It’s more than just dirt!
Dirt is a mix of gravel, sand, silt and clay but add organic matter, air and water and you have soil. Soil is fundamental for everyday life and 95% of our food comes from soil. A healthy and functioning agricultural soil sustains biological activity, maintains environmental quality, promotes plant, animal and human health, and is productive, resilient and profitable.
Traditionally, soils have been assessed on a single function, namely, plant yield or productivity. This focus ignores that healthy systems incorporate several soil benefits. Key functions that agricultural soils provide:
- Productivity – growing biomass for food, fibre and energy to create a productive and efficient system.
- Nutrient cycling – supply of nutrients to plants and microbes through decomposition of organic matter or mineral sources.
- Water circulation and storage – the ability to capture all the rain in the system through good infiltration and store it where the plant roots can access it.
- Soil biological organisms – optimised activity and diversity leads to more efficient and resilient systems.
- Greenhouse gas mitigation – long term storage or sequestration of organic carbon whilst maintaining other soil functional benefits.
To be able to establish your farms natural capacity, you need to know your soil and any climatic limitations. Characterising your soil starts with assessing the soil texture at the surface and down the profile. Look at the soil colour and smell as it can tell you many things, record the depth that roots have grown, this can point out any restricting layers that can constrain productivity. Use a field pH test kit (available from most hardware shops) to determine if your soil is in the range for nutrients to be available and support biological activity. Use guides or benchmarks to establish reasonable goals for your soils, rainfall and production system.
You can then assess the function of your soils by monitoring a range of chemical, physical and biological indicators. Utilise the tables that outline some tests and assessments for each of the five soil functions. Monitor and record over time in the same locations.
In summary
Assessment of a soil’s functioning ability starts with:
- Defining what soil health and function is for the situation
- Identifying the soil type and its limitations
- Understanding what can be changed and what can’t
- Modifying the expectation, management practice or soil
- Monitoring key soil, plant and economic attributes to measure soil function
- Reassessing the system – is it working?
There is no bad soil type, we have the soil we have, and the challenge is to identify the management activities that suit the soil texture, rainfall and production system.
Be realistic about the natural capacity of your soil. A sand in a low rainfall zone should not be compared to a loam in a higher rainfall. As much as we may like to have the same capacity as a different soil texture or region, establish expectations and work towards management or practices that can optimise what you have.
Maintaining ground cover as long as possible is one of the most important soil health activities. It provides a source of organic matter and modifies surface conditions (moisture and temperature) that affect decomposition and release of CO2 back to the atmosphere.
This article has been prepared as a part of a project supported by the Murraylands and Riverland Landscape Board through funding from the Australian Government’s National Landcare Program and Landscape Board levies.
