, 12 September 2023
Happy Bilby Day (September 12th)! Let’s get muddy and investigate what makes up different soils. Along the way, you’ll learn how bilbies play an important role in improving Australia’s soils.
Safety: This activity involves touching soils. Watch out for any sharp objects in soil and wash hands thoroughly after this activity.
Soil isn’t just “dirt”. There are 3 main non-living parts in soil: sand, silt and clay. Clay is the smallest particle out of the 3, so it has the most surface area to absorb more water compared to silt and sand. This makes clay soils the stickiest. If you made a long ribbon, then you’ve found a clay-y soil!
If you felt any gritty bits in your soil, that’ll be the sand particles. As the biggest particle compared to silt and clay, sand grains create gaps in soils. Because of these gaps, sand doesn’t stick together well and it lets water through quickly, so sandy soils will give you shorter ribbons.
Soil is also made up of living parts: plants, bugs, bacteria and decomposed materials called organic matter. If you dug up a soil sample near a plant, your soil ribbon would have felt “fluffy” to you. This is because organic matter adds gaps in soil like sand particles. But unlike sand, organic matter can hold onto water and nutrients better. As a result, it acts like a glue between sand, silt and clay particles to give plant roots gaps to grow and breathe, plus water and nutrients!
For most plants, they need the right balance of clay, silt, sand and organic matter to grow. After all, you don’t want soil to be so sticky that plant roots don’t have gaps to grow through, nor so sandy that roots can’t stay hydrated!
Male bilbies weigh up to 2.5 kilograms and females weigh up to 1.1 kilograms, yet a single bilby can dig up several tonnes of soil a year!
Credit: ©iStock.com/Ken Griffiths
The greater bilby is a small but keen digger. Every night, they look for food by digging deep holes. This mixes organic matter with other particles in deeper soil layers. This also mixes seeds from the soil surface with more nutrients and water, giving them better chances to grow and add more life to soils. In turn, this means more homes for other wildlife, and better health for the environment!
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