports greater populations of surface feeding creatures including earthworms.
Management techniques such as crop rotation and reduced tillage increase the quantity and quality of organic matter available to soil organisms and develop a more stable environment that encourages more soil biodiversity.
NSW biodiversity strategy
The Draft New South Wales Biodiversity Strategy 2010–15 identified key themes that contributed to building ecosystems that are both healthy and resilient.
Primary produces need to sustainably manage productive landscapes for a range of commercial and biodiversity outcomes. The draft strategy supported primary producers to include biodiversity goals in the sustainable management of their natural resources.
Existing efforts include:
- sustainable management of total grazing pressure from feral herbivores, over-abundant native herbivores and domestic stock
- sustainable management of soils through actions like rehabilitation efforts, minimum or no-till practices, maintaining and increasing perennial plants and the careful use of fertilisers.
There is now greater focus on agricultural production systems which encourage and enhance all aspects of native and commercial biodiversity. There are several practices that suit the local environment and increase landscape health by keeping native species that an important role in that landscape. These include:
- production systems that enhance soil health, break disease cycles and use water more efficiently
- restoration of native plant communities and expanded use of native grasses in grazing
- farming within the capabilities of the soil and topography.
Management of land within capability
To keep soils healthy, land needs to be managed within its capability. Land management practices to increase levels of organic matter in soils and its biodiversity need to be encouraged. Management practices include:
- managing grazing pressure to retain and improve plant cover
- using minimum tillage or no-till practices to maintain groundcover and improve soil structure
- maintaining and increasing perennial plants (including pasture cropping)
- careful use of fertilisers
- rehabilitation of soil through targeted earthworks, water management and seeding.
The NSW Soils Framework: Looking forward, acting now detailed existing policies and programs for soil management in New South Wales and how they are used in the approaches taken by catchment and government administration. The framework suggested new directions in NSW soil management in the areas of institutional arrangements, research and development, marketing and awareness, information exchange and capacity building, funding and incentives, policy tools, regulations and natural resources management legislation in general. A draft NSW Soils Policy based on the framework is being developed.
Public land management agencies, Local Land Services and community groups should continue to promote the management of land according to its capability including the use of sustainable soil management practices.