Compost

When people think about how productive a soil and the ways to improve productivity, they generally consider the physical and chemical characteristics like total nitrogen content, pH, salinity, and compaction. Certainly, these things are important in enhancing plant growth, but it is also important to consider that all these characteristics and many others are controlled by the amount of life in the soil. 

The soil food web is made up of living organisms responsible in performing essential functions like decomposing organic matter (e.g. composts, manures, and plant residues) and mineralising nutrients available to plants. These living organisms also enhance soil aggregation and porosity which increases water infiltration and retention and soil aeration. 

What are these organisms and their functions? Soil organisms include bacteria, fungi, algae, protozoa, nematodes, earthworms, insects, and small invertebrates. Their respective roles in soil health are explained here:

Bacteria: These are microscopic single-celled organisms present in remarkably high numbers in healthy soil, as much as one billion in one teaspoon of soil. Bacteria participate in decomposing OM to provide food for other members of the food web. They also help keep nutrients in the root zone and out of the groundwater by enhancing soil structure, which improves water flow into the soil reducing runoff and erosion. Bacteria can compete with disease-causing microorganisms as well as filtering and breaking down pollutants in the soil.

Fungi: Fungi are microscopic or macroscopic multi-celled organisms made up of root-like mycelial structures usually growing as a mass of branching thread-like strands called hyphae which push their way between soil particles and plant roots. Fungi decompose complex carbon compounds and improve organic matter accumulation. They also retain mineral nutrients in their structure resulting in reduced leaching of nutrients out of the root zone. Fungal hyphae physically bind soil particles into bigger clumps allowing air and water to be stored in the soil. They also improve plant growth by becoming associated with root structures that facilitate nutrient transport to plants and suppressing colonisation of pathogenic fungi (e.g. Phytophthora, Pythium).

Protozoa: These are single-celled animals feeding primarily on bacteria. As they consume bacteria, they release nutrients which can be used by plants. They increase the breakdown of OM matter and improve soil structure by stimulating bacterial activity. Protozoa also feed on plant pathogens as well as providing food for larger soil organisms.

Nematodes:  Nematodes are non-segmented worms up to about 1 mm in length. Some nematodes cause plant disease, but many species feed on bacteria and fungi releasing nutrients for plant use.  Aside from providing food for larger soil organisms, nematodes also help control the populations of pathogenic microbes and other pests.

Arthropods: These animals include centipedes, millipedes, spiders, crickets, beetles, and mites.  They participate in breaking down organic matter by shredding and decomposing plant litter and mixing it into the soil. They also feed on bacteria and fungi releasing plant-available nutrients, as well as feeding on insect pests and controlling their numbers. By burrowing through the soil, arthropods play a vital role in transporting nutrients, bacteria, and fungi through the soil profile, providing food to other residents in the soil microecosystem.   

Earthworms: They are the "earth movers" of the soil community. Earthworms spend their entire life consuming soil and organic matter, producing nutrient-rich "castings", and creating a network of tunnels enriched with nutrients. By building tunnels, channels are created for water infiltration and storage as well as providing aeration beneficial for root growth.

Anyone can see that a healthy soil needs a rich and diverse network of beneficial living organisms to be productive! 

A healthy soil food assists farming in the following ways:

• Fertiliser requirements will decline resulting from healthy soil food web efficiently storing and cycling nutrients.
• Minimal leaching of nitrate-nitrogen into groundwater.
• Water quality is protected when organisms effectively degrade pollutants.
• Improved soil-water storage for crop use.
• Enhanced biological activity resulting in improved soil structure.
• Decreased topsoil erosion resulting from stabilised soil structure.
• Reduced pesticide use resulting from disease suppression by a healthy soil food web.

Some of the practices in traditional agriculture are damaging to these organisms. The use of synthetic chemical fertilisers tends to reduce their population dramatically. Tilling the soil damages the soil structure resulting in population decline. Also, many local soils contain high nitrate-nitrogen because of lacking organisms to transport the nutrients to the plants, instead they are left in the soil profile in a leachable form then run-off into dams and waterways.

Let's wrap up

Compost nourishes the soil food web in several ways. 

• Compost is rich in beneficial microbes (e.g. bacteria and fungi). When applied in farms, the soil is inoculated with fresh populations to multiply.
• The organic matter in compost is already mineralised, making it ideal food for other soil organisms, especially earthworms.
• For long-term benefits, using compost as a mulch or top dressing protects the soil from sun exposure and facilitates moisture retention from rain and dew.
• Also, compost is a weed suppressant, soil conditioner, erosion controller, and pH adjuster all in one.
• The nutrients contained in compost, when used as basal fertiliser, reduce the dependent use of synthetic fertilisers. 

The cost of compost use can be easily justified when the savings in tillage, pesticide use, and irrigation are also considered. 

REMONDIS Swanbank Organics' compost is also a recycled product, locally produced, and locally distributed. We're certainly proud of the product we make right here in South East Queensland!