World Soil Day Dec 5: Not just dirt

Posted 4 December 2014

To mark World Soil Day on Friday December 5, Harper Adams University postdoctoral researcher Abigail Graceson explains why soil is not just dirt on the ground.

"That stuff on the ground is just dirt that needs to be covered up with something, right? Well, yes…and no.

Yes, it is often better if soils are ‘covered up with something’. It helps to protect the delicate structural architecture that makes up one of the most diverse environments in our world…And no, it’s not just dirt, it’s a habitat, a water store and purifier, a nutrient recycler, a growing medium.

Proper functioning of soils underpins much of our environment, so we need to work to understand and preserve the soil habitat and the processes that occur there.

Soils are highly diverse environments at multiple scales. Differences in the physical and structural properties of soils are measurable from county to county, field to field, centimetre to centimetre. The most basic properties of soil relate their ability to hold both air and water simultaneously. This means that plants can take up water and nutrients as well as oxygen through their roots enabling them to survive and grow.

Soils are able to hold on to air and water simultaneously because of their structure. All those different sized chunks or aggregates fit together, but not too closely. Smaller gaps, or pore spaces, between the aggregates will hold on to water for a longer time than larger pore spaces.

Compact the soil by squashing it and the aggregates will be pressed closer together reducing the amount of air filled pore spaces and increasing the amount of water filled pore spaces. The result of this can be a waterlogged soil which limits plant growth. The small pore spaces mean that water is not released easily.

Research that I am involved in looks at the ways in which compaction of agricultural soils can be avoided and alleviated. This means that plants can be provided with optimal growing conditions whilst a suitable habitat for the huge number of living organisms that live in soil is maintained.

I am also interested in using novel materials in growing media for sustainable urban drainage systems such as green roofs which mimic natural drainage patterns, so reducing the speed and volume of rainwater runoff."