What are the different types of soil and what are their qualities?
Clay soils are commonly encountered in Australia, with their heavy, compact nature and poor drainage being a notable issue. Comprised of very-fine particles, clay soils are poorly draining and poorly aerated. During droughts, they tend to dry out and become prone to cracking, while in wet weather, they can turn sludgy or muddy, hindering the oxygen supply to plant roots. Despite these challenges, clay soils boast high nutrient levels and are resistant to leeching. By incorporating amendments like gypsum or organic matter such as compost, clay soils can transform into an excellent growing medium, particularly suitable for plants like Citrus that can thrive in slightly heavy soils.
Sandy soils have exceptional drainage properties, acting as both an advantage and a drawback as they release water and nutrients rapidly. Although they drain well, sandy soils struggle to retain moisture and are often acidic. When enriched with organic matter like compost or manure, sandy soils can be transformed into sandy loam, striking a balance between moisture retention and efficient drainage. This composition makes them well-suited for plants such as Avocado or Blueberry.
Silt soils present a favorable middle ground between sand and clay, featuring particles large enough to allow for proper drainage while retaining moisture and nutrients. Generally fertile, silt soils may face challenges such as vulnerability to erosion, as natural erosive processes are involved in silt transportation, and a tendency to compact.
Loam soils encompass a balanced combination of clay, silt, and sand, with none dominating individually. These soils are rich in organic matter or humus, contributing to their dark, nearly black color. Black soils, often regarded as the gold standard for agriculture, boast high organic matter content, ensuring proper drainage while retaining moisture and nutrients. Loam soils remain aerated and resist compaction, providing an ideal environment for beneficial organisms like earthworms and microbes.
- Gardening Australia: Starting with soil – Great overall guide for the differing soil types commonly encountered
- Gardening Australia: How understanding your soil will improve your garden & easy tests – As described, in addition to how to improve your soil structure.
What can I do to improve my soil? I don’t have any viable soil to amend or improve what can I do?
The key to enhancing soil quality lies in the incorporation of organic matter, which serves as the foundation for a productive and fertile soil. Organic matter plays a crucial role in providing fertility, promoting drainage, retaining moisture and nutrients, and creating an optimal environment for beneficial soil life. There are various sources of organic matter that can be seamlessly incorporated through different methods, as outlined below.
One practical approach for gardeners is to use mulch, such as wood chips (especially arborist wood chips). As the mulch gradually breaks down, it enriches the soil with organic matter, enhancing both fertility and the soil structure. Simultaneously, mulches shield and nourish microbes and organisms like worms or wood roaches. These creatures create burrows, where they consume organic matter and integrate it further into the soil. An easily accessible source of mulch for gardeners is to use branches and leaves from pruning, provided they are not diseased.
Applying compost or well-rotted manures is an excellent method for introducing organic matter. Mature composts and well-rotted manures, when applied to soils, elevate the organic matter levels and offer similar benefits to mulch by nourishing beneficial organisms and microbes. Manures from animals such as cows, sheep, and horses are readily available and make excellent additions (Refer to the following Gardening Australia video for information on the difference between different manures – Which poo is right for you). Gardeners can also opt for green manure, with Fabaceae species like Lupine, Clover, or Broad Beans being particularly suitable. Once ready for application, these manures can be applied to the surface as a top-dressing, covered with mulch, or lightly tilled into the soil. Gardeners should be mindful that deep ploughing in of organic matter can accelerate the decomposition of existing humus in topsoil, potentially offsetting any additions (though this loss can be trivial in very poor, heavy clay soils with minimal topsoil). Long-term applications of composts and manures to the surface allow gradual incorporation into the soil while providing nutrients.
Raised mounds serve as an excellent and highly practical option, especially in areas characterized by poorly draining soils or thin topsoils. Opting for raised mounds provides gardeners with the opportunity to elevate the soil level for planting, ensuring that the topsoil is conducive to successful cultivation. An illustrative example of the practicality of raised mounds is evident in the cultivation of Avocado trees. Avocado trees are particularly sensitive to root rot and often encounter challenges in regions with prevalent heavy clay soils, a common soil type found across much of Australia. However, by strategically planting them on raised mounds, gardeners can elevate the root system above the problematic clay soil, creating an environment where avocado trees can flourish and thrive.
If the above solutions are impractical or if soils are unsuitable due to contamination, gardeners can still cultivate plants using containers and pots. In containers and pots, the soil medium can be chosen initially and closely controlled throughout the cultivation process.
Hortiforum 