Wormtastic Restores Soil Fertility...

Importance of soil microorganisms

Soil microorganisms include algae, bacteria, fungi, protozoa, invertebrates (earthworms) and viruses. These make up the soil biomass that may exceed 20 tonnes per hectare of fertile soil. In the absence of adequate content of organic matter, the microorganism population declines in number and variety, reducing the ecosystem functions that fertile soil provides.

Carbon cycling

Worms feeding on soil bacteria deposit carbon in castings and dissipate carbon dioxide during respiration. This carbon dioxide percolates up through the soil and is preferentially absorbed by the stomata on the underside of plant leaves. This utilization of carbon dioxide for plant growth exceeds that by photosynthesis, and is the reason pasture land is so valuable as a carbon sink.

Nitrogen assimilation

Nitrogen fixing bacteria thrive in soils with adequate organic matter in the surface layers. Moisture and temperature conditions that stimulate the growth of free-living nitrogen-fixing bacteria also stimulate plant growth. These plants can utilize the nitrogen as it is fixed from the air. Thus vigorous grassland communities can thrive in seemingly low nitrogen soils.

Conversely, nitrogen-fixers are less tolerant of soils that are compacted or low in organic matter. These soils require nitrogen to be supplied via legumes or fertilizers at the landowner’s expense. Nitrogen supplied in this way is very mobile. Its loss can lead to acid soils or undesirable effects elsewhere.

Mycorrhizal fungi

Mycorrhizal fungi form a symbiosis with the roots of about 90% of plants. Fine fungal threads wind between soil particles and grow into decomposing organic matter. The fungi absorb nutrients and water from the soil and translocate these to the host plant, receiving in exchange carbohydrates as an energy source. This symbiosis provides plants with
• faster growth
• improved nutrition, including phosphorus
• better recovery after drought
• protection from pathogens
• greater reproductive capacity.

This results in higher species diversity and enhanced competitiveness against weed growth.

Phosphorus availability

Australian soils are characterized by low levels of available phosphorus. In addition to the action of mycorrhizal fungi, soil bacteria produce phosphatase enzymes that release phosphorus otherwise locked up in our deeply weathered soils.

In bare soils, these functions cease because of the absence of carbohydrates provided by plants.

Soil stability

Microorganisms also produce sticky secretions and humic materials that cement mineral particles into crumbs or aggregates. The mycorrhizal fungal threads help bind smaller soil crumbs into larger aggregates that improve the structure and stability of the soil. This helps to prevent soil compaction and erosion.

Water conservation

Improved soil structure also increases the water holding capacity of the soil as more water is held in the pores within the soil aggregates. This is key to plant establishment, growth and persistence.

Furthermore, water is also released more slowly. It will percolate downwards slowly rather than running off sloping ground and draining rapidly into lower profiles where it may contribute to rising ground water and increasing dryland salinity.